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diff --git a/old/51645-0.txt b/old/51645-0.txt deleted file mode 100644 index a7fd989..0000000 --- a/old/51645-0.txt +++ /dev/null @@ -1,10396 +0,0 @@ -The Project Gutenberg EBook of Letters on Natural Magic Addressed to Sir -Walter Scott, Bart., by David Brewster - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Letters on Natural Magic Addressed to Sir Walter Scott, Bart. - -Author: David Brewster - -Release Date: April 3, 2016 [EBook #51645] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK LETTERS ON NATURAL MAGIC *** - - - - -Produced by Susan Skinner, Les Galloway and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - - LETTERS - - ON - - NATURAL MAGIC, - - ADDRESSED TO - - SIR WALTER SCOTT, BART. - - BY - - SIR DAVID BREWSTER, LL.D., F.R.S. - - [Illustration: Three figures on hill-top saluting sunrise] - - SEVENTH EDITION. - - LONDON: - WILLIAM TEGG AND Co., 85, QUEEN STREET. - CHEAPSIDE. - 1856. - - - - -CONTENTS. - - - LETTER I. - - Extent and interest of the subject--Science employed by - ancient governments to deceive and enslave their subjects--Influence - of the supernatural upon ignorant minds--Means - employed by the ancient magicians to establish - their authority--Derived from a knowledge of the phenomena - of Nature--From the influence of narcotic drugs - upon the victims of their delusion--From every branch of - science--Acoustics--Hydrostatics--Mechanics--Optics--M. - Salverte’s work on the occult sciences--Object of - the following letters Page 1 - - - LETTER II. - - The eye the most important of our organs--Popular description - of it--The eye is the most fertile source of mental - illusions--Disappearance of objects when their images fall - upon the base of the optic nerve--Disappearance of objects - when seen obliquely--Deceptions arising from viewing - objects in a faint light--Luminous figures created by - pressure on the eye, either from external causes or from - the fulness of the blood-vessels--Ocular spectra or accidental - colours--Remarkable effects produced by intense - light--Influence of the imagination in viewing these - spectra--Remarkable illusion produced by this affection - of the eye--Duration of impressions of light on the - eye--Thaumatrope--Improvements upon it suggested--Disappearance - of halves of objects or of one of two persons--Insensibility - of the eye to particular colours--Remarkable - optical illusion described 8 - - LETTER III. - - Subject of spectral illusions--Recent and interesting case - of Mrs. A.--Her first illusion affecting the ear--Spectral - apparition of her husband--Spectral apparition of a cat--Apparition - of a near and living relation in grave-clothes, - seen in a looking-glass--Other illusions, affecting - the ear--Spectre of a deceased friend sitting in an - easy-chair--Spectre of a coach-and-four filled with - skeletons--Accuracy and value of the preceding cases--State of - health under which they arose--Spectral apparitions are - pictures on the retina--The ideas of memory and imagination - are also pictures on the retina--General views of - the subject--Approximate explanation of spectral apparitions 37 - - - LETTER IV. - - Science used as an instrument of imposture--Deceptions - with plane and concave mirrors practised by the ancients--The - magician’s mirror--Effects of concave mirrors--Aërial - images--Images on smoke--Combination of - mirrors for producing pictures from living objects--The - mysterious dagger--Ancient miracles with concave - mirrors--Modern necromancy with them, as seen by Cellini--Description - and effects of the magic lantern--Improvements - upon it--Phantasmagoric exhibitions of - Philipstall and others--Dr. Young’s arrangement of - lenses, &c., for the Phantasmagoria--Improvements - suggested--Catadioptrical phantasmagoria for producing - the pictures from living objects--Method of cutting off - parts of the figures--Kircher’s mysterious hand-writing on - the wall--His hollow cylindrical mirror for aërial images--Cylindrical - mirror for re-forming distorted pictures--Mirrors - of variable curvature for producing caricatures 56 - - - LETTER V. - - Miscellaneous optical illusions--Conversions of cameos into - intaglios, or elevations into depressions, and the - reverse--Explanation of this class of deceptions--Singular - effects of illumination with light of one simple colour--Lamps - for producing homogeneous yellow light--Methods - of increasing the effects of this exhibition--Method of - reading the inscription of coins in the dark--Art of - deciphering the effaced inscription of coins--Explanation - of these singular effects--Apparent motion of the eyes - in portraits--Remarkable examples of this--Apparent - motion of the features of a portrait, when the eyes are - made to move--Remarkable experiment of breathing - light and darkness 98 - - - LETTER VI. - - Natural phenomena marked with the marvellous--Spectre - of the Brocken described--Analogous phenomena--Aërial - spectres seen in Cumberland--Fata Morgana in - the Straits of Messina--Objects below the horizon raised - and magnified by refraction--Singular example seen at - Hastings--Dover Castle seen through the hill on which it - stands--Erect and inverted images of distant ships seen - in the air--Similar phenomena seen in the Arctic regions--Enchanted - coast--Mr. Scoresby recognizes his father’s - ship by its aërial image--Images of cows seen in the air--Inverted - images of horses seen in South America--Lateral - images produced by refraction--Aërial spectres - by reflexion--Explanation of the preceding phenomena 127 - - - LETTER VII. - - Illusions depending on the ear--Practised by the ancients--Speaking - and singing heads of the ancients--Exhibition - of the Invisible Girl described and explained--Illusions - arising from the difficulty of determining the direction - of sounds--Singular example of this illusion--Nature of - ventriloquism--Exhibitions of some of the most celebrated - ventriloquists--M. St. Gille--Louis Brabant--M. - Alexandre--Capt. Lyon’s account of Esquimaux ventriloquists 157 - LETTER VIII. - - Musical and harmonic sounds explained--Power of breaking - glasses with the voice--Musical sounds from the - vibration of a column of air--and of solid - bodies--Kaleidophone--Singular acoustic figures produced on - sand laid on vibrating plates of glass--and on stretched - membranes--Vibration of flat rulers and cylinders of - glass--Production of silence from two sounds--Production - of darkness from two lights--Explanation of these - singular effects--Acoustic automaton--Droz’s bleating - sheep--Maillardet’s singing-bird--Vaucanson’s flute-player--His - pipe and tabor-player--Baron Kempelen’s - talking-engine--Kratzenstein’s speaking-machine--Mr. - Willis’s researches 179 - - - LETTER IX. - - Singular effects in nature depending on sound--Permanent - character of speech--Influence of great elevations on the - character of sounds, and on the powers of speech--Power - of sound in throwing down buildings--Dog killed - by sound--Sounds greatly changed under particular circumstances--Great - audibility of sounds during the night - explained--Sounds deadened in media of different - densities--Illustrated in the case of a glass of champagne--and - in that of new-fallen snow--Remarkable echoes--Reverberations - of thunder--Subterranean noises--Remarkable - one at the Solfaterra--Echo at the Menai suspension - bridge--Temporary deafness produced in diving-bells--Inaudibility - of particular sounds to particular ears--Vocal - powers of the statue of Memnon--Sounds in - granite rocks--Musical mountain of El-Nakous 212 - - - LETTER X. - - Mechanical inventions of the ancients few in number--Ancient - and modern feats of strength--Feats of Eckeberg - particularly described--General explanation of them--Real - feats of strength performed by Thomas Topham--Remarkable - power of lifting heavy persons when the - lungs are inflated--Belzoni’s feat of sustaining pyramids - of men--Deception of walking along the ceiling in an - inverted position--Pneumatic apparatus in the foot of - the house-fly for enabling it to walk in opposition to - gravity--Description of the analogous apparatus employed - by the gecko lizard for the same purpose--Apparatus used - by the Echineis remora, or sucking-fish 244 - - - LETTER XI. - - Mechanical automata of the ancients--Moving tripods--Automata - of Dædalus--Wooden pigeon of Archytas--Automatic - clock of Charlemagne--Automata made by - Turrianus for Charles V.--Camus’s automatic carriage - made for Louis XIV.--Degenne’s mechanical peacock--Vaucanson’s - duck which ate and digested its food--Du - Moulin’s automata--Baron Kempelen’s automaton chess-player--Drawing - and writing automata--Maillardet’s - conjurer--Benefits derived from the passion for automata--Examples - of wonderful machinery for useful purposes--Duncan’s - tambouring machinery--Watt’s statue-turning - machinery--Babbage’s calculating machinery 264 - - - LETTER XII. - - Wonders of chemistry--Origin, progress, and objects of - alchemy--Art of breathing fire--Employed by Barchochebas, - Eunus, &c.--Modern method--Art of walking - upon burning coals and red-hot iron, and of plunging the - hands in melted lead and boiling water--Singular property - of boiling tar--Workmen plunge their hands in - melted copper--Trial of ordeal by fire--Aldini’s incombustible - dresses--Examples of their wonderful power in - resisting flame--Power of breathing and enduring air of - high temperatures--Experiments made by Sir Joseph - Banks, Sir Charles Blagden, and Mr. Chantrey 227 - - LETTER XIII. - - Spontaneous combustion--In the absorption of air by - powdered charcoal--and of hydrogen by spongy platinum--Dobereiner’s - lamp--Spontaneous combustion in the - bowels of the earth--Burning cliffs--Burning soil--Combustion - without flame--Spontaneous combustion of human - beings--Countess Zangari--Grace Pett--Natural fire-temples - of the Guebres--Spontaneous fires in the Caspian - Sea--Springs of inflammable gas near Glasgow--Natural - light-house of Maracaybo--New elastic fluids in the - cavities--of gems--Chemical operations going on in their - cavities--Explosions produced in them by heat--Remarkable - changes of colour from chemical causes--Effects - of the nitrous oxide or Paradise gas when - breathed--Remarkable cases described--Conclusion 313 - - - - - LETTERS - - ON - - NATURAL MAGIC; - - ADDRESSED TO - - SIR WALTER SCOTT, BART. - - - - -LETTER I. - - Extent and interest of the subject--Science employed by ancient - governments to deceive and enslave their subjects--Influence - of the supernatural upon ignorant minds--Means employed by the - ancient magicians to establish their authority--Derived from a - knowledge of the phenomena of Nature--From the influence of narcotic - drugs upon the victims of their delusion--From every branch of - science--Acoustics--Hydrostatics--Mechanics--Optics--M. Salverte’s - work on the occult sciences--Object of the following letters. - - - MY DEAR SIR WALTER, - -As it was at your suggestion that I undertook to draw up a popular -account of those prodigies of the material world which have received -the appellation of _Natural Magic_, I have availed myself of the -privilege of introducing it under the shelter of your name. Although -I cannot hope to produce a volume at all approaching in interest -to that which you have contributed to the Family Library, yet the -popular character of some of the topics which belong to this branch of -Demonology may atone for the defects of the following Letters; and I -shall deem it no slight honour if they shall be considered as forming -an appropriate supplement to your valuable work. - -The subject of Natural Magic is one of great extent as well as of -deep interest. In its widest range, it embraces the history of the -governments and the superstitions of ancient times,--of the means by -which they maintained their influence over the human mind,--of the -assistance which they derived from the arts and the sciences, and from -a knowledge of the powers and phenomena of nature. When the tyrants -of antiquity were unable or unwilling to found their sovereignty on -the affections and interests of their people, they sought to entrench -themselves in the strongholds of supernatural influence, and to rule -with the delegated authority of Heaven. The prince, the priest, and the -sage, were leagued in a dark conspiracy to deceive and enslave their -species; and man, who refused his submission to a being like himself, -became the obedient slave of a spiritual despotism, and willingly bound -himself in chains when they seemed to have been forged by the gods. - -This system of imposture was greatly favoured by the ignorance of these -early ages. The human mind is at all times fond of the marvellous, -and the credulity of the individual may be often measured by his own -attachment to the truth. When knowledge was the property of only one -caste, it was by no means difficult to employ it in the subjugation -of the great mass of society. An acquaintance with the motions of the -heavenly bodies, and the variations in the state of the atmosphere, -enabled its possessor to predict astronomical and meteorological -phenomena with a frequency and an accuracy which could not fail to -invest him with a divine character. The power of bringing down fire -from the heavens, even at times when the electric influence was -itself in a state of repose, could be regarded only as a gift from -heaven. The power of rendering the human body insensible to fire was -an irresistible instrument of imposture; and in the combinations of -chemistry, and the influence of drugs and soporific embrocations on the -human frame, the ancient magicians found their most available resources. - -The secret use which was thus made of scientific discoveries and -of remarkable inventions, has no doubt prevented many of them from -reaching the present times; but though we are very ill informed -respecting the progress of the ancients in various departments of the -physical sciences, yet we have sufficient evidence that almost every -branch of knowledge had contributed its wonders to the magician’s -budget, and we may even obtain some insight into the scientific -acquirements of former ages, by a diligent study of their fables and -their miracles. - -The science of _Acoustics_ furnished the ancient sorcerers with some of -their best deceptions. The imitation of thunder in their subterranean -temples could not fail to indicate the presence of a supernatural -agent. The golden virgins whose ravishing voices resounded through the -temple of Delphos;--the stone from the river Pactolus, whose trumpet -notes scared the robber from the treasure which it guarded;--the -speaking head which uttered its oracular responses at Lesbos; and the -vocal statue of Memnon, which began at the break of day to accost the -rising sun,--were all deceptions derived from science, and from a -diligent observation of the phenomena of nature. - -The principles of _Hydrostatics_ were equally available in the work of -deception. The marvellous fountain which Pliny describes in the island -of Andros as discharging wine for seven days, and water during the rest -of the year;--the spring of oil which broke out in Rome to welcome the -return of Augustus from the Sicilian war,--the three empty urns which -filled themselves with wine at the annual feast of Bacchus in the city -of Elis,--the glass tomb of Belus which was full of oil, and which when -once emptied by Xerxes could not again be filled,--the weeping-statues, -and the perpetual lamps of the ancients,--were all the obvious effects -of the equilibrium and pressure of fluids. - -Although we have no direct evidence that the philosophers of antiquity -were skilled in _Mechanics_, yet there are indications of their -knowledge by no means equivocal in the erection of the Egyptian -obelisks, and in the transportation of huge masses of stone, and their -subsequent elevation to great heights in their temples. The powers -which they employed, and the mechanism by which they operated, have -been studiously concealed, but their existence may be inferred from -results otherwise inexplicable; and the inference derives additional -confirmation from the mechanical arrangements which seemed to have -formed a part of their religious impostures. When, in some of the -infamous mysteries of ancient Rome, the unfortunate victims were -carried off by the gods, there is reason to believe that they were -hurried away by the power of machinery; and when Apollonius, conducted -by the Indian sages to the temple of their god, felt the earth rising -and falling beneath his feet, like the agitated sea, he was no doubt -placed upon a moving floor capable of imitating the heavings of the -waves. The rapid descent of those who consulted the oracle in the -cave of Trophonius,--the moving tripods which Apollonius saw in the -Indian temples,--the walking statues at Antium, and in the temple of -Hierapolis,--and the wooden pigeon of Archytas, are specimens of the -mechanical resources of the ancient magic. - -But of all the sciences _Optics_ is the most fertile in marvellous -expedients. The power of bringing the remotest objects within the very -grasp of the observer, and of swelling into gigantic magnitude the -almost invisible bodies of the material world, never fails to inspire -with astonishment even those who understand the means by which these -prodigies are accomplished. The ancients, indeed, were not acquainted -with those combinations of lenses and mirrors which constitute the -telescope and the microscope, but they must have been familiar with -the property of lenses and mirrors to form erect and inverted images -of objects. There is reason to think that they employed them to effect -the apparition of their gods; and in some of the descriptions of the -optical displays which hallowed their ancient temples, we recognize -all the transformations of the modern phantasmagoria. - -It would be an interesting pursuit to embody the information which -history supplies respecting the fables and incantations of the ancient -superstitions, and to show how far they can be explained by the -scientific knowledge which then prevailed. This task has, to a certain -extent, been performed by M. Eusebe Salverte, in a work on the occult -sciences which has recently appeared; but notwithstanding the ingenuity -and learning which it displays, the individual facts are too scanty to -support the speculations of the author, and the descriptions are too -meagre to satisfy the curiosity of the reader.[1] - - [1] We must caution the young reader against some of the views given - in M. Salverte’s work. In his anxiety to account for everything - miraculous by natural causes, he has ascribed to the same origin some - of these events in sacred history which Christians cannot but regard - as the result of divine agency. - -In the following letters I propose to take a wider range, and to enter -into more minute and popular details. The principal phenomena of -nature, and the leading combinations of arts, which bear the impress of -a supernatural character, will pass under our review, and our attention -will be particularly called to those singular illusions of sense, by -which the most perfect organs either cease to perform their functions, -or perform them faithlessly; and where the efforts and the creations of -the mind predominate over the direct perceptions of external nature. - -In executing this plan, the task of selection is rendered extremely -difficult by the superabundance of materials, as well as from the -variety of judgments for which these materials must be prepared. Modern -science may be regarded as one vast miracle, whether we view it in -relation to the Almighty Being by whom its objects and its laws were -formed, or to the feeble intellect of man, by which its depths have -been sounded, and its mysteries explored; and if the philosopher who is -familiarized with its wonders, and who has studied them as necessary -results of general laws, never ceases to admire and adore their Author, -how great should be their effect upon less gifted minds, who must ever -view them in the light of inexplicable prodigies!--Man has in all ages -sought for a sign from heaven, and yet he has been habitually blind to -the millions of wonders with which he is surrounded. If the following -pages should contribute to abate this deplorable indifference to all -that is grand and sublime in the universe, and if they should inspire -the reader with a portion of that enthusiasm of love and gratitude -which can alone prepare the mind for its final triumph, the labours of -the author will not have been wholly fruitless. - - - - -LETTER II. - - The eye the most important of our organs--Popular description - of it--The eye is the most fertile source of mental - illusions--Disappearance of objects when their images fall - upon the base of the optic nerve--Disappearance of objects - when seen obliquely--Deceptions arising from viewing objects - in a faint light--Luminous figures created by pressure on the - eye, either from external causes or from the fulness of the - blood-vessels--Ocular spectra or accidental colours--Remarkable - effects produced by intense light--Influence of the imagination - in viewing these spectra--Remarkable illusion produced by this - affection of the eye--Duration of impressions of light on the - eye--Thaumatrope--Improvements upon it suggested--Disappearance of - halves of objects or of one of two persons--Insensibility of the eye - to particular colours--Remarkable optical illusion described. - - -Of all the organs by which we acquire a knowledge of external nature, -the eye is the most remarkable and the most important. By our other -senses the information we obtain is comparatively limited. The touch -and the taste extend no farther than the surface of our own bodies. -The sense of smell is exercised within a very narrow sphere, and that -of recognizing sounds is limited to the distance at which we hear the -bursting of a meteor and the crash of a thunderbolt. But the eye enjoys -a boundless range of observation. It takes cognizance not only of -other worlds belonging to the solar system, but of other systems of -worlds infinitely removed into the immensity of space; and when aided -by the telescope, the invention of human wisdom, it is able to discover -the forms, the phenomena, and the movements of bodies whose distance is -as inexpressible in language as it is inconceivable in thought. - -While the human eye has been admired by ordinary observers for the -beauty of its form, the power of its movements, and the variety of its -expression, it has excited the wonder of philosophers by the exquisite -mechanism of its interior, and its singular adaptation to the variety -of purposes which it has to serve. The eyeball is nearly globular, -and is about an inch in diameter. It is formed externally by a tough -opaque membrane called the _sclerotic_ coat, which forms the white of -the eye, with the exception of a small circular portion in front called -the _cornea_. This portion is perfectly transparent, and so tough in -its nature as to afford a powerful resistance to external injury. -Immediately within the cornea, and in contact with it, is the _aqueous_ -humour, a clear fluid, which occupies only a small part of the front -of the eye. Within this humour is the iris, a circular membrane, with -a hole in its centre called the _pupil_. The colour of the eye resides -in this membrane, which has the curious property of contracting and -expanding so as to diminish or enlarge the pupil,--an effect which -human ingenuity has not been able even to imitate. Behind the iris is -suspended the _crystalline_ lens, in a fine transparent capsule or bag -of the same form with itself. It is then succeeded by the _vitreous -humour_, which resembles the transparent white of an egg, and fills -up the rest of the eye. Behind the vitreous humour, there is spread -out on the inside of the eyeball a fine delicate membrane, called the -_retina_, which is an expansion of the _optic nerve_, entering the back -of the eye and communicating with the brain. - -A perspective view and horizontal section of the left eye, shown in the -annexed figure, will convey a popular idea of its structure. It is, -as it were, a small camera obscura, by means of which the pictures of -external objects are painted on the retina, and, in a way of which we -are ignorant, it conveys the impression of them to the brain. - -[Illustration: Fig. 1.] - -This wonderful organ may be considered as the sentinel which guards the -pass between the worlds of matter and of spirit, and through which all -their communications are interchanged. The optic nerve is the channel -by which the mind peruses the hand-writing of Nature on the retina, -and through which it transfers to that material tablet its decisions -and its creations. The eye is consequently the principal seat of the -supernatural. When the indications of the marvellous are addressed to -us through the ear, the mind may be startled without being deceived, -and reason may succeed in suggesting some probable source of the -illusion by which we have been alarmed: but when the eye in solitude -sees before it the forms of life, fresh in their colours and vivid in -their outline; when distant or departed friends are suddenly presented -to its view; when visible bodies disappear and reappear without any -intelligible cause; and when it beholds objects, whether real or -imaginary, for whose presence no cause can be assigned, the conviction -of supernatural agency becomes, under ordinary circumstances, -unavoidable. - -Hence it is not only an amusing but a useful occupation to acquire a -knowledge of those causes which are capable of producing so strange a -belief, whether it arises from the delusions which the mind practises -upon itself, or from the dexterity and science of others. I shall -therefore proceed to explain those illusions which have their origin in -the eye, whether they are general, or only occasionally exhibited in -particular persons, and under particular circumstances. - -There are few persons aware that when they look with one eye, there is -some particular object before them to which they are absolutely blind. -If we look with the right eye, this point is always about 15° to the -right of the object which we are viewing, or to the right of the axis -of the eye or the point of most distinct vision. If we look with the -left eye, the point is as far to the left. In order to be convinced -of this curious fact, which was discovered by M. Mariotte, place two -coloured wafers upon a sheet of white paper at the distance of three -inches, and look at the left-hand wafer with the right eye at the -distance of about 11 or 12 inches, taking care to keep the eye straight -above the wafer, and the line which joins the eyes parallel to the line -which joins the wafers. When this is done, and the left eye closed, the -right-hand wafer will no longer be visible. The same effect will be -produced if we close the right eye and look with the left eye at the -right-hand wafer. When we examine the retina to discover to what part -of it this insensibility to light belongs, we find that the image of -the invisible wafer has fallen on the base of the optic nerve, or the -place where this nerve enters the eye and expands itself to form the -retina. This point is shown in the preceding figure by a convexity at -the place where the nerve enters the eye. - -But though light of ordinary intensity makes no impression upon this -part of the eye, a very strong light does, and even when we use candles -or highly luminous bodies in place of wafers, the body does not wholly -disappear, but leaves behind a faint cloudy light, without, however, -giving anything like an image of the object from which the light -proceeds. - -When the objects are _white_ wafers upon a _black_ ground, the white -wafer absolutely disappears, and the space which it covers appears to -be completely black; and as the light which illuminates a landscape -is not much different from that of a white wafer, we should expect, -whether we use one or both eyes,[2] to see a black or a dark spot -upon every landscape, within 15° of the point which most particularly -attracts our notice. The Divine Artificer, however, has not left his -work thus imperfect. Though the base of the optic nerve is insensible -to light that falls directly upon it, yet it has been made susceptible -of receiving luminous impressions from the parts which surround it; and -the consequence of this is, that when the wafer disappears, the spot -which is occupied, in place of being black, has always the same colour -as the ground upon which the wafer is laid, being white when the wafer -is placed upon a white ground, and red when it is placed upon a red -ground. This curious effect may be rudely illustrated by comparing the -retina to a sheet of blotting-paper, and the base of the optic nerve to -a circular portion of it covered with a piece of sponge. If a shower -falls upon the paper, the protected part will not be wetted by the rain -which falls upon the sponge that covers it, but in a few seconds it -will be as effectually wetted by the moisture which it absorbs from the -wet paper with which it is surrounded. In like manner the insensible -spot on the retina is stimulated by a borrowed light, and the apparent -defect is so completely removed, that its existence can be determined -only by the experiment already described. - - [2] When both eyes are open, the object whose image falls upon the - insensible spot of the one eye is seen by the other, so that, though - it is not invisible, yet it will only be half as luminous and, - therefore two dark spots ought to be seen. - -Of the same character, but far more general in its effects, and -important in its consequences, is another illusion of the eye which -presented itself to me several years ago. When the eye is steadily -occupied in viewing any particular object, or when it takes a fixed -direction while the mind is occupied with any engrossing topic of -speculation or of grief, it suddenly loses sight of, or becomes blind -to, objects seen indirectly, or upon which it is not fully directed. -This takes place whether we use one or both eyes, and the object which -disappears will reappear without any change in the position of the -eye, while other objects will vanish and revive in succession without -any apparent cause. If a sportsman, for example, is watching with -intense interest the motions of one of his dogs, his companion, though -seen with perfect clearness by indirect vision, will vanish, and the -light of the heath or of the sky will close in upon the spot which he -occupied. - -In order to witness this illusion, put a little bit of white paper on -a green cloth, and, within three or four inches of it, place a narrow -strip of white paper. At the distance of twelve or eighteen inches, fix -one eye steadily upon the little bit of white paper, and in a short -time a part or even the whole of the strip of paper will vanish as if -it had been removed from the green cloth. It will again reappear, and -again vanish, the effect depending greatly on the steadiness with which -the eye is kept fixed. This illusion takes place when both the eyes are -open, though it is easier to observe it when one of them is closed. The -same thing happens when the object is luminous. When a candle is thus -seen by indirect vision, it never wholly disappears, but it spreads -itself out into a cloudy mass, the centre of which is blue, encircled -with a bright ring of yellow light. - -This inability of the eye to preserve a sustained vision of objects -seen obliquely, is curiously compensated by the greater sensibility of -those parts of the eye that have this defect. The eye has the power -of seeing objects with perfect distinctness only when it is directed -straight upon them; that is, all objects seen indirectly are seen -indistinctly: but it is a curious circumstance, that when we wish to -obtain a sight of a very faint star, such as one of the satellites of -Saturn, we can see it most distinctly _by looking away from it_, and -when the eye is turned full upon it it immediately disappears. - -Effects still more remarkable are produced in the eye when it views -objects that are difficult to be seen from the small degree of light -with which they happen to be illuminated. The imperfect view which we -obtain of such objects forces us to fix the eye more steadily upon -them; but the more exertion we make to ascertain what they are, the -greater difficulties do we encounter to accomplish our object. The -eye is actually thrown into a state of the most painful agitation, -the object will swell and contract, and partly disappear, and it will -again become visible when the eye has recovered from the delirium into -which it has been thrown. This phenomenon may be most distinctly seen -when the objects in a room are illuminated with the feeble gleam of a -fire almost extinguished; but it may be observed in daylight by the -sportsman when he endeavours to mark upon the monotonous heath the -particular spot where moor-game has alighted. Availing himself of -the slightest difference of tint in the adjacent heath, he keeps his -eye steadily fixed on it as he advances, but whenever the contrast of -illumination is feeble, he will invariably lose sight of his mark, -and if the retina is capable of taking it up, it is only to lose it a -second time. - -This illusion is likely to be most efficacious in the dark, when there -is just sufficient light to render white objects faintly visible, and -to persons who are either timid or credulous must prove a frequent -source of alarm. Its influence, too, is greatly aided by another -condition of the eye, into which it is thrown during partial darkness. -The pupil expands nearly to the whole width of the iris, in order to -collect the feeble light which prevails; but it is demonstrable that -in this state the eye cannot accommodate itself to see near objects -distinctly, so that the forms of persons and things actually become -more shadowy and confused when they come within the very distance at -which we count upon obtaining the best view of them. These affections -of the eye are, we are persuaded, very frequent causes of a particular -class of apparitions which are seen at night by the young and the -ignorant. The spectres which are conjured up are always _white_, -because no other colour can be seen, and they are either formed out of -inanimate objects which reflect more light than others around them, -or of animals or human beings whose colour or change of place renders -them more visible in the dark. When the eye dimly descries an inanimate -object whose different parts reflect different degrees of light, its -brighter parts may enable the spectator to keep up a continued view -of it; but the disappearance and reappearance of its fainter parts, -and the change of shape which ensues, will necessarily give it the -semblance of a living form, and if it occupies a position which is -unapproachable, and where animate objects cannot find their way, the -mind will soon transfer to it a supernatural existence. In like manner -a human figure shadowed forth in a feeble twilight may undergo similar -changes, and after being distinctly seen while it is in a situation -favourable for receiving and reflecting light, it may suddenly -disappear in a position fully before, and within the reach of, the -observer’s eye; and if this evanescence takes place in a path or road -where there was no side-way by which the figure could escape, it is -not easy for an ordinary mind to efface the impression which it cannot -fail to receive. Under such circumstances we never think of distrusting -an organ which we have never found to deceive us; and the truth of -the maxim that “seeing is believing” is too universally admitted, and -too deeply rooted in our nature, to admit on any occasion of a single -exception. - -In these observations we have supposed that the spectator bears along -with him no fears or prejudices, and is a faithful interpreter of the -phenomena presented to his senses; but if he is himself a believer -in apparitions, and unwilling to receive an ocular demonstration of -their reality, it is not difficult to conceive the picture which will -be drawn when external objects are distorted and caricatured by the -imperfect indications of his senses, and coloured with all the vivid -hues of the imagination. - -Another class of ocular deceptions have their origin in a property of -the eye which has been very imperfectly examined. The fine nervous -fabric which constitutes the retina, and which extends to the brain, -has the singular property of being _phosphorescent by pressure_. When -we press the eyeball outwards by applying the point of the finger -between it and the nose, a circle of light will be seen, which Sir -Isaac Newton describes as “a circle of colours like those in the -feather of a peacock’s tail.” He adds, that “if the eye and the -figure remain quiet, these colours vanish in a second of time; but -if the finger be moved with a quavering motion, they appear again.” -In the numerous observations which I have made on these luminous -circles, I have never been able to observe any colour but white, with -the exception of a general red tinge which is seen when the eyelids -are closed, and which is produced by the light which passes through -them. The luminous circles, too, always continue while the pressure -is applied, and they may be produced as readily after the eye has -been long in darkness as when it has been recently exposed to light. -When the pressure is very gently applied, so as to compress the fine -pulpy substance of the retina, light is immediately created when the -eye is in total darkness; and when in this state light is allowed to -fall upon it, the part compressed is more sensible to light than any -other part, and consequently appears more luminous. If we increase the -pressure, the eyeball, being filled with incompressible fluids, will -protrude all round the point of pressure, and consequently the retina -at the protruded part will be _compressed_ by the outward pressure -of the contained fluid, while the retina on each side, namely, under -the point of pressure and beyond the protruded part, will be drawn -towards the protruded part or _dilated_. Hence the part under the -finger which was originally compressed is now _dilated_, the adjacent -parts _compressed_, and the more remote parts immediately without this -_dilated_ also. Now we have observed, that when the eye is, under -these circumstances, exposed to light, there is a bright luminous -circle shading off externally and internally into total darkness. -We are led, therefore, to the important conclusions, that when the -retina is compressed in total darkness it gives out light; that when -it is compressed when exposed to light, its sensibility to light is -increased; and that when it is _dilated under exposure to light, it -becomes absolutely blind, or insensible to all luminous impressions_. - -When the body is in a state of perfect health, this phosphorescence -of the eye shows itself on many occasions. When the eye or the head -receives a sudden blow, a bright flash of light shoots from the -eyeball. In the act of sneezing, gleams of light are emitted from each -eye both during the inhalation of the air, and during its subsequent -protrusion, and in blowing air violently through the nostrils, two -patches of light appear above the axis of the eye and in front of it, -while other two luminous spots unite into one, and appear as it were -about the point of the nose when the eyes are directed to it. When -we turn the eyeball by the action of its own muscles, the retina is -affected at the place where the muscles are inserted, and there may -be seen opposite each eye, and towards the nose, two semicircles of -light, and other two extremely faint towards the temples. At particular -times, when the retina is more phosphorescent than at others, these -semicircles are expanded into complete circles of light. - -In a state of indisposition, the phosphorescence of the retina -appears in new and more alarming forms. When the stomach is under a -temporary derangement accompanied with headache, the pressure of the -blood-vessels upon the retina shows itself, in total darkness, by a -faint blue light floating before the eye, varying in its shape, and -passing away at one side. This blue light increases in intensity, -becomes _green_ and then _yellow_, and sometimes rises to _red_, all -these colours being frequently seen at once, or the mass of light -shades off into darkness. When we consider the variety of distinct -forms which in a state of perfect health the imagination can conjure -up when looking into a burning fire, or upon an irregularly shaded -surface,[3] it is easy to conceive how the masses of coloured light -which float before the eye may be moulded by the same power into those -fantastic and natural shapes, which so often haunt the couch of the -invalid, even when the mind retains its energy, and is conscious of the -illusion under which it labours. In other cases, temporary blindness -is produced by pressure upon the optic nerve, or upon the retina; and -under the excitation of fever or delirium, when the physical cause -which produces spectral forms is at its height, there is superadded a -powerful influence of the mind, which imparts a new character to the -phantasms of the senses. - - [3] A very curious example of the influence of the imagination in - creating distinct forms out of an irregularly shaded surface, is - mentioned in the life of Peter Heaman, a Swede, who was executed for - piracy and murder at Leith in 1822. We give it in his own words:-- - - “One remarkable thing was, one day as we mended a sail, it being a - very thin one, after laying it upon deck in folds, I took the tar - brush and tarred it over in the places which I thought needed to be - strengthened. But when we hoisted it up, I was astonished to see that - the tar I had put upon it represented a gallows and a man under it - without a head. The head was lying beside him. He was complete, body, - thighs, legs, arms, and in every shape like a man. Now, I oftentimes - made remarks upon it, and repeated them to the others. I always said - to them all, You may depend upon it that something will happen. I - afterwards took down the sail on a calm day, and sewed a piece of - canvas over the figure to cover it, for I could not bear to have it - always before my eyes.” - -In order to complete the history of the illusions which originate in -the eye, it will be necessary to give some account of the phenomena -called _ocular spectra_, or _accidental colours_. If we cut a figure -out of red paper, and, placing it on a sheet of white paper, view it -steadily for some seconds with one or both eyes fixed on a particular -part of it, we shall observe the red colour to become less brilliant. -If we then turn the eye from the red figure upon the white paper, -we shall see a distinct _green_ figure, which is the _spectrum_, or -accidental colour of the _red_ figure. With differently coloured -figures we shall observe differently coloured spectra, as in the -following table:-- - - COLOUR OF THE COLOUR OF THE - ORIGINAL FIGURES. SPECTRAL FIGURES. - - Red, Bluish-green. - Orange, Blue. - Yellow, Indigo. - Green, Reddish-violet. - Blue, Orange-red. - Indigo, Orange-yellow. - Violet, Yellow. - White, Black. - Black, White. - -The two last of these experiments, viz., white and black figures, may -be satisfactorily made by using a white medallion on a dark ground, and -a black profile figure. The spectrum of the former will be found to be -black, and that of the latter white. - -These ocular spectra often show themselves without any effort on -our part, and even without our knowledge. In a highly painted room, -illuminated by the sun, those parts of the furniture on which the sun -does not directly fall have always the opposite or accidental colour. -If the sun shines through a chink in a _red_ window-curtain, its light -will appear _green_, varying as in the above table, with the colour of -the curtain; and if we look at the image of a candle, reflected from -the water in a _blue_ finger-glass, it will appear _yellow_. Whenever, -in short, the eye is affected with one prevailing colour, it sees at -the same time the spectral or accidental colour, just as when a musical -string is vibrating, the ear hears at the same time its fundamental and -its harmonic sounds. - -If the prevailing light is _white_ and _very strong_, the spectra which -it produces are no longer black, but of various colours in succession. -If we look at the sun, for example, when near the horizon, or when -reflected from glass or water so as to moderate its brilliancy, and -keep the eye upon it steadily for a few seconds, we shall see, even for -hours afterwards, and whether the eyes are open or shut, a spectrum -of the sun varying in its colours. At first, with the eye open, it is -_brownish-red_ with a _sky-blue_ border, and when the eye is shut, -it is _green_ with a _red_ border. The _red_ becomes more brilliant, -and the _blue_ more vivid, till the impression is gradually worn off; -but even when they become very faint, they may be revived by a gentle -pressure on the eyeball. - -Some eyes are more susceptible than others of these spectral -impressions, and Mr. Boyle mentions an individual who continued for -years to see the spectre of the sun when he looked upon bright objects. -This fact appeared to Locke so interesting and inexplicable, that he -consulted Sir Isaac Newton respecting its cause, and drew from him the -following interesting account of a similar effect upon himself:--“The -observation you mention in Mr. Boyle’s book of colours, I once made -upon myself with the hazard of my eyes. The manner was this: I looked -a very little while upon the sun in the looking-glass with my right -eye, and then turned my eyes into a dark corner of my chamber, and -winked, to observe the impression made, and the circles of colours -which encompassed it, and how they decayed by degrees, and at last -vanished. This I repeated a second and a third time. At the third time, -when the phantasm of light and colours about it were almost vanished, -intending my fancy upon them to see their last appearance, I found, to -my amazement, that they began to return, and by little and little to -become as lively and vivid as when I had newly looked upon the sun. -But when I ceased to intend my face upon them, they vanished again. -After this I found that as often as I went into the dark, and intended -my mind upon them, as when a man looks earnestly to see anything which -is difficult to be seen, I could make the phantasm return without -looking any more upon the sun; and the oftener I made it return, the -more easily I could make it return again. And at length, by repeating -this without looking any more upon the sun, I made such an impression -on my eye, that, if I looked upon the clouds, or a book, or any bright -object, I saw upon it a round bright spot of light like the sun, and, -which is still stranger, though I looked upon the sun with my right eye -only, and not with my left, yet my fancy began to make an impression -upon my left eye as well as upon my right. For if I shut my right eye, -and looked upon a book or the clouds with my left eye, I could see the -spectrum of the sun almost as plain as with my right eye, if I did -but intend my fancy a little while upon it: for at first, if I shut -my right eye, and looked with my left, the spectrum of the sun did -not appear till I intended my fancy upon it; but by repeating, this -appeared every time more easily. And now in a few hours’ time I had -brought my eyes to such a pass, that I could look upon no bright object -with either eye but I saw the sun before me, so that I durst neither -write nor read; but to recover the use of my eyes, shut myself up in -my chamber, made dark, for three days together, and used all means -in my power to direct my imagination from the sun. For if I thought -upon him, I presently saw his picture, though I was in the dark. But -by keeping in the dark; and employing my mind about other things, I -began, in three or four days, to have more use of my eyes again; and -by forbearing to look upon bright objects, recovered them pretty well; -though not so well but that, for some months after, the spectrums -of the sun began to return as often as I began to meditate upon the -phenomena, even though I lay in bed at midnight with my curtains drawn. -But now I have been well for many years, though I am apt to think, if -I durst venture my eyes, I could still make the phantasm return by -the power of my fancy. This story I tell you, to let you understand, -that in the observation related by Mr. Boyle, the man’s fancy probably -concurred with the impression made by the sun’s light to produce that -phantasm of the sun which he constantly saw in bright objects.”[4] - - [4] See the _Edinburgh Encyclopædia_, Art. ACCIDENTAL COLOURS. - -I am not aware of any effects that had the character of supernatural -having been actually produced by the causes above described; but it -is obvious, that if a living figure had been projected against the -strong light which imprinted these durable spectra of the sun, which -might really happen when the solar rays are reflected from water, and -diffused by its ruffled surface, this figure would have necessarily -accompanied all the luminous spectres which the fancy created. Even in -ordinary lights, strange appearances may be produced by even transient -impressions; and if I am not greatly mistaken, the case which I am -about to mention is not only one which may occur, but which actually -happened. A figure dressed in _black_, and mounted upon a _white_ -horse, was riding along, exposed to the bright rays of the sun, -which, through a small opening in the clouds, was throwing its light -only upon that part of the landscape. The _black_ figure was projected -against a white cloud, and the white horse shone with particular -brilliancy by its contrast with the dark soil against which it was -seen. A person interested in the arrival of such a stranger had been -for some time following his movements with intense anxiety, but, upon -his disappearance behind a wood, was surprised to observe the spectre -of the mounted stranger in the form of a _white_ rider upon a _black_ -steed, and this spectre was seen for some time in the sky, or upon -any pale ground to which the eye was directed. Such an occurrence, -especially if accompanied with a suitable combination of events, might, -even in modern times, have formed a chapter in the history of the -marvellous. - -It is a curious circumstance, that when the image of an object is -impressed upon the retina only for a few moments, the picture which -is left is exactly of the same colour with the object. If we look, -for example, at a window at some distance from the eye, and then -transfer the eye quickly to the wall, we shall see it distinctly, but -momentarily, with _light_ panes and _dark_ bars; but in a space of -time incalculably short, this picture is succeeded by the spectral -impression of the window, which will consist of _black_ panes and -_white_ bars. The similar spectrum, or that of the same colour as the -object, is finely seen in the experiment of forming luminous circles by -whirling round a burning stick, in which case the circles are always -red. - -In virtue of this property of the eye, an object may be seen in -many places at once; and we may even exhibit at the same instant -the two opposite sides of the same object, or two pictures painted -on the opposite sides of a piece of card. It was found by a French -philosopher, M. D’Arcet, that the impression of light continued on the -retina about the eighth part of a second after the luminous body was -withdrawn, and upon this principle Dr. Paris has constructed the pretty -little instrument called the _Thaumatrope_, or the _Wonder-turner_. It -consists of a number of circular pieces of card, about two or three -inches broad, which may be twirled round with great velocity by the -application of the fore-finger and thumb of each hand to pieces of silk -string attached to opposite points of their circumference. On each -side of the circular piece of card is painted part of a picture, or -a part of a figure, in such a manner that the two parts would form a -group or a whole figure, if we could see both sides at once. Harlequin, -for example, is painted on one side, and Columbine on the other, so -that by twirling round the card the two are seen at the same time in -their usual mode of combination. The body of a Turk is drawn on one -side, and his head on the reverse, and by the rotation of the card the -head is replaced upon his shoulders. The principle of this illusion -may be extended to many other contrivances. Part of a sentence may be -written on one side of a card, and the rest on the reverse. Particular -letters may be given on one side, and others upon the other, or even -halves or parts of each letter may be put upon each side, or all these -contrivances may be combined, so that the sentiment which they express -can be understood only when all the scattered parts are united by the -revolution of the card. - -As the revolving card is virtually transparent, so that bodies beyond -it can be seen through it, the power of the illusion might be greatly -extended by introducing into the picture other figures, either animate -or inanimate. The setting sun, for example, might be introduced into a -landscape; part of the flame of a fire might be seen to issue from the -crater of a volcano, and cattle grazing in a field might make part of -the revolutionary landscape. For such purposes, however, the form of -the instrument would require to be completely changed, and the rotation -should be effected round a standing axis by wheels and pinions, and a -screen placed in front of the revolving plane with open compartments -or apertures, through which the principal figures would appear. Had -the principle of this instrument been known to the ancients, it would -doubtless have formed a powerful engine of delusion in their temples, -and might have been more effective than the optical means which they -seem to have employed for producing the apparitions of their gods. - -In certain diseased conditions of the eye, effects of a very remarkable -kind are produced. The faculty of seeing objects double is too common -to be noticed as remarkable; and though it may take place with only one -eye, yet, as it generally arises from a transient inability to direct -the axis of both eyes to the same point, it excites little notice. -That state of the eye, however, in which we lose sight of half of -every object at which we look, is more alarming and more likely to be -ascribed to the disappearance of part of the object than to a defect -of sight. Dr. Wollaston, who experienced this defect twice, informs us -that, after taking violent exercise, he “suddenly found that he could -see but half of a man whom he met, and that on attempting to read the -name of JOHNSON over a door, he saw only SON, the commencement of the -name being wholly obliterated from his view.” In this instance, the -part of the object which disappeared was towards his left; but on a -second occurrence of the same affection, the part which disappeared -was towards his right. There are many occasions on which this defect -of the eye might alarm the person who witnessed it for the first time. -At certain distances from the eye one of two persons would necessarily -disappear; and by a slight change of position either in the observer -or the person observed, the person that vanished would reappear, while -the other would disappear in his turn. The circumstances under which -these evanescences would take place could not be supposed to occur to -an ordinary observer, even if he should be aware that the cause had its -origin in himself. When a phenomenon so strange is seen by a person in -perfect health, as it generally is, and who has never had occasion to -distrust the testimony of his senses, he can scarcely refer it to any -other cause than a supernatural one. - -Among the affections of the eye which not only deceive the person who -is subject to them, but those also who witness their operation, may be -enumerated the insensibility of the eye to particular colours. This -defect is not accompanied with any imperfection of vision, or connected -with any disease either of a local or a general nature, and it has -hitherto been observed in persons who possess a strong and a sharp -sight. Mr. Huddart has described the case of one Harris, a shoemaker -at Maryport in Cumberland, who was subject to this defect in a very -remarkable degree. He seems to have been insensible to every colour, -and to have been capable of recognizing only the two opposite tints -of _black_ and _white_. “His first suspicion of this defect arose -when he was about four years old. Having by accident found in the -street a child’s stocking, he carried it to a neighbouring house to -inquire for the owner. He observed the people call it a _red stocking_, -though he did not understand why they gave it that denomination, as he -himself thought it completely described by being called a stocking. -The circumstance, however, remained in his memory, and, with other -subsequent observations, led him to the knowledge of his defect. He -observed also, that when young, other children could discern cherries -on a tree by some pretended difference of colour, though he could only -distinguish them from the leaves by their difference of size and shape. -He observed also, that by means of this difference of colour, they -could see the cherries at a greater distance than he could, though he -could see other objects at as great a distance as they, that is, where -the sight was not assisted by the colour.” Harris had two brothers, -whose perception of colours was nearly as defective as his own. One of -these, whom Mr. Huddart examined, constantly mistook _light green_ for -_yellow_, and _orange_ for _grass green_. - -Mr. Scott has described, in the Philosophical Transactions, his own -defect in perceiving colours. He states that he does not know any -_green_ in the world; that a _pink_ colour and a _pale blue_ are -perfectly alike; that he has often thought a _full red_ and a _full -green_ a good match; that he is sometimes baffled in distinguishing -a _full purple_ from a _deep blue_, but that he knows light, dark, -and middle _yellows_, and all degrees of _blue_ except _sky-blue_. “I -married my daughter to a genteel, worthy man, a few years ago; the -day before the marriage, he came to my house dressed in a new suit of -fine cloth clothes. I was much displeased that he should come, as I -supposed, in _black_, and said that he should go back to change his -colour. But my daughter said, No, no; the colour is very genteel; that -it was my eyes that deceived me. He was a gentleman of the law, in a -fine, rich, claret-coloured dress, which is as much black to my eyes as -any black that ever was dyed.” Mr. Scott’s father, his maternal uncle, -one of his sisters, and her two sons, had all the same imperfection. -Dr. Nichol has recorded a case where a naval officer purchased a -_blue_ uniform coat and waistcoat with _red_ breeches to match the -blue, and Mr. Harvey describes the case of a tailor at Plymouth, who -on one occasion repaired an article of dress with _crimson_ in place -of _black_ silk, and on another patched the elbow of a _blue_ coat -with a piece of _crimson_ cloth. It deserves to be remarked that our -celebrated countrymen, the late Mr. Dugald Stewart, Mr. Dalton, and -Mr. Troughton, have a similar difficulty in distinguishing colours. -Mr. Stewart discovered this defect when one of his family was admiring -the beauty of a Siberian crab-apple, which he could not distinguish -from the leaves but by its form and size. Mr. Dalton cannot distinguish -_blue_ from pink, and the solar spectrum consists only of two colours, -_yellow_ and _blue_. Mr. Troughton regards _red ruddy pinks_, and -brilliant _oranges_, as _yellows_, and _greens_ as _blues_, so that he -is capable only of appreciating _blue_ and _yellow_ colours. - -In all those cases which have been carefully studied, at least in -three of them, in which I have had the advantage of making personal -observations, namely, those of Mr. Troughton, Mr. Dalton, and Mr. -Liston, the eye is capable of seeing the whole of the prismatic -spectrum, the red space appearing to be yellow. If the red space -consisted of homogeneous or simple red rays, we should be led to infer -that the eyes in question were not insensible to red light, but were -merely incapable of discriminating between the impressions of red and -yellow light. I have lately shown, however, that the prismatic spectrum -consists of three equal and coincident spectra of _red_, _yellow_, and -_blue_ light, and consequently, that much yellow and a small portion -of blue light exist in the red space; and hence it follows, that those -eyes which see only two colours, viz. _yellow_ and _blue_, in the -spectrum, are really insensible to the red light of the spectrum, and -see only the yellow with the small portion of blue with which the red -is mixed. The faintness of the yellow light which is thus seen in the -red space, confirms the opinion that the retina has not appreciated the -influence of the simple red rays. - -If one of the two travellers who, in the fable of the chameleon, are -made to quarrel about the colour of that singular animal, had happened -to possess this defect of sight, they would have encountered at every -step of their journey, new grounds of dissension, without the chance -of finding an umpire who could pronounce a satisfactory decision. -Under certain circumstances, indeed, the arbiter might set aside the -opinions of both the disputants, and render it necessary to appeal to -some higher authority, - - ---- to beg he’d tell them if he knew - Whether the thing was _red_ or _blue_. - -[Illustration: _Fig. 2._] - -In the course of writing the preceding observations an ocular illusion -occurred to myself of so extraordinary a nature, that I am convinced -it never was seen before, and I think it far from probable that it -will ever be seen again. Upon directing my eyes to the candles that -were standing before me, I was surprised to observe, apparently among -my hair, and nearly straight above my head, and far without the range -of vision, a distinct image of one of the candles inclined about 45° -to the horizon, as shown at A in Fig. 2. The image was as distinct and -perfect as if it had been formed by reflection from a piece of mirror -glass, though of course much less brilliant, and the position of the -image proved that it must be formed by reflection from a perfectly flat -and highly polished surface. But where such a surface could be placed, -and how, even if it were fixed, it could reflect the image of the -candle up through my head, were difficulties not a little perplexing. -Thinking that it might be something lodged in the eyebrow, I covered -it up from the light, but the image still retained its place. I then -examined the eyelashes with as little success, and was driven to the -extreme supposition that a crystallization was taking place in some -part of the aqueous humour of the eye, and that the image was formed by -the reflection of the light of the candle from one of the crystalline -faces. In this state of uncertainty, and, I may add, of anxiety, for -this last supposition was by no means an agreeable one, I set myself -down to examine the phenomenon experimentally. I found that the image -varied its place by the motion of the head and of the eyeball, which -proved that it was either attached to the eyeball or occupied a place -where it was affected by that motion. Upon inclining the candle at -different angles, the image suffered corresponding variations of -position. In order to determine the exact place of the reflecting -substance, I now took an opaque circular body and held it between -the eye and the candle till it eclipsed the mysterious image. By -bringing the body nearer and nearer the eyeball till its shadow became -sufficiently distinct to be seen, it was easy to determine the locality -of the reflector, because the shadow of the opaque body must fall -upon it whenever the image of the candle was eclipsed. In this way I -ascertained that the reflecting body was in the upper eyelash; and I -found, that, in consequence of being disturbed, it had twice changed -its inclination, so as to represent a vertical candle in the horizontal -position B, and afterwards in the inverted position C. Still, however, -I sought for it in vain, and even with the aid of a magnifier I -could not discover it. At last, however, Mrs. B., who possesses the -perfect vision of short-sighted persons, discovered, after repeated -examinations, between two eyelashes, a minute speck, which, upon being -removed with great difficulty, turned out to be a chip of red wax not -above the hundredth part of an inch in diameter, and having its surface -so perfectly flat and so highly polished that I could see in it the -same image of the candle, by placing it extremely near the eye. This -chip of wax had no doubt received its flatness and its polish from the -surface of a seal, and had started into my eye when breaking the seal -of a letter. - -That this reflecting substance was the cause of the image of the -candle, cannot admit of a doubt; but the wonder still remains how the -images which it formed occupied so mysterious a place as to be seen -without the range of vision, and apparently through the head. In order -to explain this, let _m_ _n_, Fig. 2, be a lateral view of the eye. The -chip of wax was placed at _m_ at the root of the eyelashes, and being -nearly in contact with the outer surface of the cornea, the light of -the candle, which it reflected, passed very obliquely through the pupil -and fell upon the retina somewhere to the left of _n_, very near where -the retina terminates; but a ray thus falling obliquely on the retina -is seen, in virtue of the law of visible direction already explained, -in a line _n_ C perpendicular to the retina at the point near _n_, -where the ray fell. Hence the candle was necessarily seen through the -head as it were of the observer, and without the range of ordinary -vision. The comparative brightness of the reflected image still -surprises me; but even this, if the image really was brighter, may -be explained by the fact, that it was formed on a part of the retina -upon which light had never before fallen, and which may therefore -be supposed to be more sensible, than the parts of the membrane in -constant use, to luminous impressions. - -Independent of its interest as an example of the marvellous in vision, -the preceding fact may be considered as a proof that the retina retains -its power to its very termination near the ciliary processes, and that -the law of visible direction holds true even without the range of -ordinary vision. It is therefore possible that a reflecting surface -favourably placed on the outside of the eye, or that a reflecting -surface in the inside of the eye, may cause a luminous image to fall -nearly on the extreme margin of the retina, the consequence of which -would be, that it would be seen in the back of the head, half way -between a vertical and a horizontal line. - - - - -LETTER III. - - Subject of spectral illusions--Recent and interesting case of Mrs. - A.--Her first illusion affecting the ear--Spectral apparition of - her husband--Spectral apparition of a cat--Apparition of a near and - living relation in grave-clothes, seen in a looking-glass--Other - illusions, affecting the ear--Spectre of a deceased friend - sitting in an easy-chair--Spectre of a coach-and-four filled with - skeletons--Accuracy and value of the preceding cases--State of health - under which they arose--Spectral apparitions are pictures on the - retina--The ideas of memory and imagination are also pictures on the - retina--General views of the subject--Approximate explanation of - spectral apparitions. - - -The preceding account of the different sources of illusion to which the -eye is subject is not only useful as indicating the probable cause of -any individual deception, but it has a special importance in preparing -the mind for understanding those more vivid and permanent spectral -illusions to which some individuals have been either occasionally or -habitually subject. - -In these lesser phenomena, we find the retina so powerfully influenced -by external impressions, as to retain the view of visible objects -long after they are withdrawn: we observe it to be so excited by -local pressures of which we sometimes know neither the nature nor the -origin, as to see in total darkness moving and shapeless masses of -coloured light; and we find, as in the case of Sir Isaac Newton, and -others, that the imagination has the power of reviving the impressions -of highly luminous objects, months and even years after they were -first made. From such phenomena, the mind feels it to be no violent -transition to pass to those spectral illusions which, in particular -states of health, have haunted the most intelligent individuals, not -only in the broad light of day, but in the very heart of the social -circle. - -This curious subject has been so ably and fully treated in your -Letters on Demonology, that it would be presumptuous in me to resume -any part of it on which you have even touched; but as it forms a -necessary branch of a Treatise on Natural Magic, and as one of the most -remarkable cases on record has come within my own knowledge, I shall -make no apology for giving a full account of the different spectral -appearances which it embraces, and of adding the results of a series of -observations and experiments on which I have been long occupied, with -the view of throwing some light on this remarkable class of phenomena. - -A few years ago, I had occasion to spend some days under the same roof -with the lady to whose case I have above referred. At that time she -had seen no spectral illusions, and was acquainted with the subject -only from the interesting volume of Dr. Hibbert. In conversing with -her about the cause of these apparitions, I mentioned, that if she -should ever see such a thing, she might distinguish a genuine ghost, -existing externally, and seen as an external object, from one created -by the mind, by merely pressing one eye or straining them both, so -as to see objects double; for in this case the external object or -supposed apparition would invariably be doubled, while the impression -on the retina created by the mind would remain single. This observation -recurred to her mind when she unfortunately became subject to the same -illusions; but she was too well acquainted with their nature to require -any such evidence of their mental origin; and the state of agitation -which generally accompanies them seems to have prevented her from -making the experiment as a matter of curiosity. - -1. The first illusion to which Mrs. A. was subject was one which -affected only the ear. On the 26th of December, 1830, about half-past -four in the afternoon, she was standing near the fire in the hall, -and on the point of going up stairs to dress, when she heard, as she -supposed, her husband’s voice calling her by name, “---- Come here! -come to me!” She imagined that he was calling at the door to have it -opened, but upon going there and opening the door she was surprised to -find no person there. Upon returning to the fire, she again heard the -same voice calling out very distinctly and loudly, “---- Come, come -here!” She then opened two doors of the same room, and upon seeing no -person she returned to the fire-place. After a few moments she heard -the same voice still calling, “---- ---- Come to me, come! come away!” -in a loud, plaintive, and somewhat impatient tone. She answered as -loudly, “Where are you? I don’t know where you are;” still imagining -that he was somewhere in search of her: but receiving no answer, she -shortly went up stairs. On Mr. A.’s return to the house, about half an -hour afterwards, she inquired why he called to her so often, and where -he was; and she was, of course, greatly surprised to learn that he had -not been near the house at the time. A similar illusion, which excited -no particular notice at the time, occurred to Mrs. A. when residing at -Florence about ten years before, and when she was in perfect health. -When she was undressing after a ball, she heard a voice call her -repeatedly by name, and she was at that time unable to account for it. - -2. The next illusion which occurred to Mrs. A. was of a more alarming -character. On the 30th of December, about four o’clock in the -afternoon, Mrs. A. came down stairs into the drawing-room, which she -had quitted only a few minutes before, and on entering the room she -saw her husband, as she supposed, standing with his back to the fire. -As he had gone out to take a walk about half an hour before, she was -surprised to see him there, and asked him why he had returned so -soon. The figure looked fixedly at her with a serious and thoughtful -expression of countenance, but did not speak. Supposing that his mind -was absorbed in thought, she sat down in an arm-chair near the fire, -and within two feet at most of the figure, which she still saw standing -before her. As its eyes, however, still continued to be fixed upon her, -she said, after the lapse of a few minutes, “Why don’t you speak,----?” -The figure immediately moved off towards the window at the further end -of the room, with its eyes still gazing on her, and it passed so very -close to her in doing so, that she was struck by the circumstance of -hearing no step nor sound, nor feeling her clothes brushed against, -nor even any agitation in the air. Although she was now convinced that -the figure was not her husband, yet she never for a moment supposed -that it was anything supernatural, and was soon convinced that it was -a spectral illusion. As soon as this conviction had established itself -in her mind, she recollected the experiment which I had suggested, of -trying to double the object: but before she was able distinctly to do -this, the figure had retreated to the window, where it disappeared. -Mrs. A. immediately followed it, shook the curtains and examined the -window, the impression having been so distinct and forcible that she -was unwilling to believe that it was not a reality. Finding, however, -that the figure had no natural means of escape, she was convinced that -she had seen a spectral apparition like those recorded in Dr. Hibbert’s -work, and she consequently felt no alarm or agitation. The appearance -was seen in bright daylight, and lasted four or five minutes. When the -figure stood close to her it concealed the real objects behind it, and -the apparition was fully as vivid as the reality. - -3. On these two occasions Mrs. A. was alone, but when the next phantasm -appeared her husband was present. This took place on the 4th of -January, 1830. About ten o’clock at night, when Mr. and Mrs. A. were -sitting in the drawing-room, Mr. A. took up the poker to stir the fire, -and when he was in the act of doing this, Mrs. A. exclaimed, “Why -there’s the cat in the room!” “Where?” asked Mr. A. “There, close to -you,” she replied. “Where?” he repeated. “Why on the rug, to be sure, -between yourself and the coal-scuttle.” Mr. A., who had still the -poker in his hand, pushed it in the direction mentioned: “Take care,” -cried Mrs. A., “take care, you are hitting her with the poker.” Mr. -A. again asked her to point out exactly where she saw the cat. She -replied, ”Why sitting up there close to your feet on the rug. She is -looking at me. It is Kitty--come here, Kitty!”--There were two cats -in the house, one of which went by this name, and they were rarely if -ever in the drawing-room. At this time Mrs. A. had no idea that the -sight of the cat was an illusion. When she was asked to touch it, she -got up for the purpose, and seemed as if she were pursuing something -which moved away. She followed a few steps, and then said, “It has gone -under the chair.” Mr. A. assured her it was an illusion, but she would -not believe it. He then lifted up the chair, and Mrs. A. saw nothing -more of it. The room was then searched all over, and nothing found in -it. There was a dog lying on the hearth, who would have betrayed great -uneasiness if a cat had been in the room, but he lay perfectly quiet. -In order to be quite certain, Mr. A. rang the bell, and sent for the -two cats, both of which were found in the housekeeper’s room. - -4. About a month after this occurrence, Mrs. A., who had taken a -somewhat fatiguing drive during the day, was preparing to go to bed -about eleven o’clock at night, and, sitting before the dressing-glass, -was occupied in arranging her hair. She was in a listless and drowsy -state of mind, but fully awake. When her fingers were in active motion -among the papillotes, she was suddenly startled by seeing in the -mirror the figure of a near relation, who was then in Scotland and in -perfect health. The apparition appeared over her left shoulder, and -its eyes met hers in the glass. It was enveloped in grave-clothes, -closely pinned, as is usual with corpses, round the head, and under -the chin, and though the eyes were open, the features were solemn and -rigid. The dress was evidently a shroud, as Mrs. A. remarked even the -punctured pattern usually worked in a peculiar manner round the edges -of that garment. Mrs. A. described herself as at the time sensible of -a feeling like what we conceive of fascination, compelling her for a -time to gaze on this melancholy apparition, which was as distinct and -vivid as any reflected reality could be, the light of the candles upon -the dressing-table appearing to shine fully upon its face. After a few -minutes, she turned round to look for the reality of the form over her -shoulder; but it was not visible, and it had also disappeared from the -glass when she looked again in that direction. - -5. In the beginning of March, when Mr. A. had been about a fortnight -from home, Mrs. A. frequently heard him moving near her. Nearly every -night, as she lay awake, she distinctly heard sounds like his breathing -hard on the pillow by her side, and other sounds such as he might make -while turning in bed. - -6. On another occasion, during Mr. A.’s absence, while riding with -a neighbour, Mr.----, she heard his voice frequently as if he were -riding by his side. She heard also the tramp of his horse’s feet, and -was almost puzzled by hearing him address her at the same time with -the person really in company. His voice made remarks on the scenery, -improvements, &c., such as he probably should have done had he been -present. On this occasion, however, there was no visible apparition. - -7. On the 17th March, Mrs. A. was preparing for bed. She had dismissed -her maid, and was sitting with her feet in hot water. Having an -excellent memory, she had been thinking upon and repeating to herself -a striking passage in the Edinburgh Review, when on raising her eyes, -she saw seated in a large easy-chair before her the figure of a -deceased friend, the sister of Mr. A. The figure was dressed as had -been usual with her, with great neatness, but in a gown of a peculiar -kind, such as Mrs. A. had never seen her wear, but exactly such as had -been described to her by a common friend as having been worn by Mr. -A.’s sister during her last visit to England. Mrs. A. paid particular -attention to the dress, air, and appearance of the figure, which sat -in an easy attitude in the chair, holding a handkerchief in one hand. -Mrs. A. tried to speak to it, but experienced a difficulty in doing -so; and in about three minutes the figure disappeared. About a minute -afterwards, Mr. A. came into the room, and found Mrs. A. slightly -nervous, but fully aware of the delusive nature of the apparition. She -described it as having all the vivid colouring and apparent reality -of life; and for some hours preceding this and other visions, she -experienced a peculiar sensation in her eyes, which seemed to be -relieved when the vision had ceased. - -8. On the 5th October, between one and two o’clock in the morning, Mr. -A. was awoke by Mrs. A., who told him that she had just seen the figure -of his deceased mother draw aside the bedcurtains and appear between -them. The dress and the look of the apparition were precisely those in -which Mr. A.’s mother had been last seen by Mrs. A. at Paris, in 1824. - -9. On the 11th October, when sitting in the drawing-room, on one side -of the fire-place, she saw the figure of another deceased friend -moving towards her from the window at the further end of the room. It -approached the fire-place, and sat down in the chair opposite. As there -were several persons in the room at the time, she describes the idea -uppermost in her mind to have been a fear lest they should be alarmed -at her staring, in the way she was conscious of doing, at vacancy, and -should fancy her intellect disordered. Under the influence of this -fear, and recollecting a story of a similar effect in your work on -Demonology, which she had lately read, she summoned up the requisite -resolution to enable her to cross the space before the fire-place, and -seat herself in the same chair with the figure. The apparition remained -perfectly distinct till she sat down, as it were, in its lap, when it -vanished. - -10. On the 26th of the same month, about two P.M., Mrs. -A. was sitting in a chair by the window in the same room with her -husband. He heard her exclaim--”What have I seen?” And on looking at -her, he observed a strange expression in her eyes and countenance. -A carriage-and-four had appeared to her to be driving up the -entrance-road to the house. As it approached, she felt inclined to -go up stairs to prepare to receive company, but, as if spellbound, -she was unable to move or speak. The carriage approached, and as it -arrived within a few yards of the window, she saw the figures of -the postilions and the persons inside take the ghastly appearance of -skeletons and other hideous figures. The whole then vanished entirely, -when she uttered the above-mentioned exclamation. - -11. On the morning of the 30th October, when Mrs. A. was sitting in her -own room with a favourite dog in her lap, she distinctly saw the same -dog moving about the room during the space of about a minute or rather -more. - -12. On the 3rd December, about nine P.M., when Mr. and Mrs. A. were -sitting near each other in the drawing-room occupied in reading, Mr. -A. felt a pressure on his foot. On looking up he observed Mrs. A.’s -eyes fixed with a strong and unnatural stare on a chair about nine -or ten feet distant. Upon asking her what she saw, the expression of -her countenance changed, and upon recovering herself, she told Mr. A. -that she had seen his brother, who was alive and well at the moment in -London, seated in the opposite chair, but dressed in grave-clothes, and -with a ghastly countenance, as if scarcely alive. - -Such is a brief account of the various spectral illusions observed by -Mrs. A. In describing them I have used the very words employed by her -husband in his communications to me on the subject;[5] and the reader -may be assured that the descriptions are neither heightened by fancy, -nor amplified by invention. The high character and intelligence of -the lady, and the station of her husband in society, and as a man of -learning and science, would authenticate the most marvellous narrative, -and satisfy the most scrupulous mind, that the case has been -philosophically as well as faithfully described. In narrating events -which we regard as of a supernatural character, the mind has a strong -tendency to give more prominence to what appears to itself the most -wonderful; but from the very same cause, when we describe extraordinary -and inexplicable phenomena which we believe to be the result of natural -causes, the mind is prone to strip them of their most marvellous -points, and bring them down to the level of ordinary events. From the -very commencement of the spectral illusions seen by Mrs. A., both she -and her husband were well aware of their nature and origin, and both -of them paid the most minute attention to the circumstances which -accompanied them, not only with the view of throwing light upon so -curious a subject, but for the purpose of ascertaining their connection -with the state of health under which they appeared. - - [5] _Edinburgh Journal of Science_, New Series, No. iv. pp. 218, 219, - No. vi., p. 244, and No. viii., p. 261. - -As the spectres seen by Nicolai and others had their origin in bodily -indisposition, it becomes interesting to learn the state of Mrs. A.’s -health when she was under the influence of these illusions. During the -six weeks within which the first three illusions took place, she had -been considerably reduced and weakened by a troublesome cough, and the -weakness which this occasioned was increased by her being prevented -from taking a daily tonic. Her general health had not been strong, -and long experience has put it beyond a doubt, that her indisposition -arises from a disordered state of the digestive organs. Mrs. A. has -naturally a morbidly sensitive imagination, which so painfully affects -her corporeal impressions, that the account of any person having -suffered severe pain by accident or otherwise, occasionally produces -acute twinges of pain in the corresponding parts of her person. The -account, for example, of the amputation of an arm will produce an -instantaneous and severe sense of pain in her own arm. She is subject -to talk in her sleep with great fluency, to repeat long passages of -poetry, particularly when she is unwell, and even to cap verses for -half an hour together, never failing to quote lines beginning with the -final letter of the preceding one till her memory is exhausted. - -Although it is not probable that we shall ever be able to understand -the actual manner in which a person of sound mind beholds spectral -apparitions in the broad light of day, yet we may arrive at such a -degree of knowledge on the subject as to satisfy rational curiosity, -and to strip the phenomena of every attribute of the marvellous. -Even the vision of natural objects presents to us insurmountable -difficulties, if we seek to understand the precise part which the mind -performs in perceiving them; but the philosopher considers that he has -given a satisfactory explanation of vision, when he demonstrates that -distinct pictures of external objects are painted on the retina, and -that this membrane communicates with the brain by means of nerves of -the same substance as itself, and of which it is merely an expansion. -Here we reach the gulf which human intelligence cannot pass; and if the -presumptuous mind of man shall dare to extend its speculations farther, -it will do it only to evince its incapacity and mortify its pride. - -In his admirable work on this subject, Dr. Hibbert has shown that -spectral apparitions are nothing more than ideas or the recollected -images of the mind, which, in certain states of bodily indisposition, -have been rendered more vivid than actual impression, or, to use other -words, that the pictures in the “mind’s eye” are more vivid than the -pictures in the body’s eye. This principle has been placed by Dr. -Hibbert beyond the reach of doubt; but I propose to go much farther, -and to show that the “mind’s eye” is actually the body’s eye, and that -the retina is the common tablet on which both classes of impressions -are painted, and by means of which they receive their visual existence -according to the same optical laws. Nor is this true merely in the -case of spectral illusions; it holds good of all ideas recalled by -the memory or created by the imagination, and may be regarded as a -fundamental law in the science of pneumatology. - -It would be out of place in a work like this to adduce the experimental -evidence on which it rests, or even to explain the manner in which the -experiments themselves must be conducted: but I may state in general, -that the spectres conjured up by the memory or the fancy have always -a “local habitation,” and that they appear in front of the eye, and -partake in its movements exactly like the impressions of luminous -objects, after the objects themselves are withdrawn. - -In the healthy state of the mind and body, the relative intensity of -these two classes of impressions on the retina is nicely adjusted. The -mental pictures are transient and comparatively feeble, and in ordinary -temperaments are never capable of disturbing or effacing the direct -images of visible objects. The affairs of life could not be carried on -if the memory were to intrude bright representations of the past into -the domestic scene, or scatter them over the external landscape. The -two opposite impressions, indeed, could not co-exist: the same nervous -fibre which is carrying from the brain to the retina the figures of -memory, could not at the same instant be carrying back the impressions -of external objects from the retina to the brain. The mind cannot -perform two different functions at the same instant, and the direction -of its attention to one of the two classes of impressions necessarily -produces the extinction of the other: but so rapid is the exercise -of mental power, that the alternate appearance and disappearance -of the two contending impressions are no more recognized than the -successive observations of external objects during the twinkling of -the eyelids. If we look for example at the façade of St. Paul’s, and -without changing our position call to mind the celebrated view of -Mont Blanc from Lyons, the picture of the cathedral, though actually -impressed upon the retina, is momentarily lost sight of by the mind, -exactly like an object seen by indirect vision; and during the instant -the recollected image of the mountain, towering over the subjacent -range, is distinctly seen, but in a tone of subdued colouring and -indistinct outline. When the purpose of its recall is answered, it -quickly disappears, and the picture of the cathedral again resumes the -ascendancy. - -In darkness and solitude, when external objects no longer interfere -with the pictures of the mind, they become more vivid and distinct; -and in the state between waking and sleeping the intensity of the -impressions approaches to that of visible objects. With persons of -studious habits, who are much occupied with the operations of their -own minds, the mental pictures are much more distinct than in ordinary -persons; and in the midst of abstract thought, external objects even -cease to make any impression on the retina. A philosopher absorbed in -his contemplations experiences a temporary privation of the use of -his senses. His children or his servants will enter the room directly -before his eyes without being seen. They will speak to him without -being heard; and they will even try to rouse him from his reverie -without being felt; although his eyes, his ears, and his nerves -actually receive the impressions of light, sound, and touch. In such -cases, however, the philosopher is voluntarily pursuing a train of -thought on which his mind is deeply interested; but even ordinary -men, not much addicted to speculations of any kind, often perceive in -their mind’s eye the pictures of deceased or absent friends, or even -ludicrous creations of fancy, which have no connexion whatever with the -train of their thoughts. Like spectral apparitions they are entirely -involuntary, and though they may have sprung from a regular series of -associations, yet it is frequently impossible to discover a single link -in the chain. - -If it be true, then, that the pictures of the mind and spectral -illusions are equally impressions upon the retina, the latter will -differ in no respect from the former, but in the degree of vividness -with which they are seen; and those frightful apparitions become -nothing more than our ordinary ideas, rendered more brilliant by some -accidental and temporary derangement of the vital functions. Their -very vividness, too, which is their only characteristic, is capable -of explanation. I have already shown that the retina is rendered -more sensible to light by voluntary local pressure, as well as by -the involuntary pressure of the blood-vessels behind it; and if, by -looking at the sun, we impress upon the retina a coloured image of that -luminary, which is seen even when the eye is shut, we may by pressure -alter the colour of that image, in consequence of having increased the -sensibility of that part of the retina on which it is impressed. Hence -we may readily understand how the vividness of the mental pictures must -be increased by analogous causes. - -In the case both of Nicolai and Mrs. A. the immediate cause of the -spectres was a deranged action of the stomach. When such a derangement -is induced by poison, or by substances which act as poisons, the retina -is peculiarly affected, and the phenomena of vision are singularly -changed. Dr. Patouillet has described the case of a family of _nine_ -persons who were all driven mad by eating the root of the _hyoscyamus -niger_, or black henbane. One of them leapt into a pond, another -exclaimed that his neighbour would lose a cow in a month, and a third -vociferated that the crown piece of sixty pence would in a short time -rise to five livres. On the following day they had all recovered their -senses, but recollected nothing of what had happened. On the same day -they all saw objects double, and, what is still more remarkable, on -the third day _every object appeared to them as red as scarlet_. Now -this red light was probably nothing more than the red phosphorescence -produced by the pressure of the blood-vessels on the retina, and -analogous to the masses of _blue_, _green_, _yellow_, and _red_ light, -which have been already mentioned as produced by a similar pressure in -headaches, arising from a disordered state of the digestive organs. - -Were we to analyse the various phenomena of spectral illusions, we -should discover many circumstances favourable to these views. In those -seen by Nicolai, the individual figures were always somewhat paler than -natural objects. They sometimes grew more and more indistinct, and -became perfectly white; and, to use his own words, “he could always -distinguish with the greatest precision phantasms from phenomena.” -Nicolai sometimes saw the spectres when his eyes were shut, and -sometimes they were thus made to disappear,--effects perfectly -identical with those which arise from the impressions of very luminous -objects. Sometimes the figures vanished entirely, and at other times -only pieces of them disappeared, exactly conformable to what takes -place with objects seen by indirect vision, which most of those figures -must necessarily have been. - -Among the peculiarities of spectral illusions, there is one which -merits particular attention, namely, that they seem to cover or conceal -objects immediately beyond them. It is this circumstance more than any -other which gives them the character of reality, and at first sight it -seems difficult of explanation. The distinctness of any impression on -the retina is entirely independent of the accommodation of the eye -to the distinct vision of external objects. When the eye is at rest, -and is not accommodated to objects at any particular distance, it is -in a state for seeing distant objects most perfectly. When a distinct -spectral impression, therefore, is before it, all other objects in its -vicinity will be seen indistinctly, for while the eye is engrossed with -the vision, it is not likely to accommodate itself to any other object -in the same direction. It is quite common, too, for the eye to see only -one of two objects actually presented to it. A sportsman who has been -in the practice of shooting with both his eyes open, actually sees a -double image of the muzzle of his fowling-piece, though it is only -with one of these images that he covers his game, having no perception -whatever of the other. But there is still another principle upon which -only one of two objects may be seen at a time. If we look very steadily -and continuously at a double pattern, such as those on a carpet -composed of two single patterns of different colours, suppose _red_ and -_yellow_; and if we direct the mind particularly to the contemplation -of the red one, the green pattern will sometimes vanish entirely, -leaving the red alone visible; and by the same process the red one may -be made to disappear. In this case, however, the two patterns, like -the two images, may be seen together; but if the very same portion of -the retina is excited by the direct rays of an external object, when -it is excited by a mental impression, it can no more see them both -at the same time, than a vibrating string can give out two different -fundamental sounds. It is quite possible, however, that the brightest -parts of a spectral figure may be distinctly seen along with the -brightest parts of an object immediately behind it, but then the bright -parts of each object will fall upon different parts of the retina. - -These views are illustrated by a case mentioned by Dr. Abercrombie. A -gentleman, who was a patient of his, of an irritable habit, and liable -to a variety of uneasy sensations in his head, was sitting alone in his -dining-room in the twilight, when the door of the room was a little -open. He saw distinctly a female figure enter, wrapped in a mantle, -with the face concealed by a large black bonnet. She seemed to advance -a few steps towards him, and then stop. He had a full conviction that -the figure was an illusion of vision, and he amused himself for some -time by watching it; at the same time observing that he could see -through the figure so as to perceive the lock of the door, and other -objects behind it.[6] - - [6] Inquiries concerning the Intellectual Powers, and the - Investigation of Truth. Edinburgh, 1830. - -If these views be correct, the phenomena of spectral apparitions -are stripped of all their terror, whether we view them in their -supernatural character, or as indications of bodily indisposition. -Nicolai, even, in whose case they were accompanied with alarming -symptoms, derived pleasure from the contemplation of them, and he -not only recovered from the complaint in which they originated, but -survived them for many years.--Mrs. A., too, who sees them only at -distant intervals, and with whom they have but a fleeting existence, -will, we trust, soon lose her exclusive privilege, when the slight -indisposition which gives them birth has subsided. - - - - -LETTER IV. - - Science used as an instrument of imposture--Deceptions with plane - and concave mirrors practised by the ancients--The magician’s - mirror--Effects of concave mirrors--Aërial images--Images on - smoke--Combination of mirrors for producing pictures from living - objects--The mysterious dagger--Ancient miracles with concave - mirrors--Modern necromancy with them, as seen by Cellini--Description - and effects of the magic lantern--Improvements upon it--Phantasmagoric - exhibitions of Philipstall and others--Dr. Young’s arrangement - of lenses, &c., for the Phantasmagoria--Improvements - suggested--Catadioptrical phantasmagoria for producing the - pictures from living objects--Method of cutting off parts of the - figures--Kircher’s mysterious hand-writing on the wall--His hollow - cylindrical mirror for aërial images--Cylindrical mirror for - re-forming distorted pictures--Mirrors of variable curvature for - producing caricatures. - - -In the preceding observations man appears as the victim of his own -delusions--as the magician unable to exercise the spirits which he -has himself called into being. We shall now see him the dupe of -preconcerted imposture--the slave of his own ignorance--the prostrate -vassal of power and superstition. I have already stated that the -monarchs and priests of ancient times carried on a systematic plan -of imposing upon their subjects--a mode of government which was in -perfect accordance with their religious belief: but it will scarcely be -believed that the same delusions were practised after the establishment -of Christianity, and that even the Catholic sanctuary was often the -seat of these unhallowed machinations. Nor was it merely the low and -cunning priest who thus sought to extort money and respect from the -most ignorant of his flock: bishops and pontiffs themselves wielded -the magician’s wand over the diadem of kings and emperors, and, by -the pretended exhibition of supernatural power, made the mightiest -potentates of Europe tremble upon their thrones. It was the light of -science alone which dispelled this moral and intellectual darkness, -and it is entirely in consequence of its wide diffusion that we live -in times when sovereigns seek to reign only through the affections of -their people, and when the minister of religion asks no other reverence -but that which is inspired by the sanctity of his office and the purity -of his character. - -It was fortunate for the human race that the scanty knowledge of former -ages afforded so few elements of deception. What a tremendous engine -would have been worked against our species by the varied and powerful -machinery of modern science! Man would still have worn the shackles -which it forged, and his noble spirit would still have groaned beneath -its fatal pressure. - -There can be little doubt that the most common, as well as the most -successful, impositions of the ancients were of an optical nature, -and were practised by means of plane and concave mirrors. It has been -clearly shown by various writers that the ancients made use of mirrors -of steel, silver, and a composition of copper and tin, like those now -used for reflecting specula. It is also very probable, from a passage -in Pliny, that glass mirrors were made at Sidon; but it is evident, -that, unless the object presented to them was illuminated in a very -high degree, the images which they formed must have been very faint and -unsatisfactory. The silver mirrors, therefore, which were universally -used, and which are superior to those made of any other metal, are -likely to have been most generally employed by the ancient magicians. -They were made to give multiplied and inverted images of objects, that -is, they were plane, polygonal or many-sided, and concave. There is -one property, however, mentioned by Aulus Gellius, which has given -unnecessary perplexity to commentators. He states that there were -specula, which, when put in a particular place, gave no images of -objects, but when carried to another place, recovered their property -of reflection.[7] M. Salverte is of opinion that, in quoting Varro, -Aulus Gellius was not sufficiently acquainted with the subject, and -erred in supposing that the phenomenon depended on the _place_ instead -of the position of the mirror; but this criticism is obviously made -with the view of supporting an opinion of his own--that the property -in question may be analogous to the phenomenon of polarised light, -which, at a certain angle, refuses to suffer reflexion from particular -bodies. If this idea has any foundation, the mirror must have been of -glass or some other body not metallic, or, to speak more correctly, -there must have been _two_ such mirrors, so nicely adjusted not only -to one another, but to the light incident upon each, that the effect -could not possibly be produced but by a philosopher thoroughly -acquainted with the modern discovery of the polarisation of light -by reflexion. Without seeking for so profound an explanation of the -phenomenon, we may readily understand how a silver mirror may instantly -lose its reflecting power in a damp atmosphere, in consequence of the -precipitation of moisture upon its surface, and may immediately recover -it when transported into drier air. - - [7] _Ut speculum in loco certo positum nihil imaginet; aliorsum - translatum faciat imagines._ Aul. Gel. Noct. Attic., lib. xvi., cap. - 18. - -[Illustration: _Fig. 3._] - -One of the simplest instruments of optical deception is the plane -mirror, and when two are combined for this purpose it has been called -the magician’s mirror. An observer in front of a plane mirror sees a -distinct image of himself; but if two persons take up a mirror, and -if the one person is as much to one side of a line perpendicular to -the middle of it as the other is to the other side, they will see each -other, but not themselves. If we now suppose MC, CD, NC, CD to be the -partitions of two adjacent apartments let square openings be made in -the partitions at A and B, above five feet above the floor, and let -them be filled with plate glass, and surrounded with a picture frame, -so as to have the appearance of two mirrors. Place two mirrors, E, F, -one behind each opening at A and B, inclined 45° to the partition MN, -and so large that a person looking into the plates of glass at A and -B will not see their edges. When this is done it is obvious that a -person looking into the mirror A will not see himself, but will see any -person or figure placed at B. If he believes that he is looking into a -common mirror at A, his astonishment will be great at seeing himself -transformed into another person, or into any living animal that may be -placed at B. The success of this deception would be greatly increased -if a plane mirror, suspended by a pulley, could be brought immediately -behind the plane glass at A, and drawn up from it at pleasure. The -spectator at A, having previously seen himself in this moveable mirror, -would be still more astonished when he afterwards perceived in the same -place a face different from his own. By drawing the moveable mirror -half up, the spectator at A might see half of his own face joined to -half of the face placed at B; but in the present day the most ignorant -persons are so familiar with the properties of a looking-glass, that -it would be very difficult to employ this kind of deception with the -same success which must have attended it in a more illiterate age. The -optical reader will easily see that the mirror F and the apartment NCD -are not absolutely necessary for carrying on this deception; for the -very same effects will be produced if the person at B is stationed at -G, and looks towards the mirror F in the direction GF. As the mirror -F, however, must be placed as near to A as possible, the person at G -would be too near the partition CN, unless the mirror F was extremely -large. - -The effect of this and every similar deception is greatly increased -when the persons are illuminated with a strong light, and the rest of -the apartment as dark as possible; but whatever precautions are taken, -and however skilfully plane mirrors are combined, it is not easy to -produce with them any very successful illusions. - -The concave mirror is the staple instrument of the magician’s cabinet, -and must always perform a principal part in all optical combinations. -In order to be quite perfect, every concave mirror should have its -surface elliptical, so that if any object is placed in one focus of the -ellipse, an inverted image of it will be formed in the other focus. -This image, to a spectator rightly placed, appears suspended in the -air, so that if the mirror and the object are hid from his view, the -effect must appear to him almost supernatural. - -The method of exhibiting the effect of concave mirrors most -advantageously is shown in Fig. 4, where CD is the partition of a -room having in it a square opening EF, the centre of which is about -five feet above the floor. This opening might be surrounded with a -picture-frame, and a painting which exactly filled it might be so -connected with a pulley that it could be either slipped aside, or -raised so as to leave the frame empty. A large concave mirror MN is -then placed in another apartment, so that when any object is placed at -A, a distinct image of it may be formed in the centre of the opening -EF. Let us suppose this object to be a plaster cast of any object made -as white as possible, and placed in an _inverted_ position at A. A -strong light should then be thrown upon it by a powerful lamp, the rays -of which are prevented from reaching the opening EF. When this is done, -a spectator placed at O will see an erect image of the statue at B, -the centre of the opening, standing in the air, and differing from the -real statue only in being a little larger, while the apparition will -be wholly invisible to other spectators placed at a little distance on -each side of him. - -[Illustration: _Fig. 4._] - -If the opening EF is filled with smoke, rising either from a -chafing-dish, in which incense is burnt, or made to issue in clouds -from some opening below, the image will appear in the middle of the -smoke depicted upon it as upon a ground, and capable of being seen by -those spectators who could not see the image of the air. The rays of -light, in place of proceeding without obstruction to an eye at O, are -reflected as it were from those minute particles of which the smoke -is composed, in the same manner as a beam of light is rendered more -visible by passing through an apartment filled with dust or smoke. - -It has long been a favourite experiment to place at A a white and -strongly illuminated human skull, and to exhibit an image of it amid -the smoke of a chafing-dish at B; but a more terrific effect would be -produced if a small skeleton suspended by invisible wires were placed -as an object at A. Its image suspended in the air at B, or painted upon -smoke, could not fail to astonish the spectator. - -The difficulty of placing a living person in an inverted position, -as an object at A, has no doubt prevented the optical conjuror from -availing himself of so admirable a resource; but this difficulty may be -removed by employing a second concave mirror. The second mirror may be -so placed as to reflect towards MN the rays proceeding from an erect -living object, and to form an inverted image of this object at A. An -erect image of this inverted image will then be formed at B, either -suspended in the air, or depicted upon a wreath of smoke. This aërial -image will exhibit the precise form and colours and movements of the -living object, and it will maintain its character as an apparition if -any attempt is made by the spectator to grasp its unsubstantial fabric. - -A deception of an alarming kind, called the _Mysterious dagger_, -has been long a favourite exhibition. If a person with a drawn and -highly polished dagger, illuminated by a strong light, stands a -little farther from a concave mirror than its principal focus, he -will perceive in the air between himself and the mirror an inverted -and diminished image of his own person, with the dagger similarly -brandished. If he aims the dagger at the centre of the mirrors -concavity, the two daggers will meet point to point, and, by pushing it -still farther from him towards the mirror, the imaginary dagger will -strike at his heart. In this case it is necessary that the direction of -the real dagger coincides with a diameter of the sphere of which the -mirror is a part; but if its direction is on one side of that diameter, -the direction of the imaginary dagger will be as far on the other side -of the diameter, and the latter will aim a blow at any person who is -placed in the proper position for receiving it. If the person who bears -the real dagger is therefore placed behind a screen, or otherwise -concealed from the view of the spectator, who is made to approach to -the place of the image, the thrust of the polished steel at his breast -will not fail to produce a powerful impression. The effect of this -experiment would no doubt be increased by covering with black cloth -the person who holds the dagger, so that the image of his hand only -should be seen, as the inverted picture of him would take away from the -reality of the appearance. By using two mirrors, indeed, this defect -might be remedied, and the spectator would witness an exact image of -the assassin aiming the dagger at his life. - -The common way of making this experiment is to place a basket of fruit -above the dagger, so that a distinct aërial image of the fruit is -formed in the focus of the mirror. The spectator, having been desired -to take some fruit from the basket, approaches for that purpose, while -a person properly concealed withdraws the real basket of fruit with one -hand, and with the other advances the dagger, the image of which being -no longer covered by the fruit, strikes at the body of the astonished -spectator. - -The powers of the concave mirror have been likewise displayed in -exhibiting the apparition of an absent or deceased friend. For this -purpose, a strongly illuminated bust or picture of the person is -placed before the concave mirror, and a distinct image of the picture -will be seen either in the air or among smoke, in the manner already -described. If the background of the picture is temporarily covered with -lamp-black, so that there is no light about the picture but what falls -upon the figure, the effect will be more complete. - -As in all experiments with concave mirrors, the size of the aërial -image is to that of the real object as their distances from the mirror, -we may, by varying the distance of the object, increase or diminish the -size of the image. In doing this, however, the distance of the image -from the mirror is at the same time changed, so that it would quit the -place most suitable for its exhibition. This defect may be removed by -simultaneously changing the place both of the mirror and the object, so -that the image may remain stationary, expanding itself from a luminous -spot to a gigantic size, and again passing through all intermediate -magnitudes, till it vanishes in a cloud of light. - -Those who have studied the effects of concave mirrors of a small -size, and without the precautions necessary to ensure deception, -cannot form any idea of the magical effect produced by this class of -optical apparitions. When the instruments of illusion are themselves -concealed,--when all extraneous lights but those which illuminate -the real object are excluded,--when the mirrors are large and -well-polished, and truly formed,--the effect of the representation on -ignorant minds is altogether overpowering; while even those who know -the deception, and perfectly understand its principles, are not a -little surprised at its effects. The inferiority in the effects of a -common concave mirror to that of a well-arranged exhibition is greater -even than that of a perspective picture, hanging in an apartment, to -the same picture exhibited under all the imposing accompaniments of a -dioramic representation. - -It can scarcely be doubted, that a concave mirror was the principal -instrument by which the heathen gods were made to appear in the ancient -temples. In the imperfect accounts which have reached us of these -apparitions, we can trace all the elements of an optical illusion. In -the ancient temple of Hercules at Tyre, Pliny mentions that there was -a seat made of a consecrated stone, “from which the gods easily rose.” -Esculapius often exhibited himself to his worshippers in his temple -at Tarsus; and the temple of Enguinum in Sicily was celebrated as the -place where the goddesses exhibited themselves to mortals. Iamblichus -actually informs us, that the ancient magicians caused the gods to -appear among the vapours disengaged from fire; and when the conjuror -Maximus terrified his audience by making the statue of Hecate laugh, -while in the middle of the smoke of burning incense, he was obviously -dealing with the image of a living object dressed in the costume of the -sorceress. - -The character of these exhibitions in the ancient temples is so -admirably depicted in the following passage of Damascius, quoted by M. -Salverte, that we recognise all the optical effects which have been -already described. “In a manifestation,” says he, “which ought not to -be revealed ... there appeared on the wall of the temple a mass of -light, which at first seemed to be very remote; it transformed itself, -in coming nearer, into a face evidently divine and supernatural, of -a severe aspect, but mixed with gentleness, and extremely beautiful. -According to the institutions of a mysterious religion, the -Alexandrians honoured it as Osiris and Adonis.” - -Among more modern examples of this illusion, we may mention the case of -the Emperor Basil of Macedonia. Inconsolable at the loss of his son, -this sovereign had recourse to the prayers of the Pontiff Theodore -Santabaren, who was celebrated for his power of working miracles. The -ecclesiastical conjuror exhibited to him the image of his beloved -son, magnificently dressed and mounted upon a superb charger: the -youth rushed towards his father, threw himself into his arms, and -disappeared. M. Salverte judiciously observes, that this deception -could not have been performed by a real person who imitated the figure -of the young prince. The existence of this person, betrayed by so -remarkable a resemblance, and by the trick of the exhibition, could not -fail to have been discovered and denounced, even if we could explain -how the son could be so instantaneously disentangled from his father’s -embrace. The emperor, in short, saw the aërial image of a picture -of his son on horseback; and as the picture was brought nearer the -mirror, the image advanced into his arms, when it of course eluded his -affectionate grasp. - -These and other allusions to the operations of the ancient magic, -though sufficiently indicative of the methods which were employed, are -too meagre to convey any idea of the splendid and imposing exhibitions -which must have been displayed. A national system of deception, -intended as an instrument of government, must have brought into -requisition not merely the scientific skill of the age, but a variety -of subsidiary contrivances calculated to astonish the beholder, to -confound his judgment, to dazzle his senses, and to give a predominant -influence to the peculiar imposture which it was thought desirable -to establish. The grandeur of the means may be inferred from their -efficacy, and from the extent of their influence. - -This defect, however, is, to a certain degree, supplied by an account -of a modern necromancy, which has been left us by the celebrated -Benvenuto Cellini, and in which he himself performed an active part. - -“It happened,” says he, “through a variety of odd accidents, that I -made acquaintance with a Sicilian priest, who was a man of genius, and -well versed in the Latin and Greek authors. Happening one day to have -some conversation with him when the subject turned upon the art of -necromancy, I, who had a great desire to know something of the matter, -told him, that I had all my life felt a curiosity to be acquainted with -the mysteries of this art. - -“The priest made answer, ‘that the man must be of a resolute and -steady temper who enters upon that study.’ I replied, ‘that I had -fortitude and resolution enough, if I could but find an opportunity.’ -The priest subjoined, ‘If you think you have the heart to venture, I -will give you all the satisfaction you can desire.’ Thus we agreed -to enter upon a plan of necromancy. The priest one evening prepared -to satisfy me, and desired me to look out for a companion or two. I -invited one Vincenzio Romoli, who was my intimate acquaintance: he -brought with him a native of Pistoia, who cultivated the black art -himself. We repaired to the Colosseo, and the priest, according to the -custom of necromancers, began to draw circles upon the ground, with -the most impressive ceremonies imaginable: he likewise brought hither -asafœtida, several precious perfumes, and fire, with some compositions -also, which diffused noisome odours. As soon as he was in readiness, -he made an opening to the circle, and having taken us by the hand, -ordered the other necromancer, his partner, to throw the perfumes -into the fire at a proper time, entrusting the care of the fire and -perfumes to the rest; and thus he began his incantations. This ceremony -lasted above an hour and a half, when there appeared several legions -of devils, insomuch that the amphitheatre was quite filled with them. -I was busy about the perfumes, when the priest, perceiving there was -a considerable number of infernal spirits, turned to me and said, -‘Benvenuto, ask them something.’ I answered, ‘Let them bring me into -the company of my Sicilian mistress Angelica.’ That night he obtained -no answer of any sort; but I had received great satisfaction in having -my curiosity so far indulged. The necromancer told me it was requisite -we should go a second time, assuring me that I should be satisfied in -whatever I asked; but that I must bring with me a pure, immaculate boy. - -“I took with me a youth who was in my service, of about twelve years of -age, together with the same Vincenzio Romoli, who had been my companion -the first time, and one Agnolino Gaddi, an intimate acquaintance, whom -I likewise prevailed on to assist at the ceremony. When we came to the -place appointed, the priest having made his preparations as before, -with the same and even more striking ceremonies, placed us within the -circle, which he had likewise drawn with a more wonderful art and in a -more solemn manner than at our former meeting. Thus, having committed -the care of the perfumes and the fire to my friend Vincenzio, who was -assisted by Agnolino Gaddi, he put into my hand a pintaculo or magical -chart, and bid me turn it towards the places that he should direct me; -and under the pintaculo I held the boy. The necromancer, having begun -to make his tremendous invocations, called by their names a multitude -of demons who were the leaders of the several legions, and questioned -them, by the power of the eternal uncreated God, who lives for ever, -in the Hebrew language, as likewise in Latin and Greek; insomuch that -the amphitheatre was almost in an instant filled with demons more -numerous than at the former conjuration. Vincenzio Romoli was busied -in making a fire, with the assistance of Agnolino, and burning a great -quantity of precious perfumes. I, by the directions of the necromancer, -again desired to be in the company of my Angelica. The former thereupon -turning to me said,--’Know, they have declared that, in the space of a -month, you shall be in her company.’ - -“He thus requested me to stand resolutely by him, because the legions -were now above a thousand more in number than he had designed; and -besides, these were the most dangerous; so that, after they had -answered my question, it behoved him to be civil to them, and dismiss -them quietly. At the same time the boy under the pintaculo was in a -terrible fright, saying, that there were in that place a million of -fierce men, who threatened to destroy us; and that, moreover, four -armed giants of enormous stature were endeavouring to break into our -circle. During this time, whilst the necromancer, trembling with fear, -endeavoured by mild and gentle methods to dismiss them in the best way -he could, Vincenzio Romoli, who quivered like an aspen leaf, took care -of the perfumes. Though I was as much terrified as any of them, I did -my utmost to conceal the terror I felt; so that I greatly contributed -to inspire the rest with resolution; but the truth is, I gave myself -over for a dead man, seeing the horrid fright the necromancer was in. -The boy placed his head between his knees and said, ‘In this posture -will I die; for we shall all surely perish.’ I told him that all these -demons were under us, and what he saw was smoke and shadow; so bid -him hold up his head and take courage. No sooner did he look up than -he cried out, ‘The whole amphitheatre is burning, and the fire is -just falling upon us.’ So covering his eyes with his hands, he again -exclaimed, ‘that destruction was inevitable, and desired to see no -more.’ The necromancer entreated me to have a good heart, and take -care to burn proper perfumes; upon which I turned to Romoli, and bid -him burn all the most precious perfumes he had. At the same time I -cast my eye upon Agnolino Gaddi, who was terrified to such a degree -that he could scarce distinguish objects, and seemed to be half dead. -Seeing him in this condition, I said, ‘Agnolino, upon these occasions -a man should not yield to fear, but should stir about and give his -assistance, so come directly and put on some more of these.’ The -effects of poor Agnolino’s fear were overpowering. The boy, hearing -a crepitation, ventured once more to raise his head, when, seeing me -laugh, he began to take courage, and said ‘that the devils were flying -away with a vengeance.’ - -“In this condition we stayed, till the bell rang for morning prayers. -The boy again told us, that there remained but few devils, and these -were at a great distance. When the magician had performed the rest of -his ceremonies, he stripped off his gown, and took up a wallet full of -books which he had brought with him. - -“We all went out of the circle together, keeping as close to each other -as we possibly could, especially the boy, who had placed himself in -the middle, holding the necromancer by the coat, and me by the cloak. -As we were going to our houses in the quarter of Banchi, the boy told -us that two of the demons whom we had seen at the amphitheatre went on -before us leaping and skipping, sometimes running upon the roofs of the -houses, and sometimes upon the ground. The priest declared, that though -he had often entered magic circles, nothing so extraordinary had ever -happened to him. As we went along, he would fain persuade me to assist -with him at consecrating a brook, from which, he said, we should derive -immense riches; we should then ask the demons to discover to us the -various treasures with which the earth abounds, which would raise us to -opulence and power; but that these love-affairs were mere follies, from -whence no good could be expected. I answered, ‘that I would readily -have accepted his proposal, if I understood Latin.’ He redoubled his -persuasions, assuring me, that the knowledge of the Latin language -was by no means material. He added, that he could have Latin scholars -enough, if he had thought it worth while to look out for them, but that -he could never have met with a partner of resolution and intrepidity -equal to mine, and that I should by all means follow his advice. Whilst -we were engaged in this conversation we arrived at our respective -houses, and all that night dreamt of nothing but devils.” - -It is impossible to peruse the preceding description without being -satisfied that the legions of devils were not produced by any influence -upon the imaginations of the spectators, but were actual optical -phantasms, or the images of pictures or objects produced by one or -more concave mirrors or lenses. A fire is lighted, and perfumes and -incense are burnt, in order to create a ground for the images, and the -beholders are rigidly confined within the pale of the magic circle. The -concave mirror and the objects presented to it having been so placed -that the persons within the circle could not see the aërial image of -the objects by the rays deeply reflected from the mirror, the work of -deception was ready to begin. The attendance of the magician upon his -mirror was by no means necessary. He took his place along with the -spectators within the magic circle. The images of the devils were all -distinctly formed in the air immediately above the fire, but none of -them could be seen by those within the circle. The moment, however, -that perfumes were thrown into the fire to produce smoke, the first -wreath of smoke that rose through the place of one or more of the -images, would reflect them to the eyes of the spectator, and they could -again disappear if the wreath was not followed by another. More and -more images would be rendered visible as new wreaths of smoke arose, -and the whole group would appear at once when the smoke was uniformly -diffused over the place occupied by the images. - -The “compositions which diffused noisome odours” were intended to -intoxicate or stupify the spectators, so as to increase their liability -to deception, or to add to the real phantasms which were before their -eyes, others which were the offspring only of their own imaginations. -It is not easy to gather from the description what parts of the -exhibition were actually presented to the eyes of the spectators, and -what parts of it were imagined by themselves. It is quite evident -that the boy, as well as Agnolino Gaddi, were so overpowered with -terror that they fancied many things which they did not see; but when -the boy declares that four armed giants, of an enormous stature, were -threatening to break into the circle, he gives an accurate description -of the effect that would be produced by pushing the figures nearer the -mirror, and then magnifying their images, and causing them to advance -towards the circle. Although Cellini declares that he was trembling -with fear, yet it is quite evident that he was not entirely ignorant of -the machinery which was at work; for in order to encourage the boy, who -was almost dead with fear, he assured them that the devils were under -their power, and that “what he saw was smoke and shadow.” - -Mr. Roscoe, from whose Life of Cellini the preceding description is -taken, draws a similar conclusion from the consolatory words addressed -to the boy, and states that they “confirm him in the belief, that the -whole of these appearances, like a phantasmagoria, were merely the -effects of a magic lantern produced on volumes of smoke from various -kinds of burning wood.” In drawing this conclusion, Mr. Roscoe has -not adverted to the fact, that this exhibition took place about the -middle of the 16th century, while the magic lantern was not invented -by Kircher till towards the middle of the 17th century; Cellini -having died in 1570, and Kircher having been born in 1601. There -is no doubt that the effects described could be produced by this -instrument, but we are not entitled to have recourse to any other -means of explanation but those which were known to exist at the time -of Cellini. If we suppose, however, that the necromancer either had a -regular magic lantern, or that he had fitted up his concave mirror in -a box containing the figures of his devils, and that this box with its -lights was carried home with the party, we can easily account for the -declaration of the boy, “that as they were going home to their houses -in the quarter of Banchi, _two of the demons whom we had seen at the -amphitheatre went on before us leaping and skipping, sometimes running -upon the roofs of the houses, and sometimes upon the ground_.” - -The introduction of the magic lantern as an optical instrument -supplied the magicians of the 17th century with one of their most -valuable tools. The use of the concave mirror, which does not appear -to have been even put up into the form of an instrument, required a -separate apartment, or at least that degree of concealment which it -was difficult on ordinary occasions to command; but the magic lantern, -containing in a small compass its lamp, its lenses, and its sliding -figures, was peculiarly fitted for the itinerant conjuror, who had -neither the means of providing a less portable and more extensive -apparatus, nor the power of transporting and erecting it. - -The magic lantern shown in the annexed figure consists of a dark -lantern, AB, containing a lamp G, and a concave metallic mirror, MN, -and it is so constructed that when the lamp is lighted not a ray of -light is able to escape from it. Into the side of the lantern is fitted -a double tube, CD, the outer half of which D is capable of moving -within the other half. A large plano-convex lens C, is fixed at the -inner end of the double tube, and a small convex lens D, at the outer -end; and to the fixed tube CE, there is joined a groove EF, in which -the sliders containing the painted objects are placed, and through -which they can be moved. Each slider contains a series of figures or -pictures painted on glass with highly transparent colours. The direct -light of the lamp G, and the light reflected from the mirror MN, -falling upon the illuminating lens C, is concentrated by it so as to -throw a brilliant light upon the painting on the slider, and as this -painting is in the conjugate focus of the convex lens D, a magnified -image of it will be formed on a white wall or white cloth placed at PQ. -If the lens D is brought nearer to EF, or to the picture, the distinct -image will be more magnified, and will be formed at a greater distance -from D, so that if there is any particular distance of the image which -is more convenient than another, or any particular size of the object -which we wish, it can be obtained by varying the distance of the lens -D from EF. - -[Illustration: _Fig. 5._] - -When the image is received on an opaque ground, as is commonly the -case, the spectators are placed in the same room with the lantern; -but, for the purposes of deception, it would be necessary to place -the lantern in another apartment like the mirror in Fig. 4, and to -throw the magnified pictures on a large plate of ground glass, or a -transparent gauze screen, stretched across an opening EF, Fig. 4, made -in the partition which separates the spectators from the exhibitor. -The images might, like those of the concave mirror, be received upon -wreaths of smoke. These images are of course always inverted in -reference to the position of the painted objects; but in order to -render them really erect, we have only to invert the sliders. The -representations of the magic lantern never fail to excite a high degree -of interest, even when exhibited with the ordinary apparatus; but -by using double sliders, and varying their movements, very striking -effects may be produced. A smith, for example, is made to hammer -upon his anvil,--a figure is thrown into the attitude of terror by -the introduction of a spectral apparition, and a tempest at sea is -imitated, by having the sea on one slider, and the ships on other -sliders, to which an undulatory motion is communicated. - -The magic lantern is susceptible of great improvement in the painting -of the figures, and in the mechanism and combination of the sliders. -A painted figure, which appears well executed to the unassisted eye, -becomes a mere daub when magnified 50 or 100 times; and when we -consider what kind of artists are employed in their execution, we need -not wonder that this optical instrument has degenerated into a mere -toy for the amusement of the young. Unless for public exhibition, -the expense of exceedingly minute and spirited drawings could not be -afforded; but I have no doubt that if such drawings were executed, a -great part of the expense might be saved by engraving them on wood, and -transferring their outline to the glass sliders. - -A series of curious representations might be effected, by inserting -glass plates containing suitable figures in a trough having two of its -sides parallel, and made of plate glass. The trough must be introduced -at EF, so that the figure on the glass is at the proper distance from -the object lens D. When the trough is filled with water, or with -any transparent fluid, the picture at PQ will be seen with the same -distinctness as if the figure had been introduced by itself into the -groove EF; but if any transparent fluid of a different density from -water is mixed with it, so as to combine with it quickly or slowly, the -appearance of the figure displayed at PQ will undergo singular changes. -If spirits of wine, or any ardent spirit, are mixed with the water, so -as to produce throughout its mass partial variations of density, the -figure at PQ, will be as it were broken down into a thousand parts, -and will recover its continuity and distinctness when the two fluids -have combined. If a fluid of less density than water is laid gently -upon the water, so as to mix with it gradually, and produce a regular -diminution of density downwards--or if saline substances, soluble in -water, are laid at the bottom of the trough, the density will diminish -upwards, and the figure will undergo the most curious elongations and -contractions. Analogous effects may be produced by the application of -heat to the surface or sides of the trough, so that we may effect at -the same time both an increase and a diminution in the density of the -water, in consequence of which the magnified images will undergo the -most remarkable transformations. It is not necessary to place the glass -plate which contains the figure within the trough. It may be placed in -front of it, and by thus creating as it were an atmosphere with local -variations of density, we may exhibit the phenomena of the mirage and -of looming, in which the inverted images of ships and other objects are -seen in the air, as described in another letter. - -The power of the magic lantern has been greatly extended by placing -it on one side of the transparent screen of taffeta which receives -the images, while the spectators are placed on the other side, and -by making every part of the glass sliders opaque, excepting the part -which forms the figures. Hence all the figures appear luminous on a -black ground, and produce a much greater effect with the same degree of -illumination. An exhibition depending on these principles was brought -out by M. Philipstall in 1802, under the name of the _Phantasmagoria_, -and when it was shown in London and Edinburgh, it produced the most -impressive effects upon the spectators. The small theatre of exhibition -was lighted only by one hanging lamp, the flame of which was drawn up -into an opaque chimney or shade when the performance began. In this -“darkness visible” the curtain rose and displayed a cave with skeletons -and other terrific figures in relief upon its walls. The flickering -light was then drawn up beneath its shroud, and the spectators in total -darkness found themselves in the middle of thunder and lightning. -A thin transparent screen had, unknown to the spectators, been let -down after the disappearance of the light, and upon it the flashes of -lightning and all the subsequent appearances were represented. This -screen being half-way between the spectators and the cave which was -first shown, and being itself invisible, prevented the observers from -having any idea of the real distance of the figures, and gave them the -entire character of aërial pictures. The thunder and lightning were -followed by the figures of ghosts, skeletons, and known individuals, -whose eyes and mouth were made to move by the shifting of combined -sliders. After the first figure had been exhibited for a short time, -it began to grow less and less, as if removed to a great distance, and -at last vanished in a small cloud of light. Out of this same cloud the -germ of another figure began to appear, and gradually grew larger and -larger, and approached the spectators, till it attained its perfect -development. In this manner the head of Dr. Franklin was transformed -into a skull; figures which retired with the freshness of life came -back in the form of skeletons, and the retiring skeletons returned in -the drapery of flesh and blood. - -The exhibition of these transmutations was followed by spectres, -skeletons, and terrific figures, which, instead of receding and -vanishing as before, suddenly advanced upon the spectators, becoming -larger as they approached them, and finally vanished by appearing to -sink into the ground. The effect of this part of the exhibition was -naturally the most impressive. The spectators were not only surprised -but agitated, and many of them were of opinion that they could have -touched the figures. M. Robertson, at Paris, introduced along with his -pictures the direct shadows of living objects, which imitated coarsely -the appearance of those objects in a dark night or in moonlight. - -All these phenomena were produced by varying the distance of the magic -lantern AB, Fig 5, from the screen PQ, which remained fixed, and at the -same time keeping the image upon the screen distinct, by increasing -the distance of the lens D from the sliders in EF. When the lantern -approached to PQ, the circle of light PQ, or the section of the cone -of rays PDQ, gradually diminished, and resembled a small bright cloud, -when D was close to the screen. At this time a new figure was put -in, so that when the lantern receded from the screen, the old figure -seemed to have been transformed into the new one. Although the figure -was always at the same distance from the spectators, yet, owing to its -gradual diminution in size, it necessarily appeared to be retiring to -a distance. When the magic lantern was withdrawn from PQ, and the lens -D at the same time brought nearer to EF, the image in PQ gradually -increased in size, and therefore seemed in the same proportion to be -approaching the spectators. - -Superior as this exhibition was to any representation that had been -previously made by the magic lantern, it still laboured under several -imperfections. The figures were poorly drawn, and in other respects not -well executed, and no attempt whatever was made to remove the optical -incongruity of the figures becoming more luminous when they retired -from the observer, and more obscure when they approached to him. The -variation of the distance of the lens D from the sliders in EF was not -exactly adapted to the motion of the lantern to and from the screen, so -that the outline of the figures was not equally distinct during their -variations of magnitude. - -Dr. Thomas Young suggested the arrangement shown in Fig. 6 for -exhibiting the phantasmagoria. - -[Illustration: _Fig. 6._] - -The magic lantern is mounted on a small car H, which runs on wheels -WW. The direct light of the lamp G, and that reflected from the mirror -M, is condensed by the illuminating lenses CC, upon the transparent -figures in the opaque sliders at E, and the image of these figures is -formed at PQ, by the object lens D. When the car H is drawn back on -its wheels, the rod IK brings down the point K, and by means of the rod -KL, pushes the lens D nearer to the sliders in EF, and when the car -advances to PQ, the point K is raised, and the rod KL draws out the -lens D from the slider, so that the image is always in the conjugate -focus of D, and therefore distinctly painted on the screen. The rod KN -must be equal in length to IK, and the point I must be twice the focal -length of the lens D before the object, L being immediately under the -focus of the lens. In order to diminish the brightness of the image -when it grows small and appears remote, Dr. Young contrived that the -support of the lens D should suffer a screen S to fall and intercept a -part of the light. This method, however, has many disadvantages, and we -are satisfied, that the only way of producing a variation in the light -corresponding to the variation in the size of the image, is to use a -single illuminating lens C, and to cause it to approach EF, and throw -less light upon the figures when D is removed from EF, and to make C -recede from EF when D approaches to it. The lens C should therefore -be placed in a mean position, corresponding to a mean distance of the -screen, and to the ordinary size of the figures, and should have the -power of being removed from the slider EF, when a greater intensity of -light is required for the images when they are rendered gigantic, and -of being brought close to EF when the images are made small. The size -of the lens C ought of course to be such that the section of its cone -of rays at EF is equal to the size of the figure on the slider when C -is at its greatest distance from the slider. - -The method recommended by Dr. Young for pulling out and pushing in -the object lens D, according as the lantern approaches to or recedes -from the screen, is very ingenious and effective. It is, however, -clumsy in itself, and the connexion of the levers with the screen, -and their interposition between it and the lantern, must interfere -with the operations of the exhibitor. It is, besides, suited only to -short distances between the screen and the lantern; for when that -distance is considerable, as it must sometimes require to be, the -levers KL, KI, KT, would bend by the least strain, and become unfitted -for their purpose. For these reasons the mechanism which adjusts the -lens D should be moved by the axle of the front wheels, the tube which -contains the lens should be kept at its greatest distance from EF by -a slender spring, and should be pressed to its proper distance by the -action of a spiral cam suited to the optical relation between the two -conjugate focal distances of the lens. - -Superior as the representations of the phantasmagoria are to those of -the magic lantern, they are still liable to the defect which we have -mentioned, namely, the necessary imperfection of the minute transparent -figures when magnified. This defect cannot be remedied by employing -the most skilful artists. Even Michael Angelo would have failed in -executing a figure an inch long with transparent varnishes, when all -its imperfections were to be magnified. In order, therefore, to perfect -the art of representing phantasms, the objects must be living ones, and -in place of chalky ill-drawn figures, mimicking humanity by the most -absurd gesticulations, we shall have phantasms of the most perfect -delineation, clothed in real drapery, and displaying all the movements -of life. The apparatus by which such objects may be used, may be called -the _catadioptrical phantasmagoria_, as it operates both by reflexion -and refraction. - -[Illustration: _Fig. 7._] - -The combination of mirrors and lenses which seems best adapted for this -purpose is shown in Fig. 7, where AB is a living figure placed before -a large concave mirror MN, by means of which a diminished and inverted -image of it is formed at _ab_. If PQ is the transparent screen upon -which the image is to be shown to the spectators on the right hand of -it, a large lens LL must be so placed before the image _ab_, as to -form a distinct and erect picture of it at A´B´ upon the screen. When -the image A´B´ is required to be the exact size of AB, the lens LL -must magnify the small image _ab_ as much as the mirror MN diminishes -the figure AB. The living object AB, the mirror MN, and the lens LL, -must all be placed in a moveable car for the purpose of producing the -variations in the size of the phantasms, and the transformations of -one figure into another. The contrivance for adjusting the lens LL, to -give a distinct picture at different distances of the screen, will, of -course, be required in the present apparatus. In order to give full -effect to the phantasms, the living objects at AB will require to be -illuminated in the strongest manner, and should always be dressed -either in white or in very luminous colours; and, in order to give them -relief, a black cloth should be stretched at some distance behind them. -Many interesting effects might also be produced by introducing at AB -fine paintings and busts. - -It would lead us into too wide a field were we to detail the immense -variety of resources which the science of optics furnishes for such -exhibitions. One of these, however, is too useful to be passed without -notice. If we interpose a prism with a small refracting angle between -the image _ab_, Fig. 7, and the lens LL, the part of the figure -immediately opposite to the prism will be as it were detached from -the figure, and will be exhibited separately on the screen PQ. Let us -suppose that this part is the head of the figure. It may be detached -vertically, or lifted from the body as if it were cut off, or it may -be detached downwards and placed on the breast as if the figure were -deformed. In detaching the head vertically or laterally, an opaque -screen must be applied to prevent any part of the head from being -seen by rays which do not pass through the prism; but this and other -practical details will soon occur to those who put the method to an -experimental trial. The application of the prism is shown in Fig. 8, -where _ab_ is the inverted image formed by a concave mirror, ABC a -prism with a small refracting angle BCA, placed between _ab_ and the -lens LL, _s_ a small opaque screen, and AB the figure with its head -detached. A hand may be made to grasp the hair of the head, and the -aspect of death may be given to it, as if it had been newly cut off. -Such a representation could be easily made, and the effect upon the -spectators would be quite overpowering. The lifeless head might then be -made to recover its vitality, and be safely replaced upon the figure. -If the head A of the living object AB, Fig. 7, is covered with black -cloth, the head of a person or of an animal placed above A might be set -upon the shoulders of the figure AB by the refraction of a prism. - -[Illustration: _Fig. 8._] - -When the figure _ab_, Fig. 8, is of very small dimensions, as in the -magic lantern, a small prism of glass would answer the purpose required -of it; but in public exhibitions, where the image _ab_ must be of a -considerable size, if formed by a concave mirror, a very large prism -would be necessary. This, however, though impracticable with solid -glass, may be easily obtained by means of two large pieces of plate -glass made into a prismatic vessel and filled with water. Two of the -glasses of a carriage window would make a prism capable of doubling -the whole of the bust of a living person placed as an object at AB, -Fig. 7, so that two perfectly similar phantasms might be exhibited. In -those cases where the images before the lens LL are small, they may -be doubled and even tripled by interposing a well-prepared plate of -calcareous spar, that is, crossed by a thin film. These images would -possess the singular character of being oppositely coloured, and of -changing their distances and their colours, by slight variations in the -positions of the plate.[8] - - [8] See _Edin. Encyclopædia_, Art. OPTICS, Vol. xv., p. 611. - -In order to render the images which are formed by the glass and -water prisms as perfect as possible, it would be easy to make them -achromatic, and the figures might be multiplied to any extent by using -several prisms, having their refracting edges parallel, for the purpose -of giving a similarity of position to all the images. - -[Illustration: _Fig. 9._] - -Among the instruments of natural magic which were in use at the revival -of science, there was one invented by Kircher for exhibiting the -mysterious hand-writing on the wall of an apartment, from which the -magician and his apparatus were excluded. The annexed figure represents -this apparatus as given by Schottus. The apartment in which the -spectators are placed is between LL and GH, and there is an open window -in the - -side next LL, GH being the inside of the wall opposite to the window. -Upon the face of the plane speculum EF are written the words to be -introduced, and when a lens LL is placed at such a distance from the -speculum, and of such a focal length, that the letters and the place -of their representation are in its conjugate foci, a distinct image -of the writing will be exhibited on the wall at GH. The letters on -the speculum are of course inverted, as seen at EF, and when they are -illuminated by the sun’s rays S, as shown in the figure, a distinct -image, as Schottus assures us, may be formed at the distance of 500 -feet. In this experiment, the speculum is by no means necessary. If the -letters are cut out of an opaque card, and illuminated by the light -of the sky in the day, or by a lamp during night, their delineation -on the wall would be equally distinct. In the daytime it would be -necessary to place the letters at one end of a tube or oblong box, and -the lens at the other end. As this deception is performed when the -spectators are unprepared for any such exhibition, the warning written -in luminous letters on the wall, or any word associated with the fate -of the individual observer, could not fail to produce a singular effect -upon his mind. The words might be magnified, diminished, multiplied, -coloured, and obliterated, in a cloud of light, from which they might -again reappear by the methods already described, as applicable to the -magic lantern. - -The art of forming aërial representations was a great desideratum among -the opticians of the 17th century. Vitellio and others had made many -unsuccessful attempts to produce such images, and the speculations -of Lord Bacon on the subject are too curious to be withheld from the -reader. - -“It would be well bolted out,” says he, “whether great refractions may -not be made upon reflexions, as well as upon direct beams. For example, -take an empty basin, put an angel or what you will into it; then go so -far from the basin till you cannot see the angel, because it is not in -a right line; then fill the basin with water, and you shall see it out -of its place, because of the refraction. To proceed, therefore, put a -looking-glass into a basin of water. I suppose you shall not see the -image in a right line or at equal angles, but wide. I know not whether -this experiment may not be extended, so as you might see the image and -not the glass, which, for beauty and strangeness, were a fine proof, -for then you should see the image like a spirit in the air. As, for -example, if there be a cistern or pool of water, you shall place over -against it the picture of the devil, or what you will, so as that you -do not see the water. Then put a looking-glass in the water; now if you -can see the devil’s picture aside, not seeing the water, it would look -like the devil indeed. They have an old tale in Oxford, that Friar -Bacon walked between two steeples, which was thought to be done by -glasses, when he walked upon the ground.” - -[Illustration: _Fig. 10._] - -Kircher also devoted himself to the production of such images, and he -has given in the annexed figure his method of producing them. At the -bottom of a polished cylindrical vessel AB, he placed a figure CD, -which we presume must have been highly illuminated from below, and -to the spectators who looked into the vessel in an oblique direction -there was exhibited an image placed vertically in the air as if it -were ascending at the mouth of the vessel. Kircher assures us that he -once exhibited in this manner a representation of the Ascension of our -Saviour, and that the images were so perfect that the spectators could -not be persuaded, till they had attempted to handle them, that they -were not real substances. Although Kircher does not mention it, yet -it is manifest that the original figure AB must have been a deformed -or anamorphous drawing, in order to give a reflected image of just -proportions. We doubt, indeed, if the representation or the figure was -ever exhibited. It is entirely incompatible with the laws of reflexion. - -[Illustration: _Fig. 11._] - -Among the ingenious and beautiful deceptions of the 17th century, -we must enumerate that of the re-formation of distorted pictures -by reflexion from cylindrical and conical mirrors. In these -representations, the original image from which a perfect picture -is produced is often so completely distorted, that the eye cannot -trace in it the resemblance to any regular figure, and the greatest -degree of wonder is of course excited, whether the original image is -concealed or exposed to view. These distorted pictures may be drawn -by strict geometrical rules; but I have shown in Fig. 11 a simple and -practical method of executing them. Let MN be an accurate cylinder made -of tin-plate or of thick pasteboard. Out of the farther side of it -cut a small aperture _abcd_; and out of the nearer side cut a larger -one ABCD, the size of the picture to be distorted. Having perforated -the outline of the picture with small holes, place it on the opening -ABCD, so that its surface may be cylindrical. Let a candle or a bright -luminous object, the smaller the better, be placed at S, as far behind -the picture ABCD as the eye is afterwards to be placed before it, -and the light passing through the small holes will represent on a -horizontal plane a distorted image of the picture A´B´C´D´, which, -when sketched in outline with a pencil, and shaded or coloured, will -be ready for use. If we now substitute a polished cylindrical mirror -of the same size in place of MN, then the distorted picture, when -laid horizontally at A´B´C´D´, will be restored to its original state -when seen by reflexion at ABCD in the polished mirror. It would be -an improvement on this method to place at ABCD a thin and flexible -plate of transparent mica, having drawn upon it with a sharp point, -or painted upon it, the figure required. The projected image of this -figure at A´B´C´D´ may then be accurately copied. - -The effect of a cylindrical mirror is shown in Fig. 12, which is -copied from an old one which we have seen in use. - -[Illustration: _Fig. 12._] - -The method above described is equally applicable to concave cylindrical -mirrors, and to those of a conical form; and it may also be applied -to mirrors of variable curvature, which produce different kinds of -distortions from different parts of their surfaces. - -[Illustration: _Fig. 13._] - -By employing a mirror whose surface has a variable curvature like ABC, -Fig. 13, we obtain an instrument for producing an endless variety of -caricatures, all of which are characterised by their resemblance to -the original. If a figure MN is placed before such a mirror, it will -of course appear distorted and caricatured; but even if the figure -takes different distances and positions, the variations which the -image undergoes are neither sufficiently numerous nor remarkable to -afford much amusement. But if the figure MN is very near the mirror, -so that new distortions are produced by the different distances of -its different parts from the mirror, the most singular caricatures may -be exhibited. If the figure, for example, bends forwards his head and -the upper part of his body, they will swell in size, leaving his lower -extremities short and slender. If it draws back the upper part of the -body and advances the limbs, the opposite effect will take place. In -like manner different sides of the head, the right or the left side of -it, the brow or the chin, may be swelled and contracted at pleasure. By -stretching out the arms before the body they become like those of an -ourang-outang, and by drawing them back they dwindle into half their -regular size. All these effects, which depend chiefly on the agility -and skill of the performer, may be greatly increased by suitable -distortions in his own features and figure. The family likeness, which -is of course never lost in all the variety of figures which are thus -produced, adds greatly to the interest of the exhibition; and we have -seen individuals so annoyed at recognising their own likeness in the -hideous forms of humanity which were thus delineated, that they could -not be brought to contemplate them a second time. If the figure is -inanimate, like the small cast of a statue, the effect is very curious, -as the swelling and contracting of the parts and the sudden change -of expression give a sort of appearance of vitality to the image. -The inflexibility of such a figure, however, is unfavourable to its -transformation into caricatures. - -Interesting as these metamorphoses are, they lose in the simplicity -of the experiment much of the wonder which they could not fail to -excite if exhibited on a great scale, where the performer is invisible, -and where it is practicable to give an aërial representation of the -caricatured figures. This may be done by means of the apparatus shown -in Fig. 7,[9] where we may suppose AB to be the reduced image seen in -the reflecting surface ABC, Fig. 13.[10] By bringing this image nearer -the mirror MM, Fig. 7, a magnified and inverted image of it may be -formed at _ab_, of such a magnitude as to give the last image in PQ the -same size as life. Owing to the loss of light by the two reflexions, a -very powerful illumination would be requisite for the original figure. -If such an exhibition were well got up, the effect of it would be very -striking. - - [9] Page 86. - - [10] Page 96. - - - - -LETTER V. - - Miscellaneous optical illusions--Conversion of cameos into intaglios, - or elevations into depressions, and the reverse--Explanation of - this class of deceptions--Singular effects of illumination with - light of one simple colour--Lamps for producing homogeneous yellow - light--Methods of increasing the effect of this exhibition--Method - of reading the inscription of coins in the dark--Art of deciphering - the effaced inscription of coins--Explanation of these singular - effects--Apparent motion of the eyes in portraits--Remarkable examples - of this--Apparent motion of the features of a portrait, when the - eyes are made to move--Remarkable experiment of breathing light and - darkness. - - -In the preceding letter I have given an account of the most important -instruments of Natural Magic which depend on optical principles: but -there still remain several miscellaneous phenomena on which the stamp -of the marvellous is deeply impressed, and the study of which is -pregnant with instruction and amusement. - -One of the most curious of these is that false perception in vision -by which we conceive depressions to be elevations, and elevations -depressions, or by which intaglios are converted into cameos, and -cameos into intaglios. This curious fact seems to have been first -observed at one of the early meetings of the Royal Society of London, -when one of the members, in looking at a guinea through a compound -microscope of new construction, was surprised to see the head upon the -coin depressed, while other members could only see it embossed as it -really was. - -While using telescopes and compound microscopes, Dr. Gmelin of -Wurtemburg observed the same fact. The protuberant parts of objects -appeared to him depressed, and the depressed parts protuberant: but -what perplexed him extremely, this illusion took place at some times -and not at others, in some experiments and not in others, and appeared -to some eyes and not to others. - -After making a great number of experiments, Dr. Gmelin is said to -have constantly observed the following effects: Whenever he viewed -any object rising upon a plane of any colour whatever, provided it -was neither white nor shining, and provided the eye and the optical -tube were directly opposite to it, the elevated parts appeared -depressed, and the depressed parts elevated. This happened when he -was viewing a seal, and as often as he held the tube of the telescope -perpendicularly, and applied it in such a manner that its whole -surface almost covered the last glass of the tube. The same effect was -produced when a compound microscope was used. When the object hung -perpendicularly, from a plane, and the tube was supported horizontally -and directly opposite to it, the illusion also took place, and the -appearance was not altered when the object hung obliquely and even -horizontally. Dr. Gmelin is said to have at last discovered a method -of preventing this illusion, which was by looking, not towards the -centre of the convexity, but at first to the edges of it only, and then -gradually taking in the whole. “But why these things should so happen, -he did not pretend to determine.” - -[Illustration: _Fig. 14._] - -The best method of observing this deception is to view the engraved -seal of a watch with the eyepiece of an achromatic telescope, or with -a compound microscope, or any combination of lenses which inverts the -objects that are viewed through it.[11] The depression in the seal -will immediately appear an elevation, like the wax impression which -is taken from it; and though we know it to be hollow, and feel its -concavity with the point of our finger, the illusion is so strong -that it continues to appear a protuberance. The cause of this will be -understood from Fig. 14, where S is the window of the apartment, or -the light which illuminates the _hollow_ seal LR, whose shaded side -is of course on the same side L with the light. If we now invert the -seal, with one or more lenses, so that it may look in the opposite -direction, it will appear to the eye as in Fig. 15, with the shaded -side L farthest from the window. But as we know that the window is -still on our left hand, and that the light falls in the direction RL, -and as everybody with its shaded side farthest from the light must -necessarily be convex or protuberant, we immediately believe that the -hollow seal is now a cameo or bas-relief. The proof which the eye thus -receives of the seal being raised, overcomes the evidence of its being -hollow, derived from our actual knowledge, and from the sense of touch. -In this experiment the deception takes place from our knowing the real -direction of the light which falls upon the seal; for if the place of -the window, with respect to the seal, had been inverted as well as the -seal itself, the illusion could not have taken place. - - [11] A single convex lens will answer the purpose, provided we hold - the eye six or eight inches behind the image of the seal formed in its - conjugate focus. - -[Illustration: _Fig. 15._] - -[Illustration: _Fig. 16._] - -In order to explain this better, let us suppose the seal LR, Fig. 14, -to be illuminated with a candle S, the place of which we can change at -pleasure. If we invert LR, it will rise into a cameo, as in Fig. 15; -and if we then place another candle S on the other side of it, as in -Fig. 16, the hollow seal will be equally illuminated on all sides, and -it will sink down into a cavity or intaglio. If the two candles do not -illuminate the seal equally, or if any accidental circumstance produces -a belief that the light is wholly or principally on one side, the mind -will entertain a corresponding opinion respecting the state of the -seal, regarding it as a hollow if it believes the light to come wholly -or principally from the right hand, and as a cameo if it believes the -light to come from the left hand. - -If we use a small telescope to invert the seal, and if we cover up -all the candle but the flame, and arrange the experiment so that the -candle may be inverted along with the image, the seal will still retain -its concavity, because the shadow is still on the same side with the -illuminating body. - -If we make the same experiments with the raised impression of the seal -taken upon wax, we shall observe the very same phenomena, the seal -being depressed when it alone is inverted, and retaining its convexity -when the light is inverted along with it. - -The illusion, therefore, under our consideration is the result of an -operation of our own minds, whereby we judge of the forms of bodies by -the knowledge we have acquired of light and shadow. Hence the illusion -depends on the accuracy and extent of our knowledge on this subject; -and while some persons are under its influence, others are entirely -insensible to it. When the seal or hollow cavity is not polished, but -ground, and the surface round it of uniform colour and smoothness, -almost every person, whether young or old, learned or ignorant, will be -subject to the illusion; because the youngest and the most careless -observers cannot but know that the shadow of a hollow is always on -the side next the light, and the shadow of a protuberance on the side -opposite to the light; but if the object is the raised impression of a -seal upon wax, I have found that, when inverted, it still seemed raised -to the three youngest of six persons, while the three eldest were -subject to the deception. - -[Illustration: _Fig. 17._] - -This illusion may be dissipated by a process of reasoning arising from -the introduction of a new circumstance in the experiment. Thus, let RL, -Fig. 17, be the inverted seal, which consequently appears raised, and -let an opaque and unpolished pin, A, be placed on one side of the seal. -Its shadow will be of course opposite the candle as at B. In this case -the seal, which had become a cameo by its inversion, will now sink down -into a cavity by the introduction of the pin and its shadow; for as the -pin and its shadow are inverted, as shown in Fig. 18, while the candle -retains its place, the shadow of the pin falling in the direction AB -is a stronger proof to the eye that the light is coming from the right -hand, than the actual knowledge of the candle being on the left hand, -and therefore the cameo necessarily sinks into a cavity, or the shadow -is now on the same side as the light. This experiment will explain to -us why on some occasions an acute observer will elude the deception, -while every other person is subject to it. Let us suppose that a -particle of dust, or a little bit of wax, capable of giving a shadow, -is adhering to the surface of the seal, an ordinary observer will -take no notice of this, or if he does, he will probably not make it a -subject of consideration, and will therefore see the head on the seal -raised into a cameo; but the attentive observer, noticing the little -protuberance, and observing that its shadow lies to the left of it, -will instantly infer that the light comes in that direction, and will -still see the seal hollow. - -[Illustration: _Fig. 18._] - -I have already mentioned that in some cases even the sense of touch -does not correct the erroneous perception. We of course feel that the -part of the hollow on which the finger is placed is actually hollow; -but if we look at the other part of the hollow it will still appear -raised. - -By using two candles yielding different degrees of light, and thus -giving an uncertainty to the direction of the light, we may weaken the -illusion in any degree we choose, so as to overpower it by touch, or by -a process of reasoning. - -I have had occasion to observe a series of analogous phenomena arising -from the same cause, but produced without any instrument for inverting -the object. If AB, for example, is a plate of mother-of-pearl, and LR -a circular or any other cavity (Fig. 19) ground or turned in it, then -if this cavity is illuminated by a candle or a window at S, in place of -there being a shadow of the margin L of the hollow next the light, as -there would have been had the body been opaque, a quantity of bright -refracted light will appear where there would have been a shadow, and -the rest of the cavity will be comparatively obscure, as if it were -in shade. The necessary consequence of this is, that the cavity will -appear as an elevation when seen only by the naked eye, as it is only -an elevated surface that could have its most luminous side at L. - -[Illustration: _Fig. 19._] - -Similar illusions take place in certain pieces of polished wood, -chalcedony, and mother-of-pearl, where the surface is perfectly -smooth. This arises from there being at that place a knot or growth, -or nodule, of different transparency from the surrounding mass, and -the cause of it will be understood from Fig. 20. Let _m_ _o_ be the -surface of a mahogany table, _m_ A _o_ B a section of the table, and -_m_ _n_ _o_ a section of a knot more transparent than the rest of the -mass. Owing to the transparency of the thin edge at _o_, opposite to -the candle S, the side _o_ is illuminated, while the rest of the knot -is comparatively dark, so that, on the principles already explained, -the spot _m n o_ appears to be a hollow in the table. From this cause -arises the appearance of dimples in certain plates of chalcedony, -called hammered chalcedony, owing to its having the look of being -dimpled with a hammer. The surface on which these cavities are seen is -a section of small spherical aggregations of siliceous matter, which -exhibit the same phenomena as the cavities in wood. Mother-of-pearl -presents the very same phenomena, and it is indeed so common in this -substance, that it is nearly impossible to find a mother-of-pearl -button or counter which seems to have its surface flat, although they -are perfectly so when examined by the touch. Owing to the different -refraction of the incident light by the different growths of the shell -cut in different directions by the artificial surface, like the annual -growth of wood in a dressed plank, the surface has necessarily an -unequal and undulating appearance. - -[Illustration: _Fig. 20._] - -Among the wonders of science there are perhaps none more surprising -than the effects produced upon coloured objects by illuminating -them with homogeneous light, or light of one colour. The light which -emanates from the sun, and by which all the objects of the material -world are exhibited to us, is composed of three different colours, -_red_, _yellow_, and _blue_, by the mixture of which in different -proportions all the various hues of nature may be produced. These three -colours, when mixed in the proportion in which they occur in the sun’s -rays, compose a purely white light; but if any body on which this white -light falls shall absorb, or stop, or detain within its substance any -part of any one or more of these simple colours, it will appear to the -eye of that colour which arises from the mixture of all the rays which -it does not absorb, or of that colour which white light would have if -deprived of the colours which are absorbed. Scarlet cloth, for example, -absorbs most of the blue rays and many of the yellow, and hence appears -_red_. Yellow cloth absorbs most of the blue and many of the red rays, -and therefore appears yellow; and blue cloth absorbs most of the yellow -and red rays. If we were to illuminate the _scarlet_ cloth with pure -and unmixed _yellow_ light, it would appear _yellow_, because the -scarlet cloth does not absorb all the yellow rays, but reflects some -of them; and if we illuminate _blue_ cloth with yellow light, it will -appear nearly _black_, because it absorbs all the yellow light, and -reflects almost none of it. But whatever be the nature and colour of -the bodies on which the yellow light falls, the light which it reflects -must be yellow, for no other light falls upon them, and those which are -not capable of reflecting yellow light must appear absolutely black, -however brilliant be their colour in the light of day. - -[Illustration: _Fig. 21._] - -As the methods now discovered of producing yellow light in abundance -were not known to the ancient conjurors, nor even to those of later -times, they have never availed themselves of this valuable resource. It -has been long known that salt thrown into the wick of a flame produces -yellow light, but this light is mixed with blue and green rays, and is, -besides, so small in quantity, that it illuminates objects only that -are in the immediate vicinity of the flame. A method which I have found -capable of producing it in abundance is shown in Fig. 21, where AB is a -lamp, containing at A a large quantity of alcohol and water, or ardent -spirits, which gradually descends into a platina or metallic cup D. -This cup is strongly heated by a spirit-lamp L, inclosed in a dark -lantern, and when the diluted alcohol in D is inflamed, it will burn -with a fierce and powerful yellow flame. If the flame should not be -perfectly yellow, owing to an excess of alcohol, a proportion of salt -thrown into the cup will answer the same purpose as a further dilution -of the alcohol.[12] - - [12] See _Edinburgh Transactions_, vol. ix., p. 435. - -A monochromatic lamp for producing yellow light may be constructed most -effectually, by employing a portable gas lamp, containing compressed -oil gas. If we allow the gas to escape in a copious stream, and set it -on fire, it will form an explosive mixture with the atmospheric air, -and will no longer burn with a white flame, but will emit a bluish -and reddish light. The force of the issuing gas, or any accidental -current of air, is capable of blowing out this flame, so that it is -necessary to have a contrivance for sustaining it. The method which I -used for this purpose is shown in Fig. 22. A small gas tube _a b c_, -arising from the main burner MN of the gas lamp PQ, terminates above -the burner, and has a short tube _d e_, moveable up and down within it, -so as to be gas-tight. This tube _d e_, closed at _e_, communicates -with the hollow ring _f g_, in the inside of which four apertures are -perforated in such a manner as to throw their jets of gas to the apex -of a cone, of which _f g_ is the base. When we cause the gas to flow -from the burner M, by opening the main cock A, it will rush into the -tube _a b c d_, and issue in small flames at the four holes in the -ring _f g_. The size of these flames is regulated by the cock _b_. -The inflammation, therefore, of the ignited gas will be sustained by -these four subsidiary flames through which it passes, independent of -any agitation of the air, or of the force with which it issues from -the burner. On a projecting arm _e h_, carrying a ring _h_, I fixed a -broad collar, made of coarse cotton wick, which had been previously -soaked in a saturated solution of common salt. When the gas was allowed -to escape at M, with such force as to produce a long and broad column -of an explosive mixture of gas and atmospheric air, the bluish flame -occasioned by the explosion passes through the salted collar, and is -converted by it into a mass of homogeneous yellow light. This collar -will last a long time without any fresh supply of salt, so that the gas -lamp will yield a permanent monochromatic yellow flame, which will -last as long as there is gas in the reservoir. In place of a collar -of cotton wick, a hollow cylinder of sponge, with numerous projecting -tufts, may be used, or a collar may be similarly constructed with -asbestos cloth, and, if thought necessary, it might be supplied with a -saline solution from a capillary fountain. - -[Illustration: _Fig. 22._] - -Having thus obtained the means of illuminating any apartment with -yellow light, let the exhibition be made in a room with furniture of -various bright colours, with oil or water-coloured paintings on the -wall. The party which is to witness the experiment should be dressed -in a diversity of the gayest colours; and the brightest-coloured -flowers and highly-coloured drawings should be placed on the tables. -The room being at first lighted with ordinary lights, the bright and -gay colours of everything that it contains will be finely displayed. -If the white lights are now suddenly extinguished, and the yellow -lamps lighted, the most appalling metamorphosis will be exhibited. The -astonished individuals will no longer be able to recognize each other. -All the furniture in the room, and all the objects which it contains, -will exhibit only one colour. The flowers will lose their hues. The -paintings and drawings will appear as if they were executed in China -ink; and the gayest dresses, the brightest scarlets, the purest lilacs, -the richest blues, and the most vivid greens, will all be converted -into one monotonous yellow. The complexions of the parties, too, will -suffer a corresponding change. One pallid, death-like yellow, - - ---- like the unnatural hue - Which autumn paints upon the perished leaf, - -will envelope the young and the old, and the sallow faces will alone -escape from the metamorphosis. Each individual derives merriment from -the cadaverous appearance of his neighbour, without being sensible that -he is himself one of the ghostly assemblage. - -If, in the midst of the astonishment which is thus created, the white -lights are restored at one end of the room, while the yellow lights are -taken to the other end, one side of the dress of every person, namely, -that next the white light, will be restored to its original colours, -while the other side will retain its yellow hue. One cheek will appear -in a state of health and colour, while the other retains the paleness -of death; and, as the individuals change their position, they will -exhibit the most extraordinary transformations of colour. - -If, when all the lights are yellow, beams of white light are -transmitted through a number of holes, like those in a sieve, each -luminous spot will restore the colour of the dress or furniture upon -which it falls, and the nankeen family will appear all mottled over -with every variety of tint. If a magic lantern is employed to throw -upon the walls or upon the dresses of the company luminous figures of -flowers or animals, the dresses will be painted with these figures -in the real colour of the dress itself. Those alone who appeared in -yellow, and with yellow complexions, will, to a great degree, escape -all these singular changes. - -If red and blue light could be produced with the same facility and in -the same abundance as yellow light, the illumination of the apartment -with these lights in succession would add to the variety and wonder of -the exhibition. The red light might perhaps be procured in sufficient -quantity from the nitrate and other salts of strontian; but it would -be difficult to obtain a blue flame of sufficient intensity for the -suitable illumination of a large room. Brilliant white lights, however, -might be used, having for screens glass troughs containing a mass -one or two inches thick of a solution of the ammoniacal carbonate of -copper. This solution absorbs all the rays of the spectrum but the -blue, and the intensity of the blue light thus produced would increase -in the same proportion as the white light employed. - -Amongst the numerous experiments with which science astonishes and -sometimes even strikes terror into the ignorant, there is none more -calculated to produce this effect than that of displaying to the eye in -absolute darkness the legend or inscription upon a coin. To do this, -take a silver coin (I have always used an old one), and after polishing -the surface as much as possible, make the parts of it which are raised -rough by the action of an acid, the parts not raised, or those which -are to be rendered darkest, retaining their polish. If the coin thus -prepared is placed upon a mass of red-hot iron, and removed into a dark -room, the inscription upon it will become less luminous than the rest, -so that it may be distinctly read by the spectator. The mass of red-hot -iron should be concealed from the observer’s eye, both for the purpose -of rendering the eye fitter for observing the effect, and of removing -all doubt that the inscription is really read in the dark, that is, -without receiving any light, direct or reflected, from any other body. -If, in place of polishing the depressed parts and roughening its raised -parts, we make the raised parts polished and roughen the depressed -parts, the inscription will now be less luminous than the depressed -parts, and we shall still be able to read it, from its being as it were -written in black letters on a white ground. The first time I made this -experiment, without being aware of what would be the result, I used -a French shilling of Louis XV., and I was not a little surprised to -observe upon its surface, in black letters, the inscription BENEDICTUM -SIT NOMEN DEI. - -The most surprising form of this experiment is when we use a coin -from which the inscription has been either wholly obliterated, or -obliterated in such a degree as to be illegible. When such a coin is -laid upon the red-hot iron, the letters and figures become oxidated, -and the film of oxide radiating more powerfully than the rest of the -coin, the illegible inscription may be now distinctly read, to the -great surprise of the observer, who had examined the blank surface of -the coin previous to its being placed upon the hot iron. The different -appearances of the same coin, according as the raised parts are -polished or roughened, are shown in Fig. 23 and 24. - -In order to explain the cause of these remarkable effects, we must -notice a method which has been long known, though never explained, of -deciphering the inscriptions on worn-out coins. This is done by merely -placing the coin upon a hot iron; an oxidation takes place over the -whole surface of the coin, the film of oxide changing its tint with the -intensity or continuance of the heat. The parts, however, where the -letters of the inscription had existed, oxidate at a different rate -from the surrounding parts, so that these letters exhibit their shape, -and become legible in consequence of the film of oxide which covers -them having a different thickness, and therefore reflecting a different -tint from that of the adjacent parts. The tints thus developed -sometimes pass through many orders of brilliant colours, particularly -_pink_ and _green_, and settle in a bronze, and sometimes a black tint, -resting upon the inscription alone. In some cases the tint left on the -trace of the letters is so very faint that it can just be seen, and may -be entirely removed by a slight rub of the finger. - -[Illustration: _Fig. 23._] - -[Illustration: _Fig. 24._] - -When the experiment is often repeated with the same coin, and the -oxidations successively removed after each experiment, the film of -oxide continues to diminish, and at last ceases to make its appearance. -It recovers the property, however, in the course of time. When the -coin is put upon the hot iron, and consequently when the oxidation -is the greatest, a considerable smoke arises from the coin, and this -diminishes like the film of oxide by frequent repetition. A coin -which had ceased to emit this smoke, smoked slightly after having been -exposed twelve hours to the air. I have found, from numerous trials, -that it is always the raised parts of the coin, and in modern coins the -elevated ledge round the inscription, that become first oxidated. In an -English shilling of 1816, this ledge exhibited a brilliant yellow tint -before it appeared on any other part of the coin. - -If we use a uniform and homogeneous disc of silver that has never been -hammered or compressed, its surface will oxidate equally, provided all -its parts are equally heated. In the process of converting this disc -into a coin, the _sunk_ parts have obviously been _most compressed_ -by the prominent parts of the die, and the _elevated_ parts _least -compressed_, the metal being in the latter left as it were in its -natural state. The raised letters and figures on a coin have therefore -less density than the other parts, and these parts oxidate sooner or -at a lower temperature. When the letters of the legend are worn off by -friction, the parts immediately below them have also less density than -the surrounding metal, and the site as it were of the letters therefore -receives from heat a degree of oxidation, and a colour different from -that of the surrounding surface. Hence we obtain an explanation of the -revival of the invisible letters by oxidation. - -The same influence of difference of density may be observed in -the beautiful oxidations which are produced on the surface of -highly-polished steel, heated in contact with air, at temperatures -between 430° and 630° of Fahrenheit.[13] When the steel has hard -portions called pins by the workmen, the uniform tint of the film of -oxide stops near these hard portions, which always exhibit colours -different from those of the rest of the mass. These parts, on account -of their increased density, absorb the oxygen of atmospheric air less -copiously than the surrounding portions. Hence we see the cause why -steel expanded by heat absorbs oxygen, which when united with the -metal, forms the coloured superficial film. As the heat increases, -a greater quantity of oxygen is absorbed, and the film increases in -thickness. - - [13] See _Edinburgh Encyclopædia_, Art. STEEL, vol. xviii., p. 387. - -These observations enable us to explain the legibility of inscriptions -in the dark, whether the coin is in a perfect state, or the letters -of it worn off. All _black_ or _rough_ surfaces radiate light more -copiously than _polished_ or _smooth_ surfaces, and hence the -inscription is _luminous_ when it is _rough_, and _obscure_ when it is -polished, and the letters covered with black oxide are more luminous -than the adjacent parts, on account of the superior radiation of light -by the black oxide which covers them. - -By the means now described, invisible writing might be conveyed by -impressing it upon a metallic surface, and afterwards erasing it by -grinding and polishing that surface perfectly smooth. When exposed to -a proper degree of heat, the secret would display itself written in -oxidated letters. Many amusing experiments might be made upon the same -principle. - -A series of curious and sometimes alarming deceptions, arises from the -representation of objects in perspective upon a plane surface. One of -the most interesting of these depends on the principles which regulate -the apparent direction of the eyes in a portrait. Dr. Wollaston has -thought this subject of sufficient importance to be treated at some -length in the Philosophical Transactions. When we look at any person -we direct to them both our face and our eyes, and in this position -the circular iris will be in the middle of the white of the eye ball, -or, what is the same thing, there will be the same quantity of white -on each side of the iris. If the eyes are now moved to either side, -while the head remains fixed, we shall readily judge of the change of -their direction by the greater or less quantity of white on each side -of the iris. This test, however, accurate as it is, enables us only to -estimate the extent to which the eyes deviate in direction from the -direction of the face to which they belong. But their direction in -reference to the person who views them is entirely a different matter; -and Dr. Wollaston is of opinion, that we are not guided by the eyes -alone, but are unconsciously aided by the concurrent position of the -entire face. - -[Illustration: _Fig. 26._] - -If a skilful painter draws a pair of eyes with great correctness -directed to the spectator, and deviating from the general position of -the face as much as is usual in good portraits, it is very difficult -to determine their direction, and they will appear to have different -directions to different persons. But what is very curious, Dr. -Wollaston has shown that the same pair of eyes may be made to direct -themselves either to or from the spectator by the addition of other -features in which the position of the face is changed. Thus, in Fig. -25, the pair of eyes are looking intently at the spectator, and the -face has a corresponding direction; but when we cover up the face in -Fig. 25 with the face in Fig. 26, which looks to the right, the eyes -change their direction, and look to the right also. In like manner, -eyes drawn originally to look a little to the right or the left of -the spectator, may be made to look directly at him by adding suitable -features. - -[Illustration: _Fig. 25._] - -The nose is obviously the principal feature which produces this -change of direction, as it is more subject to change of perspective -than any of the other features; but Dr. Wollaston has shown by a very -accurate experiment, that even a small portion of the nose introduced -with the features will carry the eyes along with it. He obtained four -exact copies of the same pair of eyes looking at the spectator, by -transferring them upon copper from a steel plate, and having added to -each of two pair of them a nose, in one case directed to the right, -and in the other to the left, and to each of the other two pair a very -small portion of the upper part of the nose, all the four pair of eyes -lost their front direction, and looked to the right or to the left, -according to the direction of the nose, or of the portion of it which -was added. - -But the effect thus produced is not limited, as Dr. Wollaston -remarks, to the mere change in the direction of the eyes, “for a -total difference of character may be given to the same eyes by a due -representation of the other features. A lost look of devout abstraction -in an uplifted countenance, may be exchanged for an appearance of -inquisitive archness in the leer of a younger face turned downwards and -obliquely towards the opposite side,” as in Fig. 27, 28. This, however, -is perhaps not an exact expression of the fact. The new character -which is said to be given to the eyes is given only to the eyes in -combination with the new features, or, what is probably more correct, -the inquisitive archness is in the other features, and the eye does not -belie it. - -Dr. Wollaston has not noticed the converse of these illusions, in which -a change of direction is given to fixed features by a change in the -direction of the eyes. This effect is finely seen in some magic lantern -sliders, where a pair of eyes is made to move in the head of a figure, -which invariably follows the motion of the eyeballs. - -[Illustration: _Fig. 28._] - -[Illustration: _Fig. 27._] - -Having thus determined the influence which the general perspective of -the face has upon the apparent direction of the eyes in a portrait, Dr. -Wollaston applies it to the explanation of the well-known fact, that -when the eyes of a portrait look at a spectator in front of it they -will follow him, and appear to look at him in every other direction. -This curious fact, which has received less consideration than it -merits, has been often skilfully employed by the novelist, in alarming -the fears or exciting the courage of his hero. On returning to the -hall of his ancestors, his attention is powerfully fixed on the grim -portraits which surround him. The parts which they have respectively -performed in the family history rise to his mind: his own actions, -whether good or evil, are called up in contrast, and as the preserver -or the destroyer of his line, he stands, as it were, in judgment before -them. His imagination, thus excited by conflicting feelings, transfers -a sort of vitality to the canvas, and if the personages do not “start -from their frames,” they will at least bend upon him their frowns or -their approbation. It is in vain that he tries to evade their scrutiny. -Wherever he goes their eyes eagerly pursue him; they will seem even to -look at him over their shoulders, and he will find it impossible to -shun their gaze but by quitting the apartment. - -As the spectator in this case changes his position in a horizontal -plane, the effect which we have described is accompanied by an apparent -diminution in the breadth of the human face, from only seven or eight -inches till it disappears at a great obliquity. In moving, therefore, -from a front view to the most oblique view of the face, the change in -its apparent breadth is so slow that the apparent motion of the head of -the figure is scarcely recognized as it follows the spectator. But if -the perspective figure has a great breadth in a horizontal plane, such -as a soldier firing his musket, an artilleryman his piece of ordnance, -a bowman drawing his bow, or a lancer pushing his spear, the apparent -breadth of the figure will vary from five to six feet or upwards till -it disappears, and therefore the change of apparent magnitude is -sufficiently rapid to give the figure the dreaded appearance of turning -round, and following the spectator. One of the best examples of this -must have been often observed in the foreshortened figure of a dead -body lying horizontally, which has the appearance of following the -observer with great rapidity, and turning round upon the head as the -centre of motion. - -The cause of this phenomenon is easily explained. Let us suppose a -portrait with its face and its eyes directed straight in front, so as -to look at the spectator. Let a straight line be drawn through the -tip of the nose and half way between the eyes, which we shall call the -middle line. On each side of this middle line there will be the same -breadth of head, of cheek, of chin, and of neck, and each iris will be -in the middle of the white of the eye. If we now go to one side, the -apparent horizontal breadth of every part of the head and face will -be diminished, but the parts on each side of the middle line will be -diminished equally, and at any position, however oblique, there will be -the same breadth of face on each side of the middle line, and the iris -will be in the centre of the white of the eyeball, so that the portrait -preserves all the characters of a figure looking at the spectator, and -must necessarily do so wherever he stands. - -This explanation might be illustrated by a picture which represents -three artillerymen, each firing a piece of ordnance in parallel -directions. Let the gun of the middle one be pointed accurately to the -eye of the spectator, so that he sees neither its right side nor its -left, nor its upper nor its under side, but directly down its muzzle, -so that if there was an opening in the breech he would see through -it. In like manner the spectator will see the left side of the gun on -his left hand, and the right side of the gun on his right hand. If -the spectator now changes his place, and takes ever such an oblique -position, either laterally or vertically, he must still see the same -thing; because nothing else is presented to his view. The gun of the -middle soldier must always point to his eye, and the other guns to the -right and left of him. They must therefore all three seem to move as -he moves, and follow his eye in all its changes of place. The same -observations are of course applicable to buildings and streets seen in -perspective. - -In common portraits the apparent motion of the head is generally -rendered indistinct by the canvas being imperfectly stretched, as -the slightest concavity or convexity entirely deforms the face when -the obliquity is considerable. The deception is therefore best seen -when the painting is executed on a very flat board, and in colours -sufficiently vivid to represent every line in the face with tolerable -distinctness at great obliquities. This distinctness of outline is -indeed necessary to a satisfactory exhibition of this optical illusion. -The most perfect exhibition, indeed, that I ever saw of it was in the -case of a painting of a ship upon a sign-board executed in strongly -gilt lines. It contained a view of the stern and side of a ship in the -stocks, and, owing to the flatness of the board and the brightness of -the lines, the gradual development of the figure, from the most violent -foreshortening at great obliquities till it attained its perfect form, -was an effect which surprised every person that saw it. - -[Illustration: _Fig. 29._] - -The only other optical illusion which our limits will permit us to -explain, is the very remarkable experiment of what may be truly called -_breathing light or darkness_. Let S be a candle whose light falls at -an angle of 56° 45´ upon two glass plates A, B, placed close to each -other, and let the reflected rays AC, BD, fall at the same angle upon -two similar plates, C, D, but so placed that the plane of reflexion -from the latter is at right angles to the plane of reflexion from the -former. An eye placed at E, and looking at the same time into the two -plates C and D, will see very faint images of the candle S, which by a -slight adjustment of the plates, may be made to disappear almost wholly -allowing the plate C to remain as it is, change the position of D, till -its inclination to the ray BD is diminished about 3°, or made nearly -53° 11´. When this is done, the image that had disappeared on looking -into D will be restored, so that the spectator at E, upon looking into -the two mirrors C, D, will see no light in C, because the candle has -nearly disappeared, while the candle is distinctly seen in D. If, while -the spectator is looking into these two mirrors, either he or another -person breathes upon them gently and quickly, the breath will revive -the extinguished image in C, and will extinguish the visible image -in D. The following is the cause of this singular result. The light -AC, BD, is polarized by reflexion from the plates A, B, because it is -incident at the polarizing angle of 56° 45´ for glass. When we breathe -upon the plates C, D, we form upon their surface a thin film of water, -whose polarizing angle is 53° 11´, so that if the polarized rays AC, -BD, fell upon the plates C, D, at an angle of 53° 11´, the candle from -which they proceeded would not be visible, or they would not suffer -reflexion from the plates C, D. At all other angles the light would -be reflected and the candles visible. Now the plate D is placed at an -angle of 53° 11´ and C at an angle of 56° 45´, so that when a film -of water is breathed upon them the light will be reflected from the -latter, and none from the former; that is, the act of breathing upon -the plates will restore the invisible and extinguish the visible image. - - - - -LETTER VI. - - Natural phenomena marked with the marvellous--Spectre of the - Brocken described--Analogous phenomena--Aërial spectres seen in - Cumberland--Fata Morgana in the Straits of Messina--Objects below the - horizon raised and magnified by refraction--Singular example seen at - Hastings--Dover Castle seen through the hill on which it stands--Erect - and inverted images of distant ships seen in the air--Similar - phenomena seen in the Arctic regions--Enchanted coast--Mr. - Scoresby recognizes his father’s ship by its aërial image--Images - of cows seen in the air--Inverted image of horses seen in South - America--Lateral images produced by refraction--Aërial spectres by - reflexion--Explanation of the preceding phenomena. - - -Among the wonders of the natural world which are every day presented -to us, without either exciting our surprise or attracting our notice, -some are occasionally displayed which possess all the characters of -supernatural phenomena. In the names by which they are familiarly -known, we recognize the terror which they inspired, and even now, -when science has reduced them to the level of natural phenomena, and -developed the causes from which they arise, they still retain their -primitive importance, and are watched by the philosopher with as -intense an interest as when they were deemed the immediate effects -of Divine power. Among these phenomena we may enumerate the _Spectre -of the Brocken_, the _Fata Morgana_ of the Straits of Messina, the -_Spectre Ships_ which appear in the air, and the other extraordinary -effects of the _Mirage_.[14] - - [14] In the Sanscrit, says Baron Humboldt, the phenomenon of the - Mirage is called _Mriga Trichna_, “thirst or desire of the antelope,” - no doubt because this animal _Mriga_, compelled by thirst, _Trichna_, - approaches those barren plains where, from the effect of unequal - refraction, he thinks he perceives the undulating surface of the - waters.--_Personal Narrative_, vol. iii., p. 554. - -The Brocken is the name of the loftiest of the Hartz mountains, a -picturesque range which lies in the kingdom of Hanover. It is elevated -3,300 feet above the sea, and commands the view of a plain seventy -leagues in extent, occupying nearly the two-hundredth part of the -whole of Europe, and animated with a population of above five millions -of inhabitants. From the earliest periods of authentic history, the -Brocken has been the seat of the marvellous. On its summits are still -seen huge blocks of granite called the Sorcerer’s Chair and the Altar. -A spring of pure water is known by the name of the Magic Fountain, -and the Anemone of the Brocken is distinguished by the title of the -Sorcerer’s Flower. These names are supposed to have originated in the -rites of the great idol Cortho, whom the Saxons worshipped in secret -on the summit of the Brocken, when Christianity was extending her -benignant sway over the subjacent plains. - -As the locality of these idolatrous rites, the Brocken must have been -much frequented, and we can scarcely doubt that the spectre which now -so often haunts it at sunrise must have been observed from the earliest -times; but it is nowhere mentioned that this phenomenon was in any -way associated with the objects of their idolatrous worship. One of -the best accounts of the spectre of the Brocken is that which is given -by M. Haue, who saw it on the 23rd of May, 1797. After having been on -the summit of the mountain no less than thirty times, he had at last -the good fortune of witnessing the object of his curiosity. The sun -rose about four o’clock in the morning through a serene atmosphere. -In the south-west, towards Achtermannshohe, a brisk west wind carried -before it the transparent vapours, which had not yet been condensed -into thick heavy clouds. About a quarter past four he went towards the -inn, and looked round to see whether the atmosphere would afford him a -free prospect towards the south-west, when he observed at a very great -distance, towards Achtermannshohe, a human figure of a monstrous size. -His hat having been almost carried away by a violent gust of wind, -he suddenly raised his hand to his head to protect his hat, and the -colossal figure did the same. He immediately made another movement by -bending his body,--an action which was repeated by the spectral figure. -M. Haue was desirous of making further experiments, but the figure -disappeared. He remained, however, in the same position, expecting -its return, and in a few minutes it again made its appearance on the -Achtermannshohe, when it mimicked his gestures as before. He then -called the landlord of the inn, and having both taken the same position -which he had before, they looked towards the Achtermannshohe, but saw -nothing. In a very short space of time, however, two colossal figures -were formed over the above eminence, and after bending their bodies -and imitating the gestures of the two spectators, they disappeared. -Retaining their position, and keeping their eyes still fixed upon the -same spot, the two gigantic spectres again stood before them, _and were -joined by a third_. Every movement that they made was imitated by the -three figures, but the effect varied in its intensity, being sometimes -weak and faint, and at other times strong and well defined. - -[Illustration: _Fig. 30._] - -In the year 1798, M. Jordan saw the same phenomenon at sunrise, and -under similar circumstances, but with less distinctness, and without -any duplication of the figures.[15] - - [15] See J. F. Gmelin’s _Gottingischen Journal der Wissenchaften_, - vol. i., part iii., 1798. - -Phenomena perfectly analogous to the preceding, though seen under less -imposing circumstances, have been often witnessed. When the spectator -sees his own shadow opposite to the sun upon a mass of thin fleecy -vapour passing near him, it not only imitates all his movements, but -its head is distinctly encircled with a halo of light. The aërial -figure is often not larger than life, its size and its apparent -distance depending, as we shall afterwards see, upon particular causes. -I have often seen a similar shadow when bathing in a bright summer’s -day in an extensive pool of deep water. When the fine mud deposited -at the bottom of the pool is disturbed by the feet of the bather, so -as to be disseminated through the mass of water in the direction of -his shadow, his shadow is no longer a shapeless mass formed upon the -bottom, but is a regular figure formed upon the floating particles of -mud, and having the head surrounded with a halo, not only luminous, but -consisting of distinct radiations. - -One of the most interesting accounts of aërial spectres with which we -are acquainted has been given by Mr. James Clarke, in his Survey of the -Lakes of Cumberland, and the accuracy of this account was confirmed by -the attestations of two of the persons by whom the phenomena were first -seen. On a summer’s evening, in the year 1743, when Daniel Stricket, -servant to John Wren, of Wilton Hall, was sitting at the door along -with his master, they saw the figure of a man with a dog pursuing some -horses along Souterfell-side, a place so extremely steep, that a horse -could scarcely travel upon it at all. The figures appeared to run at -an amazing pace, till they got out of sight at the lower end of the -Fell. On the following morning, Stricket and his master ascended the -steep side of the mountain, in the full expectation of finding the man -dead, and of picking up some of the shoes of the horses, which they -thought must have been cast while galloping at such a furious rate. -Their expectations, however, were disappointed. No traces, either of -man or horse, could be found, and they could not even discover upon the -turf the single mark of a horse’s hoof. These strange appearances seen -at the same time by two different persons in perfect health, could not -fail to make a deep impression on their minds. They at first concealed -what they had seen, but they at length disclosed it, and were laughed -at for their credulity. - -In the following year, on the 23rd June, 1744, Daniel Stricket, who -was then servant to Mr. Lancaster, of Blakehills, (a place near -Wilton Hall, and both of which places are only about half a mile -from Souterfell,) was walking, about seven o’clock in the evening, -a little above the house, when he saw a troop of horsemen riding -on Souterfell-side, in pretty close ranks, and at a brisk pace. -Recollecting the ridicule that had been cast upon him the preceding -year, he continued to observe the figures for some time in silence; -but being at last convinced that there could be no deception in the -matter, he went to the house, and informed his master that he had -something curious to show him. They accordingly went out together; but -before Stricket had pointed out the place, Mr. Lancaster’s son had -discovered the aërial figures. The family was then summoned to the -spot, and the phenomena were seen alike by them all. The equestrian -figures seemed to come from the lowest parts of Souterfell, and became -visible at a place called Knott. They then advanced in regular troops -along the side of the Fell, till they came opposite to Blakehills, when -they went over the mountain, after describing a kind of curvilineal -path. The pace at which the figures moved was a regular swift walk, -and they continued to be seen for upwards of two hours, the approach -of darkness alone preventing them from being visible. Many troops -were seen in succession; and frequently the last but one in a troop -quitted his position, galloped to the front, and took up the same pace -with the rest. The changes in the figures were seen equally by all -the spectators, and the view of them was not confined to the farm of -Blakehills only, but they were seen by every person at every cottage -within the distance of a mile, the number of persons who saw them -amounting to about twenty-six. The attestation of these facts, signed -by Lancaster and Stricket, bears the date of the 21st July, 1785. - -These extraordinary sights were received not only with distrust, but -with absolute incredulity. They were not even honoured with a place in -the records of natural phenomena, and the philosophers of the day were -neither in possession of analogous facts, nor were they acquainted with -those principles of atmospherical refraction upon which they depend. -The strange phenomena, indeed, of the _Fata Morgana_, or the _Castles -of the Fairy Morgana_, had been long before observed, and had been -described by Kircher in the 17th century, but they presented nothing -so mysterious as the aërial troopers of Souterfell; and the general -characters of the two phenomena were so unlike, that even a philosopher -might have been excused for ascribing them to different causes. - -This singular exhibition has been frequently seen in the straits of -Messina, between Sicily and the coast of Italy, and whenever it takes -place, the people, in a state of exultation, as if it were not only -a pleasing but a lucky phenomenon, hurry down to the sea, exclaiming -_Morgana, Morgana!_ When the rays of the rising sun form an angle -of 45° on the sea of Reggio, and when the surface of the water is -perfectly unruffled, either by the wind or the current, a spectator -placed upon an eminence in the city, and having his back to the sun -and his face to the sea, observes upon the surface of the water superb -palaces, with their balconies and windows, lofty towers, herds and -flocks grazing in wooded valleys and fertile plains; armies of men -on horseback and on foot, with multiplied fragments of buildings, -such as columns, pilasters, and arches. These objects pass rapidly in -succession along the surface of the sea during the brief period of -their appearance. The various objects thus enumerated are pictures -of palaces and buildings actually existing on shore, and the living -objects are of course only seen when they happen to form a part of the -general landscape. - -If, at the time that these phenomena are visible, the atmosphere is -charged with vapour or dense exhalations, the same objects which are -depicted upon the sea will be seen also in the air, occupying a space -which extends from the surface to the height of twenty-five feet. These -images, however, are less distinctly delineated than the former. - -If the air is in such a state as to deposit dew, and is capable of -forming the rainbow, the objects will be seen only on the surface of -the sea; but they all appear fringed with red, yellow, and blue light, -as if they were seen through a prism. - -In our own country, and in our own times, facts still more -extraordinary have been witnessed. From Hastings, on the coast of -Sussex, the cliffs on the French coast are fifty miles distant, -and they are actually hid by the convexity of the earth; that is, -a straight line drawn from Hastings to the French coast would pass -through the sea. On Wednesday, the 26th of July, 1798, about five -o’clock in the afternoon, Mr. Latham, a Fellow of the Royal Society, -then residing at Hastings, was surprised to see a crowd of people -running to the sea-side. Upon inquiry into the cause of this, he -learned that the coast of France could be seen by the naked eye, and -he immediately went down to witness so singular a sight. He distinctly -saw the cliffs extending for some leagues along the French coast, and -they appeared as if they were only a few miles off. They gradually -appeared more and more elevated, and seemed to approach nearer to the -eye. The sailors with whom Mr. Latham walked along the waters edge were -at first unwilling to believe in the reality of the appearance; but -they soon became so thoroughly convinced of it, that they pointed out -and named to him the different places which they had been accustomed to -visit, and which they conceived to be as near as if they were sailing -at a small distance into the harbour. These appearances continued for -nearly an hour, the cliffs sometimes appearing brighter and nearer, and -at other times fainter and more remote. Mr. Latham then went upon the -eastern cliff or hill, which is of considerable height, when, as he -remarks, a most beautiful scene presented itself to his view. He beheld -at once Dungeness, Dover cliffs, and the French coast all along from -Calais, Boulogne, &c., to St. Vallery, and, as some of the fishermen -affirmed, as far west as Dieppe. With the help of a telescope, the -French fishing-boats were plainly seen at anchor, and the different -colours of the land upon the heights, together with the buildings, were -perfectly discernible. Mr. Latham likewise states that the cape of land -called Dungeness, which extends nearly two miles into the sea, and is -about sixteen miles in a straight line from Hastings, appeared as if -quite close to it, and the vessels and fishing-boats which were sailing -between the two places appeared equally near, and were magnified to -a high degree. These curious phenomena continued “in the highest -splendour” till past eight o’clock, although a black cloud had for some -time totally obscured the face of the sun. - -A phenomenon no less marvellous was seen by Professor Vince, of -Cambridge, and another gentleman, on the 6th of August, 1806, at -Ramsgate. The summits _v w x y_ of the four turrets of Dover Castle -are usually seen over the hill AB, upon which it stands, lying between -Ramsgate and Dover; but on the day above-mentioned, at seven o’clock in -the evening, when the air was very still and a little hazy, not only -were the tops _v w x y_ of the four towers of Dover Castle seen over -the adjacent hill AB, _but the whole of the Castle, m n r s, appeared -as if it were situated on the side of the hill next Ramsgate_, and -rising above the hill as much as usual. This phenomenon was so very -singular and unexpected, that at first sight Dr. Vince thought it an -illusion; but upon continuing his observations, he became satisfied -that it was a real image of the Castle. Upon this he gave a telescope -to a person present, who, upon attentive examination, saw also a -very clear image of the Castle as the Doctor had described it. He -continued to observe it for about twenty minutes, during which time the -appearance remained precisely the same; but rain coming on, they were -prevented from making any further observations. Between the observers -and the land from which the hill rises there was about six miles of -sea, and from thence to the top of the hill there was about the same -distance. Their own height above the surface of the water was about -seventy feet. - -[Illustration: _Fig. 31._] - -This illusion derived great force from the remarkable circumstance, -that the hill itself did not appear through the image, as it might have -been expected to do. The image of the castle was very strong and well -defined, and though the rays from the hill behind it must undoubtedly -have come to the eye, yet the strength of the image of the castle so -far obscured the background, that it made no sensible impression on the -observers. Their attention was of course principally directed to the -image of the castle; but if the hill behind had been at all visible, -Dr. Vince conceives that it could not have escaped their observation, -as they continued to look at it for a considerable time with a good -telescope. - -[Illustration: _Fig. 32._] - -Hitherto our aërial visions have been seen only in their erect and -natural positions, either projected against the ground or elevated -in the air; but cases have occurred in which both erect and inverted -images of objects have been seen in the air, sometimes singly, -sometimes combined, sometimes when the real object was invisible, and -sometimes when a part of it had begun to show itself to the spectator. - -In the year 1793, Mr. Huddart, when residing at Allonby, in Cumberland, -perceived the inverted image of a ship beneath the image, as shown -in Fig. 32; but Dr. Vince, who afterwards observed this phenomenon -under a greater variety of forms, found that the ship, which was here -considered the real one, was only an erect image of the real ship, -which was at that time beneath the horizon, and wholly invisible. - -[Illustration: _Fig. 33._] - -In August, 1798, Dr. Vince observed a great variety of these aërial -images of vessels approaching the horizon. Sometimes there was seen -only one inverted image above the real ship, and this was generally the -case when the real ship was full in view. But when the real ship was -just begin beginning to show its top-mast above the horizon, as at A, -Fig. 33, two aërial images of it were seen, one at B inverted, and the -other in its natural position at C. In this case the sea was distinctly -visible between the erect and inverted images, but in other cases the -hull of the one image was immediately in contact with the hull of the -other. - -Analogous phenomena were seen by Captain Scoresby when navigating -with the ship Baffin the icy sea in the immediate neighbourhood of -West Greenland. On the 28th of June, 1820, he observed about eighteen -sail of ships at the distance of ten or fifteen miles. The sun had -shone during the day without the interposition of a cloud, and its -rays were peculiarly powerful. The intensity of its light occasioned a -painful sensation in the eyes, while its heat softened the tar in the -rigging of the ship, and melted the snow on the surrounding ice with -such rapidity that pools of fresh water were formed on almost every -place, and thousands of rills carried the excess into the sea. There -was scarcely a breath of wind: the sea was as smooth as a mirror. The -surrounding ice was crowded together, and exhibited every variety, from -the smallest lumps to the most magnificent sheets. Bears traversed the -fields and floes in unusual numbers, and many whales sported in the -recesses and openings among the drift ice. About six in the evening, a -light breeze at N.W. having sprung up, a thin stratus or “fog bank,” -at first considerably illuminated by the sun, appeared in the same -quarter, and gradually rose to the altitude of about a quarter of a -degree. At this time most of the ships navigating at the distance -of ten or fifteen miles began to change their form and magnitude, -and when examined by a telescope from the mast-head, exhibited some -extraordinary appearances, which differed at almost every point of the -compass. One ship had a perfect image, as dark and distinct as the -original, united to its mast-head in a reverse position. Two others -presented two distinct inverted images in the air, one of them a -perfect figure of the original, and the other wanting the hull. Two -or three more were strangely distorted, their masts appearing of at -least twice their proper height, the top-gallant mast forming one-half -of the total elevation; and other vessels exhibited an appearance -totally different from all the preceding, being as it were compressed, -in place of elongated. Their masts seemed to be scarcely one-half of -their proper altitude, in consequence of which one would have supposed -that they were greatly heeled-to one side, or in the position called -careening. Along with all the images of the ships a reflexion of the -ice, sometimes in two strata, also appeared in the air, and these -reflexions suggested the idea of cliffs composed of vertical columns of -alabaster. - -On the 15th, 16th, and 17th of the same month, Mr. Scoresby observed -similar phenomena, sometimes extending continuously through half the -circumference of the horizon, and at other times appearing only in -detached spots in various quarters. The inverted images of distant -vessels were often seen in the air, _while the ships themselves were -far beyond the reach of vision_. Some ships were elevated to twice -their proper height, while others were compressed almost to a line. -Hummocks of ice were surprisingly enlarged, and every prominent object -in a proper position was either magnified or distorted. - -But of all the phenomena witnessed by Mr. Scoresby, that of the -_Enchanted Coast_, as it may be called, must have been the most -remarkable. This singular effect was seen on the 18th of July, when -the sky was clear, and a tremulous and perfectly transparent vapour -was particularly sensible and profuse: at nine o’clock in the morning, -when the phenomenon was first seen, the thermometer stood at 42° -Fahr.; but in the preceding evening it must have been greatly lower, -as the sea was in many places covered with a considerable pellicle -of new ice,--a circumstance, which, in the very warmest time of the -year, must be considered as quite extraordinary, especially when it -is known that 10° farther to the north no freezing of the sea at -this season had ever before been observed. Having approached on this -occasion so near the unexplored shore of Greenland that the land -appeared distinct and bold, Mr. Scoresby was anxious to obtain a -drawing of it; but on making the attempt he found that the outline -was constantly changing, and he was induced to examine the coast with -a telescope, and to sketch the various appearances which presented -themselves. These are shown, without any regard to their proper order, -in Fig. 34, which we shall describe in Mr. Scoresby’s own words: “The -general telescopic appearance of the coast was that of an extensive -ancient city abounding with the ruins of castles, obelisks, churches, -and monuments, with other large and conspicuous buildings. Some of -the hills seemed to be surmounted by turrets, battlements, spires, -and pinnacles; while others, subjected to one or two reflexions, -exhibited large masses of rock, apparently suspended in the air, at a -considerable elevation above the actual termination of the mountains to -which they referred. The whole exhibition was a grand phantasmagoria. -Scarcely was any particular portion sketched before it changed its -appearance, and assumed the form of an object totally different. It -was perhaps alternately a castle, a cathedral, or an obelisk; then -expanding horizontally, and coalescing with the adjoining hills, united -the intermediate valleys, though some miles in width, by a bridge -of a single arch, of the most magnificent appearance and extent. -Notwithstanding these repeated changes, the various figures represented -in the drawing had all the distinctness of reality; and not only the -different strata, but also the veins of the rocks, with the wreaths of -snow occupying ravines and fissures, form sharp and distinct lines, -and exhibited every appearance of the most perfect solidity.” - -[Illustration: _Fig. 34._] - -One of the most remarkable facts respecting aërial images presented -itself to Mr. Scoresby in a later voyage which he performed to the -coast of Greenland in 1822. Having seen an inverted image of a ship -in the air, he directed to it his telescope; he was able to discover -it to be his father’s ship, which was at the time below the horizon. -“It was,” says he, “so well defined, that I could distinguish by a -telescope every sail, the general rig of the ship, and its particular -character; insomuch, that I confidently pronounced it to be my father’s -ship, the _Fame_, which it afterwards proved to be; though, on -comparing notes with my father, I found that our relative position, at -the time, gave a distance from one another very nearly thirty miles, -being about seventeen miles beyond the horizon, and some leagues beyond -the limit of direct vision. I was so struck with the peculiarity of -the circumstance, that I mentioned it to the officer of the watch, -stating my full conviction that the _Fame_ was then cruising in the -neighbouring inlet.” - -Several curious effects of the mirage were observed by Baron Humboldt -during his travels in South America. When he was residing at Cumana, -he frequently saw the islands of Picuita and Boracha suspended in the -air, and sometimes with an inverted image. On one occasion he observed -small fishing-boats swimming in the air, during more than three or -four minutes, above the well-defined horizon of the sea; and when they -were viewed through a telescope, one of the boats had an inverted -image accompanying it in its movements. This distinguished traveller -observed similar phenomena in the barren steppes of the Caraccas, and -on the borders of the Orinoco, where the river is surrounded by sandy -plains. Little hills and chains of hills appeared suspended in the -air, when seen from the steppes, at three or four leagues’ distance. -Palm-trees standing single in the Llanos appeared to be cut off at -bottom, as if a stratum of air separated them from the ground; and, as -in the African desert, plains destitute of vegetation appeared to be -rivers or lakes. At the Mesa de Pavona M. Humboldt and M. Bonpland _saw -cows suspended in the air_ at the distance of 1000 toises, and having -their feet elevated 3’ 20” above the soil. In this case the images were -erect, but the travellers learned from good authority that _inverted -images of horses had been seen suspended in the air_ near Calabozo. - -In all these cases of aërial spectres, the images were directly above -the real object; but a curious case was observed by Messrs. Jurine and -Soret on the 17th September, 1818, where the image of the vessel was -on one side of the real one. About 10 P.M. a barque at the distance -of about 4000 toises from Bellerive, on the lake of Geneva, was seen -approaching to Geneva by the _left_ bank of the lake, and at the same -time an image of the sails was observed above the water, which, instead -of following the direction of the barque, separated from it, and -appeared to approach Geneva by the right bank of the lake, the _image_ -moving from _east_ to _west_, while the _barque_ moved from _north_ to -_south_. When the image first separated from the barque they had both -the same magnitude, but the image diminished as it receded from it, -and was reduced to one-half when the phenomenon disappeared. - -A very unusual example of aërial spectres occurred to Dr. A. P. Buchan -while walking on the cliff about a mile to the east of Brighton, on the -morning of the 28th of November, 1804. “While watching the rising of -the sun,” says he, “I turned my eyes directly towards the sea, just as -the solar disk emerged from the surface of the water, and saw the face -of the cliff on which I was standing represented precisely opposite to -me at some distance on the ocean. Calling the attention of my companion -to this appearance, we discerned our own figures standing on the summit -of the apparent opposite cliff, as well as the representation of the -windmill near at hand. - -“The reflected images were most distinct precisely opposite to where -we stood, and the false cliff seemed to fade away, and to draw near -to the real one, in proportion as it receded towards the west. This -phenomenon lasted about ten minutes, or till the sun had risen nearly -his own diameter above the surface of the ocean. The whole then seemed -to be elevated into the air, and successively disappeared, giving an -impression very similar to that which is produced by the drawing up of -a drop-scene in a theatre. The horizon was cloudy, or perhaps it might -with more propriety be said that the surface of the sea was covered -with a dense fog of many yards in height, and which gradually receded -before the rays of the sun.” - -An illusion of a different kind, though not less interesting, is -described by the Rev. Mr. Hughes in his Travels in Greece, as seen -from the summit of Mount Ætna. “I must not forget to mention,” says -he, “one extraordinary phenomenon, which we observed, and for which I -have searched in vain for a satisfactory solution. At the extremity -of the vast shadow which Ætna projects across the island, appeared a -perfect and distinct image of the mountain itself elevated above the -horizon, and diminished as if viewed in a concave mirror. Where or what -the reflector could be which exhibited this image, I cannot conceive; -we could not be mistaken in its appearance, for all our party observed -it, and we had been prepared for it beforehand by our Catanian friends. -It remained visible about _ten_ minutes, and disappeared as the shadow -decreased. Mr. Jones observed the same phenomenon, as well as some -other friends with whom I conversed upon the subject in England.” - -It is impossible to study the preceding phenomena without being -impressed with the conviction, that nature is full of the marvellous, -and that the progress of science and the diffusion of knowledge -are alone capable of dispelling the fears which her wonders must -necessarily excite even in enlightened minds. When a spectre haunts -the couch of the sick, or follows the susceptible vision of the -invalid, a consciousness of indisposition divests the apparition of -much of its terror, while its invisibility to surrounding friends -soon stamps it with the impress of a false perception. The spectres -of the conjuror, too, however skilfully they may be raised, quickly -lose their supernatural character; and even the most ignorant beholder -regards the modern magician as but an ordinary man, who borrows from -the sciences the best working implements of his art. But when, in the -midst of solitude, and in situations where the mind is undisturbed -by sublunary cares, we see our own image delineated in the air, and -mimicking in gigantic perspective the tiny movements of humanity;--when -we see troops in military array performing their evolutions on the very -face of an almost inaccessible precipice--when, in the eye of day, a -mountain seems to become transparent, and exhibits on one side of it a -castle which we know to exist only on the other; when distant objects, -concealed by the roundness of the earth, and beyond the cognisance of -the telescope, are actually transferred over the intervening convexity -and presented in distinct and magnified outline to our accurate -examination;--when such varied and striking phantasms are seen also by -all around us, and therefore appear in the character of real phenomena -of nature, our impressions of supernatural agency can only be removed -by a distinct and satisfactory knowledge of the causes which gave them -birth. - -It is only within the last forty years that science has brought these -atmospherical spectres within the circle of her dominion; and not only -are all their phenomena susceptible of distinct explanation, but we can -even reproduce them on a small scale with the simplest elements of our -optical apparatus. - -[Illustration: _Fig. 35._] - -In order to convey a general idea of the causes of these phenomena, let -ABCD, Fig. 35, be a glass trough filled with water, and let a small -ship be placed at S. An eye situated about E, will see the top-mast -of the ship S, directly through the plate of glass BD. Fix a convex -lens _a_ of short focus upon the plate of glass BD, and a little above -a straight line SE joining the ship and the eye; and immediately above -the convex lens a place _a_ concave one _b_. The eye will now see, -through the convex lens _a_, an _inverted_ image of the ship at S´, -and through the concave lens _b_, an erect image of the ship at S´´, -representing in a general way the phenomena shown in Fig. 33. But it -will be asked, where are the lenses in nature to produce these effects? -This question is easily answered. If we take a tin tube with glass -plates at each end, and fill it with water, and if we cool it on the -outside with ice, it will act like a _concave_ lens when the cooling -effect has reached the axis; and, on the other hand, if we heat the -same tube filled with water, on the outside, it will act as a _convex_ -glass. In the first case the density of the water diminishes towards -the centre, and in the second it increases towards the centre. The -very same effects are produced in the air, only a greater tract of air -is necessary for showing the effect produced, by heating and cooling it -unequally. If we now remove the lenses _a_, _b_, and hold a heated iron -horizontally above the water in the trough ABC, the heat will gradually -descend, expanding or rendering rarer the upper portions of the fluid. -If, when the heat has reached within a little of the bottom, we look -through the trough at the ship S in the direction ES´, we shall see -an inverted image at S´, and an erect one at S´´; and if we hide from -the eye at E all the ship S, excepting the top-mast, we shall have an -exact representation of the phenomenon in Fig. 33. The experiment will -succeed better with oil in place of water; and the same result may be -obtained without heat, by pouring clear syrup into the glass trough -till it is nearly one-third full, and then filling it up with water. -The water will gradually incorporate with the syrup, and produce, as -Dr. Wollaston has shown, a regular gradation of density, diminishing -from that of the pure syrup to that of the pure water. Similar effects -may be obtained by using masses of transparent solids, such as glass, -rock-salt, &c. - -Now it is easy to conceive how the changes of density which we can -thus produce artificially may be produced in nature. If, in serene -weather, the surface of the sea is much colder than the air of the -atmosphere, as it frequently is, and as it was to a very great degree -during the phenomena described by Mr. Scoresby, the air next the sea -will gradually become colder and colder, by giving out its heat to -the water; and the air immediately above will give out its heat to -the cooler air immediately below it, so that the air from the surface -of the sea, to a considerable height upwards, will gradually diminish -in density, and therefore must produce the very phenomena we have -described. - -[Illustration: _Fig. 36._] - -The phenomenon of Dover Castle seen on the Ramsgate side of the hill, -was produced by the air being more dense near the ground and above the -sea than at greater heights, and hence the rays proceeding from the -castle reached the eye in curve lines, and the cause of its occupying -its natural position on the hill, and not being seen in the air, was -that the top of the hill itself, in consequence of being so near the -castle, suffered the same change from the varying density of the -air, and therefore the castle and the hill were equally elevated and -retained their relative positions. The reason why the image of the -castle and hill appeared erect was, that the rays from the top and -bottom of the castle had not crossed before they reached Ramsgate; but -as they met at Ramsgate, an eye at a greater distance from the castle, -and in the path of the rays, would have seen the image inverted. This -will be better understood from the preceding diagram, which represents -the actual progress of the rays, from a ship SP, concealed from the -observer at E by the convexity of the earth PQE. A ray proceeding from -the keel of the ship P is refracted into the curve line P _c x c_ E, -and a ray proceeding from the top-mast S, is refracted in the direction -S _d x d_ E, the two rays crossing at _x_, and proceeding to the eye -E with the ray from the keel P uppermost; hence the ship must appear -inverted as at _s p_. Now if the eye E of the observer had been placed -nearer the ship as at _x_, before the rays crossed, as was the case at -Ramsgate, it would have seen an erect image of the ship raised a little -above the real ship SP. Rays S _m_, S _n_, proceeding higher up in the -air, are refracted in the directions S _m m_ E, S _n n_ E, but do not -cross before they reach the eye, and therefore they afford the erect -image of the ship shown at _s´ p´_. - -The aërial troopers seen at Souterfell were produced by the very -same process as the spectre of Dover Castle, having been brought by -unequal refraction from one side of the hill to the other. It is not -our business to discover how a troop of soldiers came to be performing -their evolutions on the other side of Souterfell; but if there was then -no road along which they could be marching, it is highly probable that -they were troops exercising among the hills in secret, previously to -the breaking out of the rebellion in 1745. - -The image of the Genevese barque which was seen sailing at a distance -from the real one, arose from the same cause as the images of ships in -the air; with this difference only, that in this case the strata of -equal density were vertical or perpendicular to the water, whereas, -in the former cases they were horizontal or parallel to the water. -The state of the air which produced the lateral image may be produced -by a headland or island, or even rocks, near the surface, and covered -with water. These headlands, islands, or sunken rocks being powerfully -heated by the sun in the daytime, will heat the air immediately above -them, while the adjacent air over the sea will retain its former -coolness and density. Hence there will necessarily arise a gradation -of density varying in the same horizontal direction, or where the -lines of equal density are vertical. If we suppose the very same state -of the air to exist in a horizontal plane which exists in a vertical -plane, in Fig. 36, then the same images would be seen in a horizontal -line, viz., an inverted one at _s p_, and an erect one at _s´p´_. In -the case of the Genevese barque, the rays had not crossed before they -reached the eye, and therefore the image was an erect one. Had the -real Genevese barque been concealed by some promontory or other cause -from the observation of Messrs. Jurine and Soret, they might have -attached a supernatural character to the spectral image, especially if -they had seen it gradually decay, and finally disappear on the still -and unbroken surface of the lake. No similar fact had been previously -observed, and there were no circumstances in the case to have excited -the suspicion that it was the spectre of a real vessel produced by -unequal refraction. - -The spectre of the Brocken and other phenomena of the same kind, have -essentially a different origin from those which arise from unequal -refraction. They are merely shadows of the observer projected on dense -vapour or thin fleecy clouds, which have the power of reflecting much -light. They are seen most frequently at sunrise, because it is at that -time that the vapours and clouds necessary for their production are -most likely to be generated; and they can be seen only when the sun -is throwing his rays horizontally, because the shadow of the observer -would otherwise be thrown either up in the air, or down upon the -ground. If there are two persons looking at the phenomenon, as when -M. Haue and the landlord saw it together, each observer will see his -own image most distinctly, and the head will be more distinct than the -rest of the figure, because the rays of the sun will be more copiously -reflected at a perpendicular incidence: and as, from this cause, the -light reflected from the vapour or cloud becomes fainter farther from -the shadow, the appearance of a halo round the head of the observer is -frequently visible. M. Haue mentions the extraordinary circumstance -of the two spectres of him and the landlord being joined by a _third -figure_, but he unfortunately does not inform us which of the two -figures was doubled, for it is impossible that a person could have -joined their party unobserved. It is very probable that the new spectre -forms a natural addition to the group, as we have represented it in -Fig. 30; and, if this was the case, it could only have been produced by -a duplication of one of the figures produced by unequal refraction. - -The reflected spectre of Dr. Buchan standing upon the cliff at -Brighton, arose from a cause to which we have not yet adverted. It was -obviously no shadow, for it is certain, from the locality, that the -rays of the sun fell upon the face of the cliff and upon his person at -an angle of about 73° from the perpendicular, so as to illuminate them -strongly. Now, there are two ways in which such an image may have been -reflected, namely, either from strata of air of variable density, or -from a vertical stratum of vapour, consisting of exceedingly minute -globules of water. Whenever light suffers refraction, either in passing -at once from one medium into another, or from one part of the same -medium into another of different density, a portion of it suffers -reflexion. If an object, therefore, were strongly illuminated, a -sufficiently distinct image, or rather shadow of it, might be seen by -reflexion from strata of air of different density. As the temperature -at which moisture is deposited in the atmosphere varies with the -density of the air, then at the same temperature moisture might be -depositing in a stratum of one density, while no deposition is taking -place in the adjacent stratum of a different density. Hence there would -exist, as it were in the air, a vertical wall or stratum of minute -globules of water, from the surface of which a sufficiently distinct -image of a highly illuminated object might be reflected. That this -is possible may be proved by breathing upon glass. If the particles -deposited upon the glass are large, then no distinct reflection will -take place; but if the particles be very small, we shall see a distinct -image formed by the surface of the aqueous film. - -The phenomena of the Fata Morgana have been too imperfectly described -to enable us to offer a satisfactory explanation of them. The aërial -images are obviously those formed by unequal refraction. The pictures -seen on the sea may be either the aërial images reflected from its -surface, or from a stratum of dense vapour, or they may be the direct -reflexions from the objects themselves. The coloured images, as -described by Minasi, have never been seen in any analogous phenomena, -and require to be better described before they can be submitted to -scientific examination. - -The representation of ships in the air by unequal refraction has no -doubt given rise in early times to those superstitions which have -prevailed in different countries respecting “phantom ships,” as Mr. -Washington Irving calls them, which always sail in the eye of the -wind, and plough their way through the smooth sea, where there is -not a breath of wind upon its surface. In his beautiful story of the -storm ship, which makes its way up the Hudson against wind and tide, -this elegant writer has finely embodied one of the most interesting -superstitions of the early American colonists. The Flying Dutchman had, -in all probability, a similar origin; and the wizard beacon-keeper of -the Isle of France, who saw in the air the vessels bound to the island -long before they appeared in the offing, must have derived his power -from a diligent observation of the phenomena of nature. - - - - -LETTER VII. - - Illusions depending on the ear--Practised by the ancients--Speaking - and singing heads of the ancients--Exhibition of the Invisible Girl - described and explained--Illusions arising from the difficulty - of determining the direction of sounds--Singular example of this - illusion--Nature of ventriloquism--Exhibitions of some of the - most celebrated ventriloquists--M. St. Gille--Louis Brabant--M. - Alexandre--Capt. Lyon’s account of Esquimaux ventriloquists. - - -Next to the eye, the ear is the most fertile source of our illusions, -and the ancient magicians seem to have been very successful in turning -to their purposes the doctrines of sound. In the Labyrinth of Egypt, -which contained twelve palaces and 1500 subterraneous apartments, the -gods were made to speak in a voice of thunder; and Pliny, in whose -time this singular structure existed, informs us, that some of the -palaces were so constructed that their doors could not be opened -without permitting the peals of thunder to be heard in the interior. -When Darius Hystaspes ascended the throne, and allowed his subjects to -prostrate themselves before him as a god, the divinity of his character -was impressed upon his worshippers by the bursts of thunder and flashes -of lightning which accompanied their devotion. History has of course -not informed us how these effects were produced; but it is probable -that, in the subterraneous and vaulted apartments of the Egyptian -labyrinth, the reverberated sounds arising from the mere opening and -shutting of the doors themselves afforded a sufficient imitation of -ordinary thunder. In the palace of the Persian king, however, a more -artificial imitation is likely to have been employed, and it is not -improbable that the method used in our modern theatres was known to -the ancients. A thin sheet of iron, three or four feet long, such as -that used for German stoves, is held by one corner between the finger -and the thumb, and allowed to hang freely by its own weight. The hand -is then moved or shaken horizontally, so as to agitate the corner in a -direction at right angles to the surface of the sheet. By this simple -process a great variety of sounds may be produced, varying from the -deep growl of distant thunder to those loud and explosive bursts which -rattle in quick succession from clouds immediately over our heads. -The operator soon acquires great power over this instrument, so as -to be able to produce from it any intensity and character of sound -that may be required. The same effect may be produced by sheets of -tin-plate, and by thin plates of mica; but, on account of their small -size, the sound is shorter and more acute. In modern exhibitions an -admirable imitation of lightning is produced by throwing the powder of -rosin, or the dust of lycopodium, through a flame; and the rattling -showers of rain which accompany these meteors are well imitated by a -well-regulated shower of peas. - -The principal pieces of acoustic mechanism used by the ancients were -_speaking_ or _singing heads_, which were constructed for the purpose -of representing the gods, or of uttering oracular responses. Among -these, the speaking head of Orpheus, which uttered its responses -at Lesbos, is one of the most famous. It was celebrated not only -throughout Greece, but even in Persia; and it had the credit of -predicting, in the equivocal language of the heathen oracles, the -bloody death which terminated the expedition of Cyrus the Great into -Scythia. Odin, the mighty magician of the North, who imported into -Scandinavia the magical arts of the East, possessed a speaking head, -said to be that of the sage Minos, which he had enchased in gold, -and which uttered responses that had all the authority of a divine -revelation. The celebrated mechanic Gerbert, who filled the papal chair -A.D. 1000, under the name of Sylvester II., constructed a speaking -head of brass. Albertus Magnus is said to have executed a head in -the thirteenth century, which not only moved but spoke. It was made -of earthenware, and Thomas Aquinas is said to have been so terrified -when he saw it, that he broke it in pieces; upon which the mechanist -exclaimed, “There goes the labour of thirty years!” - -It has been supposed by some authors, that in the ancient -speaking-machines the deception is effected by means of ventriloquism, -the voice issuing from the juggler himself; but it is more probable -that the sound was conveyed by pipes from a person in another apartment -to the mouth of the figure. Lucian, indeed, expressly informs us, -that the impostor Alexander made his figure of Æsculapius speak, by -transmitting his voice through the gullet of a crane to the mouth of -the statue; and that this method was general appears from a passage in -Theodoretus, who assures us, that in the fourth century, when Bishop -Theophilus broke to pieces the statues at Alexandria, he found some -which were hollow, and which were so placed against a wall, that the -priest could conceal himself behind them; and address the ignorant -spectators through their mouths. - -Even in modern times, speaking-machines have been constructed on this -principle. The figure is frequently a mere head placed upon a hollow -pedestal, which, in order to promote the deception, contains a pair of -bellows, a sounding-board, a cylinder and pipes supposed to represent -the organs of speech. In other cases these are dispensed with, and a -simple wooden head utters its sounds through a speaking trumpet. At the -court of Charles II., this deception was exhibited with great effect by -one Thomas Irson, an Englishman; and when the astonishment had become -very general, a popish priest was discovered by one of the pages in -an adjoining apartment. The questions had been proposed to the wooden -figure by whispering into its ear, and this learned personage had -answered them all with great ability, by speaking through a pipe in the -same language in which the questions were proposed. Professor Beckmann -informs us that children and women were generally concealed either in -the juggler’s box or in the adjacent apartment, and that the juggler -gave them every assistance by means of signs previously agreed upon. -When one of these exhibitions was shown at Göttingen, the Professor -was allowed, on the promise of secrecy, to witness the process of -deception. He saw the assistant in another room, standing before the -pipe with a card in his hand, upon which the signs agreed upon had -been marked, and he had been introduced so privately into the house -that even the landlady was ignorant of his being there. - -An exhibition of the very same kind has been brought forward in our -own day, under the name of the _Invisible Girl_; and as the mechanism -employed was extremely ingenious, and is well fitted to convey an idea -of this class of deceptions, we shall give a detailed description of it. - -[Illustration: _Fig. 37._] - -The machinery, as constructed by M. Charles, is shown in fig. 37 in -perspective, and a plan of it in Fig. 38. The four upright posts A, A, -A, A, are united at top by a cross rail B, B, and by two similar rails -at bottom. Four bent wires a, _a_, _a_, _a_, proceeded from the top -of these posts, and terminated at _c_. A hollow copper ball M, about -a foot in diameter, was suspended from these wires by four slender -ribands _b_, _b_, _b_, _b_, and into the copper ball were fixed the -extremities of four trumpets T, T, T, T, with their mouths outwards. - -[Illustration: _Fig. 38._] - -The apparatus now described was all that was visible to the spectator; -and though fixed in one spot, yet it had the appearance of a piece of -separate machinery, which might have occupied any other part of the -room. When one of the spectators was requested by the exhibitor to -propose some question, he did it by speaking into one of the trumpets -at T. An appropriate answer was then returned from all the trumpets, -and the sound issued with sufficient intensity to be heard by an ear -applied to any of them, and yet it was so weak that it appeared to come -from a person of very diminutive size. Hence the sound was supposed to -come from an invisible girl, though the real speaker was a full-grown -woman. The invisible lady conversed in different languages, sang -beautifully, and made the most lively and appropriate remarks on the -persons in the room. - -This exhibition was obviously far more wonderful than the speaking -heads which we have described, as the latter invariably communicated -with a wall, or with a pedestal through which pipes could be carried -into the next apartment. But the ball M and its trumpets communicated -with nothing through which sound could be conveyed. The spectator -satisfied himself by examination that the ribands _b_, _b_, were real -ribands, which concealed nothing, and which could convey no sound; and -as he never conceived that the ordinary piece of frame-work AB could -be of any other use than its apparent one of supporting the sphere M, -and defending it from the spectators, he was left in utter amazement -respecting the origin of the sound, and his surprise was increased -by the difference between the sounds which were uttered and those of -ordinary speech. - -Though the spectators were thus deceived by their own reasoning, -yet the process of deception was a very simple one. In two of the -horizontal railings A, A, Fig. 38, opposite the trumpet mouths T, -there was an aperture communicating with a pipe or tube which went -to the vertical post B, and descending it, as shown at TAA, Fig. 39, -went beneath the floor _f f_, in the direction _p p_, and entered the -apartment N, where the invisible lady sat. On the side of the partition -about _h_, there was a small hole through which the lady saw what was -going on in the exhibition-room, and communications were no doubt made -to her by signals from the person who attended the machine. When one of -the spectators asked a question by speaking into one of the trumpets -T, the sound was reflected from the mouth of the trumpet back to the -aperture at A, in the horizontal rail, Fig. 38, and was distinctly -conveyed along the closed tube into the apartment N. In like manner the -answer issued from the aperture A, and being reflected back to the ear -of the spectator by the trumpet, he heard the sounds with that change -of character which they receive when transmitted through a tube and -then reflected to the ear. - -[Illustration: _Fig. 39._] - -The surprise of the auditors was greatly increased by the circumstance, -that an answer was returned to questions put in a whisper, and also -by the conviction that nobody but a person in the middle of the -audience could observe the circumstances to which the invisible figure -frequently adverted. - -Although the performances of speaking heads were generally effected -by the methods now described, yet there is reason to think that the -ventriloquist sometimes presided at the exhibition, and deceived the -audience by his extraordinary powers of illusion. There is no species -of deception more irresistible in its effects than that which arises -from the uncertainty with which we judge of the direction and distance -of sounds. Every person must have noticed how a sound in their own ears -is often mistaken for some loud noise moderated by the distance from -which it is supposed to come; and the sportsman must have frequently -been surprised at the existence of musical sounds humming remotely in -the extended heath, when it was only the wind sounding in the barrel -of his gun. The great proportion of apparitions that haunt old castles -and apartments associated with death, exist only in the sounds which -accompany them. The imagination even of the boldest inmate of a place -hallowed by superstition, will transfer some trifling sound near his -own person to a direction and to a distance very different from the -truth, and the sound which otherwise might have no peculiar complexion -will derive another character from its new locality. Spurning the idea -of a supernatural origin, he determines to unmask the spectre, and -grapple with it in its den. All the inmates of the house are found -to be asleep--even the quadrupeds are in their lair--there is not a -breath of wind to ruffle the lake that reflects through the casement -the reclining crescent of the night; and the massive walls in which he -is enclosed forbid the idea that he has been disturbed by the warping -of panelling or the bending of partitions. His search is vain; and -he remains master of his own secret, till he has another opportunity -of investigation. The same sound again disturbs him, and, modified -probably by his own position at the time, it may perhaps appear to -come in a direction slightly different from the last. His searches are -resumed, and he is again disappointed. If this incident should recur -night after night with the same result--if the sound should appear to -depend upon his own motions, or be any how associated with himself, -with his present feelings, or with his past history, his personal -courage will give way; a superstitious dread, at which he himself -perhaps laughs, will seize his mind; and he will rather believe that -the sounds have a supernatural origin, than that they could continue to -issue from a spot where he knows there is no natural cause for their -production. - -I have had occasion to have personal knowledge of a case much -stronger than that which has now been put. A gentleman, devoid of all -superstitious feelings, and living in a house free from any gloomy -associations, heard night after night in his bed-room a singular noise, -unlike any ordinary sound to which he was accustomed. He had slept in -the same room for years without hearing it, and he attributed it at -first to some change of circumstances in the roof or in the walls of -the room, but after the strictest examination no cause could be found -for it. It occurred only once in the night; it was heard almost every -night, with few interruptions. It was over in an instant, and it never -took place till after the gentleman had gone to bed. It was always -distinctly heard by his companion, to whose time of going to bed it had -no relation. It depended on the gentleman alone, and it followed him -into another apartment with another bed, on the opposite side of the -house. Accustomed to such investigations, he made the most diligent -but fruitless search into its cause. The consideration that the sound -had a special reference to him alone, operated upon his imagination, -and he did not scruple to acknowledge that the recurrence of the -mysterious sound produced a superstitious feeling at the moment. Many -months afterwards it was found that the sound arose from the partial -opening of the door of a wardrobe which was within a few feet of the -gentleman’s head, and which had been taken into the other apartment. -This wardrobe was almost always opened before he retired to bed, and -the door being a little too tight, it gradually forced itself open -with a sort of dull sound, resembling the note of a drum. As the door -had only started half an inch out of its place, its change of position -never attracted attention. The sound, indeed, seemed to come in a -different direction, and from a greater distance. - -When sounds so mysterious in their origin are heard by persons -predisposed to a belief in the marvellous, their influence over the -mind must be very powerful. An inquiry into their origin, if it is made -at all, will be made more in the hope of confirming than of removing -the original impression, and the unfortunate victim of his own fears -will also be the willing dupe of his own judgment. - -This uncertainty with respect to the direction of sound is the -foundation of the art of ventriloquism. If we place ten men in a row -at such a distance from us that they are included in the angle within -which we cannot judge of the direction of sound, and if in a calm day -each of them speaks in succession, we shall not be able with closed -eyes to determine from which of the ten men any of the sounds proceed, -and we shall be incapable of perceiving that there is any difference -in the direction of the sounds emitted by the two outermost. If a man -and a child are placed within the same angle, and if the man speaks -with the accent of a child without any corresponding motion in his -mouth or face, we shall necessarily believe that the voice comes from -the child; nay, if the child is so distant from the man that the voice -actually appears to us to come from the man, we shall still continue -in the belief that the child is the speaker; and this conviction would -acquire additional strength if the child favoured the deception, by -accommodating its features and gestures to the words spoken by the -man. So powerful, indeed, is the influence of this deception, that if -a jack-ass, placed near the man, were to open its mouth, and shake -its head responsive to the words uttered by his neighbour, we should -rather believe that the ass spoke than that the sounds proceeded from -a person whose mouth was shut, and the muscles of whose face were in -perfect repose. If our imagination were even directed to a marble -statue or a lump of inanimate matter, as the source from which we were -to expect the sounds to issue, we would still be deceived, and would -refer the sounds even to these lifeless objects. The illusion would be -greatly promoted, if the voice were totally different in its tone and -character from that of the man from whom it really comes; and if he -occasionally speaks in his own full and measured voice, the belief will -be irresistible that the assumed voice proceeds from the quadruped or -from the inanimate object. - -When the sounds which are required to proceed from any given object -are such as they are actually calculated to yield, the process of -deception is extremely easy; and it may be successfully executed, even -if the angle between the real and the supposed direction of the sound -is much greater than the angle of uncertainty. Mr. Dugald Stewart -has stated some cases in which deceptions of this kind were very -perfect. He mentions his having seen a person who, by counterfeiting -the gesticulations of a performer on the violin, while he imitated the -music by his voice, riveted the eyes of his audience on the instrument, -though every sound they heard proceeded from his own mouth. The late -Savile Carey, who imitated the whistling of the wind through a narrow -chink, told Mr. Stewart that he had frequently practised this deception -in the corner of a coffee-house, and that he seldom failed to see some -of the company rise to examine the tightness of the windows, while -others, more intent on their newspapers, contented themselves with -putting on their hats and buttoning their coats. Mr. Stewart likewise -mentions an exhibition formerly common in some of the continental -theatres, where a performer on the stage displayed the dumb-show of -singing with his lips and eyes and gestures, while another person -unseen supplied the music with his voice. The deception in this case -he found to be at first so complete as to impose upon the nicest ear -and the quickest eye; but in the progress of the entertainment, he -became distinctly sensible of the imposition, and sometimes wondered -that it should have misled him for a moment. In this case there -can be no doubt that the deception was at first the work of the -imagination, and was not sustained by the acoustic principle. The real -and the mock singer were too distant, and when the influence of the -imagination subsided, the true direction of the sound was discovered. -This detection of the imposture, however, may have arisen from another -cause. If the mock singer happened to change the position of his head, -while the real singer made no corresponding change in his voice, the -attentive spectator would at once notice this incongruity, and discover -the imposition. - -In many of the feats of ventriloquism the performer contrives, under -some pretence or other, to conceal his face, but ventriloquists of -great distinction, such as M. Alexandre, practise their art without any -such concealment. - -Ventriloquism loses its distinctive character if its imitations are -not performed by a voice from the belly. The voice, indeed, does not -actually come from that region; but when the ventriloquist utters -sounds from the larynx without moving the muscles of his face, he -gives them strength by a powerful action of the abdominal muscles. -Hence he speaks by means of his belly, although the throat is the real -source from whence the sounds proceed. Mr. Dugald Stewart has doubted -the fact, that ventriloquists possess the power of fetching a voice -from within: he cannot conceive what aid could be derived from such -an extraordinary power; and he considers that the imagination, when -seconded by such powers of imitation as some mimics possess, is quite -sufficient to account for all the phenomena of ventriloquism which he -has heard. This opinion, however, is strongly opposed by the remark -made to Mr. Stewart himself by a ventriloquist, “that his art would -be perfect, if it were possible only to speak distinctly without any -movement of the lips at all.” But, independent of this admission, it is -a matter of absolute certainty, that this internal power is exercised -by the true ventriloquist. In the account which the Abbé Chapelle -has given of the performances of M. St. Gille and Louis Brabant, he -distinctly states that M. St. Gille appeared to be absolutely mute -while he was exercising his art, and that no change in his countenance -could be discovered.[16] He affirms, also, that the countenance of -Louis Brabant exhibited no change, and that his lips were close and -inactive. M. Richerand, who attentively watched the performances -of M. Fitz-James, assures us that during his exhibition there was -a distention in the epigastric region, and that he could not long -continue the exertion without fatigue. - - [16] Edinburgh Journal of Science, No. xviii., p. 254. - -The influence over the human mind which the ventriloquist derives from -the skilful practice of his art is greater than that which is exercised -by any other species of conjuror. The ordinary magician requires his -theatre, his accomplices, and the instruments of his art, and he enjoys -but a local sovereignty within the precincts of his own magic circle. -The ventriloquist, on the contrary, has the supernatural always at -his command. In the open fields as well as in the crowded city, in -the private apartment as well as in the public hall, he can summon up -innumerable spirits; and though the persons of his fictitious dialogue -are not visible to the eye, yet they are unequivocally present to the -imagination of his auditors, as if they had been shadowed forth in -the silence of a spectral form. In order to convey some idea of the -influence of this illusion, I shall mention a few well-authenticated -cases of successful ventriloquism. - -M. St. Gille, a grocer of St. Germain-en-Laye, whose performances have -been recorded by the Abbé de la Chapelle, had occasion to shelter -himself from a storm in a neighbouring convent, where the monks were -in deep mourning for a much-esteemed member of their community who had -been recently buried. While lamenting over the tomb of their deceased -brother the slight honours which had been paid to his memory, a voice -was suddenly heard to issue from the roof of the choir bewailing the -condition of the deceased in purgatory, and reproving the brotherhood -for their want of zeal. The tidings of this supernatural event brought -the whole brotherhood to the church. The voice from above repeated its -lamentations and reproaches, and the whole convent fell upon their -faces, and vowed to make a reparation of their error. They accordingly -chanted in full choir a _De Profundis_, during the intervals of -which the spirit of the departed monk expressed his satisfaction at -their pious exercises. The prior afterwards inveighed against modern -scepticism on the subject of apparitions, and M. St. Gille had great -difficulty in convincing the fraternity that the whole was a deception. - -On another occasion, a commission of the Royal Academy of Sciences -at Paris, attended by several persons of the highest rank, met at St. -Germain-en-Laye to witness the performances of M. St. Gille. The real -object of their meeting was purposely withheld from a lady of the -party, who was informed that an aërial spirit had lately established -itself in the neighbourhood, and that the object of the assembly was -to investigate the matter. When the party had sat down to dinner in -the open air, the spirit addressed the lady in a voice which seemed to -come from above their heads, from the surface of the ground at a great -distance, or from a considerable depth under her feet. Having been thus -addressed at intervals during two hours, the lady was firmly convinced -of the existence of the spirit, and could with difficulty be undeceived. - -Another ventriloquist, Louis Brabant, who had been valet-de-chambre -to Francis I., turned his powers to a more profitable account. Having -fallen in love with a rich and beautiful heiress, he was rejected by -her parents as an unsuitable match for their daughter. On the death -of her father, Louis paid a visit to the widow, and he had no sooner -entered the house than she heard the voice of her deceased husband -addressing her from above, “Give my daughter in marriage to Louis -Brabant, who is a man of large fortune and excellent character. I -endure the inexpressible torments of purgatory for having refused her -to him. Obey this admonition, and give everlasting repose to the soul -of your poor husband.” This awful command could not be resisted, and -the widow announced her compliance with it. - -As our conjuror, however, required money for the completion of his -marriage, he resolved to work upon the fears of one Cornu, an old -banker at Lyons, who had amassed immense wealth by usury and extortion. -Having obtained an interview with the miser, he introduced the subjects -of demons and spectres, and the torments of purgatory; and, during an -interval of silence, the voice of the miser’s deceased father was heard -complaining of his dreadful situation in purgatory, and calling upon -his son to rescue him from his sufferings by enabling Louis Brabant to -redeem the Christians that were enslaved by the Turks. The awe-struck -miser was also threatened with eternal damnation if he did not thus -expiate his own sins; but such was the grasp that the banker took of -his gold, that the ventriloquist was obliged to pay him another visit. -On this occasion, not only his father but all his deceased relatives -appealed to him in behalf of his own soul and theirs; and such was -the loudness of their complaints, that the spirit of the banker was -subdued, and he gave the ventriloquist ten thousand crowns to liberate -the Christian captives. When the miser was afterwards undeceived, he is -said to have been so mortified that he died of vexation. - -The ventriloquists of the nineteenth century made great additions to -their art, and the performances of M. Fitz-James and M. Alexandre, -which must have been seen by many of our countrymen, were far superior -to those of their predecessors. Besides the art of speaking by the -muscles of the throat and the abdomen, without moving those of the -face, these artists had not only studied with great diligence and -success the modifications which sounds of all kinds undergo from -distance, obstructions, and other causes, but had acquired the art -of imitating them in the highest perfection. The ventriloquist was -therefore able to carry on a dialogue in which the _dramatis voces_, -as they may be called, were numerous; and when on the outside of an -apartment, he could personate a mob with its infinite variety of -noise and vociferation. Their influence over an audience was still -further extended by a singular power over the muscles of the body. M. -Fitz-James actually succeeded in making the opposite or corresponding -muscles act differently from each other; and while one side of his face -was merry and laughing, the other was full of sorrow and in tears. -At one moment he was tall, thin, and melancholic, and after pausing -behind a screen, he came out “bloated with obesity and staggering with -fulness.” M. Alexandre possessed the same power over his face and -figure; and so striking was the contrast of two of these forms, that an -excellent sculptor, Mr. Joseph, has perpetuated them in marble. - -This new acquirement of the ventriloquist enabled him, in his own -single person and with his own single voice, to represent upon the -stage a dramatic composition which would have required the assistance -of several actors. Although only one character in the piece could be -seen at the same time, yet they all appeared during its performance, -and the change of face and figure on the part of the ventriloquist was -so perfect, that his personal identity could not be recognized in the -_dramatis personæ_. This deception was rendered still more complete by -a particular construction of the dresses, which enabled the performer -to reappear in a new character after an interval so short that the -audience necessarily believed that it was another person. - -It is a curious circumstance that Captain Lyon found among the -Esquimaux of Igloolik ventriloquists of no mean skill. There is much -rivalry among the professors of the art, who do not expose each -other’s secrets, and their exhibitions derive great importance from -the rarity of their occurrence. The following account of one of them -is so interesting that we shall give the whole of it in Captain Lyon’s -words:-- - -“Amongst our Igloolik acquaintances were two females and a few male -wizards, of whom the principal was Toolemak. This personage was cunning -and intelligent; and, whether professionally, or from his skill in -the chase, but perhaps from both reasons, was considered by all the -tribe as a man of importance. As I invariably paid great deference -to his opinion on all subjects connected with his calling, he freely -communicated to me his superior knowledge, and did not scruple to -allow of my being present at his interviews with Tornga, or his -patron spirit. In consequence of this, I took an early opportunity -of requesting my friend to exhibit his skill in my cabin. His old -wife was with him, and by much flattery and an accidental display -of a glittering knife and some beads, she assisted me in obtaining -my request. All light excluded, our sorcerer began chanting to his -wife with great vehemence, and she in return answered by singing -the Amna-aya, which was not discontinued during the whole ceremony. -As far as I could hear, he afterwards began turning himself rapidly -round, and in a loud, powerful voice vociferated for Tornga with great -impatience, at the same time blowing and snorting like a walrus. His -noise, impatience, and agitation increased every moment, and he at -length seated himself on the deck, varying his tones, and making a -rustling with his clothes. Suddenly the voice seemed smothered, and was -so managed as to sound as if retreating beneath the deck, each moment -becoming more distant, and ultimately giving the idea of being many -feet below the cabin, when it ceased entirely. His wife now, in answer -to my queries, informed me very seriously, that he had dived, and that -he would send up Tornga. Accordingly, in about half a minute, a distant -blowing was heard very slowly approaching, and a voice, which differed -from that at first heard, was at times mingled with the blowing, until -at length both sounds became distinct, and the old woman informed -me that Tornga was come to answer my questions. I accordingly asked -several questions of the sagacious spirit, to each of which inquiries I -received an answer by two loud claps on the deck, which I was given to -understand were favourable. - -“A very hollow, yet powerful voice, certainly much different from the -tones of Toolemak, now chanted for some time, and a strange jumble of -hisses, groans, shouts, and gabblings like a turkey, succeeded in rapid -order. The old woman sang with increased energy; and as I took it for -granted that this was all intended to astonish the Kabloona, I cried -repeatedly that I was very much afraid. This, as I expected, added fuel -to the fire, until the poor immortal, exhausted by its own might, asked -leave to retire. - -“The voice gradually sank from our hearing as at first, and a very -indistinct hissing succeeded; in its advance it sounded like the tone -produced by the wind on the brass chord of an Æolian harp. This was -soon changed to a rapid hiss like that of a rocket, and Toolemak with -a yell announced his return. I had held my breath at the first distant -hissing, and twice exhausted myself, yet our conjuror did not once -respire, and even his returning and powerful yell was uttered without a -previous stop or inspiration of air. - -“Light being admitted, our wizard, as might be expected, was in a -profuse perspiration, and certainly much exhausted by his exertions, -which had continued for at least half an hour. We now observed a couple -of bunches, each consisting of two stripes of white deer-skin, and a -long piece of sinew, attached to the back of his coat. These we had not -seen before, and were informed that they had been sewn on by Tornga -while he was below.”[17] - - [17] _Private Journal of_ Captain G. F. Lyon. London, 1824, pp. 358, - 361. - -Captain Lyon had the good fortune to witness another of Toolemak’s -exhibitions, and he was much struck with the wonderful steadiness of -the wizard throughout the whole performance, which lasted an hour and -a half. He did not once appear to move, for he was so close to the -skin behind which Captain Lyon sat, that if he had done so he must -have perceived it. Captain Lyon did not hear the least rustling of his -clothes, or even distinguish his breathing, although his outcries were -made with great exertion.[18] - - [18] Id. p. 366. - - - - -LETTER VIII. - - Musical and harmonic sounds explained--Power of breaking glasses - with the voice--Musical sounds from the vibration of a column - of air--and of solid bodies--Kaleidophone--Singular acoustic - figures produced on sand laid on vibrating plates of glass--and - on stretched membranes--Vibration of flat rulers and cylinders - of glass--Production of silence from two sounds--Production - of darkness from two lights--Explanation of these singular - effects--Acoustic automaton--Droz’s bleating sheep--Maillardet’s - singing-bird--Vaucanson’s flute-player--His pipe and - tabor-player--Baron Kempelen’s talking-engine--Kratzenstein’s - speaking-machine--Mr. Willis’s researches. - - -Among the discoveries of modern science, there are few more remarkable -than those which relate to the production of harmonic sounds. We -are all familiar with the effects of musical instruments, from the -deep-toned voice of the organ to the wiry shrill of the Jew’s harp. -We sit entranced under their magical influence, whether the ear is -charmed with the melody of their sounds, or the heart agitated by the -sympathies which they rouse. But though we may admire their external -form, and the skill of the artist who constructed them, we never think -of inquiring into the cause of such extraordinary combinations. - -Sounds of all kinds are conveyed to the organ of hearing through the -air; and if this element were to be destroyed, all nature would be -buried in the deepest silence. Noises of every variety, whether they -are musical or discordant, high or low, move through the air of our -atmosphere at the surface of the earth with a velocity of 1090 feet -in a second, or 765 miles per hour; but in sulphurous acid gas sound -moves only through 751 feet in a second, while in hydrogen gas it moves -with the great velocity of 3000 feet. Along fluid and solid bodies, -its progress is still more rapid. Through water it moves at the rate -of 4708 feet in a second, through tin at the rate of 8175 feet, and -through iron, glass, and some kinds of wood, at the rate of 18,530 feet. - -When a number of single and separate sounds follow each other in rapid -succession, they produce a continued sound, in the same manner as a -continuous circle of light is produced by whirling round a burning -stick before the eye. In order that the sound may appear a single one -to the ear, nearly sixteen separate sounds must follow one another -every second. When these sounds are exactly similar, and recur at equal -intervals, they form a musical sound. In order to produce such sounds -from the air, it must receive at least sixteen equally distant impulses -or strokes in a second. The most common way of producing this effect is -by a string or wire A B, Fig. 40, stretched between the fixed points A, -B. If this string is taken by the middle and pulled aside, or if it is -suddenly struck, it will vibrate between its two fixed points, as shown -in the figure, passing alternately on each side of its axis A B, the -vibrations gradually diminishing by the resistance of the air till the -string is brought to rest. Its vibrations, however, may be kept up, by -drawing a rosined fiddle-bow across it, and while it is vibrating it -will give out a sound corresponding to the rapidity of its vibrations, -and arising from the successive blows or impulses given to the air by -the string. This sound is called the fundamental sound of the string, -and its acuteness or sharpness increases with the number of vibrations -which the string performs in a second. - -[Illustration: _Fig. 40._] - -If we now touch the vibrating string A´ B lightly with the finger, -or with a feather at the middle point C, Fig. 40, it will give out a -more acute but fainter sound than before, and while the extent of its -vibrations is diminished, their frequency is doubled. In like manner, -if we touch the string A´´ B´´, Fig. 40, at a point C, so that A´´ C is -one-third of A´´ B´´, the note will be still more acute, and correspond -to thrice the number of vibrations. All this might have been expected; -but the wonderful part of the experiment is, that the vibrating string -A´ B´ divides itself at C into two parts A´ C, C B´, the part A´ C -vibrating round A and C as fixed points, and the part C B´ round C and -B´, but always so that the part A´ C is at the same distance on the -one side of the axis A´ B´ as at A _m_ C, while the part C B is on -the other side, as at C _n_ B. Hence the point C, being always pulled -by equal and opposite forces, remains at rest as if it were absolutely -fixed. This stationary point is called a _node_, and the vibrating -portions A´_m_ C, C _n_ B´ loops. The very same is true of the string -A´´ B´´, the points C and D being stationary points; and upon the -same principle a string may be divided into any number of vibrating -portions. In order to prove that the string is actually vibrating in -these equal subdivisions, we have only to place a piece of light paper -with a notch in it on different parts of the string. At the nodes C and -D it will remain perfectly at rest, while at _m_ or _n_ in the middle -of the loops it will be thrown off or violently agitated. - -The acute sounds given out by each of the vibrating portions are called -_harmonic sounds_, and they accompany the fundamental sound of the -string in the very same manner as we have already seen that the eye -sees the accidental or harmonic colours while it is affected with the -fundamental colour. - -The subdivision of the string, and consequently the production of -harmonic sounds, may be effected without touching the string at all, -and by means of a sympathetic action conveyed by the air. If a string -A B, for example, Fig. 40, is at rest, and if a shorter string A´´ C, -one third of its length, fixed at the two points A´´ and C, is set -vibrating in the same room, the string A B will be set vibrating in -three loops like A´´ B´´, giving out the same harmonic sounds as the -small string A´´ C. - -It is owing to this property of sounding bodies that singers with great -power of voice are able to break into pieces a large tumbler glass, by -singing close to it its proper fundamental note; and it is from the -same sympathetic communication of vibrations that two pendulum clocks -fixed to the same wall, or two watches lying upon the same table, will -take the same rate of going, though they would not agree with one -another if placed in separate apartments. Mr. Ellicott even observed -that the pendulum of the one clock will stop that of the other, and -that the stopped pendulum will, after a certain time, resume its -vibrations, and in its turn stop the vibrations of the other pendulum. - -The production of musical sounds by the vibrations of a column of air -in a pipe is familiar to every person, but the extraordinary mechanism -by which it is effected is known principally to philosophers. A column -of air in a pipe may be set vibrating by blowing over the open end of -it, as is done in Pan’s pipes; or by blowing over a hole in its side, -as in the flute; or by blowing through an aperture called a reed, -with a flexible tongue, as in the clarionet. In order to understand -the nature of this vibration, let AB, Fig. 41, be a pipe or tube, and -let us place in it a spiral spring AB, in which the coil or spire are -at equal distances, each end of the spiral being fixed to the end of -the tube. This elastic spring may be supposed to represent the air in -the pipe, which is of equal density throughout. If we take hold of -the spring at _m_, and push the point _m_ towards A and towards B in -succession, it will give us a good idea of the vibration of an elastic -column of air. When _m_ is pushed towards A, the spiral spring will -be compressed or condensed, as shown at _m_ A, No. 2, while at the -other end it will be dilated or rarefied, as shown at _m_ B, and in -the middle of the tube it will have the same degree of compression as -in No. 1. When the string is drawn to the other end of the tube B, the -spring will be, as in No. 3, condensed at the end B, and dilated at -the end A. Now when a column of air vibrates in a pipe AB, the whole -of it rushes alternately from B to A, as in No. 2, and from A to B as -in No. 3, being condensed at the end A, No. 2, and dilated or rarefied -at the end B, while in No. 3 it is rarefied at A and condensed at B, -preserving its natural density at the middle point between A and B. In -the case of the spring the ends AB are alternately pushed outwards and -pulled inwards by the spring, the end A being pushed outwards in No. 2, -and B pulled inwards, while in No. 3 A is pulled inwards and B pushed -outwards. - -[Illustration: _Fig. 41._] - -That the air vibrating in a pipe is actually in the state now -described, may be shown by boring small holes in the pipe, and putting -over them pieces of a fine membrane. The membrane opposite to the -middle part between A and B where the particles of the air have the -greatest motion, will be violently agitated, while at points nearer the -ends A and B it will be less and less affected. - -[Illustration: _Fig. 42._] - -Let us now suppose two pipes, AB, BC, to be joined together as in Fig. -42, and to be separated by a fixed partition at B; and let a spiral -spring be fixed in each. Let the spring AB be now pushed to the end -A, while the spring BC is pushed to C, as in No. 1, and back again, -as in No. 2, but always in opposite directions; then it is obvious -that the partition B is in No. 1 drawn in opposite directions towards -A and towards C, and always with forces equal to each other: that is, -when B is drawn slightly towards A, which it is at the beginning of -the motion, it is also drawn slightly towards C; and when it is drawn -forcibly towards A, as it is at the end of the motion of the spring, -it is also drawn forcibly towards C. If the partition B, therefore, is -moveable, it will still remain fixed during the opposite excursions -of the spiral springs; nay, if we remove the partition, and hook the -end of one spiral spring to the end of the other, the node or point of -junction will remain stationary during the movements of the springs, -because at every instant that point is drawn by equal and opposite -forces. If _three_, _four_, or _five_ spiral springs are joined in a -similar manner, we may conceive them all vibrating between their nodes -in the same manner. - -Upon the very same principles we may conceive a long column of air -without partitions dividing itself into two, three, or four smaller -columns, each of which will vibrate between its nodes in the same -manner as the spiral spring. At the middle point of each small -vibrating column, the air will be of its natural density, like that -of the atmosphere; while at the nodes B, &c. it will be in a state of -condensation and rarefaction alternately. - -If, when the air is vibrating in one column in the pipe AB, as in Fig. -41, No. 2, 3, we conceive a hole made in the middle, the atmospheric -air will not rush in to disturb the vibration, because the air within -the pipe and without it has exactly the same density. Nay, if, instead -of a single hole, we were to cut a ring out of the pipe at the middle -point, the column would vibrate as before. But if we bore a hole -between the middle and one of the ends, where the vibrating column -must be either in a state of condensation or rarefaction, the air must -either rush out or rush in, in order to establish the equilibrium. -The air opposite the hole will then be brought to the state of the -external air, like that in the middle of the pipe; it will become the -middle of a vibrating column: and the whole column of air, instead of -vibrating as one, will vibrate as two columns, each column vibrating -with twice the velocity, and yielding harmonic sounds along with the -fundamental sound of the whole columns, in the same manner as we have -already explained with regard to vibrating strings. By opening other -holes we may subdivide a vibrating column into any number of smaller -vibrating columns. The holes in flutes, clarionets, &c. are made for -this purpose. When they are all closed up, the air vibrates in one -column; and by opening and shutting the different holes in succession, -the number of vibrating columns is increased or diminished at pleasure, -and consequently the harmonic sounds will vary in a similar manner. - -Curious as these phenomena are, they are still surpassed by those -which are exhibited during the vibration of solid bodies. A rod or -bar of metal or glass may be made to vibrate either longitudinally or -laterally. - -An iron rod will vibrate longitudinally, like a column of air, if we -strike it at one end in the direction of its length; or rub it in -the same direction with a wetted finger, and it will admit the same -fundamental note as a column of air _ten_ or _eleven_ times as long, -because sound moves so much faster in iron than in air. When the -iron rod is thus vibrating along its length, the very same changes -which we have shown in Fig. 41, as produced in a spiral spring, or -in a column of air, take place in the solid metal. All its particles -move alternately towards A and towards B, the metal being in the one -case condensed at the end to which the particles move, and expanded -at the end from which they move, and retaining its natural density -in the middle of the rod. If we now hold this rod in the middle, by -the finger and thumb lightly applied, and rub it in the middle either -of AB or BC with a piece of cloth sprinkled with powdered rosin, -or with a well-rosined fiddle-bow drawn across the rod, it will -divide itself into two vibrating portions AB, BC, each of which will -vibrate, as shown in Fig. 42, like the two adjacent columns of air, -the section of the rod, or the particles which compose that section -at B, being at perfect rest. By holding the rod at any intermediate -point between A and B, so that the distance from A to the finger and -thumb is one-third, one-fourth, one-fifth, &c. of the whole length AC, -and rubbing one of the divisions in the middle, the rod will divide -itself into 3, 4, 5, &c. vibrating portions, and give out corresponding -harmonic sounds. - -[Illustration: _Fig. 43._] - -A rod of iron may be made to vibrate laterally or transversely, by -fixing one end of it firmly, as in a vice, and leaving the other free, -or by having both ends free or both fixed. When a rod, fixed at one -end and free at the other, is made to vibrate, its mode of vibrating -may be rendered evident to the eye; and for the purpose of doing -this, Mr. Wheatstone has contrived a curious instrument, called the -_Kaleidophone_, which is shown in Fig. 43. It consists of a circular -base of wood AB, about _nine_ inches in diameter and one inch thick, -and having four brass sockets firmly fixed into it at C, D, E, and F. -Into these sockets are screwed four vertical steel rods C, D, E, and -F, about thirteen or fourteen inches long; one being a square rod, -another a bent cylindrical one, and the other two cylindrical ones of -different diameters. On the extremities of these rods are fixed small -quicksilvered glass beads, either singly or in groups, so that when -the instrument is placed in the light of the sun or in that of a lamp, -bright images of the sun or flame are seen reflected on each bead. If -any of these rods is set vibrating, these luminous images will form -continuous and returning curve lines in a state of constant variation, -each different rod giving curves of different characters, as shown in -Fig. 44. - -[Illustration: _Fig. 44._] - -The Melodion, an instrument of great power, embracing five octaves, -operates by means of the vibrations of metallic rods of unequal -lengths, fixed at one end and free at the other.[19] A narrow and thin -plate of copper is screwed to the free extremity of each rod, and at -right angles to its length; and its surface is covered with a small -piece of felt, impregnated with rosin. This narrow band is placed near -the circumference of a revolving cylinder, and, by touching the key, -it is made to descend till it touches the revolving cylinder, and -gives out its sound. The sweetness and power of this instrument are -unrivalled; and such is the character of its tones, that persons of a -nervous temperament are often entirely overpowered by its effects. - - [19] See _Edinburgh Encyclopædia_, Art. SCIENCE, Curiosities in, Vol. - xvii., p. 563. - -The vibrations of plates of metal or glass of various forms exhibit -a series of the most extraordinary phenomena, which are capable of -being shown by very simple means. These phenomena are displayed in an -infinite variety of regular figures assumed by sand or fine lycopodium -powder, strewed over the surface of the glass plate. In order to -produce these figures, we must pinch or damp the plate at one or more -places, and when the sand is strewed upon its surface, it is thrown -into vibrations by drawing a fiddle-bow over different parts of its -circumference. The method of damping or pinching plates is shown in -Fig. 45. In No. 1, a square plate of glass AB, ground smooth at its -edges, is pinched by the finger and thumb. In No. 2, a circular plate -is held by the thumb against the top _c_ of a perpendicular rod, and -damped by the fingers at two different points of its circumference. -In No. 3 it is damped at three points of its circumference; _c_ and -_d_ by the thumb and finger, and at _e_ by pressing it against a fixed -obstacle _a b_. By means of a clamp like that at No. 4, it may be -damped at a greater number of points. - -[Illustration: _Fig. 45._ - N^o 1 N^o 2 - N^o 3 N^o 4 -] - -[Illustration: _Fig. 46._ - N^o 1 N^o 2 - N^o 3 N^o 4 -] - -If we take a _square_ plate of glass, such as that shown in Fig. 46, -No. 1, and, pinching it at its centre, draw the fiddle-bow near one of -its angles, the sand will accumulate in the form of a cross, as shown -in the figure, being thrown off the parts of the plate that are in a -state of vibration, and settling in the nodes or parts which are at -rest. If the bow is drawn across the middle of one of the edges, the -sand will accumulate as in No. 2. If the plate is pinched at N, No. 3, -and the bow applied at F and perpendicular to AB, the sand will arrange -itself in three parallel lines, perpendicular to a fourth passing -through F and N. But if the point N, where it is pinched, is a little -farther from the edge than in No. 3, the parallel lines will change -into curves as in No. 4. - -If the plate of glass is circular, and pinched at its centre, and also -at a point of its circumference, and if the bow is applied at a point -45° from the last point, the figure of the sand will be as in Fig. 47, -No. 1. If with the same plate, similarly pinched, the bow is drawn over -a part 30° from the pinched point of the circumference, the sand will -form six radii as in No. 2. When the centre of the plate is left free, -a different set of figures is produced, as shown in No. 3 and No. 4. -When the plate is pinched near its edge, and the bow applied 45° from -the point pinched, a circle of sand will pass through that point, and -two diameters of sand, at right angles to each other, will be formed as -in No. 3. When a point of the circumference is pressed against a fixed -obstacle, and the bow applied 30° from that point, the figure in No. 4 -is produced. - -[Illustration: _Fig. 47._ - - No. 1. No. 2. - No. 3. No. 4.] - -If, in place of a solid plate, we strew the sand over a stretched -membrane, the sand will form itself into figures, even when the -vibrations are communicated to the membrane through the air. In order -to make these experiments, we must stretch a thin sheet of wet paper, -such as vegetable paper, over the mouth of a tumbler-glass with a -footstalk, and fix it to the edges with glue. When the paper is dry, a -thin layer of dry sand is strewed upon its surface. If we place this -membrane upon a table, and hold immediately above it, and parallel -to the membrane, a plate of glass vibrating so as to give any of the -figures shown in Fig. 47, the sand upon the membrane will imitate -exactly the figure upon the glass. If the glass plate, in place of -vibrating horizontally, is made to vibrate in an inclined position, the -figures on the membrane will change with the inclination, and the sand -will assume the most curious arrangements. The figures thus produced -vary with the size of the membrane, with its material, its tension, and -its shape. When the same figure occurs several times in succession, a -breath upon the paper will change its degree of tension, and produce -an entirely new figure, which, as the temporary moisture evaporates, -will return to the original figure, through a number of intermediate -ones. The pipe of an organ at the distance of a few feet, or the notes -of a flute at the distance of half a foot, will arrange the sand on the -membrane into figures which perpetually change with the sound that is -produced. - -The manner in which flat rulers and cylinders of glass perform their -vibrations is very remarkable. If a glass plate about twenty-seven -inches long, six-tenths of an inch broad, and six hundredths of an -inch thick, is held by the edges between the finger and thumb, and has -its lower surface, near either end, rubbed with a piece of wet cloth, -sand laid upon its upper surface will arrange itself in parallel lines -at right angles to the length of the plate. If the place of these lines -is marked with a dot of ink, and the other side of the glass ruler is -turned upwards, and the ruler made to vibrate as before, the sand will -now accumulate in lines intermediate between the former lines, so that -the motions of one-half the thickness of the glass ruler are precisely -the reverse of those of the corresponding parts of the other half. - -As these singular phenomena have not yet been made available by the -scientific conjuror, we must be satisfied with this brief notice of -them; but there is still one property of sound, which has its analogy -also in light, too remarkable to be passed without notice. This -property has more of the marvellous in it than any result within the -wide range of the sciences. _Two loud sounds may be made to produce -silence, and two strong lights may be made to produce darkness!_ - -If two equal and similar strings, or the columns of air in two equal -and similar pipes, perform exactly 100 vibrations in a second, -they will produce each equal waves of sound, and these waves will -conspire in generating an uninterrupted sound, double of either of -the sounds, heard separately. If the two strings or the two columns -of air are not in unison, but nearly so, as in the case where the -one vibrates 100 and the other 101 times in a second, then at the -first vibration the two sounds will form one of double the strength -of either; but the one will gradually gain upon the other, till at -the fiftieth vibration it has gained half a vibration on the other. -At this instant the two sounds will _destroy one another_, and an -interval of perfect silence will take place. The sound will instantly -commence, and gradually increase till it becomes loudest at the -hundredth vibration, where the two vibrations conspire in producing -a sound double of either. An interval of silence will again occur at -the 150th, 250th, 350th vibration, or every second, while a sound of -double the strength of either will be heard at the 200th, 300th, and -400th vibration. When the unison is very defective, or when there is -a great difference between the number of vibrations which the two -strings or columns of air perform in a second, the successive sounds -and intervals of silence resemble a rattle. With a powerful organ, the -effect of this experiment is very fine, the repetition of the sounds -_wow_--_wow_--_wow_--representing the double sound and the interval -of silence which arise from the total extinction of the two separate -sounds. - -The phenomenon corresponding to this in the case of light is perhaps -still more surprising. If a beam of _red_ light issues from a luminous -point, and falls upon the retina, we shall see distinctly the luminous -object from which it proceeds; but if another pencil of red light -issues from another luminous point, anyhow situated, provided the -difference between its distance and that of the other luminous point -from the point of the retina, on which the first beam fell, is the -258th thousandth part of an inch, or exactly _twice_, _thrice_, _four_ -times, &c., that distance; and if this second beam falls upon the -same point of the retina, the one light will increase the intensity -of the other, and the eye will see _twice_ as much light as when it -received only one of the beams separately. All this is nothing more -than what might be expected from our ordinary experience. But if -the difference in the distances of the two luminous points is only -_one-half_ of the 258th thousandth part of an inch, or 1½, 2½, 3½, -4½, times that distance, _the one light will extinguish the other and -produce absolute darkness_. If the two luminous points are so situated, -that the difference of their distances from the point of the retina is -intermediate between 1 and 1½, or 2 and 2½, above the 258th thousandth -part of an inch, the intensity of the effect which they produce will -vary from absolute darkness to double the intensity of either light. At -1¼, 2¼, 3¼ times, &c., the 258th thousandth of an inch, the intensity -of the two combined lights will be equal only to one of them acting -singly. If the lights, in place of falling upon the retina, fall upon -a sheet of white paper, the very same effect will be produced, a black -spot being produced in the one case, and a bright white one in the -other, and intermediate degrees of brightness in intermediate cases. If -the two lights are _violet_, the difference of distances at which the -preceding phenomena will be produced will be the 157th thousandth part -of an inch, and it will be intermediate between the 258th and the 157th -thousandth part of an inch for the intermediate colours. This curious -phenomenon may be easily shown to the eye, by admitting the sun’s light -into a dark room through a small hole about the 40th or 50th part of -an inch in diameter, and receiving the light on a sheet of paper. If -we hold a needle or piece of slender wire in this light, and examine -its shadow, we shall find that the shadow consists of bright and dark -stripes succeeding each other alternately, the stripe in the very -middle or axis of the shadow being a bright one. The rays of light -which are bent into the shadow, and which meet in the very middle of -the shadow, have exactly the same length of path, so that they form a -bright fringe of double the intensity of either; but the rays which -fall upon a point of the shadow at a certain distance from the middle, -have a difference in the length of their paths, corresponding to the -difference at which the lights destroy each other, so that a _black_ -stripe is produced on each side of the middle bright one. At a greater -distance from the middle, the difference becomes such as to produce a -bright stripe, and so on, a bright and a dark stripe succeeding each -other to the margin of the shadow. - -The explanation which philosophers have given of these strange -phenomena is very satisfactory, and may be easily understood. When a -wave is made on the surface of a still pool of water, by plunging a -stone into it, the wave advances along the surface, while the water -itself is never carried forward, but merely rises into a height and -falls into a hollow, each portion of the surface experiencing an -elevation and a depression in its turn. If we suppose two waves equal -and similar to be produced by two separate stones, and if they reach -the same spot at the same time, that is, if the two elevations should -exactly coincide, they would unite their effects, and produce a -wave twice the size of either; but if the one wave should be just so -far before the other, that the hollow of the one coincided with the -elevation of the other, and the elevation of the one with the hollow -of the other, the two waves would obliterate or destroy one another, -the elevation as it were of the one filling up half the hollow of the -other, and the hollow of the one taking away half the elevation of the -other, so as to reduce the surface to a level. These effects will be -actually exhibited by throwing two equal stones into a pool of water, -and it will be seen that there are certain lines of a hyperbolic form -where the water is quite smooth, in consequence of the equal waves -obliterating one another, while, in other adjacent parts, the water is -raised to a height corresponding to both the waves united. - -In the tides of the ocean we have a fine example of the same principle. -The two immense waves arising from the action of the sun and moon upon -the ocean produce our spring-tides by their combination, or when the -elevations of each coincide; and our neap-tides, when the elevation of -the one wave coincides with the depression of the other. If the sun and -moon had exerted exactly the same force upon the ocean, or produced -tide waves of the same size, then our neap-tides would have disappeared -altogether, and the spring-tide would have been a wave double of the -wave produced by the sun and moon separately. An example of the effect -of the equality of the two waves occurs in the port of Batsha, where -the two waves arrive by channels of different lengths, and actually -obliterate each other. - -Now, as sound is produced by undulations or waves in the air, and -as light is supposed to be produced by waves or undulations in an -ethereal medium, filling all nature, and occupying the pores of -transparent bodies, the successive production of sound and silence by -two loud sounds, or of light and darkness by two bright lights, may be -explained in the very same manner as we have explained the increase -and the obliteration of waves formed on the surface of water. If this -theory of light be correct, then the breadth of a wave of _red_ light -will be the 258th thousandth part of an inch, the breadth of a wave of -green light the 207th thousandth part of an inch, and the breadth of a -wave of violet light the 157th thousandth part of an inch. - -Among the wonders of modern skill, we must enumerate those beautiful -automata by which the motions and actions of man and other animals have -been successfully imitated. I shall therefore describe at present some -of the most remarkable acoustic automata, in which the production of -musical and vocal sounds has been the principal object of the artist. - -Many very ingenious pieces of acoustic mechanism have been from time to -time exhibited in Europe. The celebrated Swiss mechanist, M. le Droz, -constructed for the King of Spain the figure of a sheep, which imitated -in the most perfect manner the bleating of that animal; and likewise -the figure of a dog watching a basket of fruit, which, when any of the -fruit was taken away, never ceased barking till it was replaced. - -The singing-bird of M. Maillardet, which he exhibited in Edinburgh -many years ago, is still more wonderful.[20] An oval box, about three -inches long, was set upon the table, and in an instant the lid flew up, -and a bird of the size of the humming-bird, and of the most beautiful -plumage, started from its nest. After fluttering its wings, it opened -its bill and performed four different kinds of the most beautiful -warbling. It then darted down into its nest, and the lid closed upon -it. The moving power in this piece of mechanism is said to have been -springs which continued their action only four minutes. As there was -no room within so small a figure for accommodating pipes to produce -the great variety of notes which were warbled, the artist used only -one tube, and produced all the variety of sounds by shortening and -lengthening it with a moveable piston. - - [20] A similar piece of mechanism had been previously made by M. le - Droz. - -Ingenious as these pieces of mechanism are, they sink into -insignificance when compared with the machinery of M. Vaucanson, which -had previously astonished all Europe. His two principal automata were -the flute-player, and the pipe and tabor-player. The flute-player -was completed in 1736, and wherever it was exhibited it produced the -greatest sensation. When it came to Paris it was received with great -suspicion. The French savants recollected the story of M. Raisin, -the organist of Troyes, who exhibited an automaton player upon the -harpsichord, which astonished the French court by the variety of -its powers. The curiosity of the king could not be restrained, and -in consequence of his insisting upon examining the mechanism, there -was found in the figure a pretty little musician five years of age. -It was natural, therefore, that a similar piece of mechanism should -be received with some distrust; but this feeling was soon removed -by M. Vaucanson, who exhibited and explained to a committee of the -Academy of Sciences the whole of the mechanism. This learned body -was astonished at the ingenuity which it displayed; and they did not -hesitate to state, that the machinery employed for producing the sounds -of the flute performed in the most exact manner the very operations -of the most expert flute-player, and that the artist had imitated the -effects produced, and the means employed by nature, with an accuracy -which exceeded all expectation. In 1738, M. Vaucanson published a -memoir, approved of by the Academy, in which he gave a full description -of the machinery employed, and of the principles of its construction. -Following this memoir, I shall therefore attempt to give as popular a -description of the automaton as can be done without lengthened details -and numerous figures. - -The body of the flute-player was about 5½ feet high, and was placed -upon a piece of rock, surrounding a square pedestal 4½ feet high by 3½ -feet wide. When the panel which formed the front of the pedestal was -opened, there was seen on the right a clock movement, which, by the -aid of several wheels, gave a rotatory motion to a steel axis about -2½ feet long, having cranks at six equidistant points of its length, -but lying in different directions. To each crank was attached a cord, -which descended and was fixed by its other end to the upper board of a -pair of bellows, 2½ feet long and 6 inches wide. Six pair of bellows -arranged along the bottom of the pedestal were then wrought, or made to -blow in succession, by turning the steel axis. - -At the upper face of the pedestal, and upon each pair of bellows is a -double pulley, one of whose rims is 3 inches in diameter, and the other -1½. The cord which proceeds from the crank coils round the smaller -of these pulleys, and that which is fixed to the upper board of the -bellows goes round the larger pulley. By this means the upper board of -the bellows is made to rise higher than if the cords went directly from -them to the cranks. - -Round the larger rims of three of these pulleys, viz. those on the -right hand, there are coiled three cords, which, by means of several -smaller pulleys, terminate in the upper boards of other three pair of -bellows placed on the top of the box. - -The tension of each cord when it begins to raise the board of the -bellows to which it is attached, gives motion to a lever placed above -it between the axis and the double pulley in the middle and lower -region of the box. The other end of this lever keeps open the valve in -the lower board of the bellows, and allows the air to enter freely, -while the upper board is rising to increase the capacity of the -bellows. By this means there is not only power gained, in so far as the -air gains easier admission through the valve, but the fluttering noise -produced by the action of the air upon the valves is entirely avoided, -and the nine pair of bellows are wrought with great ease, and without -any concussion or noise. - -These nine bellows discharge their wind into three different and -separate tubes. Each tube receives the wind of three bellows, the upper -boards of one of the three pair being loaded with a weight of four -pounds, those of the second three pair with a weight of two pounds, -and those of the other three pair with no weight at all. These three -tubes ascended through the body of the figure and terminated in three -small reservoirs placed in its trunk. These reservoirs were thus united -into one, which, ascending into the throat, formed by its enlargement -the cavity of the mouth terminated by two small lips, which rested -upon the whole of the flute. These lips had the power of opening more -or less, and by a particular mechanism, they could advance or recede -from the hole in the flute. Within the cavity of the mouth there is a -small moveable tongue for opening and shutting the passage for the wind -through the lips of the figure. - -The motions of the fingers, lips, and tongue of the figure were -produced by means of a revolving cylinder, thirty inches long and -twenty-one in diameter. By means of pegs and brass staples fixed in -fifteen different divisions in its circumference, fifteen different -levers, similar to those in a barrel organ, were raised and depressed. -Seven of these regulated the motions of the seven fingers for stopping -the holes of the flute, which they did by means of steel chains rising -through the body, and directed by pulleys to the shoulder, elbow, and -fingers. Other three of the levers communicating with the valves of the -three reservoirs, regulated the ingress of the air, so as to produce a -stronger or a weaker tone. Another lever opened the lips so as to give -a free passage to the air, and another contracted them for the opposite -purpose. A third lever drew them backwards from the orifice of the -flute, and a fourth pushed them forward. The remaining lever enabled -the tongue to stop up the orifice of the flute. - -Such is a very brief view of the general mechanism by which the -requisite motions of the flute-player were produced. The airs which it -played were probably equal to those executed by a living performer, and -its construction, as well as its performances, continued for many years -to delight and astonish the philosophers and musicians of Europe. - -Encouraged by the success of this machine, M. Vaucanson exhibited in -1741 other automata, which were equally, if not more, admired. One of -these was the automaton duck, which performed all the motions of that -animal, and not only ate its food, but digested it;[21] and the other -was his pipe and tabor-player, a piece of mechanism which required -all the resources of his fertile genius. Having begun this machine -before he was aware of its peculiar difficulties, he was often about -to abandon it in despair, but his patience and his ingenuity combined, -enabled him not only to surmount every difficulty, but to construct an -automaton which performed complete airs, and greatly excelled the most -esteemed performers on the pipe and tabor. - - [21] See Letter XI. - -The figure stands on a pedestal, and is dressed like a dancing -shepherd. He holds in one hand a flageolet, and in the other the stick -with which he beats the tambourine as an accompaniment to the airs of -the flageolet, about twenty of which it is capable of performing. The -flageolet has only three holes, and the variety of its tones depends -principally on a proper variation of the force of the wind, and on the -different degrees with which the orifices are covered. These variations -in the force of the wind required to be given with a rapidity which -the ear can scarcely follow, and the articulation of the tongue was -required for the quickest notes, otherwise the effect was far from -agreeable. As the human tongue is not capable of giving the requisite -articulations to a rapid succession of notes, and generally slurs -over one-half of them, the automaton was thus able to excel the best -performers, as it played complete airs with articulations of the tongue -at every note. - -In constructing this machine, M. Vaucanson observed that the flageolet -must be a most fatiguing instrument for the human lungs, as the muscles -of the chest must make an effort equal to fifty-six pounds in order to -produce the highest notes. A single ounce was sufficient for the lowest -notes: so that we may, from this circumstance, form an idea of the -variety of intermediate effects required to be produced. - -While M. Vaucanson was engaged in the construction of these wonderful -machines, his mind was filled with the strange idea of constructing -an automaton containing the whole mechanism of the circulation of -the blood. From some birds which he made, he was satisfied of its -practicability; but as the whole vascular system required to be made -of elastic gum or caoutchouc, it was supposed that it could only be -executed in the country where the caoutchouc tree was indigenous. -Louis XVI. took a deep interest in the execution of this machine. -It was agreed that a skilful anatomist should proceed to Guiana to -superintend the construction of the blood-vessels, and the king -had not only approved of, but had given orders for, the voyage. -Difficulties, however, were thrown in the way, Vaucanson became -disgusted, and the scheme was abandoned. - -The two automata which we have described were purchased by Professor -Bayreuss of Helmstadt; but we have not been able to learn whether or -not they still exist. - -[Illustration: _Fig. 48._] - -Towards the end of the eighteenth century a bold and almost successful -attempt was made to construct a _talking automaton_. In the year 1779, -the Imperial Academy of Sciences at St. Petersburgh proposed, as the -subject of one of their annual prizes, an inquiry into the nature -of the vowel sounds, A, E, I, O, and U, and the construction of an -instrument for artificially imitating them. This prize was gained by -M. Kratzenstein, who showed that all the vowels could be distinctly -pronounced by blowing through a reed into the lower ends of the pipes -of the annexed figures, as shown in Fig. 48, where the corresponding -vowels are marked on the different pipes. The vowel I is pronounced by -merely blowing into the pipe _a b_, of the pipe marked I, without the -use of a reed. - -[Illustration: _Fig. 49._] - -About the same time that Kratzenstein was engaged in these researches, -M. Kempelen of Vienna, a celebrated mechanician, was occupied with the -same subject. In his first attempt he produced the vowel sounds, by -adapting a reed R, Fig. 49, to the bottom of a funnel-shaped cavity -A B, and placing his hand in various positions within the funnel. -This contrivance, however, was not fitted for his purpose, but after -long study, and a diligent examination of the organs of speech, he -contrived a hollow oval box, divided into two portions attached by a -hinge so as to resemble jaws. This box received the sound which issued -from the tube connected with the reed, and by opening and closing the -jaws, he produced the sounds, A, O, OU, and an imperfect E, but no -indications of an I. After two years’ labour he succeeded in obtaining -from different jaws the sounds of the consonants P, M, L, and by means -of these vowels and consonants, he could compose syllables and words, -such as _mama_, _papa_, _aula_, _lama_, _mulo_. The sounds of two -adjacent letters, however, ran into each other, and an aspiration -followed some of the consonants; so that, instead of _papa_, the word -sounded _phaa-ph-a_; these difficulties he contrived with much labour -to surmount, and he found it necessary to imitate the human organs of -speech by having only one mouth and one glottis. The mouth consisted -of a funnel, or bell-shaped piece of elastic gum, which approximated, -by its physical properties, to the softness and flexibility of the -human organs.[22] To the mouth-piece was added a nose made of two tin -tubes, which communicated with the mouth. When both these tubes were -open, and the mouth-piece closed, a perfect M was produced; and when -one was closed and the other open, an N was sounded. M. Kempelen could -have succeeded in obtaining the four letters D, G, K, T, but, by using -a P instead of them, and modifying the sound in a particular manner, -he contrived to deceive the ear by a tolerable resemblance of these -letters. - - [22] Had M. Kempelen known the modern discovery of giving glue any - degree of softness, by mixing it with molasses or sugar, which is - always absorbing moisture from the atmosphere, he might have obtained - a still more perfect imitation of the human organs. - -There seems to be no doubt that he at last was able to produce entire -words and sentences, such as _opera_, _astronomy_, _Constantinopolis_, -_Vous êtes mon ami, Je vous aime de tout mon cœur, Venez avec moi à -Paris, Leopoldus secundus, Romanorum imperator semper Augustus_, &c., -but he never fitted up a speaking figure; and probably, from being -dissatisfied with the general result of his labours, he exhibited only -to his private friends the effects of the apparatus, which was fitted -up in the form of a box. - -This box was rectangular, and about three feet long, and was placed -upon a table, and covered with a cloth. When any particular word was -mentioned by the company, M. Kempelen caused the machine to pronounce -it, by introducing his hands beneath the cloth, and apparently giving -motion to some parts of the apparatus. Mr. Thomas Collinson, who had -seen this machine in London, mentions, in a letter to Dr. Hutton, that -he afterwards saw it at M. Kempelen’s own house in Vienna, and that he -then gave it the same word to be pronounced which he gave it in London, -viz. the word _Exploitation_, which, he assures us, it again distinctly -pronounced with the French accent. - -M. Kratzenstein seems to have been equally unsuccessful; for though he -assured M. de Lalande, when he saw him in Paris, in 1786, that he had -made a machine which could speak pretty well, and though he showed him -some of the apparatus by which it could sound the vowels, and even such -syllables as _papa_ and _mama_, yet there is no reason to believe that -he had accomplished more than this. - -The labours of Kratzenstein and Kempelen have been recently pursued -with great success by our ingenious countryman, Mr. Willis, of -Cambridge. In repeating Kempelen’s experiment, shown in Fig. 49, he -used a shallower cavity, such as that in Fig. 50, and found that he -could entirely dispense with the introduction of the hand, and could -obtain the whole series of vowels by sliding a flat board C D over the -mouth of the cavity. Mr. Willis then conceived the idea of adapting to -the reed cylindrical tubes, whose length could be varied by sliding -joints. When the tube was greatly less than the length of a stopped -pipe in unison with the reed, it sounded I, and by increasing the -length of the tube, it gave E, A, O, and U, in succession. But what was -very unexpected, when the tube was so much lengthened as to be 1½ times -the length of a stopped pipe in unison with the reed, the vowels began -to be again sounded in an inverted order, viz. U, O, A, E, and then -again in a direct order, I, E, A, O, U, when the length of the tube was -equal to twice that of a stopped pipe, in unison with the reed. - -[Illustration: _Fig. 50._] - -Some important discoveries have been recently made by M. Savart -respecting the mechanism of the human voice;[23] and we have no doubt -that, before another century is completed, a _Talking_ and a _Singing -machine_ will be numbered among the conquests of Science. - - [23] See _Edinburgh Journal of Science_, No. viii., p. 200. - - - - -LETTER IX. - - Singular effects in nature depending on sound--Permanent character - of speech--Influence of great elevations on the character of - sounds, and on the powers of speech--Power of sound in throwing - down buildings--Dog killed by sound--Sounds greatly changed under - particular circumstances--Great audibility of sounds during - the night explained--Sounds deadened in media of different - densities--Illustrated in the case of a glass of champagne--and - in that of new-fallen snow--Remarkable echoes--Reverberations of - thunder--Subterranean noises--Remarkable one at the Solfaterra--Echo - at the Menai suspension bridge--Temporary deafness produced in - diving-bells--Inaudibility of particular sounds to particular - ears--Vocal powers of the statue of Memnon--Sounds in granite - rocks--Musical mountain of El-Nakous. - - -Although, among the phenomena of the material world, there is scarcely -one which, when well considered, is not an object of wonder, yet those -which we have been accustomed to witness from our infancy lose all -their interest from the frequency of their occurrence, while to the -natives of other countries they are unceasing objects of astonishment -and delight. The inhabitant of a tropical climate is confounded at -the sight of falling snow, and he almost discredits the evidence of -his senses when he sees a frozen river carrying loaded waggons on its -surface. The diffusion of knowledge by books, as well as by frequent -communication between the natives of different quarters of the globe, -has deprived this class of local wonders of their influence, and the -Indian and the Scandinavian can visit each other’s lands without any -violent excitement of surprise. Still, however, there are phenomena -of rare occurrence, of which no description can convey the idea, and -which continue to be as deeply marked with the marvellous as if they -had been previously unknown. Among these we may rank the remarkable -modifications which sound undergoes in particular situations and under -particular circumstances. - -In the ordinary intercourse of life, we recognize individuals as -much by their voice as by the features of their face and the form of -their body. A friend who has been long absent will often stand before -us as a stranger, till his voice supplies us with the full power of -recognition. The brand imprinted by time on his outer form may have -effaced the youthful image which the memory had cherished, but the -original character of his voice and its yet remembered tones will -remain unimpaired. - -An old friend with a new face is not more common in its moral than in -its physical acceptation; and though the sagacity of proverbial wisdom -has not supplied us with the counterpart in relation to the human -voice, yet the influence of its immutability over the mind has been -recorded by the poet in some of his most powerful conceptions. When -Manfred was unable to recognize in the hectic phantom of Astarte the -endeared lineaments of the being whom he loved, the mere utterance of -his name recalled “the voice which was his music,” and invested her -with the desired reality. - - Say on, say on-- - I live but in the sound--It is thy voice! - - BYRON. - -The permanence of character thus impressed upon speech exists only in -those regions to whose atmosphere our vocal organs are adapted. If -either the speaker or the hearer is placed in air differing greatly in -density from that to which they are accustomed, the voice of the one -will emit different sounds, or the same sounds will produce a different -impression on the ear of the other. But if both parties are placed in -this new atmosphere, their tones of communication will suffer the most -remarkable change. The two extreme positions, where such effects become -sufficiently striking, are in the compressed air of the diving-bell, -when it is immersed to a great depth in the sea, or in the rarefied -atmosphere which prevails on the summit of the Himalaya or the Andes. - -In the region of common life, and even at the stillest hour of night, -the ear seldom rests from its toils. When the voice of man and the -bustle of his labours have ceased, the sounds of insect life are -redoubled; the night breeze awakens among the rustling leaves, and the -swell of the distant ocean, and the sounds of the falling cataract or -of the murmuring brook, fill the air with their pure and solemn music. -The sublimity of deep silence is not to be found even in the steppes -of the Volga, or in the forests of the Orinoco. It can be felt only in -those lofty regions - - Where the tops of the Andes, - Shoot soaringly forth. - -As the traveller rises above the limit of life and motion, and enters -the region of habitual solitude, the death-like silence which prevails -around him is rendered still more striking by the diminished density -of the air which he breathes. The voice of his fellow traveller ceases -to be heard even at a moderate distance, and sounds which would stun -the ear at a lower level make but a feeble impression. The report of -a pistol on the top of Mont Blanc is no louder than that of an Indian -cracker. But while the thinness of the air thus subdues the loudest -sounds, the voice itself undergoes a singular change: the muscular -energy by which we speak experiences a great diminution, and our powers -of utterance, as well as our power of hearing, are thus singularly -modified. Were the magician, therefore, who is desirous to impress upon -his victim or upon his pupil the conviction of his supernatural power, -to carry him, under the injunction of silence, - - ----------------------------- to breathe - The difficult air of the iced mountain’s top, - Where the birds dare not build, nor insect’s wing - Flit o’er the herbless granite, - -he would experience little difficulty in asserting his power over -the elements, and still less in subsequently communicating the same -influence to his companion. - -But though the air at the tops of our highest mountains is scarcely -capable of transmitting sounds of ordinary intensity, yet sounds of -extraordinary power force their way through its most attenuated strata. -At elevations where the air is three thousand times more rare than -that which we breathe, the explosion of meteors is heard like the -sound of cannon on the surface of the earth, and the whole air is often -violently agitated by the sound. This fact alone may give us some idea -of the tremendous nature of the forces which such explosions create, -and it is fortunate for our species that they are confined to the upper -regions of the atmosphere. If the same explosions were to take place in -the dense air which rests upon the earth, our habitations and our lives -would be exposed to the most imminent peril. - -Buildings have often been thrown down by violent concussions of the -air, occasioned either by the sound of great guns or by loud thunder, -and the most serious effects upon human and animal life have been -produced by the same cause. Most persons have experienced the stunning -pain produced in the ear, when placed near a cannon that is discharged. -Deafness has frequently been the result of such sudden concussions, -and, if we may reason from analogy, death itself must often have -been the consequence. When peace was proclaimed in London, in 1697, -two troops of horse were dismounted and drawn up in line in order to -fire their volleys. Opposite the centre of the line was the door of a -butcher’s shop, where there was a large mastiff dog of great courage. -This dog was sleeping by the fire, but when the first volley was fired, -it immediately started up, ran into another room, and hid itself under -a bed. On the firing of the second volley, the dog rose, ran several -times about the room trembling violently, and apparently in great -agony. When the third volley was fired, the dog ran about once or twice -with great violence and instantly fell down dead, throwing up blood -from his mouth and nose. - -Sounds of known character and intensity are often singularly changed -even at the surface of the earth, according to the state of the ground -and the conditions of the clouds. On the extended heath, where there -are no solid objects capable of reflecting or modifying sound, the -sportsman must frequently have noticed the unaccountable variety of -sounds which are produced by the report of his fowling-piece. Sometimes -they are flat and prolonged, at other times short and sharp, and -sometimes the noise is so strange that it is referred to some mistake -in the loading of the gun. These variations, however, arise entirely -from the state of the air, and from the nature and proximity of the -superjacent clouds. In pure air of uniform density the sound is sharp -and soon over, as the undulations of the air advance without any -interrupting obstacles. In a foggy atmosphere, or where the vapours -produced by heat are seen dancing as it were in the air, the sound is -dull and prolonged; and when these clouds are immediately over-head, a -succession of echoes from them produces a continued or reverberating -sound. When the French astronomers were determining the velocity of -sound by firing great guns, they observed that the report was always -single and sharp under a perfectly clear sky, but indistinct, and -attended by a long-continued roll like thunder, when a cloud covered -a considerable part of the horizon. It is no doubt owing to the same -cause, namely, the reflexion from the clouds, that the thunder rolls -through the heavens, as if it were produced by a succession of electric -explosions. - -The great audibility of sounds during the night is a phenomenon of -considerable interest, and one which had been observed even by the -ancients. In crowded cities or in their vicinity, the effect was -generally ascribed to the rest of animated beings; while in localities -where such an explanation was inapplicable, it was supposed to arise -from a favourable direction of the prevailing wind. Baron Humboldt -was particularly struck with this phenomenon when he first heard the -rushing of the great cataracts of the Orinoco in the plain which -surrounds the Mission of the Apures. These sounds he regarded as -three times louder during the night than during the day. Some authors -ascribed this fact to the cessation of the humming of insects, the -singing of birds, and the action of the wind on the leaves of the -trees, but M. Humboldt justly maintains that this cannot be the cause -of it on the Orinoco, where the buzz of insects is much louder in the -night than in the day, and where the breeze never rises till after -sunset. Hence he was led to ascribe the phenomenon to the perfect -transparency and uniform density of the air, which can exist only at -night after the heat of the ground has been uniformly diffused through -the atmosphere. When the rays of the sun have been beating on the -ground during the day, currents of hot air of different temperatures, -and consequently of different densities, are constantly ascending from -the ground and mixing with the cold air above. The air thus ceases -to be a homogeneous medium, and every person must have observed the -effects of it upon objects seen through it which are very indistinctly -visible, and have a tremulous motion, as if they were “dancing in -the air.” The very same effect is perceived when we look at objects -through spirits and water that are not perfectly mixed, or when we view -distant objects over a red-hot poker or over a flame. In all these -cases the light suffers refraction in passing from a medium of one -density into a medium of a different density, and the refracted rays -are constantly changing their direction as the different currents rise -in succession. Analogous effects are produced when sound passes through -a mixed medium, whether it consists of two different mediums or of one -medium where portions of it have different densities. As sound moves -with different velocities through media of different densities, the -wave which produces the sound will be partly reflected in passing from -one medium to the other, and the direction of the transmission wave -changed: and hence in passing through such media different portions of -the wave will reach the ear at different times, and thus destroy the -sharpness and distinctness of the sound. This may be proved by many -striking facts. If we put a bell in a receiver containing a mixture of -hydrogen gas and atmospheric air, the sound of the bell can scarcely be -heard. During a shower of rain or of snow, noises are greatly deadened; -and when sound is transmitted along an iron wire or an iron pipe of -sufficient length, we actually hear two sounds, one transmitted more -rapidly through the solid, and the other more slowly through the air. -The same property is well illustrated by an elegant and easily repeated -experiment of Chladni’s. When sparkling champagne is poured into a tall -glass till it is half full, the glass loses its power of ringing by a -stroke upon its edge, and emits only a disagreeable and puffy sound. -This effect will continue while the wine is filled with bubbles of -air, or as long as the effervescence lasts; but when the effervescence -begins to subside the sound becomes clearer and clearer, and the glass -rings as usual when the air-bubbles have vanished. If we reproduce -the effervescence by stirring the champagne with a piece of bread, the -glass will again cease to ring. The same experiment will succeed with -other effervescing fluids. - -The difference in the audibility of sounds that pass over homogeneous -and over mixed media is sometimes so remarkable as to astonish those -who witness it. The following fact is given on the evidence of an -officer who observed it:--When the British and the American forces -were encamped on each side of a river, the outposts were so near, that -the form of individuals could be easily distinguished. An American -drummer made his appearance, and began to beat his drum; but though -the motion of his arms was distinctly seen, not a single sound reached -the ear of the observer. A coating of snow that had newly fallen upon -the ground, and the thickness of the atmosphere, had conspired to -obstruct the sound. An effect the very reverse of this is produced by -a coating of glazed or hardened snow, or by an extended surface of ice -or water. Lieutenant Foster was able to carry on a conversation with -a sailor across Port Bowen Harbour, a distance of no less than a mile -and a quarter, and the sound of great guns has been heard at distances -varying from 120 to 200 miles. Over hard and dry ground of a uniform -character, or where a thin soil rests upon a continuous stratum of -rock, the sound is heard at a great distance, and hence it is the -practice among many Eastern tribes to ascertain the approach of an -enemy by applying the ear to the ground. - -Many remarkable phenomena in the natural world are produced by the -reflexion and concentration of sound. Every person is familiar with -the ordinary _echo_ which arises from the reflexion of sound from an -even surface, such as the face of a wall, of a house, of a rock, of -a hill, or of a cloud. As sound moves at the rate of 1090 feet in a -second, and as the sound which returns to the person who emits it has -travelled over a space equal to twice his distance from the reflecting -surface, the distance in feet of the body which occasions the echo may -be readily found by multiplying 545 by the number of seconds which -elapse between the emission of the sound and its return in the form of -an echo. This kind of echo, where the same person is the speaker and -the hearer, never takes place, unless when the observer is immediately -in front of the reflecting surface, or when a line drawn from his mouth -to the flat surface is nearly perpendicular to it, because in this -case alone the wave of sound is reflected in the very same direction -from the wall in which it reaches it. If the speaker places himself -on one side of this line, then the echo will be heard most distinctly -by another person as far on the other side of it, because the waves -of sound are reflected like light, so that the angle of incidence or -the inclination at which the sound falls upon the reflected surface -is equal to the angle of reflexion, or the inclination at which the -sound is returned from the wall. If two persons, therefore, are placed -before the reflecting wall, the one will hear the echo of the sound -emitted by the other, and obstacles may intervene between these two -persons, so that neither of them hears the direct sound emitted by the -other; in the same manner as the same persons similarly placed before -a looking-glass would see each other distinctly by reflexion, though -objects might obstruct their direct view of each other. - -Hitherto we have supposed that there is only one reflecting surface, -in which case there will be only one echo; but if there are several -reflecting surfaces, as in the case in an amphitheatre of mountains, -or during a thunder-storm, where there are several strata or masses -of clouds; or if there are two parallel or inclined surfaces between -which the sound can be repeatedly reflected, or if the surface is -curved, so that the sound reflected from one part falls upon another -part, like the sides of a polygon inscribed in a circle,--in all these -cases there will be numerous echoes, which produce a very singular -effect. Nothing can be more grand and sublime than the primary and -secondary echoes of a piece of ordnance discharged in an amphitheatre -of precipitous mountains. The direct or primary echoes from each -reflecting surface reach the ear in succession, according to their -different distances, and these are either blended with or succeeded -by the secondary echoes, which terminate in a prolonged growl, ending -in absolute silence. Of the same character are the reverberated claps -of a thunderbolt reflected from the surrounding clouds, and dying -away in the distance. The echo which is produced by parallel walls -is finely illustrated at the Marquis of Simonetta’s villa near Milan, -which has been described by Addison and Keysler, and which we believe -is that described by Mr. Southwell in the Philosophical Transactions -for 1746. Perpendicular to the main body of this villa there extend two -parallel wings about fifty-eight paces distant from each other, and the -surfaces of which are unbroken either with doors or windows. The sound -of the human voice, or rather a word quickly pronounced, is repeated -above forty times, and the report of a pistol from fifty-six to sixty -times. The repetitions, however, follow in such rapid succession that -it is difficult to reckon them, unless early in the morning before the -equal temperature of the atmosphere is disturbed, or in a calm, still -evening. The echoes appear to be best heard from a window in the main -building between the two projecting walls, from which the pistol also -is fired. Dr. Plot mentions an echo in Woodstock Park which repeats -seventeen syllables by day and twenty by night. An echo on the north -side of Shipley church, in Sussex, repeats twenty-one syllables. Sir -John Herschel mentions an echo in the Manfroni palace at Venice, where -a person standing in the centre of a square room about twenty-five -feet high, with a concave roof, hears the stamp of his foot repeated -a great many times; but as his position deviates from the centre, the -echoes become feebler, and at a short distance entirely cease. The -same phenomenon, he remarks, occurs in the large room of the library -of the museum at Naples. M. Genefay has described, as existing near -Rouen, a curious oblique echo which is not heard by the person who -emits the sound. A person who sings hears only his own voice, while -those who listen hear only the echo, which sometimes seems to approach, -and at other times seems to recede from the ear; one person hears a -single sound, another several sounds, and one hears it on the right, -and another on the left, the effect always changing as the hearer -changes his position. Dr. Birch has described an extraordinary echo at -Roseneath, in Argyleshire, which certainly does not now exist. When -eight or ten notes were played upon a trumpet, they were correctly -repeated, but on a key a third lower. After a short pause, another -repetition of the notes was heard in a still lower tone, and after -another short interval they were repeated in a still lower tone. - -In the same manner as light is always lost by reflexion, so the -waves of sound are enfeebled by reflexion from ordinary surfaces, -and the echo is in such cases fainter than the original sound. If -the reflecting surface, however, is circular, sound may be condensed -and rendered stronger in the same manner as light. I have seen a -fine example of this, in the circular turn of a garden wall nearly -a mile distant from a weir across a river. When the air is pure and -homogeneous, the rushing sound of the water is reflected from the -hollow surface of the wall, and concentrated in a focus, the place of -which the ear can easily discover from the intensity of the sound being -there a maximum. A person not acquainted with the locality conceives -that the rushing noise is on the other side of the wall. - -In whispering galleries, or places where the lowest whispers are -carried to distances at which the direct sound is inaudible, the sound -may be conveyed in two ways, either by repeated reflexions from a -curved surface in the direction of the sides of a polygon inscribed -in a circle, or where the whisperer is in the focus of one reflecting -surface, and the hearer in the focus of another reflecting surface, -which is placed so as to receive the reflected sounds. The first of -these ways is exemplified in the whispering gallery of St. Paul’s, -and in the octagonal gallery of Gloucester cathedral, which conveys -a whisper seventy-five feet across the nave; and the second in the -baptistery of a church in Pisa, where the architect, Giovanni Pisano, -is said to have constructed the cupola on purpose. The cupola has an -elliptical form, and when one person whispers in one focus, it is -distinctly heard by the person placed in the other focus, but not by -those who are placed between them. The sound first reflected passes -across the cupola, and enters the ears of the intermediate persons, -but it is too feeble to be heard till it has been condensed by a -second reflexion to the other focus of ellipse. A naval officer, -who travelled through Sicily in the year 1824, gives an account of -a powerful whispering place in the cathedral of Girgenti, where the -slightest whisper is carried with perfect distinctness through a -distance of two hundred and fifty feet, from the great western door to -the cornice behind the high altar. By an unfortunate coincidence, the -focus of one of the reflecting surfaces was chosen for the place of the -confessional; and when this was accidentally discovered, the lovers -of secrets resorted to the other focus, and thus became acquainted -with confessions of the gravest import. This divulgence of scandal -continued for a considerable time, till the eager curiosity of one -of the dilettanti was punished, by hearing his wife’s avowal of her -own infidelity. This circumstance gave publicity to the whispering -peculiarity of the cathedral, and the confessional was removed to a -place of greater secrecy. - -[Illustration: _Fig. 51._] - -An echo of a very peculiar character has been described by Sir John -Herschell in his Treatise on Sound, as produced by the suspension -bridge across the Menai strait in Wales. “The sound of a blow with a -hammer,” says he, “on one of the main piers, is returned in succession -from each of the cross-beams which support the road-way, and from the -opposite pier at a distance of five hundred and seventy-six feet; and -in addition to this, the sound is many times repeated between the -water and the road-way. The effect is a series of sounds which may be -thus written: the first return is sharp and strong from the road-way -over-head; the rattling which succeeds dies away rapidly, but the -single repercussion from the opposite pier is very strong, and is -succeeded by a faint palpitation, repeating the sound at the rate of -twenty-eight times in five seconds, and which, therefore corresponds to -a distance of a hundred and eighty-four feet, or very nearly the double -interval from the road-way to the water. Thus it appears that in the -repercussion between the water and road-way, that from the latter only -affects the ear, the line drawn from the auditor to the water being -too oblique for the sound to diverge sufficiently in that direction. -Another peculiarity deserves especial notice, namely, that the echo -from the opposite pier is best heard when the auditor stands precisely -opposite to the middle of the breadth of the pier, and strikes just -on that point. As it deviates to one or the other side, the return is -proportionally fainter, and is scarcely heard by him when his station -is a little beyond the extreme edge of the pier, though another person, -stationed (on the same side of the water) at an equal distance from the -central point, so as to have the pier between them, hears it well.” - -A remarkable subterranean echo is often heard when the hoofs of a horse -or the wheels of a carriage pass over particular spots of ground. This -sound is frequently very similar to that which is produced in passing -over an arch or vault, and is commonly attributed to the existence of -natural or artificial caves beneath. As such caves have often been -constructed in times of war as places of security for persons and -property, many unavailing attempts have been made to discover hidden -treasures where their locality seemed to be indicated by subterraneous -sounds. But though these sounds are sometimes produced by excavations -in the ground, yet they generally arise from the nature of the -materials of which the ground is composed, and from their manner of -combination. If the hollow of a road has been filled up with broken -rock, or with large waterworn stones, having hollows either left -entirely empty, or filled up with materials of different density, then -the sound will be reflected in passing from the loose to the dense -materials, and there will arise a great number of echoes reaching the -ear in rapid succession, and forming by their union a hollow rumbling -sound. This principle has been very successfully applied by Sir John -Herschell to explain the subterranean sounds with which every traveller -is familiar who has visited the Solfaterra, near Naples. When the -ground at a particular place is struck violently by throwing a large -stone against it, a peculiar hollow sound is distinctly heard. This -sound has been ascribed by some geologists to the existence of a great -vault communicating with the ancient seat of the volcano, by other -writers to a reverberation from the surrounding hills with which it -is nearly concentric, and by others to the porosity of the ground. -Dr. Daubeny, who says that the hollow sound is heard when any part -of the Solfaterra is struck, accounts for it by supposing that the -hill is not made up of one entire rock, but of a number of detached -blocks, which, hanging as it were by each other, form a sort of vault -over the abyss within which the volcanic operations are going on.[24] -Mr. Forbes, who has given the latest and most interesting description -of this singular volcano,[25] agrees in opinion with Dr. Daubeny; -while Mr. Scrope[26] and Sir John Herschell concur in opinion that -no such cavities exist. “It seems most probable,” says the latter, -“that the hollow reverberation is nothing more than an assemblage -of partial echoes arising from the reflexion of successive portions -of the original sound, in its progress through the soil at the -innumerable half-coherent surfaces composing it: were the whole soil -a mass of sand, these reflexions would be so strong and frequent as -to destroy the whole impulse in too short an interval to allow of a -distinguishable after-sound. It is a case analogous to that of a strong -light thrown into a milky medium or smoky atmosphere; the whole medium -appears to shine with a nebulous undefined light. This is to the eye -what such a hollow sound is to the ear.”[27] - - [24] Description of Volcanoes, p. 170. - - [25] _Edinburgh Journal of Science_, New Series, No. i., p. 124. - - [26] Considerations on Volcanoes, and _Edinburgh Journal of Science_, - No. xx., p. 261, and No. xiv., p. 265. - - [27] Art. SOUND, _Encycl. Metrop._, § 110. - -It has been recently shown by M. Savart, that the human ear is so -extremely sensible as to be capable of appreciating sounds which -arise from about _twenty-four thousand_ vibrations in a second, and -consequently that it can hear a sound which lasts only the twenty-four -thousandth part of a second. Vibrations of such frequency afford only -a shrill squeak or chirp; and Dr. Wollaston has shown that there are -many individuals with their sense of hearing entire, who are altogether -insensible to such acute sounds, though others are painfully affected -by them. Nothing, as Sir John Herschell remarks, can be more surprising -than to see two persons, neither of them deaf, the one complaining of -the penetrating shrillness of a sound, while the other maintains there -is no sound at all. Dr. Wollaston has also shown that this is true also -of very grave sounds; so that the hearing or not hearing of musical -notes at both extremities of the scale seems to depend wholly on the -pitch or frequency of vibration constituting the note, and not upon the -intensity or loudness of the noise. This affection of the ear sometimes -appears in cases of common deafness, where a shrill tone of voice, such -as that of women and children, is often better heard than the loud and -deeper tone of men. - -Dr. Wollaston remarked, that when the mouth and nose are shut, the -tympanum or drum of the ear may be so exhausted by a forcible attempt -to take breath by the expansion of the chest, the pressure of the -external air upon the membrane gives it such a tension, that the ear -becomes insensible to grave tones, without losing in any degree the -perception of sharper sounds. Dr. Wollaston found, that after he had -got into the habit of making the experiment, so as to be able to -produce a great degree of exhaustion, his ears were insensible to -all sounds below F, marked by the bass clef. “If I strike the table -before me,” says he, “with the end of my finger, the whole board sounds -with a deep dull note. If I strike it with my nail, there is also at -the same time a sharp sound produced by quicker vibrations of parts -around the point of contact. When the ear is exhausted, it hears only -the latter sound, without perceiving in any degree the deeper note of -the whole table. In the same manner, in listening to the sound of a -carriage, the deeper rumbling noise of the body is no longer heard by -an exhausted ear; but the rattle of a chain or loose screw remains at -least as audible as before exhaustion.” Dr. Wollaston supposes that -this excessive tension of the drum of the ear, when produced by the -compressed air in the diving-bell, will also produce a corresponding -_deafness to low tones_. This curious experiment has been since made -by Dr. Colladon, when descending in the diving-bell at Howth, in 1820. -“We descended,” says he, “so slowly that we did not notice the motion -of the bell; but as soon as the bell was immersed in water, we felt -about the ears and the forehead a sense of pressure, which continued -increasing during some minutes. I did not, however, experience any pain -in the ears; but my companion suffered so much that we were obliged -to stop our descent for a short time. To remedy that inconvenience, -the workmen instructed us, after having closed our nostrils and mouth, -to endeavour to swallow, and to restrain our respiration for some -moments, in order that, by this exertion, the internal air might act -on the Eustachian tube. My companion, however, having tried it, found -himself very little relieved by this remedy. After some minutes, we -resumed our descent. My friend suffered considerably; he was pale; his -lips were totally discoloured; his appearance was that of a man on the -point of fainting; he was in involuntary low spirits, owing, perhaps, -to the violence of the pain, added to that kind of apprehension which -our situation unavoidably inspired. This appeared to me the more -remarkable, as my case was totally the reverse. I was in a state of -excitement resembling the effect of some spirituous liquor. I suffered -no pain; I experienced only a strong pressure round my head, as if an -iron circle had been bound about it. I spoke with the workmen, and had -some difficulty in hearing them. This difficulty of hearing rose to -such a height, that during three or four minutes I could not hear them -speak. I could not, indeed, hear myself speak, though I spoke as loudly -as possible; nor did even the great noise caused by the violence of the -current against the sides of the bell reach my ears.” - -The effect thus described by Dr. Colladon is different from that -anticipated by Dr. Wollaston. He was not merely deaf to low tones, but -to all sounds whatever; and I have found, by repeated experiment, that -my own ears become perfectly insensible even to the shrill tones of the -female voice, and of the voice of a child, when the drum of the ear is -thrown into a state of tension by yawning. - -With regard to sounds of high pitch at the other extremity of the -scale, Dr. Wollaston has met with persons, whose hearing was in -other respects perfect, who never heard the chirping of the _Gryllus -campestris_, which commonly occurs in hedges during a summer’s evening, -or that of the house-cricket, or the squeak of the bat, or the chirping -of the common house-sparrow. The note of the bat is a full octave -higher than that of the sparrow; and Dr. Wollaston believes that the -note of some insects may reach one octave more, as there are sounds -decidedly higher than that of a small pipe, one-fourth of an inch in -length, which he conceives cannot be far from six octaves above the -middle E of the pianoforte. “The suddenness of the transition,” says -Dr. Wollaston, “from perfect hearing to total want of perception, -occasions a degree of surprise, which renders an experiment on this -subject with a series of small pipes among several persons rather -amusing. It is curious to observe the change of feeling manifested -by various individuals of the party, in succession, as the sounds -approach and pass the limits of their hearing. Those who enjoy a -temporary triumph are often compelled in their turn to acknowledge to -how short a distance their little superiority extends.” In concluding -his interesting paper on this subject, Dr. Wollaston conjectures that -animals, like the grylli (whose powers of hearing appear to commence -nearly where ours terminate), may have the power of hearing still -sharper sounds which at present we do not know to exist, and that there -may be other insects having nothing in common with us, but who are -endowed with a power of exciting, and a sense of perceiving, vibrations -which make no impression upon our organs, while their organs are -equally insensible to the slower vibrations to which we are accustomed. - -With the view of studying the class of sounds inaudible to certain -ears, we would recommend it to the young naturalist to examine the -sounds emitted by the insect tribe, both in relation to their effect -upon the human ear, and to the mechanism by which they are produced. -The Cicadæ or locusts in North America appear, from the observations -of Dr. Hildreth,[28] to be furnished with a bagpipe on which they play -a variety of notes. “When any one passes,” says he, “they make a great -noise and screaming with their air bladder or bagpipes. These bags are -placed under, and rather behind, the wings in the axilla, something in -the manner of using the bagpipes with the bags under the arms--I could -compare them to nothing else; and, indeed, I suspect the first inventor -of the instrument borrowed his ideas from some insect of this kind. -They play a variety of notes and sounds, one of which nearly imitates -the scream of the tree toad.” - - [28] _Edinburgh Journal of Science_, No. xvii., p. 158. - -Among the acoustic wonders of the natural world may be ranked the -vocal powers of the statue of Memnon, the son of Aurora, which modern -discoveries have withdrawn from among the fables of ancient Egypt. -The history of this remarkable statue is involved in much obscurity. -Although Strabo affirms that it was overturned by an earthquake, yet as -Egypt exhibits no traces of such a convulsion, it has been generally -believed that the statue was mutilated by Cambyses. Ph. Casselius, -in his dissertation on vocal or speaking stones, quotes the remark -of the scholiast in Juvenal, “that, when mutilated by Cambyses, the -statue, which saluted both the sun and the king, afterwards saluted -only the sun.” Philostratus, in his life of Apollo, informs us, that -the statue looked to the east, and that it spoke as soon as the rays -of the rising sun fell upon its mouth. Pausanias, who saw the statue -in its dismantled state, says, that it is a statue of the sun, that -the Egyptians call it Phamenophis, and not Memnon, and _that it emits -sounds every morning at sunrise, which can be compared only to that of -the breaking of the string of the lyre_. Strabo speaks only of a single -sound which he heard; but Juvenal, who had probably heard it often -during his stay in Egypt, describes it as if it emitted several sounds: - - Dimidio magicæ resonant ubi Memnone chordæ. - Where broken Memnon sounds his magic strings. - -The simple sounds which issued from the statue were, in the progress -of time, magnified into intelligible words, and even into an oracle of -seven verses, and this prodigy has been recorded in a Greek inscription -on the left leg of the statue. But though this new faculty of the -colossus was evidently the contrivance of the Egyptian priests, yet we -are not entitled from this to call in question the simple and perfectly -credible fact that it emitted sounds. This property, indeed, it seems -to possess at the present day; for we learn,[29] that an English -traveller, Sir A. Smith, accompanied with a numerous escort, examined -the statue, and that at six o’clock in the morning he heard very -distinctly the sounds which had been so celebrated in antiquity. He -asserts that this sound does not proceed from the statue, but from the -pedestal; and he expresses his belief that it arises from the impulse -of the air upon the stones of the pedestal, which are arranged so as -to produce this surprising effect. This singular description is, to a -certain extent, confirmed by the description of Strabo, who says, that -he was quite certain that he heard a sound which proceeded either _from -the base_, or from the colossus, or from some one of the assistants. As -there were no Egyptian priests in the escort of Sir A. Smith, we may -now safely reject this last, and, for many centuries, the most probable -hypothesis. - - [29] _Revue Encyclopédique_, 1821, tome ix., p. 592. - -The explanation suggested by Sir A. Smith had been previously given in -a more specific form by M. Dussaulx, the translator of Juvenal. “The -statue,” says he, “being hollow, the heat of the sun heated the air -which it contained, and this air, issuing at some crevice, produced the -sounds of which the priests gave their own interpretation.” - -Rejecting this explanation, M. Langles, in his dissertation on the -vocal statue of Memnon, and M. Salverte, in his work on the occult -sciences, have ascribed the sounds entirely to Egyptian priestcraft; -and have even gone so far as to describe the mechanism by which -the statue not only emitted sounds, but articulated distinctly the -intonations appropriate to the seven Egyptian vowels, and consecrated -to the seven planets. M. Langles conceives that the sounds may be -produced by a series of hammers, which strike either the granite -itself, or sonorous stones like those which have been long used in -China for musical instruments. M. Salverte improves this imperfect -apparatus, by supposing that there might be adapted to these hammers a -clepsydra, or water-clock, or any other instrument fitted to measure -time, and so constructed as to put the hammers in motion at sunrise. -Not satisfied with this supposition, he conjectures that the spring of -all this mechanism was to be found in the art of concentrating the rays -of the sun, which was well known to the ancients. Between the lips of -the statue, or in some less remarkable part of it concealed from view -by its height, he conceives an aperture to be perforated, containing a -lens or a mirror capable of condensing the rays of the rising sun upon -one or more metallic levers, which by their expansion put in motion -the seven hammers in succession. Hence he explains why the sounds were -emitted only at sunrise, and when the solar rays fell upon the mouth of -the statue, and why they were never again heard till the sun returned -to the eastern horizon. As a piece of mechanism, this contrivance is -defective in not providing for the change in the sun’s amplitude, -which is very considerable even in Egypt, for as the statue and the -lens are both fixed, and as the sounds were heard at all seasons of -the year, the same lens which threw the Midsummer rays of the sun upon -the hammers could not possibly throw upon them his rays in winter. But -even if the machinery were perfect, it is obvious that it could not -have survived the mutilation of the statue, and could not, short of a -miracle, have performed its part in the time of Sir A. Smith. - -If we abandon the idea of the whole being a trick of the priesthood, -which has been generally done, and which the recent observations of -Sir A. Smith authorise us to do, we must seek some natural cause for -the phenomena similar to that suggested by Dussaulx. It is curious -to observe how the study of nature gradually dispels the consecrated -delusions of ages, and reduces to the level of ordinary facts what time -had invested with all the characters of the supernatural: and in the -present case it is no less remarkable that the problem of the statue of -Memnon should have been first solved by means of an observation made -by a solitary traveller wandering on the banks of the Orinoco. “The -granitic rock,” says Baron Humboldt, “on which we lay, is one of those -where travellers on the Orinoco have heard from time to time, towards -sunrise, subterraneous sounds resembling those of the organ. The -missionaries call these stones _loxas de musica_. ‘It is witchcraft,’ -said our young Indian pilot. We never ourselves heard these mysterious -sounds either at Carichana Vieja or in the upper Orinoco: but from -information given us by witnesses worthy of belief, the existence of a -phenomenon that seems to depend on a certain state of the atmosphere -cannot be denied. The shelves of rock are full of very narrow and -deep crevices. They are heated during the day to about 50°. I often -found their temperature at the surface during the night at 39°, the -surrounding atmosphere being at 28°. It may easily be conceived that -the difference of temperature between the subterraneous and the -external air attains its maximum about sunrise, or at that moment which -is at the same time farther from the period of the maximum of the heat -of the preceding day. May not these sounds of an organ, then, which are -heard when a person sleeps upon the rock, his ear in contact with the -stone, be the effect of a current of air that issues out through the -crevices? Does not the impulse of the air against the elastic spangles -of mica that intercept the crevices contribute to modify the sounds? -May we not admit that the ancient inhabitants of Egypt, in passing -incessantly up and down the Nile, had made the same observation on some -rock of the Thebaid, and that the music of the rocks there led to the -jugglery of the priests in the statue of Memnon?” - -This curious case of the production of sounds in granite rocks at -sunrise might have been regarded as a transatlantic wonder which was -not applicable to Egypt; but by a singular coincidence of observation, -Messrs. Jomard, Jollois, and Devilliers, who were travelling in Egypt -nearly about the same time that M. Humboldt was traversing the wilds of -South America, heard, _at sunrise, in a monument of granite_, situated -near the centre of the spot on which the palace of Carnac stands, _a -noise resembling that of a breaking string_, the very expression by -which Pausanias characterizes the sound in the Memnonian granite. The -travellers regarded these sounds as arising from the transmission -of rarefied air through the crevices of a sonorous stone, and they -were of the same opinion with Humboldt, that these sounds might have -_suggested_ to the Egyptian priests _the juggleries of the Memnonium_. -Is it not strange that the Prussian and the French travellers should -not have gone a step farther, and solved the problem of two thousand -years, by maintaining that the sound of the statue of Memnon was itself -a natural phenomenon, or a granitic sound elicited at sunrise by the -very same causes which operated on the Orinoco and in the temple of -Carnac, in place of regarding it as a trick in imitation of natural -sounds? If, as Humboldt supposes, the ancient inhabitants of Egypt -had, in passing incessantly up and down the Nile, become familiar with -the music of the granite rocks of the Thebaid, how could the imitation -of such natural and familiar sounds be regarded by the priests as a -means of deceiving the people? There could be nothing marvellous in -a colossal statue of granite giving out the very same sounds that -were given out at the same time of the day by a granite rock; and in -place of reckoning it a supernatural fact, they could regard it in no -other light than as the duplicate of a well-known natural phenomenon. -It is a mere conjecture, however, that such sounds were common in the -Thebaid; and it is therefore probable that a granite rock, possessing -the property of emitting sounds at sunrise, had been discovered by the -priests, who were at the same time the philosophers of Egypt, and that -the block had been employed in the formation of the Memnonian statue -for the purpose of impressing upon it a supernatural character, and -enabling them to maintain their influence over a credulous people. - -The inquiries of recent travellers have enabled us to corroborate -these views, and to add another remarkable example of the influence of -subterraneous sounds over superstitious minds. About three leagues to -the north of Tor in Arabia Petræa, is a mountain, within the bosom of -which the most singular sounds have been heard. The Arabs of the Desert -ascribe these sounds to a convent of monks preserved miraculously -underground; and the sound is supposed to be that of the _Nakous_, a -long narrow metallic ruler suspended horizontally, which the priest -strikes with a hammer for the purpose of assembling the monks to -prayer. A Greek was said to have seen the mountain open, and to have -descended into the subterranean convent, where he found fine gardens -and delicious water; and, in order to give proof of his descent, he -produced some fragments of consecrated bread, which he pretended to -have brought from the subterranean convent. The inhabitants of Tor -likewise declare that the camels are not only frightened, but rendered -furious, when they hear these subterraneous sounds. - -M. Seetzen, the first European traveller who visited this extraordinary -mountain, set out from Wodyel Nackel on the 17th of June, at five -o’clock in the morning. He was accompanied by a Greek Christian and -some Bedouin Arabs, and after a quarter of an hour’s walk they reached -the foot of a majestic rock of hard sand-stone. The mountain itself was -quite bare and entirely composed of it. He found inscribed upon the -rock several Greek and Arab names, and also some Koptic characters, -which proved that it had been resorted to for centuries. About noon the -party reached the foot of the mountains called _Nakous_, where at the -foot of a ridge they beheld an insulated peaked rock. This mountain -presented upon two of its sides two sandy declivities about 150 feet -high, and so inclined that the white and slightly adhering sand which -rests upon its surface is scarcely able to support itself; and when the -scorching heat of the sun destroys its feeble cohesion, or when it is -agitated by the smallest motions, it slides down the two declivities. -These declivities unite behind the insulated rock, forming an acute -angle, and like the adjacent surfaces, they are covered with steep -rocks which consist chiefly of a white and friable free-stone. - -The first sound which greeted the ears of the travellers took place -at an hour and a quarter after noon. They had climbed with great -difficulty as far as the sandy declivity, a height of seventy or -eighty feet, and had rested beneath the rocks where the pilgrims are -accustomed to listen to the sounds. - -While in the act of climbing, M. Seetzen heard the sound from beneath -his knees, and hence he was led to think that the sliding of the sand -was the cause of the sound, and not the effect of the vibration which -it occasioned. At three o’clock the sound became louder and continued -six minutes, and after having ceased for ten minutes, it was again -heard. The sound appeared to have the greatest resemblance to that -of the humming-top, rising and falling like that of an Æolian harp. -Believing that he had discovered the true origin of the sound, M. -Seetzen was anxious to repeat the experiment, and with this view he -climbed with the utmost difficulty to the highest rocks, and sliding -down as fast as he could, he endeavoured, with the help of his hands -and feet, to set the sand in motion. The effect thus produced far -exceeded his expectations, and the sand in rolling beneath him made so -loud a noise, that the earth seemed to tremble to such a degree that he -states he should certainly have been afraid if he had been ignorant of -the cause. - -M. Seetzen throws out some conjectures respecting the cause of -these sounds. Does the rolling layer of sand, says he, act like the -fiddle-bow, which, on being rubbed upon a plate of glass, raises -and distributes into regular figures the sand with which the plate -is covered? Does the adherent and fixed layer of sand perform here -the part of the plate of glass, and the neighbouring rocks that of -the sounding body? We cannot pretend to answer these questions, -but we trust that some philosopher competent to the task will have -an opportunity of examining these interesting phenomena with more -attention, and describing them with greater accuracy. - -The only person, so far as I can learn, who has visited El-Nakous, -since the time of Seetzen, is Mr. Gray, of University College, -Oxford; but he has not added much to the information acquired by his -predecessor. During the first visit which he made to the place, he -heard at the end of a quarter of an hour a low continuous murmuring -sound beneath his feet, which gradually changed into pulsations as -it became louder, so as to resemble the striking of a clock, and at -the end of five minutes it became so strong as to detach the sand. -Returning to the spot next day, he heard the sound still louder than -before. He could not observe any crevices by which the external air -could penetrate; and as the sky was serene and the air calm, he was -satisfied that the sounds could not arise from this cause.[30] - - [30] See _Edinburgh Journal of Science_, No. xi., p. 153, and No. - xiii., p. 51. - - - - -LETTER X. - - Mechanical inventions of the ancients few in number--Ancient - and modern feats of strength--Feats of Eckeberg particularly - described--General explanation of them--Real feats of strength - performed by Thomas Topham--Remarkable power of lifting heavy - persons when the lungs are inflated--Belzoni’s feat of sustaining - pyramids of men--Deception of walking along the ceiling in an - inverted position--Pneumatic apparatus in the foot of the house-fly - for enabling it to walk in opposition to gravity--Description of - the analogous apparatus employed by the gecko lizard for the same - purpose--Apparatus used by the Echineis remora, or sucking-fish. - - -The mechanical knowledge of the ancients was principally theoretical, -and though they seem to have constructed some minor pieces of mechanism -which were sufficient to delude the ignorant, yet there is no reason -for believing that they had executed any machinery that was capable -of exciting much surprise, either by its ingenuity or its magnitude. -The properties of the mechanical powers, however, seem to have been -successfully employed in performing feats of strength which were beyond -the reach even of strong men, and which could not fail to excite the -greatest wonder when exhibited by persons of ordinary size. - -Firmus, a native of Seleucia, who was executed by the Emperor Aurelian -for espousing the cause of Zenobia, was celebrated for his feats of -strength. In his account of the life of Firmus, who lived in the third -century, Vopiscus informs us, that he could suffer iron to be forged -upon an anvil placed upon his breast. In doing this he lay upon his -back, and resting his feet and shoulders against some support, his -whole body formed an arch, as we shall afterwards more particularly -explain. Until the end of the sixteenth century, the exhibition of -such feats does not seem to have been common. About the year 1703, a -native of Kent, of the name of Joyce, exhibited such feats of strength -in London and other parts of England, that he received the name of the -second Samson. His own personal strength was very great; but he had -also discovered, without the aid of theory, various positions of his -body in which men even of common strength could perform very surprising -feats. He drew against horses, and raised enormous weights; but as -he actually exhibited his power in ways which evinced the enormous -strength of his own muscles, all his feats were ascribed to the same -cause. In the course of eight or ten years, however, his methods -were discovered, and many individuals of ordinary strength exhibited -a number of his principal performances, though in a manner greatly -inferior to Joyce. - -Some time afterwards, John Charles Van Eckeberg, a native of -Harzgerode, in Anhalt, travelled through Europe under the appellation -of Samson, exhibiting very remarkable examples of his strength. -This, we believe, is the same person whose feats are particularly -described by Dr. Desaguliers. He was a man of the middle size, and -of ordinary strength; and as Dr. Desaguliers was convinced that his -feats were exhibitions of skill and not of strength, he was desirous -of discovering his methods, and with this view he went to see him, -accompanied by the Marquis of Tullibardine, Dr. Alexander Stuart, and -Dr. Pringle, and his own mechanical operator. They placed themselves -round the German, so as to be able to observe accurately all that he -did, and their success was so great that they were able to perform most -of the feats the same evening by themselves, and almost all the rest -when they had provided the proper apparatus. Dr. Desaguliers exhibited -some of the experiments before the Royal Society, and has given such a -distinct explanation of the principles on which they depend, that we -shall endeavour to give a popular account of them. - -[Illustration: _Fig. 52._] - -1. The performer sat upon an inclined board A B, placed upon a frame -C D E, with his feet abutting against the upright board C. Round his -loins was placed a strong girdle F G, to the iron ring of which at G -was fastened a rope by means of a hook. The rope passed between his -legs through a hole in the board C, and several men or two horses, -pulling at the other end of the rope, were unable to draw the -performer out of his place. His hands at G seemed to pull against the -men, but they were of no advantage to him whatever. - -[Illustration: _Fig. 53._] - -2. Another of the German’s feats is shown in Fig. 53. Having fixed the -rope above-mentioned to a strong post at A, and made it pass through -a fixed iron eye at B, to the ring in his girdle, he planted his feet -against the post at B, and raised himself from the ground by the rope, -as shown in the figure. He then suddenly stretched out his legs, and -broke the rope, falling back on a feather-bed at C, spread out to -receive him. - -3. In imitation of Firmus, he laid himself down on the ground, as shown -in Fig. 54, and when an anvil A was placed upon his breast, a man -hammered with all his force the piece of iron B, with a sledge hammer; -and sometimes two smiths cut in two with chisels a great cold bar of -iron laid upon the anvil. At other times a stone of huge dimensions, -half of which is shown at C, was laid upon his belly, and broken with a -blow of the great hammer. - -[Illustration: _Fig. 54._] - -4. The performer then placed his shoulders upon one chair and his -heels upon another, as in Fig. 55, forming, with his backbone, thighs, -and legs, an arch springing from its abutments at A and B. One or two -men then stood upon his belly, rising up and down while the performer -breathed. A stone, one and a half feet long, one foot broad, and -half a foot thick, was then laid upon his belly, and broken by a -sledge-hammer; an operation which may be performed with much less -danger than when his back touched the ground, as in Fig. 54. - -[Illustration: _Fig. 55._] - -5. His next feat was to lie down on the ground, as in Fig. 56; a man -being then placed on his knees, he draws his heels towards his body, -and, raising his knees, he lifts up the man gradually, till having -brought his knees perpendicularly under him, as in Fig. 57, he raises -his own body up, and placing his arms round the man’s legs, he rises -with him, and sets him down on some low table or eminence of the same -height as his knees. This feat he sometimes performed with two men in -place of one. - -[Illustration: _Fig. 56._] - -[Illustration: _Fig. 57._] - -6. The last and apparently the most wonderful performance of the German -is shown in Fig. 58, where he appears to raise a cannon A placed upon -a scale, the four ropes of the scale being fixed to a rope or chain -attached to his girdle in the manner already described. Previous to the -fixing of the ropes, the cannon and scale rest upon two rollers B, C; -but when all is ready, the two rollers are knocked from beneath the -scale, and the cannon is sustained by the strength of his loins. - -[Illustration: _Fig. 58._] - -The German also exhibited his strength in twisting into a screw a flat -piece of iron like A, Fig. 59. He first bent the iron into a right -angle as at B, and then wrapping his handkerchief about its broad upper -end, he held that end in his left hand, and with his right applied to -the other end, twisted about the angular point, as shown at C. Lord -Tullibardine succeeded in doing the same thing, and even untwisted one -of the irons which the German had twisted. - -[Illustration: _Fig. 59._] - -It would lead into details by no means popular were I to give a minute -explanation of the mechanical principles upon which these feats depend. -A few general observations will perhaps be sufficient for ordinary -readers. The feats Nos. 1, 2, and 6, depend entirely on the natural -strength of the bones of the pelvis, which form a double arch, which -it would require an immense force to break, by any external pressure -directed to the centre of the arch; and as the legs and thighs are -capable of sustaining four or five thousand pounds when they stand -quite upright, the performer has no difficulty in resisting the force -of two horses, or of sustaining the weight of a cannon weighing two or -three thousand pounds. - -The feat of the anvil is certainly a very surprising one. The -difficulty, however, really consists in sustaining the anvil, for when -this is done, the effect of the hammering is nothing. If the anvil -were a thin piece of iron, or even two or three times heavier than the -hammer, the performer would be killed by a few blows; but the blows -are scarcely felt when the anvil is very heavy, for the more matter -the anvil has, the greater is its inertia, and it is the less liable -to be struck out of its place; for when it has received by the blow -the whole momentum of the hammer, its velocity will be so much less -than that of the hammer, as its quantity of matter is greater. When the -blow, indeed, is struck, the man feels less of the weight of the anvil -than he did before, because in the reaction of the stone all the parts -of it round about the hammer rise towards the blow. This property is -illustrated by the well-known experiment of laying a stick with its -ends upon two drinking-glasses full of water, and striking the stick -downwards in the middle with an iron bar. The stick will in this case -be broken without breaking the glasses or spilling the water. But if -the stick is struck upwards, as if to throw it up in the air, the -glasses will break if the blow be strong, and if the blow is not very -quick, the water will be spilt without breaking the glasses. - -When the performer supports a man upon his belly as in Fig. 55, he does -it by means of the strong arch formed by his backbone, and the bones of -his legs and thighs. If there were room for them, he could bear three -or four, or, in their stead, a great stone to be broken with one blow. - -A number of feats of real and extraordinary strength were exhibited, -about a century ago, in London, by Thomas Topham, who was five feet -ten inches high, and about thirty-one years of age. He was entirely -ignorant of any of the methods for making his strength appear more -surprising, and he often performed by his own natural powers what he -learned had been done by others by artificial means. A distressing -example of this occurred in his attempt to imitate the feat of the -German Samson, by pulling against horses. Ignorant of the method which -we have already described, he seated himself on the ground with his -feet against two stirrups, and by the weight of his body he succeeded -in pulling against a single horse; but in attempting to pull against -two horses, he was lifted out of his place, and one of his knees was -shattered against the stirrups, so as to deprive him of most of the -strength of one of his legs. The following are the feats of real -strength which Dr. Desaguliers saw him perform:-- - -1. Having rubbed his fingers with coal-ashes to keep them from -slipping, he rolled up a very strong and large pewter plate. - -2. Having laid seven or eight short and strong pieces of tobacco-pipe -on the first and third finger, he broke them by the force of his middle -finger. - -3. He broke the bowl of a strong tobacco-pipe placed between his first -and third finger, by pressing his fingers together sideways. - -4. Having thrust such another bowl under his garter, his legs being -bent, he broke it to pieces by the tendons of his hams without altering -the bending of his leg. - -5. He lifted with his teeth, and held in a horizontal position for a -considerable time, a table six feet long, with half a hundred weight -hanging at the end of it. The feet of the table rested against his -knees. - -6. Holding in his right hand an iron kitchen poker three feet long and -three inches round, he struck upon his bare left arm, between the elbow -and the wrist, till he bent the poker nearly to a right angle. - -7. Taking a similar poker and holding the ends of it in his hands, and -the middle against the back of his neck, he brought both ends of it -together before him, and he then pulled it almost straight again. This -last feat was the most difficult, because the muscles which separate -the arms horizontally from each other are not so strong as those which -bring them together. - -8. He broke a rope about two inches in circumference, which was partly -wound about a cylinder four inches in diameter, having fastened the -other end of it to straps that went over his shoulder. - -9. Dr. Desaguliers saw him lift a rolling-stone of about 800lb. weight -with his hands only, standing in a frame above it, and taking hold -of a frame fastened to it. Hence Dr. Desaguliers gives the following -relative view of the strengths of individuals:-- - - Strength of the weakest men 125lbs. - Strength of very strong men 400 - Strength of Topham 800 - -The weight of Topham was about 200. - -One of the most remarkable and inexplicable experiments relative to the -strength of the human frame, which you have yourself seen and admired, -is that in which a heavy man is raised with the greatest facility, when -he is lifted up the instant that his own lungs and those of the persons -who raise him are inflated with air. This experiment was, I believe, -first shown in England a few years ago by Major H. who saw it performed -in a large party at Venice, under the direction of an officer of the -American Navy. As Major H. performed it more than once in my presence, -I shall describe as nearly as possible the method which he prescribed. -The heaviest person in the party lies down upon two chairs, his legs -being supported by the one and his back by the other. Four persons, -one at each leg and one at each shoulder, then try to raise him, and -they find his dead weight to be very great, from the difficulty they -experience in supporting him. When he is replaced in the chair, each -of the four persons takes hold of the body as before, and the person -to be lifted gives two signals by clapping his hands. At the first -signal he himself and the four lifters begin to draw a long and full -breath, and when the inhalation is completed, or the lungs filled, -the second signal is given for raising the person from the chair. To -his own surprise and that of his bearers, he rises with the greatest -facility, as if he were no heavier than a feather. On several occasions -I have observed that when one of the bearers performs his part ill, -by making the inhalation out of time, the part of the body which he -tries to raise is left as it were behind. As you have repeatedly seen -this experiment, and have performed the part both of the load and of -the bearer, you can testify how remarkable the effects appear to all -parties, and how complete is the conviction, either that the load has -been lightened, or the bearer strengthened by the prescribed process. - -At Venice, the experiment was performed in a much more imposing -manner. The heaviest man in the party was raised and sustained upon -the points of the fore-fingers of six persons. Major H. declared that -the experiment would not succeed if the person lifted were placed upon -a board, and the strength of the individuals applied to the board. He -conceived it necessary that the bearers should communicate directly -with the body to be raised. I have not had an opportunity of making any -experiments relative to these curious facts; but whether the general -effect is an illusion, or the result of known or of new principles, the -subject merits a careful investigation. - -Among the remarkable exhibitions of mechanical strength and dexterity, -we may enumerate that of supporting pyramids of men. This exhibition -is a very ancient one. It is described, though not very clearly, by -the Roman poet Claudian, and it has derived some importance in modern -times, in consequence of its having been performed in various parts of -Great Britain by the celebrated traveller Belzoni, before he entered -upon the more estimable career of an explorer of Egyptian antiquities. -The simplest form of this feat consists in placing a number of men on -each other’s shoulders, so that each row consists of a man fewer till -they form a pyramid terminating in a single person, upon whose head a -boy is sometimes placed with his feet upwards. - -Among the displays of mechanical dexterity, though not grounded on any -scientific principle, may be mentioned the art of walking along the -ceiling of an apartment with the head downwards. This exhibition, -which we have witnessed in one of the London Theatres, never failed -to excite the wonder of the audience, although the movements of the -inverted performer were not such as to inspire us with any high -ideas of the mechanism by which they were effected. The following -was probably the method by which the performer was carried along the -ceiling. Two parallel grooves or openings were made in the ceiling at -the same distance as the foot-tracks of a person walking on sand. These -grooves were narrower than the human foot, so as to permit a rope, -or chain, or strong wire, attached to the feet of the performer, to -pass through the ceiling, where they were held by two or more persons -above it. In this way the inverted performer might be carried along -by a sliding or shuffling motion, similar to that which is adopted in -walking in the dark, and in which the feet are lifted from the ground. -A more regular motion, however, might be produced by a contrivance for -attaching the rope or chain to the sole of the foot, at each step, and -subsequently detaching it. In this way, when the performer is pulled -against the ceiling by his left foot, he would lift his right foot, -and having made a step with it, and planted it against the grooves, -the rope would be attached to it, and when the rope was detached from -the left foot, it would make a similar step, while the right foot was -pulled against the ceiling. These effects might be facilitated and -rendered more natural, by attaching to the body or to the feet of -the performer strong wires invisible to the audience, and by using -friction-wheels, if a sliding motion only is required. - -[Illustration: _Fig. 60._] - -A more scientific method of walking upon the ceiling is suggested by -those beautiful pneumatic contrivances by which insects, fishes, and -even some lizards are enabled to support the weight of their bodies -against the force of gravity. The house-fly is well known to have the -power of walking in an inverted position upon the ceilings of rooms, -as well as upon the smoothest surfaces. In this case the fly does not -rest upon its legs, and must therefore adhere to the ceiling, either by -some glutinous matter upon its feet, or by the aid of some apparatus -given it for that purpose. In examining the foot of the fly with a -powerful microscope, it is found to consist of two concavities, as -shown in Figs. 60 and 61, the first of which is copied from a drawing -by G. Adams, published in 1746, and the second by J. C. Keller, a -painter at Nuremberg, who drew it for a work published in 1766. The -author of this work maintains that these concavities are only used when -the fly moves horizontally, and that, when it moves perpendicularly or -on the ceiling, they are turned up out of the way, and the progressive -motion is effected by fixing the claws shown in the figure into the -irregularities of the surface upon which the fly moves, whether it is -glass, porcelain, or any other substance. Sir Everard Home, however, -supposes, with great reason, that these concave surfaces are (like -the leathern suckers used by children for lifting stones) employed to -form a vacuum, so that the foot adheres, as it were, by suction to -the ceiling, and enables the insect to support itself in an inverted -position. - -[Illustration: _Fig. 61._] - -This conclusion Sir Everard has been led to draw from an examination -of the foot of the Lacerta Gecko. Sir Joseph Banks had mentioned to him -in the year 1815, that this lizard, which is a native of the island of -Java, comes out in the evening from the roofs of the houses, and walks -down the smooth hard-polished chunam walls in search of the flies which -settle upon them, and which are its natural food. When Sir Joseph was -at Batavia, he amused himself in catching this lizard. He stood close -to the wall at some distance from the animal, and by suddenly scraping -the wall with a long flattened pole, he was able to bring the animal to -the ground. - -Having procured from Sir Joseph a very large specimen of the Gecko, -which weighed 5¾ ounces avoirdupois, Sir Everard Home was enabled -to ascertain the peculiar mechanism by which the feet of this animal -have the power of keeping hold of a smooth hard perpendicular wall, and -carry up so heavy a weight as that of its body. - -[Illustration: _Fig. 62._] - -[Illustration: _Fig. 63._] - -The foot of the Gecko has five toes (as shown in Fig. 62), and at -the end of each of them, except the thumb, is a very sharp and -highly-curved claw. On the under surface of each toe are sixteen -transverse slits, leading to as many cavities or pockets, the depth of -which is nearly equal to the length of the slit that forms the surface. - -[Illustration: _Fig. 64._] - -This structure is shown in Figs. 63 and 64, the former representing the -under surface of one of the toes of the natural size, and the latter -a toe dissected and highly magnified, to show the appearance of the -cavities in its under surface, their fringed edge, the depth of the -cavities, and the small muscles by which they are drawn open. The edge -of the pockets or cavities is composed of rows of a beautiful fringe -which are applied to the surface on which the animal walks against -gravity, while the pockets themselves are pulled up by the muscles -attached to them, so as to form the cavities into suckers. - -This structure Sir Everard Home found to bear a considerable -resemblance to that portion of the head of the _Echineis Remora_, or -sucking-fish, by which it attaches itself to the shark, or the bottoms -of ships. This apparatus is shown in Fig. 65: it is an oval form, and -is surrounded by a broad loose moveable edge, capable of applying -itself closely to the surface on which it is set. It consists of two -rows of cartilaginous plates connected by one edge to the surface on -which they are placed, the other, on the external edge, being serrated -like that in the cavities of the feet of the Gecko. The two rows are -separated by a thin ligamentous partition, and the plates, being raised -or depressed by the voluntary muscles, form so many vacua, by means of -which the adhesion of the fish is effected. - -[Illustration: _Fig. 65._] - -These beautiful contrivances of Divine Wisdom cannot fail to arrest the -attention and excite the admiration of the reader; but though there -can be little doubt that they are pneumatic suckers wrought by the -voluntary muscles of the animals to which they belong, yet we would -recommend the further examination of them to the attention of those who -have good microscopes at their command. - - - - -LETTER XI. - - Mechanical automata of the ancients--Moving tripods--Automata - of Dædalus--Wooden pigeon of Archytas--Automatic clock of - Charlemagne--Automata made by Turrianus for Charles V.--Camus’s - automatic carriage made for Louis XIV.--Degenne’s mechanical - peacock--Vaucanson’s duck which ate and digested its food--Du - Moulin’s automata--Baron Kempelen’s automaton chess-player--Drawing - and writing automata--Maillardet’s conjurer--Benefits derived from - the passion for automata--Examples of wonderful machinery for useful - purposes--Duncan’s tambouring machinery--Watt’s statue-turning - machinery--Babbage’s calculating machinery. - - -We have already seen that the ancients had attained some degree of -perfection in the construction of automata, or pieces of mechanism -which imitated the movements of man and the lower animals. The tripods, -which Homer[31] mentions as having been constructed by Vulcan for the -banqueting-hall of the gods, advanced of their own accord to the table, -and again returned to their place. Self-moving tripods are mentioned by -Aristotle; and Philostratus informs us, in his life of Apollonius, that -this philosopher saw and admired similar pieces of mechanism among the -sages of India. - - [31] Iliad, lib. xviii., 373-378. - -Dædalus enjoys also the reputation of having constructed machines that -imitated the motions of the human body. Some of his statues are said -to have moved about spontaneously; and Plato, Aristotle, and others -have related that it was necessary to tie them, in order to prevent -them from running away. Aristotle speaks of a wooden Venus, which moved -about in consequence of quicksilver being poured into its interior; but -Callistratus, the tutor of Demosthenes, states, with some probability, -that the statues of Dædalus received their motion from the mechanical -powers. Beckmann is of opinion that the statues of Dædalus differed -only from those of the early Greeks and Egyptians in having their eyes -open and their feet and hands free, and that the reclining posture of -some, and the attitude of others, “as if ready to walk,” gave rise to -the exaggeration that they possessed the power of locomotion. This -opinion, however, cannot be maintained with any show of reason; for if -we apply such a principle in one case, we must apply it in all, and -the mind would be left in a state of utter scepticism respecting the -inventions of ancient times. - -We are informed by Aulus Gellius, on the authority of Favorinus, -that Archytas of Tarentum, who flourished about four hundred years -before Christ, constructed a wooden pigeon that was capable of flying. -Favorinus relates that, when it had once alighted, it could not again -resume its flight; and Aulus Gellius adds, that it was suspended by -balancing, and animated by a concealed aura, or spirit. - -Among the earliest pieces of modern mechanism was the curious -water-clock presented to Charlemagne by the Kaliph Haroun al Raschid. -In the dial-plate there were twelve small windows corresponding with -the divisions of the hours. The hours were indicated by the opening of -the windows, which let out little metallic balls, which struck the hour -by falling upon a brazen bell. The doors continued open till twelve -o’clock, when twelve little knights, mounted on horseback, came out -at the same instant, and after parading round the dial, shut all the -windows and returned to their apartments.[32] - - [32] Annales Loisiliani, anno 807. - -The next automata of which any distinct account has been preserved -are those of the celebrated John Muller, Regiomontanus, which have -been mentioned by Kircher, Baptista Porta, Gassendi, Lana, and Bishop -Wilkins. This philosopher is said to have constructed an artificial -eagle, which flew to meet the Emperor Maximilian when he arrived at -Nuremberg on the 7th June, 1740. After soaring aloft in the air, the -eagle is stated to have met the Emperor at some distance from the city, -and to have returned and perched upon the town gate, where it waited -his approach. When the Emperor reached the gate, the eagle stretched -out its wings, and saluted him by an inclination of its body. Muller -is likewise reported to have constructed an iron fly which was put -in motion by wheel-work, and which flew about and leapt upon the -table. At an entertainment given by this philosopher to some of his -familiar friends, the fly flew from his hand, and after performing a -considerable round, it returned again to the hand of its master. - -The Emperor Charles V., after his abdication of the throne, amused -himself in his later years with automata of various kinds. The artist -whom he employed was Janellus Turrianus of Cremona. It was his custom -after dinner to introduce upon the table figures of armed men and -horses. Some of these beat drums, others played upon flutes, while a -third set attacked each other with spears. Sometimes he let fly wooden -sparrows, which flew back again to their nest. He also exhibited -corn-mills so extremely small that they could be concealed in a glove, -yet so powerful that they could grind in a day as much corn as would -supply eight men with food for a day. - -The next piece of mechanism of sufficient interest to merit our -attention is that which was made by M. Camus, for the amusement of -Louis XIV. when a child. It consisted of a small coach, which was drawn -by two horses, and which contained the figure of a lady within, with a -footman and page behind. When this machine was placed at the extremity -of a table of the proper size, the coachman smacked his whip, and the -horses instantly set off, moving their legs in a natural manner, and -drawing the coach after them: when the coach reached the opposite edge -of the table, it turned sharply at a right angle, and proceeded along -the adjacent edge. As soon as it arrived opposite the place where the -king sat, it stopped; the page descended and opened the coach-door; the -lady alighted, and with a curtsey presented a petition, which she held -in her hand to the king. After waiting some time she again curtsied and -re-entered the carriage. The page closed the door, and having resumed -his place behind, the coachman whipped his horses and drove on. The -footman, who had previously alighted, ran after the carriage and jumped -up behind into his former place. - -Not content with imitating the movements of animals, the mechanical -genius of the 17th and 18th centuries ventured to perform by wheels -and pinions the functions of vitality. We are informed by M. Lobat, -that Gen. Degennes, a French officer who defended the colony of St. -Christopher’s against the English forces, constructed a peacock which -could walk about as if alive, pick up grains of corn from the ground, -digest them as if they had been submitted to the action of the stomach, -and afterwards discharged them in an altered form. Degennes is said to -have invented various machines of great use in navigation and gunnery, -and to have constructed clocks without weights or springs. - -The automaton of Degennes probably suggested to M. Vaucanson the idea -of constructing his celebrated duck, which excited so much interest -throughout Europe, and which was perhaps the most wonderful piece of -mechanism that was ever made. Vaucanson’s duck exactly resembled the -living animal in size and appearance. It executed accurately all its -movements and gestures, it ate and drank with avidity, performed all -the quick motions of the head and throat which are peculiar to the -living animal, and, like it, it muddled the water which it drank with -its bill. It produced also the sound of quacking in the most natural -manner. In the anatomical structure of the duck, the artist exhibited -the highest skill. Every bone in the real duck had its representative -in the automaton, and its wings were anatomically exact. Every cavity, -apophysis, and curvature was imitated, and each bone executed its -proper movements. When corn was thrown down before it, the duck -stretched out its neck to pick it up, it swallowed it, digested it, and -discharged it in a digested condition. The process of digestion was -effected by chemical solution, and not by trituration, and the food -digested in the stomach was conveyed away by tubes to the place of its -discharge. - -The automata of Vaucanson were imitated by one Du Moulin, a -silversmith, who travelled with them through Germany in 1752, and who -died at Moscow in 1765. Beckmann informs us that he saw several of them -after the machinery had been deranged; but that the artificial duck, -which he regarded as the most ingenious, was still able to eat, drink, -and move. Its ribs, which were made of wire, were covered with duck’s -feathers, and the motion was communicated through the feet of the duck -by means of a cylinder and fine chains like that of a watch. - -[Illustration: _Fig. 66._] - -[Illustration: _Fig. 67._] - -Ingenious as all these machines are, they sink into insignificance -when compared with the automaton chess-player, which for a long time -astonished and delighted the whole of Europe. In the year 1769, M. -Kempelen, a gentleman of Presburg in Hungary, constructed an automaton -chess-player, the general appearance of which is shown in the annexed -figures. The chess-player is a figure as large as life, clothed in a -Turkish dress, sitting behind a large square chest or box, three feet -and a half long, two feet deep, and two and a half high. The machine -runs on castors, and is either seen on the floor when the doors of the -apartment are thrown open, or is wheeled into the room previously to -the commencement of the exhibition. The Turkish chess-player sits on a -chair fixed to the square chest: his right arm rests on the table, and -in the left he holds a pipe, which is removed during the game, as it is -with this hand that he makes the moves. A chess-board, eighteen inches -square, and bearing the usual number of pieces, is placed before the -figure. The exhibitor then announces to the spectators his intention -of showing them the mechanism of the automaton. For this purpose he -unlocks the door A, Fig. 66, and exposes to view a small cupboard lined -with black or dark-coloured cloth, and containing cylinders, levers, -wheels, pinions, and different pieces of machinery, which _have the -appearance_ of occupying the whole space. He next opens the door B, -Fig. 67, at the back of the same cupboard, and holding a lighted candle -at the opening, he still further displays the inclosed machinery to -the spectators, placed in front of A, Fig. 66. When the candle is -withdrawn, the door B is then locked; and the exhibitor proceeds to -open the drawer G G, Fig. 66, in front of the chest. Out of this drawer -he takes a small box of counters, a set of chess-men, and a cushion for -the support of the automaton’s arm, as if this was the sole object of -the drawer. The two front doors C C, of the large cupboard, Fig. 66, -are then opened, and at the back-door D of the same cupboard, Fig. 67, -the exhibitor applies a lighted candle, as before, for the purpose of -showing its interior, which is lined with dark cloth like the other, -and contains only a few pieces of machinery. The chest is now wheeled -round, as in Fig. 67: the garments of the figure are lifted up, and the -door E in the trunk, and another door F in the thigh, are opened, the -doors B and D having been previously closed. When this exhibition of -the interior of the machine is over, the chest is wheeled back into its -original position on the floor. The doors A, C, C, in front, and the -drawer G, G, are closed and locked, and the exhibitor, after occupying -himself for some time at the back of the chest, as if he were adjusting -the mechanism, removes the pipe from the hand of the figure, and winds -up the machinery. - -The automaton is now ready to play, and when an opponent has been found -among the company, the figure takes the first move. At every move -made by the automaton, the wheels of the machine are heard in action; -the figure moves its head, and seems to look over every part of the -chess-board. When it gives check to its opponent, it shakes its head -_thrice_, and only _twice_ when it checks the queen. It likewise shakes -its head when a false move is made, replaces the adversary’s piece on -the square from which it was taken, and takes the next move itself. In -general, though not always, the automaton wins the game. - -During the progress of the game, the exhibitor often stands near the -machine, and winds it up like a clock, after it has made ten or twelve -moves. At other times he went to a corner of the room, as if it were to -consult a small square box, which stood open for this purpose. - -The chess-playing machine, as thus described, was exhibited after its -completion in Presburg, Vienna, and Paris, to thousands, and in 1783 -and 1784 it was exhibited in London and different parts of England, -without the secret of its movements having been discovered. Its -ingenious inventor, who was a gentleman and a man of education, never -pretended that the automaton itself really played the game. On the -contrary, he distinctly stated, “that the machine was a _bagatelle_, -which was not without merit in point of mechanism, but that the effects -of it appeared so marvellous only from the boldness of the conception, -and the fortunate choice of the methods adopted for promoting the -illusion.” - -Upon considering the operations of this automaton, it must have been -obvious that the game of chess was performed either by a person -enclosed in the chest, or by the exhibitor himself. The first of these -hypotheses was ingeniously excluded by the display of the interior -of the machine, for as every part contained more or less machinery, -the spectator invariably concluded that the smallest dwarf could -not be accommodated within, and this idea was strengthened by the -circumstance, that no person of this description could be discovered -in the suite of the exhibitor. Hence the conclusion was drawn, -that the exhibitor actuated the machine either by mechanical means -conveyed through its feet, or by a magnet concealed in the body of -the exhibitor. That mechanical communication was not formed between -the exhibitor and the figure, was obvious from the fact, that no such -communication was visible, and that it was not necessary to place the -machine on any particular part of the floor. Hence the opinion became -very prevalent that the agent was a magnet; but even this supposition -was excluded, for the exhibitor allowed a strong and well-armed -loadstone to be placed upon the machine during the progress of the -game. Had the moving power been a magnet, the whole action of the -machine would have been deranged by the approximation of a loadstone -concealed in the pockets of any of the spectators. - -As Baron Kempelen himself had admitted that there was an illusion -connected with the performance of the automaton, various persons -resumed the original conjecture, that it was actuated by a person -concealed in its interior, who either played the game of chess himself, -or performed the moves which the exhibitor indicated by signals. A Mr. -J. F. Freyhere, of Dresden, published a book on the subject in 1789, -in which he endeavoured to explain, by coloured plates, how the effect -was produced; and he concluded, “that a well-taught boy very thin and -tall of his age (sufficiently so that he could be concealed in a drawer -almost immediately under the chess-board), agitated the whole.” - -In another pamphlet, which had been previously published at Paris in -1785, the author not only supposed that the machine was put in motion -by a dwarf, a famous chess-player; but he goes so far as to explain -the manner in which he could be accommodated within the machine. The -invisibility of the dwarf when the doors were opened was explained by -his legs and thighs being concealed in two hollow cylinders, while the -rest of his body was out of the box, and hid by the petticoats of the -automaton. When the doors were shut, the clacks produced by the swivel -of a ratchet-wheel permitted the dwarf to change his place, and return -to the box unheard; and while the machine is wheeled about the room, -the dwarf had an opportunity of shutting the trap through which he -passed into the machine. The interior of the figure was next shown, and -the spectators were satisfied that the box contained no living agent. - -Although these views were very plausible, yet they were never generally -adopted; and when the automaton was exhibited in Great Britain in 1819 -and 1820, by M. Maelzel, it excited as intense an interest as when it -was first produced in Germany. There can be little doubt, however, -that the secret has been discovered; and an anonymous writer has -shown in a pamphlet, entitled “_An attempt to analyse the Automaton -Chess-player of_ M. Kempelen,” that it is capable of accommodating an -ordinary sized man; and he has explained in the clearest manner how the -inclosed player takes all the different positions, and performs all the -motions which are necessary to produce the effects actually observed. -The following is the substance of his observations:--The drawer G G -when closed does not extend to the back of the chest, but leaves a -space O, behind it (see Figs. 74, 75, and 76), fourteen inches broad, -eight inches high, and three feet eleven inches long. This space is -never exposed to the view of spectators. The small cupboard seen at A -is divided into two parts, by a door or screen I, Fig. 73, which is -moveable upon a hinge, and is so constructed that it closes at the same -instant that B is closed. The whole of the front compartment as far as -I is occupied with the machinery H. The other compartment behind I is -empty, and communicates with the space O behind the drawer, the floor -of this division being removed. The back of the great cupboard C C is -double, and the part P Q, to which the quadrants are attached, moves -on a joint Q, at the upper part, and forms when raised an opening S, -between the two cupboards, by carrying with it part of the partition -R, which consists of cloth tightly stretched. The false back is shown -closed in Fig. 74, while Fig. 75 shows the same back raised, so as to -form the opening S between the chambers. - -When the spectator is allowed to look into the trunk of the figure by -lifting up the dress, as in Fig. 75, it will be observed that a great -part of the space is occupied by an inner trunk N, Figs. 75, 76, which -passes off to the back in the form of an arch, and conceals from the -spectators a portion of the interior. This inner trunk N opens and -communicates with the chest by an aperture T, Fig. 77, about twelve -inches broad and fifteen high. When the false back is raised, the two -cupboards, the trunk N, and the space O behind the drawer, are all -connected together. - -[Illustration: No. 68.] - -[Illustration: No. 69.] - -The construction of the interior being thus understood, the -chess-player may be introduced into the chest through the sliding panel -U, Fig. 74. He will then raise the false back of the large cupboard, -and assume the position represented by the shaded figure in Figs. 68 -and 69. Things being in this state, the exhibitor is ready to begin his -process of deception. He first opens the door A of the small cupboard, -and from the crowded and very ingenious disposition of the machinery -within it, the eye is unable to penetrate far beyond the opening, and -the spectator concludes, without any hesitation, that the whole of the -cupboard is filled, as it appears to be, with similar machinery. This -false conclusion is greatly corroborated by observing the glimmering -light which plays among the wheel-work when the door B is opened, and a -candle held at the opening. This mode of exhibiting the interior of the -cupboard satisfies the spectator also, that no opaque body, capable of -holding or concealing any of the parts of a hidden agent, is interposed -between the light and the observer. The door B is now locked and the -screen I closed, and as this is done at the time that the light is -withdrawn, it will wholly escape observation. - -The door B is so constructed as to close by its own weight, but as the -head of the chess-player will soon be placed very near it, the secret -would be disclosed if, in turning round, the chest door should by any -accident fly open. This accident is prevented by turning the key, and, -lest this little circumstance should excite notice, it would probably -be regarded as accidental, as the keys were immediately wanted for the -other locks. - -As soon as the door B is locked, and the screen I closed, the secret -is no longer exposed to hazard, and the exhibitor proceeds to lead -the minds of the spectators still farther from the real state of -things. The door A is left open to confirm the opinion that no person -is concealed within, and that nothing can take place in the interior -without being observed. - -[Illustration: _Fig. 70._] - -The drawer GG is now opened, apparently for the purpose of looking -at the chess-men, cushion, and counters, which it contains; but -the real object of it is to give time to the player to change his -position, as shown in the annexed figure, and to replace the false -back and partition preparatory to the opening of the great cupboard. -The chess-player, as the figure shows, occupies with his body the -back compartment of the small cupboard, while his legs and thighs -are contained in the space O, behind the drawer GG, his body being -concealed by the screen I, and his limbs by the drawer GG. - -The great cupboard CC is now opened, and there is so little machinery -in it, that the eye instantly discovers that no person is concealed in -it. To make this more certain, however, a door is opened at the back, -and a lighted candle held to it, to allow the spectators to explore -every corner and recess. - -The front doors of the great and small cupboard being left open, -the chest is wheeled round to show the trunk of the figure, and the -bunch of keys is allowed to remain in the door D, as the apparent -carelessness of such a proceeding will help to remove any suspicion -which may have been excited by the locking of the door B. - -When the drapery of the figure has been raised, and the doors E and F -in the trunk and thigh opened, the chest is wheeled round again into -its original position, and the doors E and F closed. In the mean time -the player withdraws his legs from behind the drawer, as he cannot so -easily do this when the drawer GG is pushed in. - -In all these operations, the spectator flatters himself that he has -seen in succession every part of the chest, while in reality some parts -have been wholly concealed from his view, and others but imperfectly -shown, while at the present time nearly half of the chest is excluded -from view. - -[Illustration: No. 71.] - -[Illustration: No. 72.] - -When the drawer G G is pushed in, and the doors A and C closed, the -exhibitor adjusts the machinery at the back, in order to give time -to the player to take the position shown in a front view in Fig. 71, -and in profile in Fig. 72. In this position he will experience no -difficulty in executing every movement made by the automaton. As his -head is above the chess-board, he will see through the waistcoat of the -figure, as easily as through a veil, the whole of the pieces on the -board, and he can easily take up and put down a chess-man without any -other mechanism than that of a string communicating with the finger of -the figure. His right hand, being within the chest, may be employed to -keep in motion the wheel-work for producing the noise which is heard -during the moves, and to perform the other movements of the figure, -such as that of moving the head, tapping on the chest, &c. - -A very ingenious contrivance is adopted to facilitate the introduction -of the player’s left arm into the arm of the figure. To permit this, -the arm of the figure requires to be drawn backwards; and for the -purpose of concealing, and at the same time explaining this strained -attitude, a pipe is ingeniously placed in the automaton’s hand. For -this reason the pipe is not removed till all the other arrangements are -completed. When every thing has been thus prepared, the pipe is taken -from the figure, and the exhibitor winds up, as it were, the inclosed -machinery, for the double purpose of impressing upon the company the -belief that the effect is produced by machinery, and of giving a signal -to the player to put in motion the head of the automaton. - -[Illustration: _Fig. 73._] - -[Illustration: _Fig. 74._] - -This ingenious explanation of the chess automaton is, our author -states, greatly confirmed by the _regular and undeviating_ mode of -disclosing the interior of the chest; and he also shows that the facts -which have been observed respecting the winding up of the machine, -“afford positive proof that the axis turned by the key is quite free -and unconnected either with a spring or weight, or any system of -machinery.” - -In order to make the preceding description more intelligible, I shall -add the following more detailed explanation of the figures. - -Fig. 66 is a perspective view of the automaton seen in front with all -the doors thrown open. - -Fig. 67 is an elevation of the automaton, as seen from behind. - -Fig. 68 is an elevation of the front of the chest, the shaded figure -representing the inclosed player in his first position, or when the -door A is opened. - -Fig. 69 is a side elevation, the shaded figure representing the player -in the same position. - -Fig. 70 is a front elevation, the shaded figure showing the player in -his second position, or that which he takes after the door B and screen -I are closed, and the great cupboard opened. - -Fig. 71 is a front elevation, the shaded figure showing the player in -his third position, or that in which he plays the game. - -Fig. 72 is a side elevation showing the figure in the same position. - -Fig. 73 is a horizontal section of the chest through the line WW in -Fig. 71. - -Fig. 74 is a vertical section of the chest through the line XX in Fig. -73. - -[Illustration: _Fig. 75._] - -[Illustration: _Fig. 76._] - -Fig. 75 is a vertical section through the line YY Fig. 71, showing the -false back closed. - -Fig. 76 is a similar vertical section showing the false back raised. - -The following letters of reference are employed in all the figures:-- - -A. Front door of the small cupboard. - -B. Back door of ditto. - -C C. Front doors of large cupboard. - -D. Back door of ditto. - -E. Door of ditto. - -F. Door of the thigh. - -G G. The drawer. - -H. Machinery in front of the small cupboard. - -I. Screen behind the machinery. - -K. Opening caused by the removal of part of the floor of the small -cupboard. - -L. A box which serves to conceal an opening in the floor of the large -cupboard, made to facilitate the first position; and which also serves -as a seat for the third position. - -M. A similar box to receive the toes of the player in the first -position. - -N. The inner chest filling up part of the trunk. - -O. The space behind the drawer. - -P Q. The false back turning on a joint at Q. - -R. Part of the partition formed of cloth stretched tight, which is -carried up by the false back to form the opening between the chambers. - -S. The opening between the chambers. - -T. The opening connecting the trunk and chest, which is partly -concealed by the false back. - -U. Panel which is slipt aside to admit the player. - - * * * * * - -Various pieces of mechanism of wonderful ingenuity have been -constructed for the purposes of drawing and writing. One of these, -invented by M. Le Droz, the son of the celebrated Droz of Chaux le -Fonds, has been described by Mr. Collinson. The figure was the size -of life. It held in its hand a metallic style, and when a spring was -touched, so as to release a detent, the figure immediately began to -draw upon a card of Dutch vellum previously laid under its hand. -After the drawing was executed on the first card, the figure rested. -Other five cards were then put in, in succession, and upon these it -delineated in the same manner different subjects. On the first card it -drew “elegant portraits and likenesses of the king and queen facing -each other;” and Mr. Collinson remarks, that it was curious to observe -with what precision the figure lifted up its pencil in its transition -from one point of the drawing to another, without making the slightest -mistake. - -M. Maillardet has executed an automaton which both writes and draws. -The figure of a boy kneeling on one knee holds a pencil in his hand. -When the figure begins to work, an attendant dips the pencil in ink, -and adjusts the drawing-paper upon a brass tablet. Upon touching a -spring, the figure proceeds to write, and when the line is finished, -its hand returns to dot and stroke the letters when necessary. In this -manner it executes four beautiful pieces of writing in French and -English, and three landscapes, all of which occupy about one hour. - -One of the most popular pieces of mechanism which we have seen is the -magician constructed by M. Maillardet for the purpose of answering -certain given questions. A figure dressed like a magician appears -seated at the bottom of a wall, holding a wand in one hand, and a book -in the other. A number of questions ready prepared are inscribed on -oval medallions, and the spectator takes any of these which he chooses, -and to which he wishes an answer, and having placed it in a drawer -ready to receive it, the drawer shuts with a spring till the answer -is returned. The magician then rises from his seat, bows his head, -describes circles with his wand, and, consulting the book as if in deep -thought, he lifts it towards his face. Having thus appeared to ponder -over the proposed question, he raises his wand, and striking with -it the wall above his head, two folding-doors fly open, and display -an appropriate answer to the question. The doors again close, the -magician resumes his original position, and the drawer opens to return -the medallion. There are twenty of these medallions, all containing -different questions, to which the magician returns the most suitable -and striking answers. The medallions are thin plates of brass of an -elliptical form, exactly resembling each other. Some of the medallions -have a question inscribed on each side, both of which the magician -answers in succession. If the drawer is shut without a medallion being -put into it, or if a _blank_ medallion, viz., one which contains no -question, is put into the drawer, the magician rises, consults his -book, shakes his head, and resumes his seat. The folding-doors remain -shut, and the drawer is returned empty. If two medallions are put into -the drawer together, an answer is returned only to the lower one. When -the machinery is wound up, the movements continue about an hour, during -which time about fifty questions may be answered. The method by which -the different medallions acted upon the machinery, so as to produce the -proper answers to the questions which they bore, was of course kept a -secret by the inventor, but it was discovered by Mr. Brockedon, who -has kindly communicated to me an account of it. - -Upon examining the edge of the circular medallions, Mr. Brockedon -discovered in all of them, except the blanks, a small hole almost -concealed by the milling. This led Mr. Brockedon to examine the -receptacle for the medallion in the drawer, and he observed the edge -of a pin flush with the edge of the receptacle, whence the pin was -protruded by the machine into the holes in the medallion, the depth of -the hole regulating the answer. In order to prove this, Mr. B. cut a -slip from a cedar pencil small enough to enter easily the holes in the -medallion, if he found them to be of different depths. As the blank -medallions had no hole, and produced only a shake of the magician’s -head, Mr. B. took a medallion with a question, and having plugged the -hole with a bit of cedar, he cut it flush, and having placed it in the -receptacle, the conjuror shook his head, and thus bore testimony to the -truth of Mr. Brockedon’s discovery. - -M. Maillardet has constructed various other automata, representing -insects and other animals. One of these was a spider entirely made of -steel, which exhibited all the movements of the animal. It ran on the -surface of a table during three minutes, and to prevent it from running -off, its course always tended towards the centre of the table. He -constructed likewise a caterpillar, a lizard, a mouse, and a serpent. -The serpent crawls about in every direction, opens its mouth, hisses, -and darts out its tongue. - -Ingenious and beautiful as all these pieces of mechanism are, and -surprising as their effects appear even to scientific spectators, the -principal object of their inventors was to astonish and amuse the -public. We should form an erroneous judgment, however, if we suppose -that this was the only result of the ingenuity which they displayed. -The passion for automatic exhibitions, which characterized the 18th -century, gave rise to the most ingenious mechanical devices, and -introduced among the higher orders of artists habits of nice and -accurate execution in the formation of the most delicate pieces of -machinery. The same combination of the mechanical powers which made the -spider crawl, or which waved the tiny rod of the magician, contributed -in future years to purposes of higher import. Those wheels and pinions, -which almost eluded our senses by their minuteness, re-appeared in the -stupendous mechanism of our spinning-machines and our steam-engines. -The elements of the tumbling-puppet were revived in the chronometer, -which now conducts our navy through the ocean; and the shapeless wheel -which directed the hand of the drawing automaton has served, in the -present age, to guide the movements of the tambouring engine. Those -mechanical wonders, which in one century enriched only the conjuror -who used them, contributed in another to augment the wealth of the -nation; and those automatic toys, which once amused the vulgar, are now -employed in extending the power and promoting the civilization of our -species. In whatever way, indeed, the power of genius may invent or -combine, and to whatever low or even ludicrous purposes that invention -or combination may be originally applied, society receives a gift which -it can never lose; and though the value of the seed may not be at once -recognized, and though it may lie long unproductive in the ungenial -till of human knowledge, it will some time or other evolve its germ, -and yield to mankind its natural and abundant harvest. - -Did the limits of so popular a volume as this ought to be permit it, I -should have proceeded to give a general description of some of these -extraordinary pieces of machinery, the construction and effects of -which never fail to strike the spectator with surprise. This, however, -would lead me into a field too extensive, and I shall therefore confine -myself to a notice of three very remarkable pieces of mechanism which -are at present very little known to the general reader, viz., the -tambouring machine of Mr. Duncan, the statue-turning machine of Mr. -Watt, and the calculating machinery of Mr. Babbage. - -The tambouring of muslins, or the art of producing upon them ornamental -flowers and figures, has been long known and practised in Britain -as well as in other countries; but it was not long before the year -1790, that it became an object of general manufacture in the west of -Scotland, where it was chiefly carried on. At first it was under the -direction of foreigners; but their aid was not long necessary, and -it speedily extended to such a degree as to occupy, either wholly or -partially, more than 20,000 females. Many of these labourers lived -in the neighbourhood of Glasgow, which was the chief seat of the -manufacture; but others were scattered through every part of Scotland, -and supplied by agents with work and money. In Glasgow, a tambourer -of ordinary skill could not in general earn more than five or six -shillings a week by constant application; but to a labouring artisan, -who had several daughters, even these low wages formed a source of -great wealth. At the age of five years, a child capable of handling a -needle was devoted to tambouring, even though it could not earn more -than a shilling or two in a week; and the consequence of this was, that -female children were taken from school, and rendered totally unfit for -any social or domestic duty. The tambouring population, was, therefore, -of the worst kind, and it must have been regarded as a blessing rather -than as a calamity, when the work which they performed was entrusted to -regular machinery. - -Mr. John Duncan of Glasgow, the inventor of the tambouring machinery, -was one of those unfortunate individuals who benefit their species -without benefiting themselves, and who died in the meridian of life, -the victim of poverty and of national ingratitude. He conceived the -idea of bringing into action a great number of needles at the same -time, in order to shorten the process by manual labour; but he at -first was perplexed about the diversification of the pattern. This -difficulty, however, he soon surmounted by employing two forces at -right angles to each other, which gave him a new force in the direction -of the diagonal of the parallelogram, whose sides were formed by the -original forces. His first machine was very imperfect; but after two -years’ study, he formed a company, at whose expense six improved -machines were put in action, and who secured the invention by a patent. -At this time the idea of rendering the machine automatic had scarcely -occurred to him; but he afterwards succeeded in accomplishing this -great object, and the tambouring machines were placed under the -surveillance of a steam-engine. Another patent was taken for these -improvements. The reader who desires to have a minute account of these -improvements, and of the various parts of the machinery, will be amply -gratified by perusing the inventor’s own account of the machinery -in the article CHAINWORK in the Edinburgh Encyclopædia. At present -it will be sufficient to state, that the muslin to be tamboured was -suspended vertically in a frame, which was capable of being moved both -in a vertical and a horizontal direction. Sixty or more needles lying -horizontally occupied a frame in front of the muslin web. Each of these -working needles, as they are called, was attended by a feeding-needle, -which, by a circular motion round the working-needle, lodged upon the -stem of the latter the loop of the thread. The sixty needles then -penetrated the web, and, in order that they might return again without -injuring the fabric, the barb or eye of the needle, which resembled the -barb of a fishing-hook, was shut by a slider. The muslin web then took -a new position by means of the machinery that gave it its horizontal -and vertical motion, so that the sixty needles penetrated it, at their -next movement, at another point of the figure or flower. This operation -went on till sixty flowers were completed. The web was then slightly -wound up, that the needles might be opposite that part of it on which -they were to work another row of flowers. - -The flowers were generally at an inch distance, and the rows were -placed so that the flowers formed what are called diamonds. There were -seventy-two rows of flowers in a yard, so that in every square yard -there were nearly 4000 flowers, and in every piece of ten yards long -40,000. The number of loops or stitches in a flower varied with the -pattern, but on an average there were about thirty. Hence the number -of stitches in a yard were 120,000, and the number in a piece is -1,200,000. The average work done in a week by one machine was fifteen -yards, or 60,000 flowers, or 1,800,000 stitches; and by comparing this -with the work done by one person with the hand, it appeared that the -machine enabled one person to do the work of twenty-four persons. - -One of the most curious and important applications of machinery -to the arts which has been suggested in modern times, was made by -the late Mr. Watt, in the construction of a machine for copying or -reducing statues and sculpture of all kinds. The art of multiplying -busts and statues, by casts in plaster of Paris, has been the means -of diffusing a knowledge of this branch of the fine arts; but from -the fragile nature of the material, the copies thus produced were -unfit for exposure to the weather, and therefore ill calculated for -ornamenting public buildings, or for perpetuating the memory of public -achievements. A machine, therefore, which is capable of multiplying -the labours of the sculptor in the durable materials of marble or of -brass was a desideratum of the highest value, and one which could -have been expected only from a genius of the first order. During many -years Mr. Watt carried on his labours in secret, and he concealed -even his intention of constructing such a machine. After he had made -considerable progress in its execution, and had thought of securing -his invention by a patent, he learned that an ingenious individual -in his own neighbourhood had been long occupied in the same pursuit; -and Mr. Watt informed me that he had every reason to believe that -this gentleman was entirely ignorant of his labours. A proposal was -then made that the two inventors should combine their talents, and -secure the privilege by a joint patent; but Mr. Watt had experienced -so frequently the fatal operation of our patent laws, that he saw many -difficulties in the way of such an arrangement, and he was unwilling, -at his advanced age, to embark in a project so extensive, and which -seemed to require for its successful prosecution all the ardour and -ambition of a youthful mind. The scheme was therefore abandoned; -and such is the unfortunate operation of our patent laws, that the -circumstance of two individuals having made the same invention has -prevented both from bringing it to perfection, and conferring a great -practical benefit upon their species. The machine which Mr. Watt had -constructed had actually executed some excellent pieces of work. I -have seen in his house at Heathfield copies of basso-relievos, and -complete statues of a small size; and some of his friends have in their -possession other specimens of its performance. - -Of all the machines which have been constructed in modern times, -the calculating-machine is doubtless the most extraordinary. Pieces -of mechanism for performing particular arithmetical operations have -been long ago constructed, but these bear no comparison either in -ingenuity or in magnitude to the grand design conceived and nearly -executed by Mr. Babbage. Great as the power of mechanism is known to -be, yet we venture to say, that many of the most intelligent of our -readers will scarcely admit it to be possible that astronomical and -navigation tables can be accurately computed by machinery; that the -machine can itself correct the errors which it may commit; and that -the results of its calculations, when absolutely free from error, -can be printed off, without the aid of human hands, or the operation -of human intelligence. All this, however, Mr. Babbage’s machine can -do; and as I have had the advantage of seeing it actually calculate, -and of studying its construction with Mr. Babbage himself, I am able -to make the above statement on personal observation. The calculating -machine now constructing under the superintendence of the inventor -has been executed at the expense of the British Government, and is -of course their property. It consists essentially of two parts; a -calculating part, and a printing part, both of which are necessary to -the fulfilment of Mr. Babbage’s views; for the whole advantage would be -lost if the computations made by the machine were copied by human hands -and transferred to types by the common process. The greater part of the -calculating machinery is already constructed, and exhibits workmanship -of such extraordinary skill and beauty, that nothing approaching to it -has been witnessed. In order to execute it, particularly those parts of -the apparatus which are dissimilar to any used in ordinary mechanical -constructions, tools and machinery of great expense and complexity have -been invented and constructed; and in many instances contrivances of -singular ingenuity have been resorted to which cannot fail to prove -extensively useful in various branches of the mechanical arts. - -The drawings of this machinery, which form a large part of the work, -and on which all the contrivance has been bestowed, and all the -alterations made, cover upwards of 400 _square feet of surface_, and -are executed with extraordinary care and precision. - -In so complex a piece of mechanism, in which interrupted motions are -propagated simultaneously along a great variety of trains of mechanism, -it might have been supposed that obstructions would arise, or even -incompatibilities occur, from the impracticability of foreseeing -all the possible combinations of the parts; but this doubt has been -entirely removed, by the constant employment of a system of mechanical -notation invented by Mr. Babbage, which places distinctly in view, at -every instant, the progress of motion through all the parts of this or -any other machine, and by writing down in tables the times required for -all the movements, this method renders it easy to avoid all risk of two -opposite actions arriving at the same instant at any part of the engine. - -In the printing part of the machine less progress has been made in the -actual execution than in the calculating part. The cause of this is -the greater difficulty of its contrivance, not for transferring the -computations from the calculating part to the copper or other plate -destined to receive it, but for giving to the plate itself that number -and variety of movements which the forms adopted in printed tables may -call for in practice. - -The practical object of the calculating engine is to compute and print -a great variety and extent of astronomical and navigation tables, -which could not be done without enormous intellectual and manual -labour, and which, even if executed by such labour, could not be -calculated with the requisite accuracy. Mathematicians, astronomers, -and navigators, do not require to be informed of the real value of such -tables; but it may be proper to state, for the information of others, -that _seventeen_ large folio volumes of logarithmic tables alone were -calculated, at an enormous expense, by the French Government; and that -the British Government regarded these tables to be of such national -value, that they proposed to the French Board of Longitude to print -an _abridgement_ of them at the joint expense of the two nations, and -offered to advance 5000_l._ for that purpose. Besides logarithmic -tables, Mr. Babbage’s machine will calculate tables of the powers -and products of numbers, and all astronomical tables for determining -the positions of the sun, moon, and planets; and the same mechanical -principles have enabled him to integrate innumerable equations of -finite differences, that is, when the equation of differences is given, -he can, by setting an engine, produce at the end of a given time -any distant term which may be required, or any succession of terms -commencing at a distant point. - -Besides the cheapness and celerity with which this machine will perform -its work, the _absolute accuracy_ of the printed results deserves -especial notice. By peculiar contrivances, any small error produced by -accidental dust, or by any slight inaccuracy in one of the wheels, is -corrected as soon as it is transmitted to the next, and this is done -in such a manner as effectually to prevent any accumulation of small -errors from producing an erroneous figure in the result. - -In order to convey some idea of this stupendous undertaking, we may -mention the effects produced by a small trial engine constructed by -the inventor, and by which he computed the following table from the -formula _x^2_ + _x_ + 41. The figures, as they were calculated by the -machine, were not exhibited to the eye as in sliding-rules and similar -instruments, but were actually presented to the eye on two opposite -sites of the machine, the number 383, for example, appearing in figures -before the person employed in copying. - -_Table calculated by a small Trial Engine._ - - 41 131 383 797 1373 - 43 151 421 853 1447 - 47 173 461 911 1523 - 53 197 503 971 1601 - 61 223 547 1033 1681 - 71 251 593 1097 1763 - 83 281 641 1163 1847 - 97 313 691 1231 1933 - 113 347 743 1301 2021 - -While the machine was occupied in calculating this table, a friend of -the inventor undertook to write down the numbers as they appeared. -In consequence of the copyist writing quickly, he rather more than -kept pace with the engine, but as soon as five figures appeared, the -machine was at least equal in speed to the writer. At another trial -_thirty-two_ numbers of the same table were calculated in the space of -_two minutes and thirty seconds_; and as these contained _eighty-two_ -figures, the engine produced thirty-three figures every minute, or -more than one figure in every two seconds. On another occasion it -produced _forty-four_ figures per minute. This rate of computation -could be maintained for any length of time; and it is probable that few -writers are able to copy with equal speed for many hours together. - -Some of that class of individuals who envy all great men, and deny all -great inventions, have ignorantly stated that Mr. Babbage’s invention -is not new. The same persons, had it suited their purpose, would -have maintained that the invention of spectacles was an anticipation -of the telescope; but even this is more true than the allegation -that the arithmetical machines of Pascal and others were the types -of Mr. Babbage’s engine. The object of these machines was entirely -different. Their highest functions were to perform the operations of -common arithmetic. Mr. Babbage’s engine, it is true, can perform these -operations also, and can extract the roots of numbers, and approximate -to the roots of equations, and even to their impossible roots. But -this is not its object. Its function, in contradistinction to that -of all other contrivances for calculating, is to embody in machinery -the method of differences, which has never before been done; and the -effects which it is capable of producing, and the works which in the -course of a few years we expect to see it execute, will place it at an -infinite distance from all other efforts of mechanical genius.[33] - - [33] A popular account of this engine will be found in Mr. Babbage’s - interesting volume _On the Economy of Manufactures_, lately published. - - - - -LETTER XII. - - Wonders of chemistry--Origin, progress, and objects of alchemy--Art - of breathing fire--Employed by Barchochebas, Eunus, &c.--Modern - method--Art of walking upon burning coals and red-hot iron, and of - plunging the hands in melted lead and boiling water--Singular property - of boiling tar--Workmen plunge their hands in melted copper--Trial - of ordeal by fire--Aldini’s incombustible dresses--Examples of their - wonderful power in resisting flame--Power of breathing and enduring - air of high temperatures--Experiments made by Sir Joseph Banks, Sir - Charles Blagden, and Mr. Chantrey. - - -Chemistry has from its infancy been pre-eminently the science of -wonders. In her laboratory the alchemist and the magician have revelled -uncontrolled, and from her treasures was forged the sceptre which was -so long and so fatally wielded over human reason. The changes which -take place in the bodies immediately around us are too few in number -and too remote from observation to excite much of our notice; but when -the substances procured directly from nature, or formed casually by -art, become objects of investigation, they exhibit in their simple or -combined actions the most extraordinary effects. The phenomena which -they display, and the products which they form, so little resemble -those with which we are familiar, that the most phlegmatic and the -least speculative observer must have anticipated from them the creation -of new and valuable compounds. It can scarcely, therefore, be a -matter of surprise that minds of the highest order, and spirits of -the loftiest ambition, should have sought in the transmutations of -chemistry for those splendid products which were conceived to be most -conducive to human happiness. - -The disciple of Mammon grew pale over his crucible in his ardour to -convert the baser metals into gold; the philosopher pined in secret -for the universal solvent which might develop the elements of the -precious stones and yield to him the means of their production; and the -philanthropist aspired after a universal medicine, which might arrest -disease in its course, and prolong indefinitely the life of man. To -us, who live under the meridian of knowledge, such expectations must -appear as presumptuous as they were delusive; but when we consider -that gold and silver were actually produced by chemical processes from -the rude ores of lead and copper--that some of the most refractory -bodies had yielded to the disintegrating and solvent powers of chemical -agents, and that the mercurial preparations of the Arabian physicians -had operated like charms in the cure of diseases that had resisted -the feeble medicines of the times, we may find some apology for the -extravagant expectations of the alchemists. - -An object of lofty pursuit, even if it be one of impossible attainment, -is not unworthy philosophical ambition. Though we cannot scale the -summit of the volcanic cone, we may yet reach its heaving flanks; and -though we cannot decompose its loftiest fires, we may yet study the -lava which they have melted and the products which they have sublimed. -In like manner, though the philosopher’s stone has not been found, -chemistry has derived rich accessions from its search;--though the -general solvent has not been obtained, yet the diamond and the gems -have surrendered to science their adamantine strength;--and though -the elixir of life has never been distilled, yet other medicines have -soothed the “ills which flesh is heir to,” and prolonged in no slight -degree the average term of our existence. - -Thus far the pursuits of the alchemist were honourable and useful; -but when his calling was followed, as it soon was, by men prodigal -of fortune and of character, science became an instrument of crime; -secrets unattained were bartered for the gold of the credulous and the -ignorant, and books innumerable were composed to teach these pretended -secrets to the world. An intellectual reaction, however, soon took -place; and those very princes who had sought to fill their exhausted -treasuries at the furnace of the chemist, were the first to enact -laws against the frauds which they had encouraged, and to dispel the -illusions which had so long deceived their subjects. - -But even when the moral atmosphere of Europe was thus disinfected, -chemistry supplied the magician with his most lucrative wonders, and -those who could no longer delude the public with dreams of wealth and -longevity, now sought to amuse and astonish them by the exhibition -of their skill. The narrow limits of this volume will not permit me -to give even a general view of those extraordinary effects which -this popular science can display. I must therefore select from its -inexhaustible stores those topics which are most striking in their -results, and most popular in their details. - -One of the most ancient feats of magic was the art of breathing -flame,--an art which even now excites the astonishment of the vulgar. -During the insurrection of the slaves in Sicily, in the second century -before Christ, a Syrian named Eunus acquired by his knowledge the rank -of their leader. In order to establish his influence over their minds, -he pretended to possess miraculous power. When he wished to inspire his -followers with courage, he breathed flames or sparks among them from -his mouth, at the same time that he was rousing them by his eloquence. -St. Jerome informs us that the Rabbi Barchochebas, who headed the Jews -in their last revolt against Hadrian, made them believe that he was the -Messiah, by vomiting flames from his mouth; and at a later period, the -Emperor Constantius was thrown into a state of alarm when Valentinian -informed him that he had seen one of the body-guards breathing out -fire and flames. We are not acquainted with the exact methods by which -these effects were produced; but Florus informs us that Eunus filled -a perforated nut-shell with sulphur and fire, and having concealed it -in his mouth, he breathed gently through it while he was speaking. -This art is performed more simply by the modern juggler. Having rolled -together some flax or hemp, so as to form a ball the size of a walnut, -he sets it on fire, and allows it to burn till it is nearly consumed: -he then rolls round it while burning some additional flax, and by these -means the fire may be retained in it for a considerable time. At the -commencement of his exhibition he introduces the ball into his mouth, -and while he breathes through it the fire is revived, and a number -of burning sparks are projected from his mouth. These sparks are too -feeble to do any harm, provided he inhales the air through his nostrils. - -The kindred art of walking on burning coals or red-hot iron remounts to -the same antiquity. The priestesses of Diana at Castabala in Cappadocia -were accustomed, according to Strabo, to walk over burning coals; and -at the annual festival which was held in the temple of Apollo on Mount -Soracte in Etruria, the Hirpi marched over burning coals, and on this -account they were exempted from military service, and received other -privileges from the Roman Senate. This power of resisting fire was -ascribed even by Varro to the use of some liniment with which they -anointed the soles of their feet. - -Of the same character was the art of holding red-hot iron in the hands -or between the teeth, and of plunging the hands into boiling water or -melted lead. About the close of the seventeenth century, an Englishman -of the name of Richardson rendered himself famous by chewing burning -coals, pouring melted lead upon his tongue, and swallowing melted -glass. That these effects are produced partly by deception, and partly -by a previous preparation of the parts subjected to the heat, can -scarcely admit of a doubt. The fusible metal, composed of mercury, -tin, and bismuth, which melts at a low temperature, might easily have -been substituted in place of lead; and fluids of easy ebullition may -have been used in place of boiling water. A solution of spermaceti -or sulphuric ether, tinged with alkanet root, which becomes solid at -50° of Fahrenheit, and melts and boils with the heat of the hand, is -supposed to be the substance which is used at Naples when the dried -blood of St. Januarius melts spontaneously, and boils over the vessel -which contains it. - -But even when the fluid requires a high temperature to boil, it may -have other properties, which enable us to plunge our hands into it -with impunity. This is the case with boiling tar, which boils at a -temperature of 220°, even higher than that of water. Mr. Davenport -informs us, that he saw one of the workmen in the Royal Dock-yard at -Chatham immerse his naked hand in tar of that temperature. He drew up -his coat-sleeves, dipped in his hand and wrist, bringing out fluid tar, -and pouring it off from his hand as from a ladle. The tar remained in -complete contact with his skin, and he wiped it off with tow. Convinced -that there was no deception in this experiment, Mr. Davenport immersed -the entire length of his fore-finger in the boiling cauldron, and -moved it about a short time before the heat became inconvenient. Mr. -Davenport ascribes this singular effect to the slowness with which -the tar communicates its heat, which he conceives to arise from the -abundant volatile vapour which is evolved, “carrying off rapidly -the caloric in a latent state, and intervening between the tar and -the skin, so as to prevent the more rapid communication of heat.” -He conceives also, that when the hand is withdrawn, and the hot tar -adhering to it, the rapidity with which this vapour is evolved from -the surface exposed to the air cools it immediately. The workmen -informed Mr. Davenport that, if a person put his hand into the cauldron -with his glove on, he would be dreadfully burnt; but this extraordinary -result was not put to the test of observation. - -But though the conjurors with fire may have availed themselves of -these singular properties of individual bodies, yet the general secret -of their art consisted in rendering the skin of the exposed parts -callous and insensible to heat,--an effect which may be produced by -continually compressing or singeing them till the skin acquires a horny -consistence. A proof of this opinion is mentioned by Beckmann, who -assures us, that in September, 1765, when he visited the copper-works -at Awestad, one of the workmen, bribed by a little money to drink, -took some of the melted copper in his hand, and, after showing it to -the company, threw it against a wall. He then squeezed the fingers of -his horny hand close to each other, held it a few minutes under his -arm-pit, to make it perspire, as he said, and taking it again out, drew -it over a ladle filled with melted copper, some of which he skimmed -off, and moved his hand backwards and forwards very quickly by way of -ostentation. During this performance, M. Beckmann noticed a smell like -that of singed horn or leather, though the hand of the workman was -not burned. This callosity of the skin may be effected by frequently -moistening it with dilute sulphuric acid. Some allege that the juices -of certain plants produce the same effect, while others recommend the -frequent rubbing of the skin with oil. The receipt given by Albertus -Magnus for this purpose was of a different nature. It consisted of a -non-conducting calcareous paste, which was made to adhere to the skin -by the sap of the marsh-mallow, the slimy seeds of the flea-bane, and -the white of an egg. - -As the ancients were acquainted with the incombustibility of asbestos -or amianthus, and the art of weaving it into cloth, it is highly -probable that it was employed in the performance of some of their -miracles, and it is equally probable that it was subsequently used, -along with some of the processes already described, in enabling the -victims of superstition to undergo without hazard the trial of ordeal -by fire. In every country where this barbarous usage prevailed, whether -in the sanctuary of the Christian idolater, or in the pagan temple of -the Bramin, or under the wild orgies of the African savage, Providence -seems to have provided the means of meeting it with impunity. In -Catholic countries this exculpatory judgment was granted chiefly -to persons in weak health, who were incapable of using arms, and -particularly to monks and ecclesiastics, who could not avail themselves -of the trial by single combat. The fire ordeal was conducted in the -church under the inspection of the clergy: mass was at the same time -celebrated, and the iron and the victims were consecrated by the -sprinkling of holy water. The preparatory steps were also under the -direction of the priests. It was necessary that the accused should be -placed three days and three nights under their care, both before and -after the trial. Under the pretence of preventing the defendant from -preparing his hands by art, and in order to ascertain the result of -the ordeal, his hands were covered up and sealed during the three days -which preceded and followed the fiery application; and it has been -plausibly conjectured by Beckmann, that during the first three days the -preventive was applied to those whom they wished to acquit, and that -the last three days were requisite to bring back the hands to their -natural condition. In these and other cases, the accused could not -have availed himself directly of the use of asbestos gloves, unless we -could suppose them so made as to imitate the human skin at a distance; -but the fibres of that mineral may have been imbedded in a paste which -applied itself readily to all the elevations and depressions of the -skin. - -In our own times the art of defending the hands and face, and indeed -the whole body, from the action of heated iron and intense fire, has -been applied to the nobler purpose of saving human life, and rescuing -property from the flames. The revival and the improvement of this art -we owe to the benevolence and the ingenuity of the Chevalier Aldini of -Milan, who has travelled through all Europe to present this valuable -gift to his species. Sir H. Davy had long ago shown that a safety -lamp for illuminating mines, containing inflammable air, might be -constructed of wire-gauze alone, which prevented the flame within, -however large or intense, from setting fire to the inflammable air -without. This valuable property, which has been long in practical use, -he ascribed to the conducting and radiating power of the wire-gauze, -which carried off the heat of the flame, and deprived it of its power. -The Chevalier Aldini conceived the idea of applying the same material, -in combination with other badly conducting substances, as a protection -against fire. The incombustible pieces of dress which he uses for the -body, arms, and legs, are formed out of strong cloth, which has been -steeped in a solution of alum, while those for the head, hands, and -feet, are made of cloth of asbestos or amianthus. The head-dress is -a large cap which envelops the whole head down to the neck, having -suitable perforations for the eyes, nose, and mouth. The stockings and -cap are single, but the gloves are made of double amianthus cloth, to -enable the fireman to take into his hand burning or red hot bodies. The -piece of ancient asbestos cloth preserved in the Vatican was formed, -we believe, by mixing the asbestos with other fibrous substances; -but M. Aldini has executed a piece of nearly the same size, nine -feet five inches long and five feet three inches wide, which is much -stronger than the ancient piece, and possesses superior qualities, -in consequence of having been woven without the introduction of any -foreign substance. In this manufacture the fibres are prevented from -breaking by the action of steam, the cloth is made loose in its fabric, -and the threads are about the fiftieth of an inch in diameter. - -The metallic dress which is superadded to these means of defence -consists of five principal pieces, viz. a _casque_ or cap, with a mask -large enough to leave a proper space between it and the asbestos cap; a -cuirass with its brassets; a piece of armour for the trunk and thighs; -a pair of boots of double wire-gauze; and an oval shield 5 feet long -by 2½ wide, made by stretching the wire-gauze over a slender frame of -iron. All these pieces are made of iron wire-gauze, having the interval -between its threads the twenty-fifth part of an inch. - -In order to prove the efficacy of this apparatus, and inspire the -firemen with confidence in its protection, he showed them that a finger -first enveloped in asbestos, and then in a double case of wire-gauze, -might be held a long time in the flame of a spirit-lamp or candle -before the heat became inconvenient. A fireman having his hand within -a double asbestos glove, and its palm protected by a piece of asbestos -cloth, seized with impunity a large piece of red-hot iron, carried it -deliberately to the distance of 150 feet, inflamed straw with it, and -brought it back again to the furnace. On other occasions the fireman -handled blazing wood and burning substances, and walked during five -minutes upon an iron grating placed over flaming fagots. - -In order to show how the head, eyes, and lungs are protected, the -fireman put on the asbestos and wire-gauze cap, and the cuirass, and -held the shield before his breast. A fire of shavings was then lighted, -and kept burning in a large raised chafing-dish; the fireman plunged -his head into the middle of the flames with his face to the fuel, and -in that position went several times round the chafing-dish for a period -longer than a minute. In a subsequent trial, at Paris, a fireman placed -his head in the middle of a large brazier filled with flaming hay and -wood, as in Fig. 77, and resisted the action of the fire during five or -six minutes, and even ten minutes. - -[Illustration: _Fig. 77._] - -In the experiments which were made at Paris in the presence of a -committee of the Academy of Sciences, two parallel rows of straw and -brushwood, supported by iron wires, were formed at the distance of -three feet from each other, and extended thirty feet in length. When -this combustible mass was set on fire, it was necessary to stand at -the distance of eight or ten yards to avoid the heat. The flames from -both the rows seemed to fill up the whole space between them, and rose -to the height of nine or ten feet. At this moment six firemen, clothed -in the incombustible dresses, and marching at a slow pace behind each -other, repeatedly passed through the whole length between the two rows -of flame, which were constantly fed with additional combustibles. -One of the firemen carried on his back a child eight years old, in a -wicker-basket covered with metallic gauze, and the child had no other -dress than a cap made of amianthine cloth. - -In February, 1829, a still more striking experiment was made in the -yard of the barracks of St. Gervais. Two towers were erected two -stories high, and were surrounded with heaps of inflamed materials, -consisting of fagots and straw. The firemen braved the danger with -impunity. In opposition to the advice of M. Aldini, one of them, with -the basket and child, rushed into a narrow place, where the flames were -raging eight yards high. The violence of the fire was so great that he -could not be seen, while a thick black smoke spread around, throwing -out a heat which was unsupportable by the spectators. The fireman -remained so long invisible that serious doubts were entertained of his -safety. He at length, however, issued from the fiery gulf uninjured, -and proud of having succeeded in braving so great a danger. - -It is a remarkable result of these experiments, that the firemen -are able to breathe without difficulty in the middle of the flames. -This effect is owing not only to the heat being intercepted by the -wire-gauze as it passes to the lungs, in consequence of which its -temperature becomes supportable, but also to the singular power which -the body possesses of resisting great heats, and of breathing air of -high temperatures. - -A series of curious experiments were made on this subject by M. Tillet -in France, and by Dr. Fordyce and Sir Charles Blagden in England. Sir -Joseph Banks, Dr. Solander, and Sir Charles Blagden entered a room -in which the air had a temperature of 198° Fahr., and remained ten -minutes; but as the thermometer sank very rapidly, they resolved to -enter the room singly. Dr. Solander went in alone, and found the heat -210°, and Sir Joseph entered when the heat was 211°. Though exposed -to such an elevated temperature, their bodies preserved their natural -degree of heat. Whenever they breathed upon a thermometer it sank -several degrees: every expiration, particularly if strongly made, gave -a pleasant impression of coolness to their nostrils, and their cold -breath cooled their fingers whenever it reached them. On touching his -side, Sir Charles Blagden found it cold like a corpse, and yet the -heat of his body under his tongue was 98°. Hence they concluded that -the human body possesses the power of destroying a certain degree -of heat when communicated with a certain degree of quickness. This -power, however, varies greatly in different media. The same person -who experienced no inconvenience from air heated to 211°, could just -bear rectified spirits of wine at 130°, cooling oil at 129°, cooling -water at 123°, and cooling quicksilver at 117°. A familiar instance of -this occurred in the heated room. All the pieces of metal there, even -their watch-chains, felt so hot that they could scarcely bear to touch -them for a moment, while the air from which the metal had derived all -its heat was only unpleasant. Messrs. Duhamel and Tillet observed, -at Rochefoucault in France, that the girls who were accustomed to -attend ovens in a bakehouse were capable of enduring for ten minutes a -temperature of 270°. - -The same gentlemen who performed the experiments above described -ventured to expose themselves to still higher temperatures. Sir Charles -Blagden went into a room where the heat was 1° or 2° above 260°, and -remained eight minutes in this situation, frequently walking about -to all the different parts of the room, but standing still most of -the time in the coolest spot, where the heat was above 240°. The air, -though very hot, gave no pain, and Sir Charles and all the other -gentlemen were of opinion that they could support a much greater heat. -During seven minutes Sir C. Blagden’s breathing continued perfectly -good, but after that time he felt an oppression in his lungs, with -a sense of anxiety, which induced him to leave the room. His pulse -was then 144, double its ordinary quickness. In order to prove that -there was no mistake respecting the degree of heat indicated by the -thermometer, and that the air which they breathed was capable of -producing all the well-known effects of such a heat on inanimate -matter, they placed some eggs and a beef-steak upon a tin frame near -the thermometer, but more distant from the furnace than from the wall -of the room. In the space of twenty minutes the eggs were roasted quite -hard, and in forty-seven minutes the steak was not only dressed, but -almost dry. Another beef-steak, similarly placed, was rather overdone -in thirty-three minutes. In the evening, when the heat was still more -elevated, a third beef-steak was laid in the same place, and as they -had noticed that the effect of the hot air was greatly increased by -putting it in motion, they blew upon the steak with a pair of bellows, -and thus hastened the dressing of it to such a degree that the -greatest portion of it was found to be pretty well done in thirteen -minutes. - -Our distinguished countryman, Sir F. Chantrey, has very recently -exposed himself to a temperature still higher than any which we have -mentioned. The furnace which he employs for drying his moulds is about -14 feet long, 12 feet high, and 12 feet broad. When it is raised to -its highest temperature, with the doors closed, the thermometer stands -at 350°, and the iron floor is red hot. The workmen often enter it -at a temperature of 340°, walking over the iron floor with wooden -clogs, which are of course charred on the surface. On one occasion -Sir F. Chantrey, accompanied by five or six of his friends, entered -the furnace, and, after remaining two minutes, they brought out a -thermometer which stood at 320°. Some of the party experienced sharp -pains in the tips of their ears, and in the septum of the nose, while -others felt a pain in their eyes. - - - - -LETTER XIII. - - Spontaneous combustion--In the absorption of air by powdered - charcoal--and of hydrogen by spongy platinum--Dobereiner’s - lamp--Spontaneous combustion in the bowels of the earth--Burning - cliffs--Burning soil--Combustion without flame--Spontaneous combustion - of human beings--Countess Zangari--Grace Pett--Natural fire-temples - of the Guebres--Spontaneous fires in the Caspian Sea--Springs of - inflammable gas near Glasgow--Natural light-house of Maracaybo--New - elastic fluids in their cavities--of gems--Chemical operation going - on in their cavities--Explosions produced in them by heat--Remarkable - changes of colour from chemical causes--Effects of the nitrous oxide - of Paradise gas when breathed--Remarkable cases described--Conclusion. - - -Among the wonderful phenomena which chemistry presents to us, there -are few more remarkable than those of spontaneous combustion, in which -bodies both animate and inanimate emit flames, and are sometimes -entirely consumed by internal fire. One of the commonest experiments -in chemistry is that of producing inflammation by mixing two fluids -perfectly cold. Becker, we believe, was the first person who discovered -that this singular effect was produced by mixing oil of vitriol with -oil of turpentine. Borrichios showed that aqua-fortis produced the -same effect as oil of vitriol. Tournefort proved that spirit of nitre -and oil of sassafras took fire when mixed; and Homberg discovered that -the same property was possessed by many volatile oils when mixed with -spirit of nitre. - -Every person is familiar with the phenomena of heat and combustion -produced by fermentation. Ricks of hay and stacks of corn have been -frequently consumed by the heat generated during the fermentation -produced from moisture; and gunpowder-magazines, barns, and paper-mills -have been often burned by the fermentation of the materials which they -contained. Galen informs us that the dung of a pigeon is sufficient -to set fire to a house; and he assures us that he has often seen it -take fire when it had become rotten. Casati likewise relates, on good -authority, that the fire which consumed the great church of Pisa was -occasioned by the dung of pigeons that had for centuries built their -nests under its roof. - -Among the substances subject to spontaneous combustion, pulverized -or finely-powdered charcoal is one of the most remarkable. During -the last thirty years no fewer than four cases of the spontaneous -inflammation of powdered charcoal have taken place in France. When -charcoal is triturated in tuns with bronze bruisers, it is reduced -into the state of the finest powder. In this condition it has the -appearance of an unctuous fluid, and it occupies a space three times -less than it does in rods of about six inches long. In this state of -extreme division it absorbs air much more readily than it does when -in rods. This absorption, which is so slow as to require several days -for its completion, is accompanied with a disengagement of heat which -rises from 340° to 360° nearly of Fahrenheit, and which is the true -cause of the spontaneous inflammation. The inflammation commences near -the centre of the mass, at the depth of five or six inches beneath -its surface, and at this spot the temperature is always higher than -at any other. Black charcoal, strongly distilled, heats and inflames -more easily than the orange, or that which is little distilled, or -than the charcoal made in boilers. The most inflammable charcoal -must have a mass of at least 66lbs. avoirdupois, in order that it -may be susceptible of spontaneous inflammation. With the other less -inflammable varieties, the inflammation takes place only in larger -masses. - -The inflammation of powdered charcoal is more active in proportion -to the shortness of the interval between its carbonization and -trituration. The free admission of air to the surface of the charcoal -is also indispensable to its spontaneous combustion. - -Colonel Aubert, to whom we owe these interesting results, likewise -found that when sulphur and saltpetre are added to the charcoal, it -loses its power of inflaming spontaneously. But as there is still an -absorption of air and a generation of heat, he is of opinion that it -would not be prudent to leave these mixtures in too large masses after -trituration.[34] - - [34] See _Edinburgh Journal of Science_, New Series, No. viii. p. 274. - -A species of spontaneous combustion, perfectly analogous to that now -described, but produced almost instantaneously, was discovered by -Professor Dobereiner of Jena in 1824. He found that when a jet of -hydrogen gas was thrown upon recently prepared spongy platinum, the -metal became almost instantly red hot, and set fire to gas. In this -case the minutely divided platinum acted upon the hydrogen gas in the -same manner as the minutely divided charcoal acted upon common air. -Heat and combustion were produced by the absorption of both gases, -though in the one case the effect was instantaneous, and in the other -was the result of a prolonged absorption. - -[Illustration: _Fig. 78._] - -This beautiful property of spongy platinum was happily applied to the -construction of lamps for producing an instantaneous light. The form -given to the lamp by Mr. Garden of London is shown in the annexed -figure, where AB is a globe of glass, fitting tightly into another -glass globe CD by a ground shoulder _m n_. The globe AB terminates -in a hollow tapering neck _m n o p_, on the lower end of which is -placed a small cylinder of zinc _o p_. A brass tube _a b c_, is -fitted at _a_ into the neck of the globe CD, and through this tube, -which is furnished with a stop-cock _d_, the gas can escape at the -small aperture _c_. A brass pin _c f_, carrying a brass box P, is made -to slide through a hole _h_, so that the brass box P, in which the -spongy platinum is placed, can be set at any required distance from -the aperture _c_. If sulphuric acid, diluted with an equal quantity of -water, is now poured into the vessel AB by its mouth at S, now closed -with a stopper, the fluid will descend through the tube _m n o p_, and -if the cock _d_ is shut, it will compress the air contained in CD. The -dilute acid thus introduced into CD will act upon the ring of zinc _o -p_, and generate hydrogen gas, which, after the atmospheric air in CD -is let off, will gradually fill the vessel CD, the diluted acid being -forced up the tube _o p m n_, into the glass globe AB. The ring of zinc -_o p_ floats on a piece of cork, so that when CD is full of hydrogen, -the diluted acid does not touch the zinc, and consequently is prevented -from producing any more gas. The instant, however, that any gas is let -off at _c_, the pressure of the fluid in the globe AB, and tube _m n o -p_, overcomes the elasticity of the remaining gas in CD, and forces the -diluted acid up to the zinc _o p_, so as to enable it to produce more -gas to supply what has been used. - -The lamp being supplied with hydrogen in the manner now described, -it is used in the following manner. The spongy platinum in P being -brought near _c_, the cock _d_ is turned, and the gas is thrown upon -the platinum. An intense heat is immediately produced, the platinum -becomes red-hot, and the hydrogen inflames. A taper is then lighted at -the flame, and the cock _d_ is shut. Professor Cumming, of Cambridge, -found it necessary to cover up the platinum with a cap after every -experiment. This ingenious chemist likewise found, that, with platinum -foil the 9,000th part of an inch thick kept in a close tube, the -hydrogen was inflamed; but when the foil was only the 6,000th of an -inch thick, it was necessary to raise it previously to a red heat. - -Spontaneous combustion is a phenomenon which occurs very frequently -and often to a great extent within the bowels of the earth. The heat -by which it is occasioned is produced by the decomposition of mineral -bodies and other causes. This heat increases in intensity till it is -capable of melting the solid materials which are exposed to it. Gases -and aqueous vapours of powerful elasticity are generated, new fluids -of expansive energy imprisoned in cavities under great pressure are -set free, and these tremendous agents, acting under the repressing -forces of the superincumbent strata, exhibit their power in desolating -earthquakes; or, forcing their way through the superficial crust of the -globe, they waste their fury in volcanic eruptions. - -When the phenomena of spontaneous combustion take place near the -surface of the earth, its effects are of a less dangerous character, -though they frequently give birth to permanent conflagrations, which no -power can extinguish. An example of this milder species of spontaneous -combustion has been recently exhibited in the burning cliff at -Weymouth; and a still more interesting one exists at this moment near -the village of Bradley, in Staffordshire. The earth is here on fire, -and this fire has continued for nearly sixty years, and has resisted -every attempt that has been made to extinguish it. This fire, which -has reduced many acres of land to a mere calx, arises from a burning -stratum of coal about four feet thick and eight or ten yards deep, to -which the air has free access, in consequence of the main coal having -been dug from beneath it. The surface of the ground is sometimes -covered for many yards with such quantities of sulphur that it can be -easily gathered. The calx has been found to be an excellent material -for the roads, and the workmen who collect it often find large beds of -alum of an excellent quality. - -A singular species of invisible combustion, or of combustion without -flame, has been frequently noticed. I have observed this phenomenon in -the small green wax tapers in common use. When the flame is blown out, -the wick will continue red-hot for many hours; and if the taper were -regularly and carefully uncoiled, and the room kept free from currents -of air, the wick would burn on in this way till the whole of the taper -is consumed. The same effects are not produced when the colour of the -wax is red. In this experiment the wick, after the flame is blown out, -has sufficient heat to convert the wax into vapour, and this vapour -being consumed without flame, keeps the wick at its red heat. A very -disagreeable vapour is produced during this imperfect combustion of the -wax. - -Prof. Dobereiner, of Jena, observed that, when the alcohol in a spirit -of wine lamp was nearly exhausted, the wick became carbonized, and -though the flame disappeared, the carbonized part of the wick became -red-hot, and continued so while a drop of alcohol remained, provided -the air in the room was undisturbed. On one occasion the wick continued -red-hot for twenty-four hours, and a very disagreeable acid vapour was -formed. - -[Illustration: _Fig. 79._] - -On these principles depend the _lamp without flame_ which was -originally constructed by Mr. Ellis. It is shown in the annexed -figure, where AB is the lamp, and _h_ a cylindrical coil of platinum -wire, the hundredth part of an inch in diameter. This spiral is so -placed that four or five of the twelve coils of which the cylinder -consists are upon the wick, and the other seven or eight above it. If -the lamp is lighted, and continues burning till the cylindrical coil -is red-hot, then if the flame is blown out, the vapour which arises -from the alcohol will by its combustion keep the coils above the wick -red-hot, and this red heat will in its turn keep up the vaporization -of the alcohol till the whole of the alcohol is consumed. The heat of -the wire is always sufficient to kindle a piece of German fungus or -saltpetre paper, so that a sulphur match may at any time be lighted. -Mr. Gill found that a wick composed of twelve threads of the cotton -yarn commonly used for lamps will require half an ounce of alcohol to -keep the wire red-hot for eight hours. This lamp has been kept burning -for sixty hours; but it can scarcely be recommended for a bed-room, as -an acid vapour is disengaged during the burning of the alcohol. When -perfumes are dissolved in the alcohol, they are diffused through the -apartment during the slow combustion of the vapour. - -A species of combustion without flame, and analogous to that which -has been described, is exhibited in the extraordinary phenomenon of -the spontaneous combustion of living bodies. That animal bodies are -liable to internal combustion, is a fact which was well known to the -ancients. Many cases which have been adduced as examples of spontaneous -combustion are merely cases of individuals who were highly susceptible -of strong electrical excitation. In one of these cases, however, Peter -Bovisteau asserts, that the sparks of fire thus produced, reduced to -ashes the hair of a young man; and John de Viana informs us, that the -wife of Dr. Freilas, physician to the Cardinal de Royas, Archbishop of -Toledo, emitted by perspiration an inflammable matter of such a nature, -that when the ribbon which she wore over her shift was taken from her, -and exposed to the cold air, it instantly took fire, and shot forth -like grains of gunpowder. Peter Borelli has recorded a fact of the very -same kind respecting a peasant whose linen took fire, whether it was -laid up in a box when wet, or hung up in the open air. The same author -speaks of a woman who, when at the point of death, vomited flames; and -Thomas Bartholin mentions this phenomenon as having often happened to -persons who were great drinkers of wine or brandy. Ezekiel de Castro -mentions the singular case of Alexandrinus Megetius, a physician, from -one of whose vertebræ there issued a fire which scorched the eyes of -the beholders; and Krantzius relates, that during the wars of Godfrey -of Bouillon, certain people of the territory of Nevers were burning -with invisible fire, and that some of them cut off a foot or a hand -where the burning began, in order to arrest the calamity. Nor have -these effects been confined to man. In the time of the Roman consuls -Gracchus and Juventius, a flame is said to have issued from the mouth -of a bull without doing any injury to the animal. - -The reader will judge of the degree of credit which may belong to these -narrations when he examines the effects of a similar kind which have -taken place in less fabulous ages, and nearer our own times. John Henry -Cohausen informs us that a Polish gentleman in the time of the Queen -Bona Sforza, having drunk two dishes of a liquor called brandy-wine, -vomited flames, and was burned by them, and Thomas Bartholin[35] thus -describes a similar accident: “A poor woman at Paris used to drink -spirit of wine plentifully for the space of three years, so as to take -nothing else. Her body contracted such a combustible disposition, that -one night, when she lay down on a straw couch, she was all burned -to ashes except her skull and the extremities of her fingers.” John -Christ. Sturmius informs us, in the German Ephemerides, that in the -northern countries of Europe flames often evaporate from the stomachs -of those who are addicted to the drinking of strong liquors; and he -adds, “that seventeen years before, three noblemen of Courland drank by -emulation strong liquors, and two of them died scorched and suffocated -by a flame which issued from their stomachs.” - - [35] Acta Medica et Philosophica Hafniensia, 1673. - -One of the most remarkable cases of spontaneous combustion is that -of the Countess Cornelia Zangari and Bandi of Cesena, which has been -minutely described by the Reverend Joseph Bianchini, a prebend in the -city of Verona. This lady, who is in the sixty-second year of her age, -retired to bed in her usual health. Here she spent above three hours -in familiar conversation with her maid, and in saying her prayers; and -having at last fallen asleep, the door of her chamber was shut. As her -maid was not summoned at the usual hour, she went into the bed-room -to wake her mistress; but receiving no answer, she opened the window, -and saw her corpse on the floor in the most dreadful condition. At -the distance of four feet from the bed there was a heap of ashes. Her -legs, with the stockings on, remained untouched, and the head, half -burned, lay between them. Nearly all the rest of the body was reduced -to ashes. The air in the room was charged with floating soot. A small -oil lamp on the floor was covered with ashes, but had no oil in it; and -in two candlesticks, which stood upright upon a table, the cotton wick -of both the candles was left, and the tallow of both had disappeared. -The bed was not injured, and the blankets and sheets were raised on -one side, as if a person had risen up from it. From an examination -of all the circumstances of this case, it has been generally supposed -that an internal combustion had taken place; that the lady had risen -from her bed to cool herself, and that, in her way to open the window, -the combustion had overpowered her, and consumed her body by a process -in which no flame was produced which could set fire to the furniture -or the floor. The Marquis Scipio Maffei was informed by an Italian -nobleman who passed through Cesena a few days after this event, that -he heard it stated in that town, that the Countess Zangari was in -the habit, when she felt indisposed, of washing all her body with -camphorated spirit of wine. - -So recently as 1744, a similar example of spontaneous combustion -occurred in our own country, at Ipswich. A fisherman’s wife, of the -name of Grace Pett, of the parish of St. Clement’s, had been in the -habit for several years of going down stairs every night, after she was -half undressed, to smoke a pipe. She did this on the evening of the 9th -of April, 1744. Her daughter, who lay in the same bed with her, had -fallen asleep, and did not miss her mother till she awaked early in -the morning. Upon dressing herself, and going down stairs, she found -her mother’s body lying on the right side, with her head against the -grate, and extended over the hearth, with her legs on the deal floor, -and appearing like a block of wood burning with a glowing fire without -flame. Upon quenching the fire with two bowls of water, the neighbours, -whom the cries of the daughter had brought in, were almost stifled with -the smell. The trunk of the unfortunate woman was almost burned to -ashes, and appeared like a heap of charcoal covered with white ashes. -The head, arms, legs, and thighs, were also much burned. There was no -fire whatever in the grate, and the candle was burned out in the socket -of the candlestick, which stood by her. The clothes of a child on one -side of her, and a paper screen on the other, were untouched: and the -deal floor was neither singed nor discoloured. It was said that the -woman had drunk plentifully of gin overnight in welcoming a daughter -who had recently returned from Gibraltar. - -Among the phenomena of the natural world which are related to those -of spontaneous combustion, are what have been called the natural -fire-temples of the Guebres, and the igneous phenomena which are -seen in their vicinity. The ancient sect of the Guebres or Parsees, -distinguished from all other sects as the worshippers of fire, -had their origin in Persia; but, being scattered by persecution, -they sought an asylum on the shores of India. Those who refused -to expatriate themselves continued to inhabit the shores of the -Caspian Sea, and the cities of Ispahan, Yezd, and Kerman. Their great -fire-temple, called Attush Kudda, stands in the vicinity of Badku, -one of the largest and most commodious ports on the Caspian. In the -neighbourhood of this town the earth is impregnated with naphtha, an -inflammable mineral oil; and the inhabitants have no other fuel, and no -other light, but what is derived from this substance. - -The remains of the ancient fire-temples of the Guebres are still -visible about ten miles to the north-east of the town. The temple in -which the deity is worshipped under the form of fire, is a space about -thirty yards square, surrounded with a low wall, and containing many -apartments. In each of these a small volcano of sulphureous fire issues -from the ground through a furnace or funnel in the shape of a Hindoo -altar. On closing the funnel, the fire is instantly extinguished; -and by placing the ear at the aperture, a hollow sound is heard, -accompanied with a strong current of cold air, which may be lighted -at pleasure by holding to it any burning substance. The flame is of a -pale, clear colour, without any perceptible smoke, and emits a highly -sulphureous vapour, which impedes respiration, unless when the mouth -is kept beneath the level of the furnace. This action on the lungs -gives the Guebres a wan and emaciated appearance, and oppresses them -with a hectic cough, which strangers also feel while breathing this -insalubrious atmosphere. - -For about two miles in circumference, round the principal fire, the -whole ground, when scraped to the depth of two or three inches, has -the singular property of being inflamed by a burning coal. In this -case, however, it does not communicate fire to the adjacent ground: but -if the earth is dug up with a spade, and a torch brought near it, an -extensive but instantaneous conflagration takes place, in which houses -have often been destroyed, and the lives of the people exposed to -imminent danger. - -When the sky is clear and the weather serene, the springs in their -ebullition do not rise higher than two or three feet; but in gloomy -weather, and during the prevalence of stormy clouds, the springs are -in a state of the greatest ebullition, and the naphtha, which often -takes fire spontaneously at the earth’s surface, flows burning in great -quantities to the sea, which is frequently covered with it, in a state -of flame, to the distance of several leagues from the shore. - -Besides the fires in the temple, there is a large one which springs -from a natural cliff in an open situation, and which continually burns. -The general space in which this volcanic fire is most abundant is -somewhat less than a mile in circuit. It forms a low flat hill, sloping -to the sea, the soil of which is a sandy earth, mixed with stones. Mr. -Forster did not observe any violent eruption of flame in the country -around the Attush Kudda; but Kinneir informs us, that the whole country -round Badku has at times the appearance of being enveloped in flames. -“It often seems,” he adds, “as if the fire rolled down from the -mountains in large masses, and with incredible velocity; and during the -clear moonshine nights of November and December, a bright blue light is -observed at times to cover the whole western range. The fire does not -consume; and if a person finds himself in the middle of it, no warmth -is felt.” - -The inhabitants apply these natural fires to domestic purposes, by -sinking a hollow cane or merely a tube of paper, about two inches in -the ground, and by blowing upon a burning coal held near the orifice -of the tube, there issues a slight flame, which neither burns the cane -nor the paper. By means of these canes or paper tubes, from which the -fire issues, the inhabitants boil the water in their coffee-urns, and -even cook different articles of food. The flame is put out by merely -plugging up the orifice. The same tubes are employed for illuminating -houses that are not paved. The smell of naphtha is of course diffused -through the house: but after any person is accustomed to it, it ceases -to be disagreeable. The inhabitants also employ this natural fire -in calcining lime. The quantity of naphtha procured in the plain to -the south-east of Badku is enormous. It is drawn from wells, some of -which yield from 1,000 to 1,500lbs. per day. As soon as these wells -are emptied, they fill again till the naphtha rises to its original -level.[36] - - [36] See Forster’s Travels, and Kinneir’s Geog. Memoir. - -Inflammable gases issuing from the earth have been used both in -the old and the new world for domestic purposes. In the salt mine -of Gottesgabe, at Rheims, in the county of Fecklenburg, there is a -pit called the _Pit of the Wind_, from which a constant current of -inflammable gas has issued for sixty years. M. Roeder, the inspector of -the mines, has used this gas for two years, not only as a light, but -for all the purposes of domestic economy. In the pits which are not -worked, he collects the gas, and conveys it in tubes to his house. It -burns with a white and brilliant flame, has a density of about O.66, -and contains traces of carbonic acid gas and sulphuretted hydrogen.[37] - - [37] _Edinburgh Journal of Science_, No. xv., p. 183. - -Near the village of Fredonia, in North America, on the shores of -Lake Erie, are a number of burning springs, as they are called. The -inflammable gas which issues from these springs is conveyed in pipes -to the village, which is actually lighted by them.[38] - - [38] _Edinburgh Journal of Science_, No. xv., p. 183. - -In the year 1828 a copious spring of inflammable gas was discovered in -Scotland, in the bed of a rivulet which crosses the north road between -Glasgow and Edinburgh, a little to the east of the seventh mile-stone -from Glasgow, and only a few hundred yards from the house of Bedlay. -The gas is said to issue for more than half a mile along the banks of -the rivulet. Dr. Thompson, who has analysed the gas, saw it issuing -only within a space about fifty yards in length, and about half as much -in breadth. “The emission of gas was visible in a good many places -along the declivity to the rivulet in the immediate neighbourhood of a -small farm-house. The farmer had set the gas on fire in one place about -a yard square, out of which a great many small jets were issuing. It -had burnt without interruption during five weeks, and the soil (which -was clay) had assumed the appearance of pounded brick all around. - -“The flame was yellow and strong, and resembled perfectly the -appearance which _carburetted hydrogen gas_ or _fire-damp_ presents -when burnt in daylight. But the greatest issue of gas was in the -rivulet itself, distant about twenty yards from the place where the gas -was burning. The rivulet, when I visited the place, was swollen and -muddy, so as to prevent its bottom from being seen. But the gas issued -up through it in one place with great violence, as if it had been in a -state of compression under the surface of the earth; and the thickness -of the jet could not be less than two or three inches in diameter. We -set the gas on fire as it issued through the water. It burnt for some -time with a good deal of splendour; but as the rivulet was swollen, -and rushing along with great impetuosity, the regularity of the issue -was necessarily disturbed, and the gas was extinguished.” Dr. Thompson -found this gas to consist of _two_ volumes of hydrogen gas, and _one_ -volume of vapour of carbon; and as its specific gravity was 0.555, -and as it issues in great abundance, he remarks that it might be used -for filling air-balloons. “Were we assured,” he adds, “that it would -continue to issue in as great abundance as at present, it might be -employed in lighting the streets of Glasgow.”[39] - - [39] _Edinburgh Journal of Science_, No. 1, New Series, p. 71-75. - -A very curious natural phenomenon, called the _Lantern_ or _Natural -Lighthouse_ of Maracaybo, has been witnessed in South America. A bright -light is seen every night on a mountainous and uninhabited spot on the -banks of the river Catatumbo, near its junction with the Sulia. It is -easily distinguished at a greater distance than _forty_ leagues, and as -it is nearly in the meridian of the opening of the Lake of Maracaybo, -navigators are guided by it as by a light-house. This phenomenon is -not only seen from the sea-coast, but also from the interior of the -country--at Merida, for example, where M. Palacios observed it for -two years. Some persons have ascribed this remarkable phenomenon to -a thunder-storm, or to electrical explosions which might take place -daily in a pass in the mountains; and it has even been asserted, -that the rolling of thunder is heard by those who approach the spot. -Others suppose it to be an air-volcano, like those on the Caspian Sea, -and that it is caused by asphaltic soils like those of Mena. It is -more probable, however, that it is a sort of carburetted hydrogen, as -hydrogen gas is disengaged from the ground in the same district.[40] - - [40] Humboldt’s Personal Narrative, vol. iv. p. 254, note. - -Grand as the chemical operations are which are going on in the great -laboratory of Nature, and alarming as their effects appear when they -are displayed in the terrors of the earthquake and the volcano, yet -they are not more wonderful to the philosopher than the minute though -analogous operations which are often at work near our own persons, -unseen and unheeded. It is not merely in the bowels of the earth -that highly expansive elements are imprisoned and restrained, and -occasionally called into tremendous action by the excitation of heat -and other causes. Fluids and vapours of a similar character exist in -the very gems and precious stones which science has contributed to -luxury and to the arts. - -In examining with the microscope the structure of mineral bodies, I -discovered in the interior of many of the gems thousands of cavities -of various forms and sizes. Some had the shape of hollow and regularly -formed crystals; others possessed the most irregular outline, and -consisted of many cavities and branches united without order, but -all communicating with each other. These cavities sometimes occurred -singly, but most frequently in groups forming strata of cavities, at -one time perfectly flat and at another time curved. Several such -strata were often found in the same specimen, sometimes parallel to -each other, at other times inclined, and forming all varieties of -angles with the faces of the original crystal. - -These cavities, which occurred in _sapphire_, _chrysoberyl_, _topaz_, -_beryl_, _quartz_, _amethyst_, _peridot_, and other substances, were -sometimes sufficiently large to be distinctly seen by the naked eye, -but most frequently they were so small as to require a high magnifying -power to be well seen, and often they were so exceedingly minute, that -the highest magnifying powers were unable to exhibit their outline. - -[Illustration: _Fig. 80._] - -The greater number of these cavities, whether large or small, contained -two new fluids different from any hitherto known, and possessing -remarkable physical properties. These two fluids are in general -perfectly transparent and colourless, and they exist in the same cavity -in actual contact, without mixing together in the slightest degree. One -of them expands _thirty_ times more than water, and at a temperature of -about 80° of Fahrenheit it expands so as to fill up the vacuity in the -cavity. This will be understood from the annexed figure, where A B C D -is the cavity, _m n p o_ the highly expansible fluid in which at low -temperatures there is always a vacuity V, like an air-bubble in common -fluids, and A _m n_, C _o p_, the second fluid occupying the angles A -and C. When heat such as that of the hand is applied to the specimen, -the vacuity V gradually contracts in size, and wholly vanishes at a -temperature of about 80°, as shown in Fig. 81. The fluids are shaded, -as in these two figures, when they are seen by light reflected from -their surfaces. - -[Illustration: _Fig. 81._] - -[Illustration: _Fig. 82._] - -When the cavities are large, as in Fig. 82, compared with the quantity -of expansible fluid _m n p o_, the heat converts the fluid into vapour, -an effect which is shown by the circular cavity V becoming larger and -larger till it fills the whole space _m n o p_. - -When any of these cavities, whether they are filled with fluid -or with vapour, is allowed to cool, the vacuity V reappears at a -certain temperature. In the fluid cavities the fluid contracts, and -the small vacuity appears, which grows larger and larger till it -resumes its original size. When the cavities are large, several small -vacuities make their appearance and gradually unite into one, though -they sometimes remain separate. In deep cavities a very remarkable -phenomenon accompanies the reappearance of the vacuity. At the instant -that the fluid has acquired the temperature at which it quits the -sides of the cavity, an effervescence or rapid ebullition takes place, -and the transparent cavity is for a moment opaque, with an infinite -number of minute vacuities, which instantly unite into one that goes -on enlarging as the temperature diminishes. In the vapour cavities the -vapour is reconverted by the cold into fluid, and the vacuity V, Fig. -82, gradually contracts till all the vapour has been precipitated. It -is curious to observe, when a great number of cavities are seen at once -in the field of the microscope, that the vacuities all disappear and -reappear at the same instant. - -While all these changes are going on in the expansive fluid, the -other denser fluid at A and C, Fig. 80, 81, remains unchanged either -in its form or magnitude. On this account I experienced considerable -difficulty in proving that it was a fluid. The improbability of two -fluids existing in a transparent state in absolute contact, without -mixing in the slightest degree, or acting upon each other, induced -many persons to whom I showed the phenomenon to consider the lines _m -n_, _o p_, Fig. 80, 81, as a partition in the cavity, or the spaces A -_m n_, _o p_ C, either as filled with solid matter, or as corners into -which the expanding fluid would not penetrate. The regular curvature, -however, of the boundary line _m n_, _o p_, and other facts, rendered -these suppositions untenable. - -[Illustration: _Fig. 83._] - -This difficulty was at last entirely removed by the discovery of a -cavity of the form shown in the annexed figure, where A, B, and C are -three portions of the expansible fluid separated by the interposition -of the second fluid D E F. The first portion A of the expansible fluid -had four vacuities V, X, Y, Z, while the other two portions B, C, had -no vacuity. In order to determine if the vacuities of the portions B, -C, had passed over to A, I took an accurate drawing of the appearances -at a temperature of 50°, as shown in the figure, and I watched the -changes which took place in raising the temperature to 83°. The portion -A gradually expanded itself till it filled up all the four vacuities -V, X, Y, and Z, but as the portions B, C, had no vacuities, they could -expand themselves only by pushing back the supposed second fluid D E -F. This effect actually took place. The dense fluid quitted the side -of the cavity at F. The two portions B, C, of the expansible fluid -instantly united, and the dense fluid having retreated to the limit _m_ -_n_ _o_, its other limit advanced to _p_ _q_ _r_, thus proving it to -be a real fluid. This experiment, which I have often shown to others, -involves one of those rare combinations of circumstances which nature -sometimes presents to us in order to illustrate her most mysterious -operations. Had the portions B, C, been accompanied, as is usual, with -their vacuities, the interposed fluid would have remained immoveable -between the two equal and opposite expansions; but owing to the -accidental circumstance of these vacuities having passed over into the -other branch A of the cavity, the fluid yielded to the difference of -the expansive forces between which it lay, and thus exhibited its fluid -character to the eye. - -[Illustration: _Fig. 84._] - -When we examine these cavities narrowly, we find that they are actually -little laboratories, in which chemical operations are constantly going -on, and beautiful optical phenomena continually displaying themselves. -Let A B D C, for example, be the summit of a crystallized cavity in -topaz, S S representing the dense, N N the expansible fluid, bounded -by a circular line _a b c d_, and V V the vacuity in the new fluid, -bounded by the circle _e f g h_. If the face A B D C is placed under a -compound microscope, so that light may be reflected at an angle less -than that of total reflexion, and if the observer now looks through -the microscope, the temperature of the room being 50°, he will see the -second fluid S S shining with a very feeble reflected light, the dense -fluid N N with a light perceptibly brighter, and the vacuity V V with -a light of considerable brilliancy. The boundaries _a b c d_, _e f g -h_, are marked by a well-defined outline, and also by the concentric -coloured rings of thin plates produced by the extreme thinness of each -of the fluids at their edges. - -If the temperature of the room is raised slowly to 58°, a brown -spot will appear at _x_ in the centre of the vacuity V V. This spot -indicates the commencement of evaporation from the expansible fluid -below, and arises from the partial precipitation of the vapour in the -roof of the cavity. As the heat increases, the brown spot enlarges and -becomes very dark. It is then succeeded by a white spot and one or -more coloured rings rise in the centre of the vacuity. The vapour then -seems to form a drop, and all the rings disappear by retiring to the -centre, but only to reappear with new lustre. During the application -of heat, the circle _e f g h_ contracts and dilates like the pupil of -the eye. When the vaporization is so feeble as to produce only a single -ring of one or two tints of the second order, they vanish instantly -by breathing upon the crystal; but when the slight heat of the breath -reaches the fluid, it throws off fresh vapour, and the rings again -appear. - -If a drop of ether is put upon the crystal when the rings are in a -state of rapid play, the cold produced by its evaporation causes them -to disappear, till the temperature again rises. When the temperature -is perfectly uniform, the rings are stationary, as shown between V and -V in fig. 84; and it is interesting to observe the first ring produced -by the vapour swelling out to meet the first ring at the margin of -the fluid, and sometimes coming so near it that the darkest parts of -both form a broad black band. As the heat increases, the vacuity V V -diminishes and disappears at 79°, exhibiting many curious phenomena, -which we have not room to describe. - -Having fallen upon a method of opening the cavities, and looking at the -fluids, I was able to examine their properties with more attention. -When the expansible fluid first rises from the cavity upon the surface -of the topaz, it neither remains still like the fixed oils, nor -disappears like evaporable fluids. Under the influence, no doubt, of -heat and moisture, it is in a state of constant motion, now spreading -itself on a thin plate over a large surface, and now contracting itself -into a deeper and much less extended drop. These contractions and -extensions are marked by very beautiful optical phenomena. When the -fluid has stretched itself out into a thin plate, it ceases to reflect -light like the thinnest part of the soap-bubble; and when it is again -accumulated into a thicker drop, it is covered with thin coloured rings -of thin plates. - -After performing these motions, which sometimes last for ten minutes, -the fluid suddenly disappears, and leaves behind it a sort of granular -residue. When examining this with a single microscope, it again started -into a fluid state, and extended and contracted itself as before. This -was owing to the humidity of the hand which held the microscope, and -I have been able to restore by moisture the fluidity of these grains -twenty days after they were formed from the fluid. This portion was -shown to the Rev. Dr. Fleming, who remarked, that, had he observed -it accidentally, he would have ascribed its apparent vitality to the -movements of some of the animals of the genus Planaria. - -After the cavity has remained open for a day or two, the dense fluid -comes out and quickly hardens into a transparent and yellowish -resinous-looking substance, which absorbs moisture, though with less -avidity than the other. It is not volatilized by heat, and is insoluble -in water and alcohol. It readily dissolves, however, with effervescence -in the sulphuric, nitric, and muriatic acids. The residue of the -expansible fluid is volatilized by heat, and is dissolved, but without -effervescence, in the above-mentioned acids. The refractive power of -the dense fluid is about 1.295, and of the expansible one 1.131. - -The particles of the dense fluid have a very powerful attraction for -each other and for the mineral which contains them, while those of -the expansible fluid have a very slight attraction for one another, -and also for the substance of the mineral. Hence the two fluids never -mix, the dense fluid being attracted to the angles of angular cavities, -or filling the narrow necks by which two cavities communicate. The -expansible fluid, on the other hand, fills the wide parts of the -cavities, and in deep and round cavities it lies above the dense fluid. - -When the dense fluid occupies the necks which join two cavities, -it performs the singular function of a fluid valve, opening and -shutting itself according to the expansions or contractions of the -other fluid. The _fluid valves_ thus exhibited in action may suggest -some useful hints to the mechanic and the philosopher, while they -afford ground of curious speculation in reference to the functions of -animal and vegetable bodies. In the larger organizations of ordinary -animals, where gravity must in general overpower, or at least modify, -the influence of capillary attraction, such a mechanism is neither -necessary nor appropriate; but, in the lesser functions of the same -animals, and in almost all the microscopic structures of the lower -world, where the force of gravity is entirely subjected to the more -powerful energy of capillary forces, it is extremely probable that the -mechanism of immiscible fluids and fluid valves is generally adopted. - -In several cavities in minerals I have found crystallized and other -bodies, sometimes transparent crystals, sometimes black spicular -crystals, and sometimes black spheres, all of which are moveable within -the cavity. In some cavities the two new fluids occur in an indurated -state, and others I have found to be lined with a powdery matter. This -last class of cavities occurred in topaz, and they were distinguished -from all others by the extraordinary beauty and symmetry of their -form. One of these cavities represented a finely ornamented sceptre, -and, what is still more singular, the different parts of which it is -composed lay in different planes. - -When the gem which contains the highly expansive fluid is strong, and -the cavity not near the surface, heat may be applied to it without -danger; but in the course of my experiments on this subject, the -mineral has often burst with a tremendous explosion, and in one case -wounded me on the brow. An accident of the same kind occurred to a -gentleman who put a crystal into his mouth for the purpose of expanding -the fluid. The specimen burst with great force and cut his mouth, and -the fluid which was discharged from the cavity had a very disagreeable -taste. - -In the gems which are peculiarly appropriated for female ornaments, -cavities containing the expansive fluid frequently occur, and if these -cavities should happen to be very near the surface or the edge of the -stone, the fever heat of the body might be sufficient to burst them -with an alarming and even dangerous explosion. I have never heard of -any such accident having occurred; but if it has, or if it ever shall -occur, and if its naturally marvellous character shall be heightened by -any calamitous results, the phenomena described in the preceding pages -will strip it of its wonder. - -There are no facts in chemistry more interesting than those which -relate to the changes of colour, which are produced by the mixture of -fluids, and to the creation of brilliant colours by the combination -of bodies in which no colouring matter is visible. Facts of this kind -are too common and too generally known to require to be noticed in a -work like this. The art of producing such changes was known to some of -the early impostors, who endeavoured to obtain a miraculous sanction -to their particular dogmas. Marcos, the head of one of the sects that -wished to engraft paganism upon Christianity, is said to have filled -three transparent glasses with white wine, and while he prayed, the -wine in one of the glasses became red like blood, that in another -became purple, and that in the third sky-blue. Such transformations -present no difficulty to the chemist. There are several fluids, such -as some of the coloured juices of plants, which change their colour -rapidly and without any additional ingredient: and in other cases, -there would be no difficulty in making additions to fluids which should -produce a change of colour at any required instant. - -A very remarkable experiment of an analogous nature has been publicly -exhibited in modern times. Professor Beyruss, who lived at the court -of the Duke of Brunswick, one day pronounced to his highness that the -dress which he wore should during dinner became red; and the change -actually took place, to the astonishment of the prince and the rest -of his guests. M. Vogel, who has recorded this curious fact, has not -divulged the secret of the German chemist; but he observes, that if -we pour lime-water into the juice of beet-root, we shall obtain a -colourless liquid; and that a piece of white cloth dipped in this -liquid and dried rapidly, will in a few hours become red by the mere -contact of air. M. Vogel is also of opinion that this singular effect -would be accelerated in an apartment where champagne or other fluids -charged with carbonic acid are poured out in abundance. - -Among the wonders of chemistry we must number the remarkable effects -produced upon the human frame by the inhalation of _paradise_ or -_intoxicating gas_, as it has been called. This gas is known to -chemists by the name of the _nitrous oxide_, or the _gaseous oxide of -azote_, or the _protoxide of nitrogen_. It differs from atmospheric -air only in the proportion of its ingredients, atmospheric air -being composed of twenty-seven parts of oxygen, and seventy-three -of nitrogen, while the nitrous oxide consists of thirty-seven parts -of oxygen, and sixty-seven of nitrogen. The most convenient way of -procuring the gas is to expose nitrate of ammonia in a tubulated -glass retort to the heat of an Argand’s lamp between 400° and 500° of -Fahrenheit. The salt first melts; bubbles of gas begin to rise from -the mass, and in a short time a brisk effervescence takes place, which -continues till all the salt has disappeared. The products of this -operation are the nitrous oxide and water, the watery vapour being -condensed in the neck of the retort, while the gas is received over -water. The gas thus obtained is generally white, and hence, when it -is to be used for the purposes of respiration, it should remain at -least an hour over water, which will absorb the small quantity of acid -and of nitrate of ammonia which adhere to it. A pound of the nitrate -of ammonia will in this way yield five cubic feet of gas fit for the -purpose of inhalation. - -It was discovered by Sir Humphrey Davy, that this gas could be safely -taken into the lungs, and that it was capable of supporting respiration -for a few minutes. In making this experiment he was surprised to find -that it produced a singular species of intoxication, which he thus -describes: “I breathed,” says he, “three quarts of oxide from and into -a silk bag for more than half a minute without previously closing my -nose or exhausting my lungs. The first inspiration caused a slight -degree of giddiness. This was succeeded by an uncommon sense of fulness -in the head, accompanied with loss of distinct sensation and voluntary -power, a feeling analogous to that produced in the first stage of -intoxication, but unattended by pleasurable sensations.” In describing -the effects of another experiment, he says, “Having previously closed -my nostrils and exhausted my lungs, I breathed four quarts of nitrous -oxide from and into a silk bag. The first feelings were similar to -those produced in the last experiment, but in less than half a minute, -the respiration being continued, they diminished gradually, and were -succeeded by a highly pleasurable thrilling, particularly in the -chest and the extremities. The objects around me became dazzling, and -my hearing more acute. Towards the last respiration the thrilling -increased, the sense of muscular power became greater, and at last an -irresistible propensity to action was indulged in. I recollect but -indistinctly what followed; I knew that my motions were varied and -violent. These effects very rarely ceased after respiration. In ten -minutes I had recovered my natural state of mind. The thrilling in the -extremities continued longer than the other sensations. This experiment -was made in the morning; no languor or exhaustion was consequent, my -feelings through the day were as usual, and I passed the night in -undisturbed repose.” - -In giving an account of another experiment with this gas, Sir Humphrey -thus describes his feelings: “Immediately after my return from a -long journey, being fatigued, I respired nine quarts of nitrous -oxide, having been precisely thirty-three days without breathing any. -The feelings were different from those I had experienced on former -experiments. After the first six or seven respirations, I gradually -began to lose the perception of external things, and a vivid and -intense recollection of some former experiments passed through my mind, -so that I called out, ‘What an annoying concatenation of ideas!’” - -Another experiment made by the same distinguished chemist was attended -by still more remarkable results. He was shut up in an airtight -breathing-box, having a capacity of about nine and a half cubic feet, -and he allowed himself to be habituated to the excitement of the gas, -which was gradually introduced. After having undergone this operation -for an hour and a quarter, during which eighty quarts of gas were -thrown in, he came out of the box and began to respire twenty quarts -of unmingled nitrous oxide. “A thrilling,” says he, “extending from -the chest to the extremities, was almost immediately produced. I felt -a sense of tangible extension highly pleasurable in every kind; my -visible impressions were dazzling and apparently magnified; I heard -distinctly every sound in the room, and I was perfectly aware of my -situation. By degrees, as the pleasurable sensation increased, I lost -all connexion with external things; trains of vivid visible images -rapidly passed through my mind, and were connected with words in such -a manner as to produce perceptions perfectly novel. I existed in a -world of newly connected and newly modified ideas. When I was awakened -from this same delirious trance by Dr. Kinglake, who took the bag from -my mouth, indignation and pride were the first feelings produced by -the sight of the persons about me. My emotions were enthusiastic and -sublime, and for a moment I walked round the room, perfectly regardless -of what was said to me. As I recovered my former state of mind, I felt -an inclination to communicate the discoveries I had made during the -experiment. I endeavoured to recall the ideas; they were feeble and -indistinct. One recollection of terms, however, presented itself, and -with the most intense belief and prophetic manner I exclaimed to Dr. -Kinglake, ‘Nothing exists but thoughts; the universe is composed of -impressions, ideas, pleasures, and pains!’” - -These remarkable properties induced several persons to repeat the -experiment of breathing this exhilarating medicine. Its effects were, -as might have been expected, various in different individuals; but its -general effect was to produce in the gravest and most phlegmatic the -highest degree of exhilaration and happiness unaccompanied with languor -or depression. In some it created an irresistible disposition to laugh, -and in others a propensity to muscular exertion. In some it impaired -the intellectual functions, and in several it had no sensible effect, -even when it was breathed in the purest state, and in considerable -quantities. It would be an inquiry of no slight interest to ascertain -the influence of this gas over persons of various bodily temperaments, -and upon minds varying in their intellectual and moral character. - -Although Sir Humphrey Davy experienced no unpleasant effects from the -inhalation of the nitrous oxide, yet such effects are undoubtedly -produced; and there is reason to believe that even permanent changes -in the constitution may be induced by the operation of this remarkable -stimulant. Two very interesting cases of this kind presented themselves -to Professor Silliman, of Yale College, when the nitrous oxide was -administered to some of his pupils. The students had been in the habit, -for several years, of preparing this gas, and administering it to -one another, and these two cases were the only remarkable ones which -deserved to be recorded. We shall describe them in Professor Silliman’s -own words:-- - -“A gentleman, about nineteen years of age, of a sanguine temperament, -and cheerful temper, and in the most perfect health, inhaled the usual -quantity of the nitrous oxide, when prepared in the ordinary manner. -Immediately his feelings were uncommonly elevated, so that, as he -expressed it, he could not refrain from dancing and shouting. Indeed -to such a degree was he excited, that he was thrown into a frightful -fit of delirium, and his exertions became so violent, that after a -while he sank to the earth exhausted, and there remained, until having -by quiet in some degree recovered his strength, he again arose, only -to renew the most convulsive muscular efforts, and the most piercing -screams and cries; within a few moments, overpowered by the intensity -of the paroxysm, he again fell to the ground, apparently senseless, and -panting vehemently. The long continuance and violence of the affection -alarmed his companions, and they ran for professional assistance. They -were, however, encouraged by the person to whom they applied to hope -that he would come out of his trance without injury; but for the space -of two hours these symptoms continued; he was perfectly unconscious of -what he was doing, and was in every respect like a maniac. He states, -however, that his _feelings vibrated_ between perfect happiness and the -most consummate misery. In the course of the afternoon, and after the -first violent effects had subsided, he was compelled to lie down two or -three times from excessive fatigue, although he was immediately aroused -upon any one’s entering the room. The effects remained in a degree for -three or four days, accompanied by a hoarseness, which he attributed -to the exertion made while under the immediate influence of the gas. -This case should produce a degree of caution, especially in persons of -a sanguine temperament, whom, much more frequently than others, we have -seen painfully, and even alarmingly affected.” - -The other case described by Professor Silliman was that of a man of -mature age, and of a grave and respectable character. “For nearly -two years previous to his taking the gas, his health had been very -delicate, and his mind frequently gloomy and depressed. This was -peculiarly the case for a few days immediately preceding that time; -and his general state of health was such, that he was obliged almost -entirely to discontinue his studies, and was about to have recourse -to medical assistance. In this state of bodily and mental debility, -he inspired about three quarts of nitrous oxide. The consequences -were, an astonishing invigoration of his whole system, and the most -exquisite perceptions of delight. These were manifested by an uncommon -disposition for pleasantry and mirth, and by extraordinary muscular -power. The effects of the gas were felt without diminution for at least -thirty hours, and in a greater or less degree for more than a week. - -“But the most remarkable effect was that _upon the organs of taste_. -Antecedently to taking the gas, he exhibited no peculiar choice in -the articles of food, but immediately subsequent to that event, he -_manifested a taste for such things only as were sweet_, and for -several days _ate nothing but sweet cake_. Indeed this singular taste -was carried to such excess, that he used _sugar and molasses, not -only upon his bread and butter, and lighter food, but upon his meat -and vegetables_. This he continues to do even at the present time; -and although eight weeks have elapsed since he inspired the gas, he -is still found _pouring molasses over beef, fish, poultry, potatoes, -cabbage, or whatever animal or vegetable food is placed before him_. - -“His health and spirits since that time have been uniformly good, and -he attributes the restoration of his strength and mental energy to the -influence of the nitrous oxide. He is entirely regular in his mind, and -now experiences no uncommon exhilaration, but is habitually cheerful, -while before he was as habitually grave, and even to a degree gloomy.” - - * * * * * - -Such is a brief and general account of the principal phenomena of -Nature, and the most remarkable deductions of science, to which -the name of Natural Magic has been applied. If those who have not -hitherto sought for instruction and amusement in the study of the -material world, shall have found a portion of either in the preceding -pages, they will not fail to extend their inquiries to other popular -departments of science, even if they are less marked with the -attributes of the marvellous. In every region of space, from the -infinitely distant recesses of the heavens to the “dark unfathomed -caves of ocean,” the Almighty has erected monuments of miraculous -grandeur, which proclaim the power, the wisdom, and the beneficence -of their Author. The inscriptions which they bear--the hand-writing -which shines upon their walls--appeal to the understanding and to -the affections, and demand the admiration and the gratitude of every -rational being. To remain willingly ignorant of these revelations of -the Divine Power is a crime next to that of rejecting the revelation -of the Divine Will. Knowledge, indeed, is at once the handmaid and the -companion of true religion. They mutually adorn and support each other; -and beyond the immediate circle of our secular duties, they are the -only objects of rational ambition. While the calm deductions of reason -regulate the ardour of Christian zeal, the warmth of a holy enthusiasm -gives a fixed brightness to the glimmering lights of knowledge. - -It is one of the darkest spots in the history of man, that these noble -gifts have been so seldom combined. In the young mind alone can the two -kindred seeds be effectually sown; and among the improvements which -some of our public institutions require, we yet hope to witness a -national system of instruction, in which the volumes of Nature and of -Revelation shall be simultaneously perused. - - D. BREWSTER. - - ALLERLY, _April 24th, 1832_. - - - THE END. - -J. HADDON, PRINTER, CASTLE STREET, FINSBURY. - - - - -A GENERAL DESCRIPTIVE - -Catalogue - -OF THE - -FAMILY LIBRARY; - -A SERIES OF - -ORIGINAL AND SELECT WORKS. - -_The Works sold separate, at_ =3s.= =6d.= _per Volume_. - - - “BOOKS THAT YOU MAY CARRY TO THE FIRE, AND HOLD READILY IN YOUR HAND, - ARE THE MOST USEFUL AFTER ALL. A MAN WILL OFTEN LOOK AT THEM, AND BE - TEMPTED TO GO ON, WHEN HE WOULD HAVE BEEN FRIGHTENED AT BOOKS OF A - LARGER SIZE, AND OF A MORE ERUDITE APPEARANCE.”--DR. JOHNSON. - -“MR. MURRAY’S Library.... A very excellent and always entertaining -Miscellany.”--_Edinburgh Review._ - -“MR. MURRAY’S Family Library.... A title, which, from the valuable -and entertaining matter the collection contains, as well as from the -careful style of its execution, it well deserves. No family, indeed, -in which there are children to be brought up, ought to be without this -_Library_, as it furnishes the readiest resources for that education, -which ought to accompany or succeed that of the boarding-school or -the academy, and is infinitely more conducive than either to the -cultivation of the intellect.”--_Monthly Review._ - -LONDON: - -WILLIAM TEGG AND Co., - -85, QUEEN STREET, CHEAPSIDE. - - -ADDRESS. - - -It is a source of no inconsiderable gratification to find the -anticipations with which the FAMILY LIBRARY was commenced exceeded by -its success, and the liberal patronage bestowed on it. - -The best proof of this is the fact that of many of the volumes more -than 40,000 copies have been sold in this country alone. It has been -warmly commended in the journals of Great Britain, in those of France, -Germany, Italy, and other parts of Europe. - -Its general estimation is also proved by its having been reprinted in -America, and translated into most of the Continental Languages. - -Upon the copyright alone of the Works of the Series, upwards of -£12,000 has been expended, and the list of Contributors embraces the -distinguished names of - - SIR WALTER SCOTT, BART. - MR. SOUTHEY. - MR. LOCKHART. - REV. H. H. MILMAN. - WASHINGTON IRVING. - ALLAN CUNNINGHAM. - MR. TYTLER. - REV. J. WILLIAMS. - MR. BARROW (of the Admiralty). - REV. J. J. BLUNT. - REV. E. SMEDLEY. - REV. G. R. GLEIG. - SIR DAVID BREWSTER. - MR. COLERIDGE. - MAJOR SIR F. B. HEAD. - MR. DAVENPORT. - MR. CROFTON CROKER. - MR. LANDER. - CYRUS EDMONDS. - MR. BUCKE. - W. E. AYTOUN. - REV. T. CHETWODE EUSTACE. - MR. ROSCOE. - SIR FRANCIS PALGRAVE. - -With the assistance of persons of such eminent talent was commenced the -design of supplying the deficiencies of English Literature, by a series -of Standard Works, which, with excellence of execution, should combine -the advantages of lowness of price, convenience of size and form, and -elegance of illustration. - -While the moderate cost has placed the Work within the reach of all -classes of Readers, the interesting nature of the subjects, and the -popular mode of treating them, render it well suited for the perusal -of Young Persons, and calculated to stimulate in them a taste for -Literature and Science. In the beauty of its Embellishments, the FAMILY -LIBRARY has surpassed all its Contemporaries; and no pains or cost have -been spared to render each Volume as attractive externally, as it will -prove entertaining and useful on perusal. With these recommendations, -this Publication will be found to deserve a conspicuous place in every -well-selected Library; and as it may be purchased in its complete -state, or separate, _each work being complete in itself_, it will -furnish valuable Literary Presents, adapted to the means and tastes of -all classes of Purchasers. - -The Volumes of which the FAMILY LIBRARY consists, may be classed under -the following heads:-- - -Biography. - - LIFE OF NAPOLEON. - THE COURT AND CAMP OF BUONAPARTE. - LIVES OF BRITISH PAINTERS, SCULPTORS, AND ARCHITECTS. - LIFE OF COLUMBUS. - LIVES AND ADVENTURES OF THE COMPANIONS OF COLUMBUS. - LIFE OF NELSON. - LIVES OF BRITISH PHYSICIANS. - LIFE OF BRUCE. - LIVES OF SCOTTISH WORTHIES. - LIFE OF SIR ISAAC NEWTON. - LIFE OF PETER THE GREAT. - LIFE AND TIMES OF WASHINGTON. - LIFE OF ALI PASHA. - LIFE OF DUKE OF MARLBOROUGH. - LIFE OF CERVANTES. - LIFE OF CICERO. - LIFE OF RICHARD CŒUR DE LION. - LIFE OF MAHOMET. - LIVES OF ENTERPRISING MEN. - -History. - - HISTORY OF THE JEWS. - HISTORY OF INDIA. - HISTORY OF VENICE. - HISTORY OF THE ANGLO-SAXONS. - REFORMATION IN ENGLAND. - TYTLER’S GENERAL HISTORY. - DE FOE’S HISTORY OF THE PLAGUE YEAR. - NARRATIVE OF NAPOLEON’S EXPEDITION TO RUSSIA. - THE RUINS OF ANCIENT CITIES. - THE MUTINY AT THE NORE. - -Voyages and Travels. - - LANDER’S DISCOVERIES IN AFRICA. - FAMILY TOUR IN HOLLAND. - NARRATIVE OF THE MUTINY OF THE BOUNTY. - SIX MONTHS IN THE WEST INDIES. - EUSTACE’S CLASSICAL TOUR IN ITALY. - -State Trials. - - TRIALS OF CHARLES THE FIRST AND THE REGICIDES. - -Natural History and Science. - - A POPULAR NATURAL HISTORY OF INSECTS. - LETTERS ON NATURAL MAGIC. - DEMONOLOGY AND WITCHCRAFT. - WESLEY’S NATURAL PHILOSOPHY. - -Miscellaneous. - - SALMAGUNDI. BY WASHINGTON IRVING. - SKETCH BOOK. BY DITTO. - CROKER’S FAIRY LEGENDS. - KNICKERBOCKER’S NEW YORK. - SKETCHES OF IMPOSTURE AND CREDULITY. - CHRONICLES OF LONDON BRIDGE. - NARRATIVES OF PERIL AND SUFFERING. - - -THE - -FAMILY LIBRARY. - - -A NEW HISTORY OF THE ANGLO-SAXONS. - -_By_ SIR FRANCIS PALGRAVE. _With Illustrative Woodcuts._ - -This work (as the preface mentions) was intended in imitation of the -_Tales of my Grandfather_. “Let me hope,” the author says, “that -occasionally, whilst the younger branches find amusement in the tales -and adventures here brought together, some of the older folks may -not be unwilling to take this little summary in hand, as a temporary -substitute for the unmanageable folios produced by the unwearied -industry of Saville, Twysden, and Warton, and Wilkins.” - - -THE REFORMATION IN ENGLAND. - -By the REV. J. J. BLUNT. - -This is a compact but lively and entertaining sketch of the -Reformation, and the personal history of the founders of our National -Church. - -The Reformation is one of the most remarkable events in our history, -whether in relation to politics or religion; for its influence was -most powerful upon both. The reading, profession, and taste of the -author have led him to regard it chiefly in the latter light; and, -therefore, brief as the sketch is, it will not be found of the nature -of an abridgment, but a continuous though succinct account of the rise, -progress, and consummation of that great revolution of the _Church of -England_. - -⁂ This book is included in the list of works of the Society for -Promoting Christian Knowledge. - - -THE TRIALS OF CHARLES THE FIRST, - -AND OF SOME OF THE REGICIDES. - -_With Biographies of_ BRADSHAW, IRETON, HARRISON, _&c., and -Illustrative Notes, Legal and Historical. Portrait, Views, &c._ - -A clear and detailed account of the most remarkable and important of -English _Causes Célèbres_, with a narrative of the distinguishing -events of that interesting period of our history. - - -HISTORY OF THE EXPEDITION TO RUSSIA UNDERTAKEN BY THE EMPEROR NAPOLEON. - -By GENERAL COUNT PHILIP DE SEGUR. 2 Vols. - -The established interest created by Count Segur’s history renders any -commendation vain--any anticipation of its contents of no value. When -those recollections of the most disastrous campaign ever undertaken -were first published, they were charged with exaggeration, if not -falsehood; but a severe scrutiny has shown that, with the exception -of a few unimportant errors, every statement in this extraordinary -production is entitled to public confidence. The translation made -for the Family Library exhibits evidence of the utmost care, and the -misstatements into which the author inadvertently fell are corrected by -the translator. - - -THE - -LIFE OF JOHN, DUKE OF MARLBORO’. - -By CHARLES BUCKE. - -Editorial ingenuity, and economy in printing, have reduced the -varied annals of the great Marlborough within the grasp of moderate -literary industry. The editor has drawn a fair and truthful picture -of the martial Duke, lauding his political and public virtues without -concealing those blemishes that his warmest advocates confess to -be equivocal. When the balance betwixt good and evil is struck, -Marlborough stands out in bold relief in the picture of history; and -had his brilliant victories been followed by firm and honest treaties, -their effects, like those of Waterloo, would have been felt in the -happiness of the British dominions. - - -THE LIFE AND WRITINGS OF MIGUEL DE CERVANTES SAAVEDRA. - -_With Literary and Historical Illustrations by_ THOS. ROSCOE, Esq. - -It is not strange that the writings of Cervantes, with the exception -of Don Quixote, should have so long remained unknown, since it was -generally asserted that “the Spaniards had but one good book, that -one which had made all the others ridiculous.” The _chef-d’œuvre_ is -translated into every language of Europe, while the same author’s -plays and novels are sealed against all but Spanish scholars; and his -chivalrous life, previous to this publication, buried in oblivion to -which the anarchy of Spain had consigned it. Cervantes flourished in -the reign of Philip II., and was contemporary with Lope de Vega. - - -THE LIFE OF NELSON. - -By ROBERT SOUTHEY, Esq., LL.D., Poet Laureate, &c. - -_With numerous Woodcuts from Designs by_ GEORGE CRUIKSHANK, _engraved -by_ THOMPSON _and_ WILLIAMS. - -In order to promote the wishes and intention of the author, and to give -the work the widest circulation, it has been printed in its present -form, at _one-third of the original price_, with embellishments by the -most talented artists. - - “Many Lives of Nelson have been written, but one was yet wanting, - clear and concise enough to become a manual for the young sailor, - which he may carry about with him till he has treasured up the example - in his memory and in his heart.”--_Author’s Preface._ - - “A work which, as long as the English language is understood, will be - regarded as one of the finest monuments that genius ever raised to - valour.”--_Monthly Review._ - - -THE LIFE OF MAHOMET, - -FOUNDER OF THE RELIGION OF ISLAM, AND OF THE EMPIRE OF THE SARACENS. - -By REV. SAMUEL GREEN. - -With the exception of the religion of the Gospel, that of Mahomet has -produced the greatest revolution recorded in history, and effected the -greatest changes in the state of the civilized world; its history -and character, therefore, become an object of curiosity with every -enlightened mind. Considered as part of the general annals of the -world, unconnected with religion, it furnishes most interesting records -of the human race; but viewed as part of the chain of predicted events, -having a direct reference to the Christian Church, it urges a stronger -claim to our attention. The events of Mahomet’s life are to be found -in works inaccessible from their costliness, discouraging from their -bulk, and sometimes written in Eastern characters. This volume is a -compilation from the most authentic. - - -JOURNAL - -OF AN EXPEDITION TO EXPLORE THE COURSE AND TERMINATION OF THE NIGER. - -By RICHARD and JOHN LANDER. - -_With Portraits, Engravings, and a Map, showing the course of the -Niger._ - -With slight encouragement from the Colonial Office, these young men set -out on an enterprise which in all previous instances had led to death; -and all who knew the nature of the climate, and the hardships they -must encounter, predicted that the only news their countrymen would -ever receive concerning them, would be some obscure rumour of their -destruction. The narrative shows how often such predictions were on -the point of being verified. There is scarcely a misery to be endured -by human nature that these young men have not encountered; they have -been frequently on the brink of death--they have been imprisoned--they -have been sold as slaves--they have been plundered, and obliged to swim -for their lives, not sure, in the end, that they were not swimming -into greater danger--and, to crown the whole, they have been brutally -treated and nearly sacrificed to the cupidity and revenge of savages -by one of their own countrymen. In spite of all these obstacles, by -means of patience and perseverance, by enthusiasm and resignation, by -courage and long-suffering, they finally triumphed over every species -of resistance, and, what is more, completely gained their object. - -The result of Captain Clapperton’s discoveries was a very shrewd guess -that the Niger flowed westward, and into the Bight of Benin. With the -view of ascertaining this, the Landers were set down at the same point -of the coast of Guinea where the former expedition had commenced. - - -THE LIFE OF MARCUS TULLIUS CICERO. - -By J. F. HOLLINGS. - -The name of Cicero himself--the universal admiration of his genius--the -era in which he flourished--and the part he enacted, bring his memoirs -within the circle of subjects suited to domestic education. His Life, -by Middleton, is more acceptable to the learned than the learner, and -this conclusion has led to this epitome, in which the text contains the -uninterrupted personal memoir of the philosopher in a popular form; -while such information as belongs more distinctively to the department -of ancient literature is conveyed by means of notes and references. - - -SIX MONTHS IN THE WEST INDIES. - -By HENRY NELSON COLERIDGE, M.A. - -This little work, which has already received public approbation, is -calculated to amuse in no ordinary degree, for the descriptions of -scenery are vivid, the pictures of society graphic, and the adventures -and anecdotes interesting and varied. - - -LIVES - -OF THE MOST EMINENT BRITISH PAINTERS, SCULPTORS, AND ARCHITECTS. - -By ALLAN CUNNINGHAM. - -_6 vols., with Portraits of Thirty-two of the most distinguished -British Artists, &c._ - -The author has collected in six small volumes the History of Art in -England, and the Lives, Characters, and Works of its Professors,--the -materials for which were previously scattered through many volumes. -On this account, these biographies have been considered a valuable -acquisition to literature; and although the critical observations will -render them valuable to the student, yet, being free from the dry -technicalities of virtù, and abounding with personal anecdote, they are -not less alluring to the ordinary reader. - -The annals of Art, and the lives of its followers, though deficient -in the spirit-stirring incidents of the warrior and the politician, -possess an interest not less attractive. The labours and struggles -of genius, the success of perseverance, and the inutility of natural -talent separated from prudence, as exemplified in these biographies, -will afford a useful moral lesson, at the same time that the perusal of -the stories of such lives is a source of pleasure and entertainment. - - -THE HISTORY OF THE JEWS. - -By REV. H. H. MILMAN. Complete in 3 vols. - -_With Original Maps and Woodcuts._ - -With the exception of Josephus, we have no historian of the Jews, and -he lived at a period too remote and too limited to enable him to do -justice to his subject. It is true, many events have been narrated -by Rollin, and the authors of the Universal History, and noticed -by commentators,--but a narrative at once Christian and liberal in -its tone, spirited and elegant in its language, and depicting with -something like kindred enthusiasm and eloquence, the manners, wars, -religion, and policy of the most extraordinary of nations, was still -wanting. - -The object of the present work is strictly historical,--yet it affords -elucidation of many obscure passages in the Old Testament; avails -itself of the casual evidence of heathen writers; and throws new light -on the manners and customs of the “Unchanging East,” by references to -the ablest modern travellers. - - -THE NATURAL HISTORY OF INSECTS. - -_With very numerous Woodcuts. 2 vols._ - -The study of Natural History is at all times pleasing and instructive; -the object on this occasion has been to render it doubly captivating -by a plain and simple style, and by the numerous wood engravings. The -extravagant price of books of Natural History has deterred many, and it -is no exaggeration to assert that the information and embellishments -contained in these volumes could hardly be purchased in any other form -at a cost of less than several pounds. - - -COMPENDIUM OF NATURAL PHILOSOPHY: - -A SURVEY OF THE WISDOM OF GOD IN THE CREATION. - -By JOHN WESLEY. A New Edition, by ROBERT MUDIE. 3 Vols. - -John Wesley’s name is a guarantee for the moral rectitude of the -original volumes, as well as the full information which they contained -at first publication; but since that time the progress of natural -science has been greater than during the whole previous period -of human history. Following Wesley’s arrangement, the editor has -incorporated the most recent discoveries, adding many new facts to -those of Baron Cuvier: he has pursued the history of invertebrated -animals down to the very verge of animal existence, and annexed a -full account of the vegetable kingdom. The re-edited work, therefore, -is not only introductory on detached portions of nature to students, -but recapitulatory to such as have already consulted the details. It -may not be immaterial to remark that, while controverted points are -studiously avoided, the very latest discoveries are introduced, and -the language employed is free from that technicality which may gratify -pedantry with out promoting knowledge. - - -THE LIFE OF ALI PASHA OF TEPELENI - -VIZIER OF EPIRUS. - -By R. A. DAVENPORT. - -It is a common error to imagine that a greater number of individuals -rise in England than in other countries; more, certainly, attain wealth -and respectability under free than despotic governments; but it is -under the latter only that the very humblest and most illiterate, if -possessed of courage and cunning, may approach to the steps of the -throne itself. Of the numerous examples which Turkish history affords, -none ran a more celebrated career than Ali Pasha. Rendering himself -independent by a series of rebellions, his throne was supported by the -blood of thousands; yet, notwithstanding the means by which he acquired -power, Napoleon treated with him,--Lord Byron was his guest,--and -England accepted his friendship. Turkish history, being a record of the -indulgence of the worst passions of human nature, is always a terrible -romance, but the life of Ali Pasha exceeds in guilt and horror the -most infamous periods of Ottoman history. The great tragedy in which he -performed so principal a part, was concluded by his own assassination -in the throne-room of his palace, in a manner almost too merciful for -such a ferocious monster. - - -THE HISTORY OF BRITISH INDIA. - -By the REV. G. R. GLEIG, F.R.S. 4 Vols. - -_With a Map and 10 Engravings._ - -A History of India in a portable form, and familiar style, having been -considered a desideratum, the present work was undertaken. It commences -with the early annals and first civilization of the Hindoos, traces the -progress and decline of the Mahometan power, and brings the history of -the success of the British arms down to the permanent establishment of -the India Company, and the foundation of that stupendous Empire. It is -among the annals of the East that the real _Romance of History_ must -be sought. In the variety of marvellous incidents, the unexpected turn -of events, the sudden alternation of fortune, we might fancy we were -reading an Oriental fable--a tale from the Arabian Nights, rather than -sober history. - - -SKETCHES FROM THE HISTORY OF VENICE. - -_With eight Views after Prout, twenty-nine Cuts after_ TITIAN, _Maps, -etc._ - -Few can explore for themselves the treasures of the Italian Chronicles. -The author of this work has laid open their stores for the benefit of -English readers,--gleaning from them characteristic incidents, amusing -stories and anecdotes; while he has sustained all the dignity of -historical research. - -The writer has avoided the mistakes into which mere compilers fall;--he -has not sunk into a mere annalist, transcribing a dry register of -facts, but he either passes over entirely, or touches very slightly, -events of minor importance, and reserves himself for those more -momentous and interesting transactions which require to be more fully -displayed. The beauty of style in which these volumes are written -has attracted general notice, and the applause of the most competent -judges,--in this respect, indeed, they yield to no work of the series. - - -LETTERS ON DEMONOLOGY AND WITCHCRAFT. - -By SIR WALTER SCOTT, BART. - -No subject could have been better adapted to the lamented author of -“Waverley” than “the history of that dark chapter of human nature” to -which this volume is devoted. Sir Walter has given sufficient evidence -in his novels and romances of his acquaintance with the superstitions -of our own and remoter times. In this volume he has laid open the -stores of his memory and reading, has condensed and elucidated the -subject; in many cases explaining by natural causes occurrences -supposed to be supernatural. - - -LETTERS ON NATURAL MAGIC. - -ADDRESSED TO SIR WALTER SCOTT. - -By SIR DAVID BREWSTER, K.G.H. - -_A New Edition, Illustrated with upwards of 80 Woodcuts._ - -The author of this volume passes under review “the principal phenomena -of nature and the leading constructions of art which bear the impress -of a supernatural character,” and more especially “those singular -illusions of sense by which the most perfect organs either fail to -perform their functions or perform them faithlessly, and where the -efforts and the creations of the mind predominate over the direct -perceptions of external nature.” - -These are themes full of interest and worthy of the labour bestowed -upon them by the philosophic author. It is lamentable to think how -many minds rest contented with the most unphilosophical apology for -ignorance, by designating the acts they do not examine, wonders or -mysteries,--while to the mass of men, such acts are inexplicable, -except on some theory of superhuman agency, as absurd as it is -erroneous. The Letters of Sir David Brewster will disabuse both -classes. To the first, he furnishes philosophical data for explaining -many hitherto puzzling appearances--to the last, he supplies the means -of escape from absurdities calculated to retain them in mental slavery. - -The eye and the ear are of course the great organs of deception, -and accordingly optical illusions occupy a considerable portion of -the volume. The illusions depending on the ear succeed, and after -these, we are treated with amusing descriptions of feats of strength, -of mechanical automata, and of some of the more popular wonders of -chemistry. Under each of these divisions, anecdotes of the most -interesting kind illustrate the author’s explanations, and no subject, -in itself grave and important, was ever on the whole treated in a more -amusing manner. - - -LIFE AND TIMES OF WASHINGTON. - -By CYRUS R. EDMONDS. 2 Vols. - -As the foundation of the American Republic is attributable to British -error, its history is identified with our own. Those who have related -the events of that memorable period, and drawn the character of -the patriot-general, living too near the epoch, were dazzled, and -discovered only the beauty of republican principles. Written when -party-feeling had died away, and limited monarchy allowed to vindicate -its superiority, Mr. Edmonds’s Life of Washington is free from that -nationality which disfigures biography, and fearlessly defends British -institutions against the advocates of democracy. The more voluminous -memoirs of the virtuous republican chief abound with American -prejudices; these volumes are English both in style and sentiment. - - -THE LIFE OF NAPOLEON BUONAPARTE. - -_With 15 Engravings on Steel and Wood, by_ FINDEN _and_ THOMPSON; _the -Woodcuts from Designs by_ GEO. CRUIKSHANK. - -The fact that since the publication of this work, SEVEN-AND-TWENTY -THOUSAND copies have been disposed of in this country, beside various -editions in America,--will speak more in its favour than the most -artful and high-flown praise. It is an epitome of all that has been -_proved_ to be true concerning the career of the most extraordinary -man of the last thousand years. We possessed no previous epitome of -his history; and notwithstanding the smallness of space into which it -is compressed, the narrative is clear. The Life of Napoleon, doubly -interesting when relieved of the tediousness of useless detail, has -never been better told. Volumes so rich in information will be devoured -by youth, and are worthy to be consulted by the maturest reader. - -The work is written with fairness and impartiality, free from -party-spirit, and the author has interwoven with his narrative all the -new illustrations and anecdotes furnished by Bourrienne and the other -fast-following memoirs of the French press. - - -THE RUINS OF ANCIENT CITIES. - -By CHARLES BUCKE. 2 Vols. _Illustrated._ - -Cities, like men, flourish and decay, and each possess their annals. -The poetic conception of personifying these broken records of natural -grandeur originated with the editor himself; but, in carrying out his -design, he acknowledges Rollin as his guide. This elegant and accurate -writer confesses that he does not hesitate to rifle the cabinets of -others to enrich his own; that he often transcribed without quoting, -and introduced solid reflections borrowed from the sterling works of -others. This compilation is also a beautiful bead-roll, the precious -production of many minds: it is a fair fabric of costly materials -raised by a literary architect, whose industry, experience, and -candour, are already acknowledged by the public. - - -SALMAGUNDI; - -OR, THE WHIM-WHAMS AND OPINIONS OF LAUNCELOT LANGSTAFF, ESQ. - -_With numerous Cuts by_ GEORGE CRUIKSHANK. - -The earliest paintings of the greatest masters sometimes differ -considerably from those of their maturer years, and not unfrequently -surpass them in brilliancy and freshness. If the Salmagundi Papers be -compared with the subsequent works of the same author, they will not be -found inferior in originality, vivacity, or virtuous tendency. While -satire is the adopted weapon of chastisement, it wounds the vicious -only. “We have,” say the authors, “no fear of the censures of the -wise, good, or fair, for they will ever be sacred from our attacks. -We reverence the wise, love the good, and adore the fair: we declare -ourselves champions in their cause--in the cause of morality--and we -throw our gauntlet to all the world besides.” - - -THE LIFE OF PETER THE GREAT. - -_By_ JOHN BARROW, Esq., F.R.S., _Author of the “Eventful History of the -Mutiny of the Bounty.” With Portrait._ - -The author of this Biographical Memoir has arranged the scattered -fragments of Histories, Lives, Anecdotes, and Notices, manuscript or -print, of one of the most extraordinary characters that ever appeared -in the world, in any age or country;--being full of contradictions, yet -consistent; a promoter of literature, arts, and sciences, yet without -education; “he gave a polish,” says Voltaire, “to his nation, and was -himself a savage;” he taught his people the art of war, of which he was -himself ignorant; from the first glance of a cock-boat, five hundred -miles from the sea, he became an expert ship-builder, created a fleet, -partly constructed with his own hands, made himself an expert sailor, a -skilful pilot, a great captain: in short, he changed the manners, the -habits, the laws of the people, and the very face of the country. - - -SKETCHES OF IMPOSTURE, DECEPTION, AND CREDULITY. - -Credulity is so comprehensive a term, that greater difficulties are -encountered in selecting than multiplying examples. These “Sketches” -take an extensive range over the Pagan superstitions--tell of pretended -Messiahs, false prophets, and mock miracles--describe Hindoo and other -Oriental deceptions in religious worship--relate of royal impostors, -military stratagems, literary cheats, and commercial bubbles--unfold -the mysteries of thefts and forgeries, and conclude with an interesting -account of the delusions of alchemy and medical frauds. The work may -be considered as a supplement to Scott’s “Letters on Demonology,” and -Brewster’s on “Natural Magic.” - - -THE CHRONICLES OF LONDON BRIDGE. - -By AN ANTIQUARY. _Illustrated._ - -This is an original work, and the reader will at once perceive that -the “Nominis umbra” of “An Antiquary” conceals a mind of no ordinary -mould--the possessor of no common store of erudition. A velvet cushion -has been the nucleus of the History of the Reformed Church--a library -chair that of a history of literature. In this volume London Bridge is -selected as the bond that is to bind, the avenue that is to lead from, -ancient to modern London. Much valuable civic history and legend is -here adorned with language, precise, classical, and nervous; while the -illustrations, fifty-six in number, present more perfect reminiscences -of society and manners in the olden time than the most technical and -laboured descriptions. - - -THE LIFE OF ALEXANDER THE GREAT. - -By the REV. JOHN WILLIAMS, M.A., - -_Head Master of the Edinburgh Academy. Map and Woodcuts._ - -This volume fills a blank in the Historical Library, and furnishes a -capital school-manual. It is not confined to the mere exploits of the -Macedonian hero, but contains a masterly view of the times in which -he lived, and of the manners, customs, etc. of the Greeks, Persians, -Egyptians, Arabs, and Indians, and other nations. The whole story is -told in a manner calculated to stimulate the curiosity and rouse the -reflection of the youthful reader. - - -THE - -SKETCH BOOK OF GEOFFRY CRAYON, ESQ. - -_2 Vols._ - -Had Mr. Irving left no other memorial of his genius than the Sketch -Book, it would be alone sufficient to a pedestal in the Palatine -Library of the XIXth. century. Justly may he contend with the -“Enchanter of the North” in the rare quality of story-telling, for -never was a tale more pleasantly told than “_The Legend of the Sleepy -Hollow_.” Neither is there a more exquisitely beautiful or sentimental -fragment in all the heart-moving scenes drawn by that able and amiable -writer than Irving’s sketch of “_The Broken Heart_.” - - -VOYAGES AND DISCOVERIES OF - -THE COMPANIONS OF COLUMBUS. - -By WASHINGTON IRVING. _With Illustrations._ - -The extraordinary actions and adventures of these men may be said to -unite romance and truth. Chivalry had left the land, and launched -upon the deep in the ships of these Spanish discoverers. Contempt -of danger, and fortitude of suffering, a passion for vain-glorious -exploit, and a bigoted zeal for the propagation of their faith, are -the characteristics of these marine heroes. The extravagant career of -the daring Ojeda, particularly his adventures along the coast of Terra -Firma, and the wild shores of Cuba--the sad story of Nicuessa--the -singular cruise of Juan Ponce de Leon, who fell upon the coast of -Florida, in his search after an imaginary fountain of youth--and above -all, the chequered fortunes of Vasco Nunez de Balboa, whose discovery -of the Pacific Ocean forms one of the most beautiful and striking -incidents in the history of the New World,--are so many examples of -knight-errantry upon the high seas. The charm of Mr. Irving’s style has -never been displayed more strikingly than in this little manual of true -romance. - - -THE UNIVERSAL HISTORY FROM THE CREATION OF THE WORLD. - -By ALEXANDER FRASER TYTLER, LORD WOODHOUSELEE. - -_6 Vols._ - -Perhaps few works in general literature were ever produced more -synthetically, or with more vigilant caution than “The Universal -History.” Mr. Gilpin requested his most learned and judicious friends -to criticize his MSS., and for many years they were submitted to this -wholesome ordeal. The Universal History at first appeared in the form -of Lectures, and was received with the most entire approbation of -the students. The sketch thus carefully made for oral delivery was -gradually filled up, and the picture completed in every part. - -The Author’s style is terse, lucid, and nervous, and his plan not only -moral, but more instructive than any hitherto pursued in treating of -general history. - - -THE LIFE OF SIR ISAAC NEWTON. - -By SIR DAVID BREWSTER, LL.D., F.R.S. - -_Portrait and Woodcuts._ - -This is the only extended life of the greatest of English philosophers. -In attempting to fill up this gap in our philosophic and scientific -literature, Sir David Brewster has not only sought out, from resources -hitherto unknown, every fresh and novel particular regarding his -life, but has given the most lucid explanation of Newton’s great -discoveries--and has endeavoured to render these intelligible to all -classes of readers. - - -A JOURNAL OF THE PLAGUE YEAR. - -By DANIEL DE FOE. - -_A New Edition, with Historical Notes by_ E. W. BRAYLEY, F.S.A. - -“From De Foe’s History of the Plague we may derive more information -than from all the other publications on the subject put together. -He has collected all the facts attending the rise, progress, and -termination of the malady; an accurate report of the number of deaths, -as published by authority; a faithful account of the regulations -adopted to arrest and mitigate its fury. But that which imparts life -to the whole, and forms its distinguishing feature, is its descriptive -imagery. The effects upon the affrighted minds of the inhabitants are -depicted with all the genuine pathos of nature, without any aim at -effect, but with the ease and simplicity of real life.” - - -A CLASSICAL TOUR THROUGH ITALY. - -By the REV. T. CHETWODE EUSTACE. - -_Seventh Edition. With great Additions and Translations of the various -Quotations from Ancient and Modern Authors. 3 Vols._ - -It was the fate of Eustace, like that of Bruce, to see his labours -rejected, and his veracity impeached; nor did these painful -insinuations originate in the chance of ignorance. His honesty was also -called in question. But truth in both instances eventually prevailed, -and the writings of both these amiable but injured travellers are -now appealed to as standard works. Eustace’s Journey is not only the -most accurate in topography, architecture, and politics, but is, -_par excellence, the classical_ tour through this land of poetry and -painting. Those tourists who would soar above Eustace, have vainly -sought to depreciate his learning. Those whose lot was cast below him, -have gathered from his rich plumage; but neither had the courage to -pass him by in silence. In this edition, which is sold at one-third the -cost of the earlier ones, the discoveries made by excavation since the -author’s, death have been introduced. - - -THE EVENTFUL HISTORY OF - -THE MUTINY AND PIRATICAL SEIZURE OF THE BOUNTY. - -By JOHN BARROW, Esq., _Secretary to the Admiralty. With Five Plates -from Original Sketches._ - -“The Author of this little volume has brought into one connected view -what has hitherto appeared only in detached fragments--and some of -these not generally accessible--the historical narrative of an event -which deeply interested the public at the time of its occurrence, and -from which the naval service in particular, in all its ranks, may still -draw instructive and useful lessons. - -“The story in itself is replete with interest. We are taught by the -Book of Sacred History, that the disobedience of our first parents -entailed on our globe of earth a sinful and a suffering race; in -our time there has sprung up from the most abandoned of this sinful -family--from pirates, mutineers, and murderers--a little society, -which, under the precepts of that sacred volume, is characterized -by religion, morality, and innocence. The discovery of this happy -people, as unexpected as it was accidental, and all that regards their -condition and history, partake so much of the romantic, as to render -the story not ill-adapted for an epic poem.”--_Author’s Preface._ - - -FAIRY LEGENDS - -AND TRADITIONS OF THE SOUTH OF IRELAND. - -By T. CROFTON CROKER. _With numerous Cuts._ - -Fairy Tales epitomize the customs, and manners, and superstitions of -a people in by-gone times, and are therefore valuable as auxiliary to -the interpretation of history. Mr. Croker’s Irish Legends are rich -in that racy humour that characterizes his countrymen, and appear to -have exhausted the traditionary treasures of the Emerald Isle. The -Illustrations are also redolent of Hibernian wit and genius,--they are -spirited designs, and in the happiest manner of Messrs. Brooke and -Maclise, with whose merits the public are familiar. - - -THE LIFE AND TIMES OF RICHARD I. - -SURNAMED CŒUR-DE-LION, KING OF ENGLAND. - -By WILLIAM E. AYTOUN, _Author of “Bothwell,” a Poem_. - -None of our monarchs has achieved a wider fame than Cœur-de-Lion, yet -his personal history is of all others least studied or understood. -All men know that he rebelled against his father, but comparatively -few are aware of the cause. All know that he conducted a crusade, and -encountered Saladin; but few are acquainted with the extent of his -conquests, or the causes which drove him back a fugitive to Europe. No -period of the romantic ages is more interesting, or better entitled to -a close examination. - - -NARRATIVES OF PERIL AND SUFFERING. - -By R. A. DAVENPORT. _2 Vols._ - -This wide field for the display of taste, talent, and general -acquaintance with the history of man in his social character, has -been occupied by Mr. Davenport, a veteran in elegant literature; -and the popularity which his selections from the children of sorrow -has acquired, is equal to that of his most successful labours. In -collecting so many tales of woe and of enterprise, the author disclaims -the mere vanity of having produced a work of amusement; he seeks -to inculcate the salutary lesson, “that there are few things that -may not be accomplished by perseverance and courage, accompanied by -self-command and presence of mind.” - - -THE LIFE OF BRUCE, - -THE AFRICAN TRAVELLER. - -By Major Sir FRANCIS B. HEAD, _Author of “Rough Notes,” &c._ - -Bruce’s Travels, as originally published, occupy five quarto volumes, -mixed up with Abyssinian history, and speculations on Egyptian -mythology. The author has contrived to compress into this little -volume the best parts of Bruce’s Life and voluminous and expensive -Travels, without omitting one incident of importance and interest. He -has vindicated the character of Bruce, by confronting the statements -of his accusers with the testimony of later travellers. The narrative -had been allowed universally to possess the interest of a romance, -from the graphic style in which he has described his adventures and -sufferings, and the strange people and countries which he visited: but -Major Head has secured for Bruce the credit of a trustworthy authority, -in addition to the reputation of an entertaining narrator. - - -THE COURT AND CAMP OF BUONAPARTE. - -_With a full-length portrait of Prince Talleyrand, and other Portraits._ - -This volume is a suitable and indispensable companion to the Life of -Napoleon. It contains the cream “of many hundred volumes,” in the -shape of Memoirs, Lives, Narratives, Anecdotes, &c., connected with -Buonaparte, with which the press of France has for fifteen years been -teeming. It presents rapid, but vigorous sketches of the Emperor’s -Brothers, Wives, Sisters, Ministers, Marshals, and Generals; and those -who wish for competent knowledge of “_Napoleon and his Times_,” will -find no work in the English language which conveys such information in -a more concise shape or a more lively manner. - - -THE LIFE AND VOYAGES OF CHRISTOPHER COLUMBUS. - -By WASHINGTON IRVING. _Abridged by him from his larger Work. With -Portraits, Maps, &c._ - -This little work has become a universal school-book in America. It -contains all that is most important in the original, in a form more -condensed, and more within the reach of the general reader; while the -story is told with the same spirit and grace as in the great work. As -a book of entertainment, it will bear comparison with any biographical -sketch of the age. - - -LIVES OF EMINENT BRITISH PHYSICIANS. - -_With fine Portraits and Woodcuts._ - -The Lives of Physicians furnish a theme by no means deficient in -interest and value. From them have proceeded some of the greatest -benefactors of the human race; their history abounds in instances -of individuals, who, obscure and small, have, by the vigour of their -understanding and their perseverance, raised themselves among the -great of the land. The memoirs of Cullen, Hunter, and Baillie, afford -striking examples of talent and perseverance triumphing in the midst of -difficulties. - -Of the topics discussed in the course of this volume, the most -prominent are--_The Discovery of the Circulation of the Blood_, by -Harvey. _The Sweating Sickness in the time of Edward III._ _A Sketch of -the Great Plague of London, in 1664-5._ _Jenner’s invaluable Discovery -of Vaccination._ - -To this edition the names of Clutterbuck, Paris, Merriman, Chambers, -and Halford, have been added. - - -HISTORY OF NEW YORK, - -FROM THE BEGINNING OF THE WORLD TO THE END OF THE DUTCH DYNASTY. - -By DIEDRICH KNICKERBOCKER. _Plates after_ CRUIKSHANK. - -This is a satirical production, in which the follies of the day are -humorously depicted in the persons and costume of the ancient Dutch -colonists who founded New York. The scene is local, the application -directed to that city, to recent occurrences in the history of the -United States, and of measures of the government of the Model Republic. -The satire, however, is not personal, but aimed at human character and -conduct, and may, therefore, be generally felt. - - -LIVES OF INDIVIDUALS - -WHO RAISED THEMSELVES FROM POVERTY TO EMINENCE OR FORTUNE. - -By R. A. DAVENPORT. - -The object of this work is not merely to inculcate a moral lesson to -youth, but to encourage virtue generally by creating submission to the -law of opinion. When mankind perceive meritorious exertions in every -rank rewarded, and in numerous instances crowned with success, they are -more strongly supported in their resistance to difficulties, and more -boldly encounter and conquer them. This single volume includes the most -varied memoirs; whence it will appear that industry and perseverance, -accompanied by rectitude of intention, obtain their merited reward in -every civilized nation of our globe. - - -HISTORY OF THE MUTINY AT SPITHEAD AND THE NORE. - -By J. NEALE, Esq., Author of “Cavendish.” - -_With an Inquiry into its Origin and Treatment. With a Portrait of_ -RICHARD PARKER. - -Resistance to authorities necessarily enlists so few abettors, that, -even when it originates in cruelty, injustice, and injury, its -correction is demanded by the voice of the nation. To this feeling must -be traced the flagrant partiality of our historians in describing the -Mutiny of the Nore, and their misrepresentation of the causes of that -calamity. Viewed at this distance of time, it is remembered as the -foundation of that splendid and perfect discipline which has ever since -pervaded and adorned the fleet, and as the cause for abolishing the -despotic practice of impressment. But from these memorable movements -legislators may receive a lesson, and learn how much more faithful -freemen are than slaves to a state in danger, and more binding the ties -of gratitude and affection than the terror of tyranny. This is the -moral reduced from the Mutiny of the Nore in the present history. - - -TOUR THROUGH SOUTH HOLLAND AND UP THE RHINE. - -_With 10 Views, from Designs of_ LIEUT.-COL. BATTY. - -It is strange that the history and condition of Holland should be so -little known, and that it till now should never have been made the -subject of a popular work. The object of this little book is not merely -to afford entertainment, but to furnish that valuable and practical -information, which will render it a desirable _guide-book_ to all who -are tempted to take a summer’s trip across Holland, up the Rhine, and -through Belgium; visiting Rotterdam, the Hague, Amsterdam, Cologne, -Coblentz, Frankfort, Brussels, and Antwerp. - - -THE LIVES OF SCOTTISH WORTHIES. - -By PATRICK FRASER TYTLER, Esq. _3 Vols._ - -“Truth is strange, stranger than fiction.”--The romantic annals of -Scotland, and the characters of her ancient heroes--Wallace, Bruce, and -the like,--will go far to convert this expression into an axiom. - -HADDON, BROTHERS, AND CO., PRINTERS, CASTLE STREET, FINSBURY. - - - * * * * * - - -Transcriber’s Notes - -Obvious typographical errors have been silently corrected and -hyphenation has been standardised. 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