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diff --git a/43715.txt b/43715.txt deleted file mode 100644 index 622de39..0000000 --- a/43715.txt +++ /dev/null @@ -1,4167 +0,0 @@ -The Project Gutenberg EBook of Meteoric astronomy, by Daniel Kirkwood - -This eBook is for the use of anyone anywhere 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/license - - -Title: Meteoric astronomy: - A treatise on shooting-stars, fire-balls, and aerolites - -Author: Daniel Kirkwood - -Release Date: September 14, 2013 [EBook #43715] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK METEORIC ASTRONOMY *** - - - - -Produced by sp1nd, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - -[Illustration: _Fig. 1._ - -The Solar System.] - - - - - METEORIC ASTRONOMY: - - A TREATISE - - ON - - SHOOTING-STARS, FIRE-BALLS, - - AND - - AEROLITES. - - - BY - - DANIEL KIRKWOOD, LL.D. - - PROFESSOR OF MATHEMATICS IN WASHINGTON AND JEFFERSON COLLEGE. - - [Illustration] - - PHILADELPHIA: - J. B. LIPPINCOTT & CO. - 1867. - - - - - Entered, according to Act of Congress, in the year 1867, by - - DANIEL KIRKWOOD, LL.D., - - In the Clerk's Office of the District Court of the United States - for the Western District of Pennsylvania. - - - - -PREFACE. - - -Aristotle and other ancient writers regarded comets as meteors -generated in the atmosphere. This opinion was generally accepted, even -by the learned, until the observations of Tycho, near the close of the -sixteenth century, showed those mysterious objects to be more distant -than the moon, thus raising them to the dignity of _celestial_ bodies. -An achievement somewhat similar, and certainly no less interesting, -was reserved for the astronomers of the _nineteenth_ century. This was -the great discovery that _shooting-stars, fire-balls, and meteoric -stones, are, like comets, cosmical bodies moving in conic sections -about the sun_. DR. HALLEY was the first to foretell the return of a -comet, and the year 1759 will ever be known in history as that which -witnessed the fulfillment of his prophecy. But in the department of -_meteoric_ astronomy, a similar honor must now be awarded to the late -DR. OLBERS. Soon after the great star-shower of 1833 he inferred from -a comparison of recorded facts that the November display attains -a maximum at intervals of thirty-three or thirty-four years. He -accordingly designated 1866 or 1867 as the time of its probable return; -and the night of November 13th of the former year must always be -memorable as affording the first verification of _his_ prediction. On -that night several thousand meteors were observed in one hour from a -single station. This remarkable display, together with the fact that -another still more brilliant is looked for in November, 1867, has -given meteoric astronomy a more than ordinary degree of interest in -the public mind. To gratify, in some measure, the curiosity which has -been awakened, by presenting in a popular form the principal results of -observation and study in this new field of research, is the main design -of the following work. - -The first two chapters contain a popular view of what is known in -regard to the star-showers of August and November, and also of some -other epochs. The third is a description, in chronological order, -of the most important falls of meteoric stones, together with the -phenomena attending their descent. The fourth and following chapters -to the eleventh inclusive, discuss various questions in the theory -of meteors: such, for instance, as the relative number of aerolitic -falls during different parts of the day, and also of the year; the -coexistence of the different forms of meteoric matter in the same -rings; meteoric dust; the stability of the solar system; the doctrine -of a resisting medium; the extent of the atmosphere as indicated by -meteors; the meteoric theory of solar heat; and the phenomena of -variable and temporary stars. The twelfth chapter regards the rings -of Saturn as dense meteoric swarms, and accounts for the principal -interval between them. The thirteenth presents various facts, not -previously noticed, respecting the asteroid zone between Mars and -Jupiter, with suggestions concerning their cause or explanation. - -As the nebular hypothesis furnishes a plausible account of the origin -of meteoric streams, it seemed desirable to present an intelligible -view of that celebrated theory. This accordingly forms the subject of -the closing chapter. - -The greater part of the following treatise, it is proper to remark, was -written before the publication (in England) of Dr. Phipson's volume on -"Meteors, Aerolites, and Falling-stars." The author has had that work -before him, however, while completing his manuscript, and has availed -himself of some of the accounts there given of recent phenomena. - -CANONSBURG, PA, _May, 1867_. - - - - -CONTENTS. - - - PAGE - INTRODUCTION 7 - - - CHAPTER I. - - The Meteors of November 12th-14th 13 - - - CHAPTER II. - - Other Meteoric Rings 26 - - - CHAPTER III. - - Aerolites 35 - - - CHAPTER IV. - - Conjectures in Regard to Meteoric Epochs 50 - - - CHAPTER V. - - Geographical Distribution of Meteoric Stones--Do - Aerolitic Falls occur more frequently by Day than by - Night?--Do Meteorites, Bolides, and the matter of ordinary - Shooting-stars, coexist in the same Rings? 56 - - - CHAPTER VI. - - Phenomena supposed to be Meteoric--Meteoric Dust--Dark Days 65 - - - CHAPTER VII. - - Researches of Reichenbach--Theory of Meteors--Stability of - the Solar System--Doctrine of a Resisting Medium 74 - - CHAPTER VIII. - - Does the Number of Aerolitic Falls vary with the Earth's - Distance from the Sun?--Relative Numbers observed in the - Forenoon and Afternoon--Extent of the Atmosphere as indicated - by Meteors 79 - - - CHAPTER IX. - - The Meteoric Theory of Solar Heat 84 - - - CHAPTER X. - - Will the Meteoric Theory account for the Phenomena of - Variable and Temporary Stars? 92 - - - CHAPTER XI. - - The Lunar and Solar Theories of the Origin of Aerolites 96 - - - CHAPTER XII. - - The Rings of Saturn 102 - - - CHAPTER XIII. - - The Asteroid Ring between Mars and Jupiter 105 - - - CHAPTER XIV. - - Origin of Meteors--The Nebular Hypothesis 112 - - - APPENDIX 123 - - - - -INTRODUCTION. - -A GENERAL VIEW OF THE SOLAR SYSTEM. - - -THE SOLAR SYSTEM consists of the sun, together with the planets and -comets which revolve around him as the center of their motions. The sun -is the great controlling orb of this system, and the source of light -and heat to its various members. Its magnitude is one million four -hundred thousand times greater than that of the earth, and it contains -more than seven hundred times as much matter as all the planets put -together. - -MERCURY is the nearest planet to the sun; its mean distance being about -thirty-seven millions of miles. Its diameter is about three thousand -miles, and it completes its orbital revolution in 88 days. - -VENUS, the next member of the system, is sometimes our morning and -sometimes our evening star. Its magnitude is almost exactly the same as -that of the earth. It revolves round the sun in 225 days. - -THE EARTH is the third planet from the sun in the order of distance; -the radius of its orbit being about ninety-five millions of miles. It -is attended by one satellite--the moon--the diameter of which is 2160 -miles. - -MARS is the first planet exterior to the earth's orbit. It is -considerably smaller than the earth, and has no satellite. It revolves -round the sun in 687 days. - -THE ASTEROIDS.--Since the commencement of the present century a -remarkable zone of telescopic planets has been discovered immediately -exterior to the orbit of Mars. These bodies are extremely small; some -of them probably containing less matter than the largest mountains on -the earth's surface. More than ninety members of the group are known at -present, and the number is annually increasing. - -JUPITER, the first planet exterior to the asteroids, is nearly five -hundred millions of miles from the sun, and revolves round him in a -little less than twelve years. This planet is ninety thousand miles in -diameter and contains more than twice as much matter as all the other -planets, primary and secondary, put together. Jupiter is attended by -four moons or satellites. - -SATURN is the seventh planet in the order of distance--counting the -asteroids as one. Its orbit is about four hundred millions of miles -beyond that of Jupiter. This planet is attended by eight satellites, -and is surrounded by three broad, flat rings. Saturn is seventy-six -thousand miles in diameter, and its mass or quantity of matter is more -than twice that of all the other planets except Jupiter. - -URANUS is at double the distance of Saturn, or nineteen times that -of the earth. Its diameter is about thirty-five thousand miles, and -its period of revolution, eighty-four years. It is attended by four -satellites. - -NEPTUNE is the most remote known member of the system; its distance -being nearly three thousand millions of miles. It is somewhat larger -than Uranus; has certainly one satellite, and probably several more. -Its period is about one hundred and sixty-five years. A cannon-ball -flying at the rate of five hundred miles per hour would not reach the -orbit of Neptune from the sun in less than six hundred and eighty years. - -These planets all move round the sun in the same direction--from west -to east. Their motions are nearly circular, and also nearly in the same -plane. Their orbits, except that of Neptune, are represented in the -frontispiece. It is proper to remark, however, that all representations -of the solar system by maps and planetariums must give an exceedingly -erroneous view either of the magnitudes or distances of its various -members. If the earth, for instance, be denoted by a ball half an -inch in diameter, the diameter of the sun, according to the same -scale (sixteen thousand miles to the inch), will be between four and -five feet; that of the earth's orbit, about one thousand feet; while -that of Neptune's orbit will be nearly six miles. To give an accurate -representation of the solar system at a single view is therefore -plainly impracticable. - -COMETS.--The number of comets belonging to our system is unknown. The -appearance of more than seven hundred has been recorded, and of this -number, the elements of about two hundred have been computed. They move -in very eccentric orbits--some, perhaps, in parabolas or hyperbolas. - -THE ZODIACAL LIGHT is a term first applied by Dominic Cassini, in -1683, to a faint nebulous aurora, somewhat resembling the milky-way, -apparently of a conical or lenticular form, having its base toward -the sun, and its axis nearly in the direction of the ecliptic. The -most favorable time for observing it is when its axis is most nearly -perpendicular to the horizon. This, in our latitudes, occurs in March -for the evening, and in October for the morning. The angular distance -of its vertex from the sun is frequently seventy or eighty degrees, -while sometimes, though rarely (except within the tropics), it exceeds -even one hundred degrees. - -The zodiacal light is probably identical with the meteor called -_trabes_ by _Pliny_ and _Seneca_. It was noticed in the latter part -of the sixteenth century by Tycho Brahe, who "considered it to be an -abnormal spring-evening twilight." It was described by Descartes -about the year 1630, and again by Childrey in 1661. The first accurate -description of the phenomenon was given, however, by Cassini. This -astronomer supposed the appearance to be produced by the blended -light of an innumerable multitude of extremely small planetary bodies -revolving in a ring about the sun. The appearance of the phenomenon as -seen in this country is represented in Fig. 2. - -[Illustration: Fig. 2.] - -For general readers it may not be improper to premise the following -explanations: - -Meteors are of two kinds, _cosmical_ and _terrestrial_: the former -traverse the interplanetary spaces; the latter originate in the earth's -atmosphere. - -_Bolides_ is a general name for meteoric fire-balls of greater -magnitude than shooting-stars. - -The _period_ of a planet, comet, or meteor is the time which it -occupies in completing one orbital revolution. - -The motion of a heavenly body is said to be _direct_ when it is from -west to east; and _retrograde_ when it is from east to west. - -_Encke's Hypothesis of a Resisting Medium._--The time occupied by -Encke's comet in completing its revolution about the sun is becoming -less and less at each successive return. Professor Encke explains -this fact by supposing the interplanetary spaces to be filled with an -extremely rare fluid, the resistance of which to the cometary motion -produces the observed contraction of the orbit. - - - - -METEORIC ASTRONOMY. - - - - -CHAPTER I. - -SHOOTING-STARS. - - -I. The Meteors of November 12th-14th. - -Although shooting-stars have doubtless been observed in all ages of the -world, they have never, until recently, attracted the special attention -of scientific men. The first exact observations of the phenomena were -undertaken, about the close of the last century, by Messrs. Brandes and -Benzenberg. The importance, however, of this new department of research -was not generally recognized till after the brilliant meteoric display -of November 13th, 1833. This shower of fire can never be forgotten -by those who witnessed it.[1] The display was observed from the West -Indies to British America, and from 60 deg. to 100 deg. west longitude from -Greenwich. Captain Hammond, of the ship Restitution, had just arrived -at Salem, Massachusetts, where he observed the phenomenon from midnight -till daylight. He noticed with astonishment that precisely one year -before, viz., on the 13th of November, 1832, he had observed a similar -appearance (although the meteors were less numerous) at Mocha, in -Arabia. It was soon found, moreover, as a further and most remarkable -coincidence, that an extraordinary fall of meteors had been witnessed -on the 12th of November, 1799. This was seen and described by Andrew -Ellicott, Esq., who was then at sea near Cape Florida. It was also -observed in Cumana, South America, by Humboldt, who states that it -was "simultaneously seen in the new continent, from the equator to -New Herrnhut, in Greenland (lat. 64 deg. 14'), and between 46 deg. and 82 deg. -longitude." - -This wonderful correspondence of dates excited a very lively interest -throughout the scientific world. It was inferred that a recurrence -of the phenomenon might be expected, and accordingly arrangements -were made for systematic observations on the 12th, 13th, and 14th of -November. The periodicity of the shower was thus, in a very short -time, placed wholly beyond question. The examination of old historical -records led to the discovery of at least 12 appearances of the November -shower previous to the great fall of 1833. The descriptions of these -phenomena will be found collected in an interesting article by Prof. -H. A. Newton, in the _American Journal of Science and Arts_, for May, -1864. They occurred in the years 902, 931, 934, 1002, 1101, 1202, -1366, 1533, 1602, 1698, 1799, and 1832. Besides these 12 enumerated by -Professor Newton as "the predecessors of the great exhibition on the -morning of November 13th, 1833," we find 6 others, less distinctly -marked, in the catalogue of M. Quetelet.[2] These were in the years -1787, 1818, 1822, 1823, 1828, and 1831. From 1883 to 1849, inclusive, -Quetelet's catalogue indicates 11 partial returns of the November -shower; making in all, up to the latter date, 29. In 1835, November -13th, a straw roof was set on fire by a meteoric fire-ball, in the -department de l'Aine, France. On the 12th of November, 1837, "at 8 -o'clock in the evening, the attention of observers in various parts -of Great Britain was directed to a bright luminous body, apparently -proceeding from the North, which, after making a rapid descent, in the -manner of a rocket, suddenly burst, and scattering its particles into -various beautiful forms, vanished in the atmosphere. This was succeeded -by others all similar to the first, both in shape and the manner of its -ultimate disappearance. The whole display terminated at ten o'clock, -when dark clouds, which continued up till a late hour, overspread the -earth, preventing any further observations."--_Milner's Gallery of -Nature_, p. 142. - -In 1838, November 12th-13th, meteors were observed in unusual numbers -at Vienna. One of extraordinary brilliancy, having an apparent -magnitude equal to that of the full moon, was seen near Cherburg. - -On several other returns of the November epoch the number of meteors -observed has been greater than on ordinary nights; the distinctly -marked exhibitions, however, up to 1866, have all been enumerated. - - -THE SHOWER OF NOVEMBER 14, 1866. - -The fact that all great displays of the November meteors have -taken place at intervals of thirty-three or thirty-four years, or -some multiple of that period, had led to a general expectation of -a brilliant shower in 1866. In this country, however, the public -curiosity was much disappointed. The numbers seen were greater than -on ordinary nights, but not such as would have attracted any special -attention. The greatest number recorded at any one station was seen at -New Haven, by Prof. Newton. On the night of the 12th, 694 were counted -in five hours and twenty minutes, and on the following night, 881 -in five hours. This was about six times the ordinary number. A more -brilliant display was, however, witnessed in Europe. Meteors began -to appear in unusual frequency about eleven o'clock on the night of -the 13th, and continued to increase with great rapidity for more than -two hours; the maximum being reached a little after one o'clock. The -Edinburgh _Scotsman_, of November 14th, contains a highly interesting -description of the phenomenon as observed at that city. "Standing on -the Calton Hill, and looking westward," the editor remarks,--"with -the Observatory shutting out the lights of Prince's Street--it was -easy for the eye to delude the imagination into fancying some distant -enemy bombarding Edinburgh Castle from long range; and the occasional -cessation of the shower for a few seconds, only to break out again with -more numerous and more brilliant drops of fire, served to countenance -this fancy. Again, turning eastward, it was possible now and then to -catch broken glimpses of the train of one of the meteors through the -grim dark pillars of that ruin of most successful manufacture, the -National Monument; and in fact from no point in or out of the city was -it possible to watch the strange rain of stars, pervading as it did all -points of the heavens, without pleased interest, and a kindling of the -imagination, and often a touch of deeper feeling that bordered on awe. -The spectacle, of which the loftiest and most elaborate description -could but be at the best imperfect--which truly should have been seen -to be imagined--will not soon pass from the memories of those to whose -minds were last night presented the mysterious activities and boundless -fecundities of that universe of the heavens, the very unchangeableness -of whose beauty has to many made it monotonous and of no interest." - -The appearance of the phenomenon, as witnessed at London, is minutely -described in the _Times_ of November 15th. The shower occurred chiefly -between the hours of twelve and two. About one o'clock a single -observer counted 200 in two minutes. The whole number seen at Greenwich -was 8485. The shower was also observed in different countries on the -continent. - - -_The Meteors of 1866 compared with those of former Displays._ - -The star shower of 1866 was much inferior to those of 1799 and -1833.[3] With these exceptions, however, it has, perhaps, been -scarcely surpassed during the last 500 years. Historians represent the -meteors of 902 as innumerable, and as moving like rain in all possible -directions.[4] The exhibition of 1202 was no less magnificent. The -stars, it is said, were seen to dash against each other like swarms of -locusts; the phenomenon lasting till daybreak.[5] The shower of 1366 -is thus described in a Portuguese chronicle, quoted by Humboldt: "In -the year 1366, twenty-two days of the month of October being past, -three months before the death of the king, Dom Pedro (of Portugal), -there was in the heavens a movement of stars, such as men never before -saw or heard of. At midnight, and for some time after, all the stars -moved from the east to the west; and after being collected together, -they began to move, some in one direction, and others in another. -And afterward they fell from the sky in such numbers, and so thickly -together, that as they descended low in the air, they seemed large and -fiery, and the sky and the air seemed to be in flames, and even the -earth appeared as if ready to take fire. That portion of the sky where -there were no stars, seemed to be divided into many parts, and this -lasted for a long time." - -The following is Humboldt's description of the shower of 1799, as -witnessed by himself and Bonpland, in Cumana, South America: "From half -after two, the most extraordinary luminous meteors were seen toward the -east.... Thousands of bolides and falling stars succeeded each other -during four hours. They filled a space in the sky extending from the -true east 30 deg. toward the north and south. In an amplitude of 60 deg. the -meteors were seen to rise above the horizon at E. N. E. and at E., -describe arcs more or less extended, and fall toward the south, after -having followed the direction of the meridian. Some of them attained a -height of 40 deg., and all exceeded 25 deg. or 30 deg..... Mr. Bonpland relates, -that from the beginning of the phenomenon there was not a space in -the firmament equal in extent to three diameters of the moon, that -was not filled at every instant with bolides and falling-stars.... -The Guaiqueries in the Indian suburb came out and asserted that the -firework had begun at one o'clock.... The phenomenon ceased by degrees -after four o'clock, and the bolides and falling-stars became less -frequent; but we still distinguished some toward the northeast a -quarter of an hour after sunrise." - - -DISCUSSION OF THE PHENOMENA. - -Since the memorable display of November 13th, 1833, the phenomena of -shooting-stars have been observed and discussed by Brandes, Benzenberg, -Olbers, Saigey, Heis, Olmsted, Herrick, Twining, Newton, Greg, and many -others. In the elaborate paper of Professor Olmsted, it was shown that -the meteors had their origin at a distance of more than 2000 miles -from the earth's surface; that their paths diverged from a common point -near the star _Gamma Leonis_; that in a number of instances they became -visible about 80 miles from the earth's surface; that their velocity -was comparable to that of the earth in its orbit; and that in some -cases their extinction occurred at an elevation of 30 miles. It was -inferred, moreover, that they consisted of combustible matter which -took fire and was consumed in passing through the atmosphere; that this -matter was derived from a nebulous body revolving round the sun in an -elliptical orbit, but little inclined to the plane of the ecliptic; -that its aphelion was near that point of the earth's orbit through -which we annually pass about the 13th of November--the perihelion being -a little within the orbit of Mercury; and finally that its period was -about one-half that of the earth. Dr. Olmsted subsequently modified his -theory, having been led by further observations to regard the zodiacal -light as the nebulous body from which the shooting-stars are derived. -The latter hypothesis was also adopted by the celebrated Biot. - -The fact that the position of the radiant point does not change with -the earth's rotation, places the cosmical origin of the meteors wholly -beyond question. The theory of a closed ring of nebulous matter -revolving round the sun in an elliptical orbit which intersects that -of the earth, affords a simple and satisfactory explanation of the -phenomena. This theory was adopted by Humboldt, Arago, and others, -shortly after the occurrence of the meteoric shower of 1833. That the -body which furnishes the material of these meteors moves in a closed -or elliptical orbit is evident from the periodicity of the shower. It -is also manifest from the partial recurrence of the phenomenon from -year to year, that the matter is diffused around the orbit; while the -extraordinary falls of 1833, 1799, 1366, and 1202, prove the diffusion -to be far from uniform. - - -ELEMENTS OF THE ORBIT. - -Future observations, it may be hoped, will ultimately lead to an -accurate determination of the elements of this ring: many years, -however, will probably elapse before all the circumstances of its -motion can be satisfactorily known. Professor Newton, of Yale College, -has led the way in an able discussion of the observations.[6] He has -shown that the different parts of the ring are, in all probability, of -very unequal density; that the motion is retrograde; and that the time, -during which the meteors complete a revolution about the sun, must be -limited to one of five accurately determined periods, viz.: 180.05 -days, 185.54 days, 354.62 days, 376.5 days, or 33.25 years. He makes -the inclination of the ring to the ecliptic about 17 deg.. The five periods -specified, he remarks, "are not all equally probable. Some of the -members of the group which visited us last November [1863] gave us the -means of locating approximately the central point of the region from -which the paths diverge. Mr. G. A. Nolen has, by graphical processes -specially devised for the purpose, found its longitude to be 142 deg., and -its latitude 8 deg. 30'. This longitude is very nearly that of the point -in the ecliptic toward which the earth is moving. Hence the point -from which the absolute motion of the bodies is directed (being in a -great circle through the other two points) has the same longitude. The -absolute motion of each meteor, then, is directed very nearly at right -angles to a line from it to the sun, the deviation being probably not -more than two or three degrees. - -"Now, if in one year the group make 2 +- 1/33.25 revolutions, there is -only a small portion of the orbit near the aphelion which fulfills the -above condition. In like manner, if the periodic time is 33.25 years, -only a small portion of the orbit near the perihelion fulfills it. -On the other hand, if the annual motion is 1 +- 1/33.25 revolutions, -the required condition is answered through a large part of the orbit. -Inasmuch as no reason appears why the earth should meet a group near -its apsides rather than elsewhere, we must regard it as more probable -that the group makes in one year either 1 + 1/33.25, or 1 - 1/33.25 -revolutions." - -Professor Newton concludes that the third of the above-mentioned -periods, viz., 354.62 days, combines the greatest amount of probability -of being the true one. We grant the force of the reasons assigned for -its adoption. At least one consideration, however, in favor of the -long period of 33.25 years is by no means destitute of weight: of -nearly 100 known bodies which revolve about the sun in orbits of small -eccentricity, not one has a retrograde motion. Now if this striking -fact has resulted from a general cause, how shall we account for the -backward motion of a meteoric ring, in an orbit almost circular, and -but little inclined to the plane of the ecliptic? In such a case, is -not the preponderance of probability in favor of the longer period? - -A revolution in 33.25 years corresponds to an ellipse whose major axis -is 20.6. Consequently the aphelion distance would be somewhat greater -than the mean distance of Uranus. It may also be worthy of note, that -five periods of the ring would be very nearly equal to two of Uranus. - -The _Monthly Notices of the Royal Astronomical Society_ for December, -1866, and January, 1867, contain numerous articles on the star shower -of November 13th-14th, 1866. Sir John Herschel carefully observed the -phenomena, and his conclusions in regard to the orbit are confirmatory -of those of Professor Newton. "We are constrained to conclude," he -remarks, "that the true line of direction, in space of each meteor's -flight, lay in a plane at right angles to the earth's radius vector at -the moment; and that therefore, except in the improbable assumption -that the meteor was at that moment _in perihelio_ or _in aphelio_, its -orbit would not deviate greatly from the circular form." The question -is one to be decided by observation, and the only meteor whose track -and time of flight seem to have been well observed, is that described -by Professor Newton in _Silliman's Journal_ for January, 1867, p. 86. -The velocity in this case, if the estimated time of flight was nearly -correct, was _inconsistent with the theory of a circular orbit_. - -It is also worthy of notice that Dr. Oppolzer's elements of the first -comet of 1866 resemble, in a remarkable manner, those of the meteoric -ring, supposing the latter to have a period of about 33-1/4 years. -Schiaparelli's elements of the November ring, and Oppolzer's elements -of the comet of 1866, are as follows: - - November Comet of - Meteors. 1866. - - Longitude of perihelion 56 deg. 25' 60 deg. 28' - Longitude of ascending node. 231 28 231 26 - Inclination 17 44 17 18 - Perihelion distance 0.9873 0.9765 - Eccentricity 0.9046 0.9054 - Semi-axis major 10.3400 10.3240 - Period, in years 33.2500 33.1760 - Motion Retrograde. Retrograde. - -It seems very improbable that these coincidences should be accidental. -Leverrier and other astronomers have found elements of the meteoric -orbit agreeing closely with those given by Schiaparelli. Should the -identity of the orbits be fully confirmed, it will follow that the -comet of 1866 _is a very large meteor_ of the November stream. - -The researches of Professor C. Bruhns, of Leipzig, in regard to this -group of meteors afford a probable explanation of the division of -Biela's comet--a phenomenon which has greatly perplexed astronomers for -the last twenty years. Adopting the period of 33-1/4 years, Professor -Bruhns finds that the comet passed extremely near, and probably -_through_ the meteoric ring near the last of December, 1845. It is easy -to perceive that such a collision might produce the separation soon -afterward observed. - -As the comet of Biela makes three revolutions in twenty years, it was -again at this intersection, or approximate intersection of orbits about -the end of 1865. But although the comet's position, with respect to -the earth, was the same as in 1845-6, and although astronomers watched -eagerly for its appearance, their search was unsuccessful. In short, -_the comet is lost_. The denser portion of the meteoric stream was then -approaching its perihelion. A portion of the arc had even passed that -point, as a meteoric shower was observed at Greenwich on the 13th of -November, 1865.[7] The motion of the meteoric stream is retrograde; -that of the comet, direct. Did the latter plunge into the former, and -was its non appearance the result of such collision and entanglement? - -[Illustration: Fig. 3. - -_Probable Orbit of the November Meteors._] - - - - -CHAPTER II. - -OTHER METEORIC RINGS. - - -II. The Meteors of August 6th-11th. - -Muschenbroek, in his _Introduction to Natural Philosophy_, published -in 1762, called attention to the fact that shooting-stars are more -abundant in August than in any other part of the year. The annual -periodicity of the maximum on the 9th or 10th of the month was -first shown, however, by Quetelet, shortly after the discovery of -the yearly return of the November phenomenon. Since that time an -extraordinary number of meteors has been regularly observed, both -in Europe and America, from the 7th to the 11th of the month; the -greatest number being generally seen on the 10th. In 1839, Edward Heis, -of Aix-la-Chapelle, saw 160 meteors in one hour on the night of the -10th. In 1842, he saw 34 in ten minutes at the time of the maximum. In -1861, on the night of the 10th, four observers, watching together at -New Haven, saw in three hours--from ten to one o'clock--289 meteors. -On the same night, at Natick, Massachusetts, two observers saw 397 -in about seven hours. At London, Mercer County, Pennsylvania, on the -night of August 9th, 1866, Samuel S. Gilson, Esq., watching alone, saw -72 meteors in forty minutes, and, with an assistant, 117 in one hour -and fifteen minutes. Generally, the number observed per hour, at the -time of the August maximum, is about nine times as great as on ordinary -nights. Like the November meteors, they have a common "radiant;" that -is, their tracks, when produced backward, meet, or nearly meet, in a -particular point in the constellation Perseus. - -Of the 315 meteoric displays given in Quetelet's "Catalogue des -principales apparitions d'etoiles filantes," 63 seem to have been -derived from the August ring. The first 11 of these, with one -exception, were observed in China during the last days of July, as -follows: - - 1 A.D. 811, July 25th. - 2 820, " 25th-30th. - 3 824, " 26th-28th. - 4 830, " 26th. - 5 833, " 27th. - 6 835, " 26th. - 7 841, " 25th-30th. - 8 924, " 27th-30th. - 9 925, " 27th-30th. - 10 926, " 27th-30th. - 11 933, " 25th-30th. - -The next dates are 1243, August 2d, and 1451, August 7th. A comparison -of these dates indicates a forward motion of the node of the ring along -the ecliptic. This was pointed out several years since by Boguslawski. -A similar motion of the node has also been found in the case of the -November ring. That these points should be stationary is, indeed, -altogether improbable. The nodes of all the planetary orbits, it is -well known, have a secular variation. - -On the evening of August 10th, 1861, at about 11h. 30m., a meteor -was seen by Mr. E. C. Herrick and Prof. A. C. Twining, at New -Haven, Connecticut, which "was much more splendid than Venus, and -left a train of sparks which remained luminous for twenty seconds -after the meteor disappeared." The same meteor was also accurately -observed at Burlington, New Jersey, by Mr. Benjamin V. Marsh. It was -"conformable,"--that is, its track produced backward passed through the -common radiant--and it was undoubtedly a member of the August group. -The observations were discussed by Professor H. A. Newton, of Yale -College, who deduced from them the following approximate elements of -the ring:[8] - - Semi-axis major 0.84 - Eccentricity 0.28 - Perihelion distance 0.60 - Inclination 84 deg. - Period 281 days. - Motion, retrograde. - -The earth moving at the rate of 68,000 miles per hour, is at least five -days in passing entirely through the ring. This gives a thickness of -more than 8,000,000 miles. - -The result of Professor Newton's researches on the orbit of this ring, -though undertaken with inadequate data, and hence, in some respects, -probably far from correct, is nevertheless highly interesting as being -the first attempt to determine the orbit of shooting-stars. More recent -investigations have shown a remarkable resemblance between the elements -of these meteors and those of the third comet of 1862. The former, by -Schiaparelli, and the latter, by Oppolzer, are as follows: - - - Meteors of August 10th. Comet III., 1862. - - Longitude of perihelion 343 deg. 38' 344 deg. 41 - Ascending node 138 16 137 27 - Inclination 63 3 66 25 - Perihelion distance 0.9643 0.9626 - Period 105 years(?). 123 years(?). - Motion Retrograde. Retrograde. - -This similarity is too great to be accidental. _The August meteors and -the third comet of 1862 probably belong to the same ring._ - - -III. The Meteors of April 18th-26th. - -The following dates of the April meteoric showers are extracted from -Quetelet's table previously referred to: - - 1 A.D. 401, April 9th. - 2 538, " 7th. - 3 839, " 17th. - 4 927, " 17th. - 5 934, " 18th. - 6 1009, " 16th. - 7 1094, " 10th. - 8 1096, " 10th. - 9 1122, " 11th. - 10 1123, " 11th. - 11 1803, " 20th. - 12 1838, " 20th. - 13 1841, " 19th. - 14 1850, " 11th-17th. - -The display of 401 was witnessed in China, and is described as "very -remarkable." That of 1803 was best observed in Virginia, and was at its -maximum between one and three o'clock. The alarm of fire had called -many of the inhabitants of Richmond from their houses, so that the -phenomenon was generally witnessed. The meteors "seemed to fall from -every point in the heavens, in such numbers as to resemble a shower of -sky-rockets." Some were of extraordinary magnitude. "One in particular, -appeared to fall from the zenith, of the apparent size of a ball 18 -inches in diameter, that lighted the whole hemisphere for several -seconds." - -The probability that the meteoric falls about the 20th of April are -derived from a ring which intersects the earth's orbit, was first -suggested by Arago, in 1836. The preceding list indicates a forward -motion of the node. The radiant, according to Mr. Greg, is about -_Corona_. The number of meteors observed in 1838, 1841, and 1850, was -not very extraordinary. Recent observations indicate April 9th-12th as -another epoch. The radiant is in Virgo. - - -IV. The Meteors of December 6th-13th. - -On the 13th of December, 1795, a large meteoric stone fell in England. -On the night, between the 6th and 7th of December, 1798, Professor -Brandes, then a student in Goettingen, saw 2000 shooting-stars. On -the 11th of the month, 1836, a fall of meteoric stones, described by -Humboldt as "enormous," occurred near the village of Macao, in Brazil. -During the last few years unusual numbers of shooting-stars have been -noticed by different observers from the 10th to the 13th; the maximum -occurring about the 11th. From A.D. 848, December 2d, to 1847, December -8th-10th, we find 14 star showers in Quetelet's catalogue, derived, -probably, from this meteoric stream. As in other cases, the dates -seem to show a progressive motion of the node. The position of the -radiant, as determined by Benjamin V. Marsh, Esq., of Philadelphia, -from observations in 1861 and 1862, and also by R. P. Greg, Esq., of -Manchester, England, is at a point midway between Castor and Pollux. - - -V. The Meteors of January 2d-3d. - -About the middle of the present century, Mr. Julius Schmidt, of Bonn, -a distinguished and accurate observer, designated the 2d of January as -a meteoric epoch; characterizing it, however, as "probably somewhat -doubtful." Recent observations, especially those of R. P. Greg, Esq., -have fully confirmed it. The meteors for several hours are said to be -as numerous as at the August maximum. The radiant is near the star -_Beta_ of the constellation Boeotes. - -Quetelet's list contains at least five exhibitions which belong to this -epoch. Two or three others may also be referred to it with more or less -probability. - - * * * * * - -Several other meteoric epochs have been indicated; some of which, -however, must yet be regarded as doubtful. In thirty years, from 1809 -to 1839, 12 falls of bolides and meteoric stones occurred from the 27th -to the 29th of November. Such coincidences can hardly be accidental. -Unusual numbers of shooting-stars have also been seen about the 27th -of July; from the 15th to the 19th of October, and about the middle -of February. The radiant, for the last-mentioned epoch, is in _Leo -Minor_. The numbers observed in October are said to be at present -increasing. At least seven of the exhibitions in Quetelet's catalogue -are referable to this epoch. It is worthy of remark, moreover, that -three of the dates specified by Mr. Greg as _aerolite_ epochs are -coincident with those of shooting-stars; viz., February 15th-19th, July -26th, and December 13th. The whole number of exhibitions enumerated -in Quetelet's catalogue is 315. In eighty-two instances the day of -the month on which the phenomenon occurred is not specified. Nearly -two-thirds of the remainder, as we have seen, belong to established -epochs, and the periodicity of others will perhaps yet be discovered. -But reasons are not wanting for believing that our system is traversed -by numerous meteoric streams besides those which actually intersect the -earth's orbit. The asteroid region between Mars and Jupiter is probably -occupied by such an annulus. The number of these asteroids increases -as their magnitudes diminish; and this doubtless continues to be the -case far below the limit of telescopic discovery. The zodiacal light -is probably a dense meteoric ring, or rather, perhaps, a number of -rings. We speak of it as _dense_ in comparison with others, which are -invisible except by the ignition of their particles in passing through -the atmosphere. From a discussion of the motions of the perihelia of -Mercury and Mars, Leverrier has inferred the existence of two rings of -minute asteroids; one within the orbit of Mercury, whose mass is nearly -equal to that of Mercury himself; the other at the mean distance of the -earth, whose mass cannot _exceed_ the tenth part of the mass of the -earth. - -Within the last few years a distinguished European savant, Buys-Ballot, -of Utrecht, has discovered a short period of variation in the amount -of solar heat received by the earth: the time from one maximum to -another exceeding the period of the sun's apparent rotation by about -twelve hours. The variation cannot therefore be due to any inequality -in the heating power of the different portions of the sun's surface. -The discoverer has suggested that it may be produced by a meteoric -ring, whose period slightly exceeds that of the sun's rotation. Such -a zone might influence our temperature by partially intercepting the -solar heat. - - -GENERAL REMARKS. - -1. The average number of shooting-stars seen in a clear, moonless -night by a single observer, is about 8 per hour. _One_ observer, -however, sees only about one-fourth of those visible from his point of -observation. About 30 per hour might therefore be seen by watching the -entire hemisphere. In other words, 720 shooting-stars per day could be -seen by the naked eye at any one point of the earth's surface, did the -sun, moon, and clouds permit. - -2. The mean altitude of shooting-stars above the earth's surface is -about 60 miles. - -3. The number visible over the whole earth is about 10,460 times the -number to be seen at any one point. Hence the average number of those -daily entering the atmosphere and having sufficient magnitude to be -seen by the naked eye, is about 7,532,600. - -4. The observations of Pape and Winnecke indicate that the number of -meteors visible through the telescope, employed by the latter, is about -53 times the number visible to the naked eye, or about 400,000,000 -per day.[9] This is two per day, or 73,000 per century, for every -square mile of the earth's surface. By increasing the optical power, -this number would probably be indefinitely increased. At special -times, moreover, such as the epochs of the great meteoric showers, -the addition of foreign matter to our atmosphere is much greater than -ordinary. It becomes, therefore, an interesting question whether -sensible changes may not thus be produced in the atmosphere of our -planet. - -5. In August, 1863, 20 shooting-stars were doubly observed in England; -that is, they were seen at two different stations. The average weight -of these meteors, estimated--in accordance with the mechanical theory -of heat--from the quantity of light emitted, was a little more than two -ounces. - -6. A meteoric mass exterior to the atmosphere, and consequently -non-luminous, was observed on the evening of October 4th, 1864, by -Edward Heis, a distinguished European astronomer. It entered the field -of view as he was observing the milky way, and he was enabled to follow -it over 11 or 12 degrees of its path. It eclipsed, while in view, a -number of the fixed stars. - - - - -CHAPTER III. - -AEROLITES. - - -It is now well known that much greater variety obtains in the structure -of the solar system than was formerly supposed. This is true, not only -in regard to the magnitudes and densities of the bodies composing it, -but also in respect to the forms of their orbits. The whole number -of planets, primary and secondary, known to the immortal author of -the _Mecanique Celeste_, was only 29. This number has been more than -quadrupled in the last quarter of a century. In Laplace's view, -moreover, all comets were strangers within the solar domain, having -entered it from without. It is now believed that a large proportion -originated in the system and belong properly to it. - -The gradation of planetary magnitudes, omitting such bodies as differ -but little from those given, is presented at one view in the following -table: - - Name. Diameter in miles. - - Jupiter 90,000 - Uranus 35,000 - The Earth 7,926 - Mercury 3,000 - The Moon 2,160 - Rhea, Saturn's 5th satellite 1,200 - Dione " 4th " 500 - Vesta[10] 260 - Juno 104 - Melpomene 52 - Polyhymnia 35 - Isis 25 - Atalanta 20 - Hestia 15 - -The diminution doubtless continues indefinitely below the present limit -of optical power. If, however, the orbits have small eccentricity, such -asteroids could not become known to us unless their mean distances were -nearly the same with that of the earth. But from the following table it -will be seen that the variety is no less distinctly marked in the forms -of the orbits: - - Name. Eccentricity. - - Venus 0.00683 - The Earth 0.01677 - Jupiter 0.04824 - Metis 0.12410 - Mercury 0.20562 - Pallas 0.24000 - Polyhymnia 0.33820 - Faye's comet 0.55660 - D'Arrest's " 0.66090 - Biela's " 0.75580 - Encke's " 0.84670 - Halley's " 0.96740 - Fourth comet of 1857 0.98140 - Fifth comet of 1858 (Donati's) 0.99620 - Third comet of 1827 0.99927 - -Were the eccentricities of the nearest asteroids equal to that of -Faye's comet, they would in perihelion intersect the earth's orbit. -Now, in the case of both asteroids and comets, the smallest are the -most numerous; and as this doubtless continues below the limit of -telescopic discovery, the earth ought to encounter such bodies in -its annual motion. _It actually does so._ The number of _cometoids_ -thus encountered in the form of _meteoric stones_, _fire-balls_, -and _shooting-stars_ in the course of a single year amounts to many -millions. The extremely minute, and such as consist of matter in the -gaseous form, are consumed or dissipated in the upper regions of the -atmosphere. No deposit from ordinary shooting-stars has ever been known -to reach the earth's surface. But there is probably great variety -in the physical constitution of the bodies encountered; and though -comparatively few contain a sufficient amount of matter in the solid -form to reach the surface of our planet, scarcely a year passes without -the fall of meteoric stones in some part of the earth, either singly or -in clusters. Now, when we consider how small a proportion of the whole -number are probably observed, it is obvious that the actual occurrence -of the phenomenon can be by no means rare.[11] - -Although numerous instances of the fall of aerolites had been -recorded, some of them apparently well authenticated, the occurrence -long appeared too marvelous and improbable to gain credence with -scientific men. Such a shower of rocky fragments occurred, however, -on the 26th of April, 1803, at L'Aigle, in France, as forever to -dissipate all doubt on the subject. At one o'clock P.M., the heavens -being almost cloudless, a tremendous noise, like that of thunder, was -heard, and at the same time an immense fire-ball was seen moving with -great rapidity through the atmosphere. This was followed by a violent -explosion which lasted several minutes, and which was heard not only at -L'Aigle, but in every direction around it to the distance of seventy -miles. Immediately after a great number of meteoric stones fell to the -earth, generally penetrating to some distance beneath the surface. The -largest of these fragments weighed 17-1/2 pounds. This occurrence very -naturally excited great attention. M. Biot, under the authority of the -government, repaired to L'Aigle, collected the various facts in regard -to the phenomenon, took the depositions of witnesses, etc., and finally -embraced the results of his investigations in an elaborate memoir. - -It would not comport with the design of the present treatise to give -an extended list of these phenomena. The following account, however, -includes the most important instances of the fall of aerolites, and -also of the displays of meteoric fire-balls. - -1. According to Livy a number of meteoric stones fell on the Alban -Hill, near Rome, about the year 654 B.C. This is the most ancient fall -of aerolites on record. - -2. 468 B.C., about the year in which Socrates was born. A mass of rock, -described as "of the size of two millstones," fell at AEgos Potamos, in -Thrace. An attempt to rediscover this meteoric mass, so celebrated in -antiquity, was recently made, but without success. Notwithstanding -this failure, Humboldt expressed the hope that, as such a body would be -difficult to destroy, it may yet be found, "since the region in which -it fell is now become so easy of access to European travelers." - -3. 921 A.D. An immense aerolite fell into the river (a branch of the -Tiber) at Narni, in Italy. It projected three or four feet above the -surface of the water. - -4. 1492, November 7th. An aerolite, weighing two hundred and -seventy-six pounds, fell at Ensisheim, in Alsace, penetrating the earth -to the depth of three feet. This stone, or the greater portion of it, -may still be seen at Ensisheim. - -5. 1511, September 14th. At noon an almost total darkening of the -heavens occurred at Crema. "During this midnight gloom," says a writer -of that period, "unheard-of thunders, mingled with awful lightnings, -resounded through the heavens. * * * On the plain of Crema, where never -before was seen a stone the size of an egg, there fell pieces of rock -of enormous dimensions and of immense weight. It is said that ten of -these were found weighing a hundred pounds each." A monk was struck -dead at Crema by one of these rocky fragments. This terrific meteoric -display is said to have lasted two hours, and 1200 aerolites were -subsequently found. - -6. 1637, November 29th. A stone, weighing fifty-four pounds, fell on -Mount Vaison, in Provence. - -7. 1650, March 30th. A Franciscan monk was killed at Milan by the fall -of a meteoric stone. - -8. 1674. Two Swedish sailors were killed on ship-board by the fall of -an aerolite. - -9. 1686, July 19th. An extraordinary fire-ball was seen in England; -its motion being opposite to that of the earth in its orbit. Halley -pronounced this meteor a cosmical body. (See Philos. Transact., vol. -xxix.) - -10. 1706, June 7th. A stone weighing seventy-two pounds fell at -Larissa, in Macedonia. - -11. 1719, March 19th. Another great meteor was seen in England. Its -explosion occurred at an elevation of 69 miles. Notwithstanding its -height, however, the report was like that of a broadside, and so great -was the concussion that windows and doors were violently shaken. - -12. 1751, May 26th. Two meteoric masses, consisting almost wholly of -iron, fell near Agram, the capital of Croatia. The larger fragment, -which weighs seventy-two pounds, is now in Vienna. - -13. 1756. The concussion produced by a meteoric explosion threw down -chimneys at Aix, in Provence, and was mistaken for an earthquake. - -14. 1771, July 17th. A large meteor exploded near Paris, at an -elevation of 25 miles. - -15. 1783, August 18th. A fire-ball of extraordinary magnitude was seen -in Scotland, England, and France. It produced a rumbling sound like -distant thunder, although its elevation above the earth's surface was -50 miles at the time of its explosion. The velocity of its motion was -equal to that of the earth in its orbit, and its diameter, according to -Sir Charles Blagden, was about half a mile. - -16. 1790, July 24th. Between nine and ten o'clock at night a very large -igneous meteor was seen near Bourdeaux, France. Over Barbotan a loud -explosion was heard, which was followed by a shower of meteoric stones -of various magnitudes. - -17. 1794, July. A fall of about a dozen aerolites occurred at Sienna, -Tuscany. - -18. 1795, December 13th. A large meteoric stone fell near Wold Cottage, -in Yorkshire, England. The following account of the phenomenon is -taken from Milner's _Gallery of Nature_, p. 134: "Several persons -heard the report of an explosion in the air, followed by a hissing -sound; and afterward felt a shock, as if a heavy body had fallen to the -ground at a little distance from them. One of these, a plowman, saw -a huge stone falling toward the earth, eight or nine yards from the -place where he stood. It threw up the mould on every side; and after -penetrating through the soil, lodged some inches deep in solid chalk -rock. Upon being raised, the stone was found to weigh fifty-six pounds. -It fell in the afternoon of a mild but hazy day, during which there -was no thunder or lightning; and the noise of the explosion was heard -through a considerable district." - -19. 1796, February 19th. A stone of ten pounds' weight fell in Portugal. - -20. 1798, March 12th. A stone weighing twenty pounds fell at Sules, -near Ville Franche. - -21. 1798, March 17th. An aerolite weighing about twenty pounds fell at -Sale, Department of the Rhone. - -22. 1798, December 19th. A shower of meteoric stones fell at Benares, -in the East Indies. An interesting account of the phenomenon was given -by J. Lloyd Williams, F.R.S., then a resident in Bengal. The sky had -been perfectly clear for several days. At eight o'clock in the evening -a large meteor appeared, which was attended with a loud rumbling -noise. Immediately after the explosion a sound was heard like that of -heavy bodies falling in the neighborhood. Next morning the fresh earth -was found turned up in many places, and aerolites of various sizes were -discovered beneath the surface. - -23. 1803, April 26th. The shower at L'Aigle, previously described. - -24. 1807, December 14th. A large meteor exploded over Weston, -Connecticut. The height, direction, velocity, and magnitude of this -body were ably discussed by Dr. Bowditch in a memoir communicated -to the American Academy of Arts and Sciences in 1815. The following -condensed statement of the principal facts, embodied in Dr. Bowditch's -paper, is extracted from the _People's Magazine_ for January 25th, 1834: - -"The meteor of 1807 was observed about a quarter-past six on Monday -morning. The day had just dawned, and there was little light except -from the moon, which was just setting. It seemed to be half the -diameter of the full moon; and passed, like a globe of fire, across -the northern margin of the sky. It passed behind some clouds, and when -it came out it flashed like heat lightning. It had a train of light, -and appeared like a burning fire-brand carried against the wind. It -continued in sight about half a minute, and, in about an equal space -after it faded, three loud and distinct reports, like those of a -four-pounder near at hand, were heard. Then followed a quick succession -of smaller reports, seeming like what soldiers call a running fire. The -appearance of the meteor was as if it took three successive throes, or -leaps, and at each explosion a rushing of stones was heard through the -air, some of which struck the ground with a heavy fall. - -"The first fall was in the town of Huntington, near the house of Mr. -Merwin Burr. He was standing in the road, in front of his house, when -the stone fell, and struck a rock of granite about fifty feet from him, -with a loud noise. The rock was stained a dark-red color, and the stone -was principally shivered into very small fragments, which were thrown -around to a distance of twenty feet. The largest piece was about the -size of a goose egg, and was still warm. - -"The stones of the second explosion fell about five miles distant, near -Mr. William Prince's residence, in Weston. He and his family were in -bed when they heard the explosion, and also heard a heavy body fall to -the earth. They afterward found a hole in the earth, about twenty-five -feet from the house, like a newly dug post-hole, about one foot in -diameter, and two feet deep, in which they found a meteoric stone -buried, which weighed thirty-five pounds. Another mass fell half a mile -distant, upon a rock, which it split in two, and was itself shivered to -pieces. Another piece, weighing thirteen pounds, fell a half a mile to -the northeast, into a plowed field. - -"At the last explosion, a mass of stone fell in a field belonging to -Mr. Elijah Seely, about thirty rods from the house. This stone falling -on a ledge, was shivered to pieces. It plowed up a large portion of the -ground, and scattered the earth and stones to the distance of fifty or -a hundred feet. Some cattle that were near were very much frightened, -and jumped into an inclosure. It was concluded that this last stone, -before being broken, must have weighed about two hundred pounds. These -stones were all of a similar nature, and different from any commonly -found on this globe. When first found, they were easily reduced to -powder by the fingers, but by exposure to the air they gradually -hardened." - -25. 1859, November 15th. Between nine and ten o'clock in the morning, -an extraordinary meteor was seen in several of the New England States, -New York, New Jersey, the District of Columbia, and Virginia. The -apparent diameter of the head was nearly equal to that of the sun, -and it had a train, notwithstanding the bright sunshine, several -degrees in length. Its disappearance on the coast of the Atlantic was -followed by a series of the most terrific explosions. It is believed -to have descended into the water, probably into Delaware Bay. A highly -interesting account of this meteor, by Prof. Loomis, may be found in -the _American Journal of Science and Arts_ for January, 1860. - -26. 1860, May 1st. About twenty minutes before one o'clock P.M., -a shower of meteoric stones--one of the most extraordinary on -record--fell in the S. W. corner of Guernsey County, Ohio. Full -accounts of the phenomena are given in _Silliman's Journal_ for July, -1860, and January and July, 1861, by Professors E. B. Andrews, E. -W. Evans, J. L. Smith, and D. W. Johnson. From these interesting -papers we learn that the course of the meteor was about 40 deg. west of -north. Its visible track was over Washington and Noble Counties, and -the prolongation of its projection, on the earth's surface, passes -directly through New Concord, in the S. E. corner of Muskingum County. -The height of the meteor, when seen, was about 40 miles, and its path -was nearly parallel with the earth's surface. The sky, at the time, -was, for the most part, covered with clouds over northwestern Ohio, so -that if any portion of the meteoric mass continued on its course, it -was invisible. The velocity of the meteor, in relation to the earth's -surface, was from 3 to 4 miles per second; and hence its absolute -velocity in the solar system was from 20 to 21 miles per second. This -would indicate an orbit of considerable eccentricity. - -"At New Concord,[12] Muskingum County, where the meteoric stones fell, -and in the immediate neighborhood, there were many distinct and loud -reports heard. At New Concord there were first heard in the sky, a -little southeast of the zenith, a loud detonation, which was compared -to that of a cannon fired at the distance of half a mile. After an -interval of ten seconds another similar report. After two or three -seconds another, and so on with diminishing intervals. Twenty-three -distinct detonations were heard, after which the sounds became blended -together and were compared to the rattling fire of an awkward squad of -soldiers, and by others to the roar of a railway train. These sounds, -with their reverberations, are thought to have continued for two -minutes. The last sounds seemed to come from a point in the southeast -45 deg. below the zenith. The result of this cannonading was the falling -of a large number of stony meteorites upon an area of about ten miles -long by three wide. The sky was cloudy, but some of the stones were -seen first as 'black specks,' then as 'black birds,' and finally -falling to the ground. A few were picked up within twenty or thirty -minutes. The warmest was no warmer than if it had lain on the ground -exposed to the sun's rays. They penetrated the earth from two to three -feet. The largest stone, which weighed one hundred and three pounds, -struck the earth at the foot of a large oak tree, and, after cutting -off two roots, one five inches in diameter, and grazing a third root, -it descended two feet ten inches into hard clay. This stone was found -resting under a root that was not cut off. This would seemingly imply -that it entered the earth obliquely." - -Over thirty of the stones which fell were discovered, while doubtless -many, especially of the smaller, being deeply buried beneath the soil, -entirely escaped observation. The weight of the largest ten was four -hundred and eighteen pounds. - -27. 1864, May 14th. Early in the evening a very large and brilliant -meteor was seen in France, from Paris to the Spanish border. At -Montauban, and in the vicinity, loud explosions were heard, and showers -of meteoric stones fell near the villages of Orgueil and Nohic. The -principal facts in regard to this meteor are the following: - - Elevation when first seen, over 55 miles. - " at the time of its explosion 20 " - Inclination of its path to the horizon 20 deg. or 25 deg. - Velocity per second, about 20 miles, - -or equal to that of the earth's orbital motion. "This example," says -Prof. Newton, "affords the strongest proof that the detonating and -stone-producing meteors are phenomena not essentially unlike." - -The foregoing list contains but a small proportion even of those -meteoric stones the date of whose fall is known. But besides these, -other masses have been found so closely similar in structure to -aerolites whose descent has been observed, as to leave no doubt in -regard to their origin. One of these is a mass of iron and nickel, -weighing sixteen hundred and eighty pounds, found by the traveler -Pallas, in 1749, at Abakansk, in Siberia. This immense aerolite may be -seen in the Imperial Museum at St. Petersburg. On the plain of Otumpa, -in Buenos Ayres, is a meteoric mass 7-1/2 feet in length, partly buried -in the ground. Its estimated weight is thirty-three thousand six -hundred pounds. A specimen of this stone, weighing fourteen hundred -pounds, has been removed and deposited in one of the rooms of the -British Museum. A similar block, of meteoric origin, weighing twelve -or thirteen thousand pounds, was discovered some years since in the -Province of Bahia, in Brazil. - -Some of the inferences derived from the examination of meteoric stones, -and the consideration of the phenomena attending their fall, are the -following: - -1. R. P. Greg, Esq., of Manchester, England, who has made luminous -meteors a special study, has found that meteoric stone-falls occur -with greater frequency than usual on or about particular days. He -calls attention especially to five aerolite epochs, viz.: February -15th-19th; May 19th; July 26th; November 29th, and December 13th. - -2. It is worthy of remark that no new elements have been found in -meteoric stones. Humboldt, in his _Cosmos_, called attention to this -interesting fact. "I would ask," he remarks, "why the elementary -substances that compose one group of cosmical bodies, or one planetary -system, may not in a great measure be identical? Why should we not -adopt this view, since we may conjecture that these planetary bodies, -like all the larger or smaller agglomerated masses revolving round -the sun, have been thrown off from the once far more expanded solar -atmosphere, and have been formed from vaporous rings describing their -orbits round the central body?"[13] - -3. But while aerolites contain no elements but such as are found in -the earth's crust, the manner in which these elements are combined -and arranged is so peculiar that a skillful mineralogist will readily -distinguish them from terrestrial substances. - -4. Of the eighteen or nineteen elements hitherto observed in meteoric -stones, iron is found in the greatest abundance. The specific gravities -vary from 1.94 to 7.901: the former being that of the stone of Alais, -the latter, that of the meteorite of Wayne County, Ohio, described by -Professor J. L. Smith in _Silliman's Journal_ for November, 1864, p. -385. In most cases, however, the specific gravity is about 3 or 4. - -5. The contemplation of the heavenly bodies has often produced -in thoughtful minds an intense desire to know something of their -nature and physical constitution. This curiosity is gratified in the -examination of aerolites. To handle, weigh, inspect, and analyze -bodies that have wandered unnumbered ages through the planetary -spaces--perhaps approaching in their perihelia within a comparatively -short distance of the solar surface, and again receding in their -aphelia to the limits of the planetary system--must naturally excite a -train of pleasurable emotions. - -6. It is highly probable that in pre-historic times, before the solar -system had reached its present stage of maturity, those chaotic -wanderers were more numerous in the vicinity of the earth's orbit than -in recent epochs. Even now the interior planets, Mercury and Venus, -appear to be moving through the masses of matter which constitute -the zodiacal light. It would seem probable, therefore, that they are -receiving from this source much greater accretions of matter than the -earth. - -7. As Mercury's orbit is very eccentric, he is beyond his mean distance -during much more than half his period. Hence, probably, the greater -increments of meteoric matter are derived from such portions of the -zodiacal light as have a longer period than Mercury himself. If so, the -tendency would be to diminish slowly the planet's mean motion. Such a -lengthening of the period has been actually discovered.[14] - - - - -CHAPTER IV. - -CONJECTURES IN REGARD TO METEORIC EPOCHS. - - -It is highly probable that aerolites and shooting-stars are derived -either from rings thrown off in the planes of the solar or planetary -equators, or from streams of nebulous matter drawn into the solar -system by the sun's attraction. Such annuli or streams would probably -each furnish an immense number of meteor-asteroids. If any rings -intersect the earth's orbit, our planet must encounter such masses as -happen at the same time to be passing the point of intersection. This -must be repeated _at the same epoch_ in different years; the frequency -of the encounter of course depending on the closeness and regularity -with which the masses are distributed around the ring. Accordingly it -has been found that not only the meteors of November 14th and of the -epochs named in Chapter II. have their respective radiants, but also -those of many other nights. Mr. Alexander S. Herschel, of Collingwood, -England, states that fifty-six such points of divergence are now well -established. We have mentioned in a previous chapter that Mr. Greg, of -Manchester, has specified several epochs at which fire-balls appear, -and meteoric stone-falls occur, with unusual frequency. The number -of these periods will probably be increased by future observations. -Perhaps the following facts may justify the designation of July -13th-14th as such an epoch: - -1. On the 13th of July, 1797, a large fire-ball was seen in Goettingen. - -2. On the 14th of July, 1801, a fire-ball was seen in Montgaillard. - -3. On the 14th of July, 1845, a brilliant meteor was seen in London. - -4. On the 13th of July, 1846, at about 9h. and 30m. P.M., a brilliant -fire-ball passed over Maryland and Pennsylvania, and was seen also in -Virginia, Delaware, New Jersey, New York, and Connecticut. Its course -was north, about thirty degrees east, and the projection of its path -on the earth's surface passed about four miles west of Lancaster, -Pennsylvania, and nearly through Mauch Chunk, in Carbon County. When -west of Philadelphia its angle of elevation, as seen from that city, -was forty-two degrees. Consequently its altitude, when near Lancaster, -was about fifty-nine miles. The projection of its visible path, on the -earth's surface, was at least two hundred and fifty miles in length. -Its height, when nearest Gettysburg, was about seventy miles, and it -disappeared at an elevation of about eighteen miles, near the south -corner of Wayne County, Pennsylvania. Its apparent diameter, as seen -from York and Lancaster, was about half that of the moon, and its -estimated heliocentric velocity was between twenty and twenty-five -miles. - -The author was assured by persons in Harford County, Maryland, and also -in York, Pennsylvania, that shortly after the disappearance of the -meteor a distinct report, like that of a distant cannon, was heard. -As might be expected, their estimates of the interval which elapsed -were different; but Daniel M. Ettinger, Esq., of York, who was paying -particular attention, in expectation of a report, stated that it was -a little over six minutes. This would indicate a distance of about -seventy-five miles. The sound could not therefore have resulted from -an explosion at or near the termination of the meteor's observed path. -The inclination of the meteoric track to the surface of the earth -was such that the body could not have passed out of the atmosphere. -As no aerolites, however, were found beneath any part of its path, -perhaps the entire mass may have been dissipated before reaching the -earth.--_Silliman's Journal_ for May, 1866. - -5. On the 14th of July, 1847, a remarkable fall of aerolites was -witnessed at Braunau, in Bohemia. Humboldt states that "the fallen -masses of stone were so hot, that, after six hours, they could not be -touched without causing a burn." An analysis of some of the fragments, -by Fischer and Duflos, gave the following result: - - Iron 91.862 - Nickel 5.517 - Cobalt 0.529 - Copper, manganese, arsenic, calcium, magnesium, - silicium, carbon, chlorine and sulphur. 2.072 - ------- - 100.000 - -6. On the 13th of July, 1848, a brilliant fire-ball was seen at -Stone-Easton, Somerset, England. - -7. On the 13th of July, 1852, a large bolide was seen in London. - -8. On the 14th of July, 1854, a fire-ball was seen at Senftenberg. - -9. On the 13th of July, 1855, a meteor, three times as large as -Jupiter, was seen at Nottingham, England. - -10. "One of the most celebrated falls that have occurred of late years -is that which happened on the 14th of July, 1860, between two and -half-past two in the afternoon, at Dhurmsala, in India. The aerolite in -question fell with a most fearful noise, and terrified the inhabitants -of the district not a little. Several fragments were picked up by -the natives, and carried religiously away, with the impression that -they had been thrown from the summit of the Himalayas by an invisible -Divinity. Lord Canning forwarded some of these stones to the British -Museum and to the Vienna Museum. Mr. J. R. Saunders also sent some -of the stones to Europe. It appears that, soon after their fall, the -stones were _intensely cold_.[15] They are ordinary earthy aerolites, -having a specific gravity of 3.151, containing fragments of iron and -iron pyrites; they have an uneven texture, and a pale-gray color." - -11. At a quarter-past ten o'clock on the evening of July 13th, 1864, -a large fire-ball was seen in New England.[16] The hour of its -appearance, it will be observed, was nearly the same with that of the -bolide of July 13th, 1846; and it is also worthy of remark that their -_directions_ were nearly the same. The meteor of 1864 had a tail three -or four degrees in length, and the body, like that of 1846, exploded -with a loud report. - -12. On the 8th of July, 1186, an aerolite fell at Mons, in Belgium -(Quetelet's _Physique du Globe_, p. 320). A forward motion of the node, -somewhat less than that observed in the rings of November and August, -would give a correspondence of dates between the falls of 1186, 1847, -and 1860. - -With the exception of the last, which is doubtful, these phenomena all -occurred within a period of 67 years. - - -THE EPOCH OF NOVEMBER 29. - -It has been stated that in different years meteoric stones have -fallen about the 29th of November. One of the most recent aerolites -which can be assigned to this epoch is that which fell on the 30th of -November, 1850, at Shalka, in Bengal. It may be mentioned, as at least -a coincidence, that the earth passes the approximate intersection of -her orbit with that of Biela's comet at the date of this epoch. Do -other bodies besides the two Biela comets move in the same ellipse? It -is worthy of remark that two star showers have been observed at this -date: one in China, A.D. 930, the other in Europe, 1850 (see Quetelet's -Catalogue). It is certainly important that the meteors of this epoch -should be carefully studied. - - - - -CHAPTER V. - - GEOGRAPHICAL DISTRIBUTION OF METEORIC STONES--DO AEROLITIC FALLS - OCCUR MORE FREQUENTLY BY DAY THAN BY NIGHT?--DO METEORITES, - BOLIDES, AND THE MATTER OF ORDINARY SHOOTING-STARS, COEXIST IN - THE SAME RINGS? - - -Professor Charles Upham Shepard, of Amherst College, who has devoted -special attention to the study of meteoric stones, has designated two -districts of country, one in each continent, but both in the northern -hemisphere, in which more than nine-tenths of all known aerolites have -fallen. He remarks: "The fall of aerolites is confined principally -to two zones; the one belonging to America is between 33 deg. and 44 deg. -north latitude, and is about 25 deg. in length. Its direction is more or -less from northeast to southwest, following the general line of the -Atlantic coast. Of all known occurrences of this phenomenon during the -last fifty years, 92.8 per cent. have taken place within these limits, -and mostly in the neighborhood of the sea. The zone of the Eastern -continent--with the exception that it extends ten degrees more to the -north--lies between the same degrees of latitude, and follows a similar -northeast direction, but is more than twice the length of the American -zone. Of all the observed falls of aerolites, 90.9 per cent. have taken -place within this area, and were also concentrated in that half of the -zone which extends along the Atlantic." - -The facts as stated by Professor Shepard are, of course, -unquestionable. It seems, however, extremely improbable that the -districts specified should receive a much larger proportion of -aerolites than others of equal extent. How, then, are the facts to be -accounted for? We answer, the number of aerolites _seen_ to fall in a -country depends upon the number of its inhabitants. The ocean, deserts, -and uninhabited portions of the earth's surface afford no instances -of such phenomena, simply for the want of observers. In sparsely -settled countries the fall of aerolites would not unfrequently escape -observation; and as such bodies generally penetrate the earth to some -depth, the chances of discovery, when the fall is not observed, must be -exceedingly rare. Now the part of the American continent designated by -Professor Shepard, it will be noticed, is the oldest and most thickly -settled part of the United States; while that of the Eastern continent -stretches in like manner across the most densely populated countries -of Europe. This fact alone, in all probability, affords a sufficient -explanation of Prof. Shepard's statement.[17] - -_Do aerolites fall more frequently by day than by night?_--Mr. -Alexander S. Herschel, of Collingwood, England, has with much care and -industry collected and collated the known facts in regard to bolides -and aerolites. One result of his investigations is that a much greater -number of meteoric stones are observed to fall by day than by night. -From this he infers that, for the most part, the orbits in which -they move are _interior_ to that of the earth. The fact, however, is -obviously susceptible of a very different explanation--an explanation -quite similar to that of the frequent falls in particular districts. -_At night the number of observers is incomparably less; and hence many -aerolites escape detection._ There would seem to be no cause, reason, -or antecedent probability of these falls being more frequent at one -hour than another in the whole twenty-four. - -_The coexistence of meteorites, bolides, and the matter of -shooting-stars in the same rings?_--It has been stated on a previous -page that several aerolite epochs are coincident with those of -shooting-stars. Is the number of such cases sufficient to justify the -conclusion that the correspondence of dates is not accidental? We will -consider, - - -I. The Epoch of November 11th-14th. - -1. 1548, November 6th. A very large detonating meteor was seen at -Mansfield, Thuringia, at two o'clock in the morning. The known rate of -movement of the node brings this meteor within the November epoch. - -2. 1624, November 7th. A large fire-ball was seen at Tubingen. The -motion of the node brings this also within the epoch. - -3. 1765, November 11th. A bright meteoric light was observed at -Frankfort. - -4. 1791, November 11th. A large meteor was seen at Goettingen and -Lilienthal. - -5. 1803, November 13th. A fire-ball, twenty-three miles high, was seen -at London and Edinburgh. - -6. 1803, November 13th. A splendid meteor was seen at Dover and Harts. - -7. 1808, November 11th. A fire-ball was seen in England. - -8. 1818, November 13th. A fire-ball was seen at Gosport. - -9. 1819, November 13th. A fire-ball was seen at St. Domingo. - -10. 1820, November 12th. A large detonating meteor was seen at -Cholimschk, Russia. - -11. 1822, November 12th. A fire-ball appeared at Potsdam. - -12. 1828, November 12th. A meteor was seen in full sunshine at Sury, -France. - -13. 1831, November 13th. A fire-ball was seen at Bruneck. - -14. 1831, November 13th. A brilliant meteor was seen in the North of -Spain. - -15. 1833, November 12th. A fire-ball was seen in Germany. - -16. 1833, November 13th. A meteor, two-thirds the size of the moon, was -seen during the great meteoric shower in the United States. - -17. 1834, November 13th. A large fire-ball was seen in North America. - -18. 1835, November 13th. Several aerolites fell near Belmont, -Department de l'Ain, France. - -19. 1836, November 11th. An aerolitic fall occurred at Macao, Brazil. - -20. 1837, November 12th. A remarkable fire-ball was seen in England. - -21. 1838, November 13th. A large fire-ball was seen at Cherbourg. - -22. 1849, November 13th. An extraordinary meteor appeared in Italy. -"Seen in the southern sky. Varied in color; a bright cloud visible one -and a half hour after; according to some a detonation heard fifteen -minutes after bursting. Seen also like a stream of fire between Tunis -and Tripolis, where a shower of stones fell; some of them into the town -of Tripolis itself." - -23. 1849, November 13th. A large meteor was seen at Mecklenburg and -Breslau. - -24. 1856, November 12th. A meteoric stone fell at Trenzano, Italy. - -25. 1866, November 14th. At Athens, Greece, a large number of -bolides was seen by Mr. J. F. Julius Schmidt, during the shower of -shooting-stars. One of these fire-balls was of the first class, and -left a train which was visible one hour to the naked eye. - - -II. The Epoch of August 7th-11th. - -1. 1642, August 4th. A meteoric stone fell in Suffolk County, England. - -2. 1650, August 6th. An aerolite fell in Holland. The observed motion -of the node brings both these stone-falls within the epoch. - -3. 1765, August 9th. A large bolide was seen at Greenwich. - -4. 1773, August 8th. A fire-ball was seen at Northallerton. - -5. 1800, August 8th. A large meteor was seen in different parts of -North America. - -6. 1802, August 10th. A fire-ball appeared at Quedlinburg. - -7. 1807, August 9th. A bolide was seen at Nurenberg. - -8. 1810, August 10th. A stone weighing seven and three-quarter pounds -fell at Tipperary, Ireland. - -9. 1816, August 7th. In Hungary a large fire-ball was seen to burst, -with detonations. - -10. 1817, August 7th. A brilliant fire-ball was seen at Augsburg. - -11. 1818, August 10th. A meteoric stone, weighing seven pounds, fell at -Slobodka, Russia. - -12. 1822, August 7th. A meteorite fell at Kadonah, Agra. - -13. 1822, August 7th. A large meteor was seen in Moravia. - -14. 1822, August 11th. "A large mass of fire fell down with a great -explosion" near Coblentz. - -15. 1823, August 7th. Two meteoric stones fell in Nobleboro', Maine. - -16. 1826, August 8th. A fire-ball was seen at Odensee. - -17. 1826, August 11th. A bright meteor appeared at Halle. - -18. 1833, August 10th. A fire-ball was seen at Worcestershire, England. - -19. 1834, August 10th. A bolide appeared at Brussels. - -20. 1838, August 9th. A fine meteor was seen in Germany. - -21. 1839, August 7th. A splendid fire-ball was seen at sea. - -22. 1840, August 7th. A bolide appeared at Naples. - -23. 1841, August 10th. An aerolite fell at Iwan, Hungary. - -24. 1842, August 9th. A greenish fire-ball was seen at Hamburg. - -25. 1844, August 8th. A large meteor was seen in Brittany. - -26. 1844, August 10th. A fire-ball was seen at Hamburg. - -27. 1845, August 10th. A brilliant meteor was seen at London and Oxford. - -28. 1847, August 9th. A large irregular meteor, "like a bright cloud of -smoke," was seen at Brussels. - -29. 1850, August 10th. A meteor as large as the moon was seen in -Ireland. - -30. 1850, August 10th. A very large bolide was observed in Paris. - -31. 1850, August 11th. A fire-ball was seen in Paris. - -32. 1853, August 7th. A bolide was observed at Glasgow. - -33. 1853, August 7th. A meteor twice as large as Venus was seen at -Paris. - -34. 1853, August 9th. A large meteor was seen to separate into two -parts. - -35. 1855, August 10th. A bluish meteor, five times as large as Jupiter, -was seen at Nottingham. - -36. 1857, August 11th. A bolide was seen in Paris. - -37. 1859, August 7th. A detonating meteor appeared in Germany. - -38. 1859, August 11th. A meteoric stone fell near Albany, New York. - -39. 1859, August 11th. A fine meteor was seen at Athens. - -40. 1862, August 8th. A meteoric stone-fall occurred at Pillistfer, -Russia. - -41. 1863, August 11th. An aerolite fell at Shytal, India. - - -III. The Epoch of December 6th-13th. - -The following falls of meteoric stones have occurred at this epoch: - -1. 1795, December 13th. At Wold Cottage, England. - -2. 1798, December 13th. At Benares, India. - -3. 1803, December 13th. At Maessing, Bavaria. - -4. 1813, December 13th. At Luotolaks, Finland. - -5. 1858, December 9th. At Ausson, France. - -6. 1863, December 7th. At Tirlemont, Belgium. - -7. 1863, December 10th. At Inly, near Trebizond.[18] - - -IV. The Epoch of April 18th-26th. - -For this epoch we have the following aerolites: - -1. 1803, April 26th. At L'Aigle, France. - -2. 1808, April 19th. At Casignano, Parma, Italy. - -3. 1838, April 18th. At Abkurpore, India. - -4. 1842, April 26th. At Milena, Croatia. - - -V. The Epoch of April 9th-12th. - -1. 1805, April 10th. At Doroninsk, Russia. - -2. 1812, April 10th. At Toulouse, France. - -3. 1818, April 10th. At Zaborzika, Russia. - -4. 1864, April 12th. At Nerft, Russia. - -The foregoing lists, which might be extended, are sufficient to -establish the fact that meteoric stones are but the largest masses in -the nebulous rings from which showers of shooting-stars are derived; a -fact worthy of consideration whatever theory may be adopted in regard -to the origin of such annuli. - - - - -CHAPTER VI. - -PHENOMENA SUPPOSED TO BE METEORIC--METEORIC DUST--DARK DAYS. - - -It is well known that great variety has been found in the composition -of aerolites. While some are extremely hard, others are of such a -nature as to be easily reducible to powder. It is not impossible -that when some of the latter class explode in the atmosphere they -are completely pulverized, so that, reaching the earth in extremely -minute particles, they are never discovered. It is very unlikely, -moreover, that of the millions of shooting-stars that daily penetrate -the atmosphere nothing whatever in the solid form should ever reach the -earth's surface. Indeed, the celebrated Reichenbach, who devoted great -attention to this subject, believed that he had actually discovered -such deposits of meteoric matter. Chladni and others have detailed -instances of the fall of _dust_, supposed to be meteoric, from the -upper regions of the atmosphere. The following may be regarded, with -more or less probability, as instances of such phenomena: - -1. A.D. 475, November 5th or 6th. A shower of black dust fell in the -vicinity of Constantinople. Immediately before or about the time of -the fall, according to old accounts, "the heavens appeared to be on -fire," which seems to indicate a meteoric display of an extraordinary -character. - -2. On the 3d of December, 1586, a considerable quantity of dark-colored -matter fell from the atmosphere, at Verde, in Hanover. The fall was -attended by intense light, as well as by a loud report resembling -thunder. The substance which fell was hot when it reached the earth, -as the planks on which a portion of it was found were slightly burnt, -or charred. The date of this occurrence, allowance being made for the -movement of the node, is included within the limits of the meteoric -epoch of December 6th-13th. - -3. About a century later, viz., on the 31st of January, 1686, a very -extensive deposit of blackish matter, in appearance somewhat resembling -charred paper, took place in Norway and other countries in the north -of Europe. A portion of this substance, which had been carefully -preserved, was analyzed by Grotthus, and found to contain iron, silica, -and other elements frequently met with in aerolites. - -4. On the 15th of November, 1755, red rain fell in Sweden and Russia, -and on the same day in Switzerland. It gave a reddish color to the -waters of Lake Constance, to which it also imparted an acid taste. The -rain which fell on this occasion deposited a sediment whose particles -were attracted by the magnet. - -5. In 1791 a luminous meteor exploded over the Atlantic Ocean, and at -the same time a quantity of matter resembling sand descended to the -surface. - -6. According to Chladni the explosion of a large bolide over Peru, on -the 27th of August, 1792, was followed by a shower of cindery matter, -the fall of which continued during three consecutive days. - -7. On the 13th and 14th of March, 1813, a shower of red dust fell in -Calabria, Tuscany, and Friuli. The deposit was sufficient to impart -its color to the snow which was then upon the ground. That this dust -was meteoric can scarcely be doubted, since at the same time a shower -of aerolites fell at Cutro, in Calabria, attended by two loud reports -resembling thunder. The shower of dust continued several hours, and was -accompanied by a noise which was compared to the distant dashing of the -waves of the ocean.[19] - -8. In November, 1819, black rain and snow fell in Canada. - -9. On the 3d of May, 1831, red rain fell near Giessen. It deposited a -dark-colored sediment which Dr. Zimmermann found to contain silica, -oxide of iron, and various other substances observed in aerolites. - -It is well known that quantities of sand are often conveyed, by the -trade-winds, from the continent of Africa and deposited in the ocean. -Such sand-showers have sometimes occurred several hundred miles from -the coast. Volcanic matter also has been occasionally carried a -considerable distance. The phenomena above described cannot, however, -be referred to such causes; and there can be little doubt that most, if -not all of them, were of meteoric origin. - -There is, in all probability, a regular gradation from the smallest -visible shooting-stars to bolides and aerolites. No doubt a great -number of very small meteoric stones penetrate beneath the earth's -surface and escape observation. An interesting account of the -accidental discovery of such _celestial pebbles_ has recently been -given by Professor Haidinger, of Vienna. The meteor from which they -were derived _was but little larger than an ordinary shooting-star_. -Its track was visible, however, until it terminated at the earth's -surface. Professor Haidinger's account is as follows: On the 31st -of July, 1859, about half-past nine o'clock in the evening, three -inhabitants of the bourg of Montpreis, in Styria, saw a small luminous -globe, very similar to a shooting-star, and followed by a luminous -streak in the heavens, fall directly to the earth, which it attained -close to the chateau that exists in the locality. The fall was -accompanied by a whistling or hissing noise in the air, and terminated -by a _slight_ detonation. The three observers, rushing to the spot -where the meteor fell, immediately found a small cavity in the hard, -sandy soil, from which they extracted three small meteoric stones about -the size of nuts, and a quantity of black powder. For five to eight -seconds these stones continued in a _state of incandescence_, and it -was necessary to allow upwards of a quarter of an hour to elapse before -they could be touched without inflicting a burn. They appear to have -been ordinary meteoric stones, covered with the usual black rind. The -possessors would not give them up to be analyzed. The details of this -remarkable occurrence of the fall of an extremely small meteor, we owe -to Herr Deschann, Conservator of the Museum of Laibach, in Carniola, -and member of the Austrian Chamber of Deputies. - -The following is perhaps the only instance on record in which a -shooting-star _lower than the clouds_ has been undoubtedly observed. -The date is one at which meteors are said to be more than usually -numerous; and the radiant point for the epoch has been recently -determined, by British observers, to be about _Gamma Cygni_. The -meteor was seen by Mr. David Trowbridge, of Hector, Schuyler County, -New York, who says: "On the evening of July 26th, 1866, about 8h. -15m. P.M., a very bright meteor flashed out in Cygnus, and moved from -east to west with great rapidity. Its path was about 30 deg. after I saw -it. Height above the northern horizon about 50 deg.. Duration of flight -from one-half to one second. It left a beautiful train. The head was -red and train blue. It was certainly _below_ the clouds. It passed -between me and some cirro-stratus clouds, so dense as to hide ordinary -stars completely. Several others that saw it said it was _below_ the -clouds."--_Silliman's Journal_ for Sept. 1866. It seems altogether -probable that when a meteor thus descends, before its explosion or -dissipation, into the lower atmospheric strata, at least portions of -its mass must reach the earth's surface. - - -METEORIC TRANSITS--DARK DAYS. - -If shooting-stars and aerolites are derived from meteoric rings -revolving round the sun in orbits nearly intersecting that of the -earth, then (1) these masses must sometimes transit the solar disk; (2) -if any of the rings contain either individual masses of considerable -magnitude, or sufficiently dense swarms of meteoric asteroids, such -transits may sometimes be observed; (3) the passage of a dense meteoric -cluster over the solar disk must partially intercept the sun's light -and heat; and (4) should both nodes of the ring very nearly intersect -the earth's orbit, meteoric falls might occur when the earth is at -either; in which case the epochs would be separated by an interval -of about six months. Have any such phenomena as those indicated been -actually observed? - -The passage of dark spots across the sun, having a much more rapid -motion than the solar maculae, has been frequently noticed. The -following instances are well authenticated: - -1779, June 17th. About mid-day the eminent French astronomer, Messier, -saw a great number of black points crossing the sun. Rapidly moving -spots were also seen by Pastorff on the following dates: - -1822, October 23d, - -1823, July 24th and 25th, - -1836, October 18th, - -and on several subsequent occasions the same astronomer witnessed -similar phenomena. Another transit of this kind has been seen quite -recently. On the 8th of May, 1865, a small black spot was seen by -Coumbary to cross the solar disk. It seems difficult to account for -these appearances (so frequently seen by experienced observers) unless -we regard them as meteoric masses. - - -PARTIAL INTERCEPTION OF THE SUN'S LIGHT AND HEAT. - -Numerous instances are on record of partial obscurations of the sun -which could not be accounted for by any known cause. Cases of such -phenomena took place, according to Humboldt, in the years 1090, 1203, -and 1547. Another so-called _dark day_ occurred on the 12th of May, -1706, and several more (some of still later date) might be specified. -Chladni and other physicists have regarded the transit of meteoric -masses as the most probable cause of these obscurations. It is proper -to remark, however, that the eminent French astronomer, Faye, who -has given the subject much attention, finds little or no evidence in -support of this conjecture. - -An examination of meteorological records is said to have established -two epochs of abnormal cold, viz., about the 12th of February and the -12th of May. The former was pointed out by Brandes about the beginning -of the present century; the latter by Maedler, in 1834. The May epoch -occurs when the earth is in conjunction with one of the nodes of the -November meteoric ring; and that of February has a similar relation -to the August meteors. M. Erman, a distinguished German scientist, -soon after the discovery of the August and November meteoric epochs, -suggested that those depressions of temperature might be explained -by the intervention of the meteoric zones between the earth and the -sun. The period, however, of the November meteors being still somewhat -doubtful, their position with respect to the earth about the 12th of -May is also uncertain. But however this may be, the following dates -of aerolitic falls seem to indicate May 8th-14th, or especially May -12th-13th, as a meteoric epoch: - -(_a_) May 8th, 1829, Forsyth, Georgia, U. S. A. - -(_b_) May 8th, 1846, Macerata, Italy. - -(_c_) May 9th, 1827, Nashville, Tennessee, U. S. A. - -(_d_) May 12th, 1861, Goruckpore, India. - -(_e_) May 13th, 1831, Vouille, France. - -(_f_) May 13th, 1855, Oesel, Baltic Sea. - -(_g_) May 13th, 1855, Bremevoerde, Hanover. - -(_h_) May 14th, 1861, near Villanova, in Catalonia, Spain. - -(_i_) May 14th, 1864, Orgueil, France. - -All the foregoing, except that of May 14th, 1861, may be found in -Shepard's list, _Silliman's Journal_ for January, 1867. - -It has been shown in a former chapter that more than seven millions -of shooting-stars of sufficient magnitude to be seen by the naked eye -daily enter the earth's atmosphere. As the small ones are the most -numerous, it is not improbable that an indefinitely greater number of -meteoric particles, too minute to be visible, are being constantly, in -this manner, arrested in their orbital motion. Now, it would certainly -be a very unwarranted conclusion that these atmospheric increments are -all of a permanently gaseous form. In view of this strong probability -that meteoric dust is daily reaching the earth's surface, Baron von -Reichenbach, of Vienna, conceived the idea of attempting its discovery. -Ascending to the tops of some of the German mountains, he carefully -collected small quantities of the soil from positions in which it had -not been disturbed by man. This matter, on being analyzed, was found -to contain small portions of nickel and cobalt--elements rarely found -in the mineral masses scattered over the earth's surface, but very -frequently met with in aerolites. In short, Reichenbach believed, and -certainly not without some probability, that he had detected minute -portions of meteoric matter. - - - - -CHAPTER VII. - - FURTHER RESEARCHES OF REICHENBACH--THEORY OF METEORS--STABILITY OF - THE SOLAR SYSTEM--DOCTRINE OF A RESISTING MEDIUM. - - -The able and original researches of the celebrated Reichenbach, who has -made meteoric phenomena the subject of long-continued and enthusiastic -investigation, have attracted the general attention of scientific men. -It is proposed to present, in the following chapter, a brief _resume_ -of his views and conclusions. - -1. _The Constitution of Comets._--It is a remarkable fact that cometary -matter has no refractive power, as is manifest from the observations of -stars seen through their substance.[20] These bodies, therefore, are -not gaseous; and the most probable theory in regard to their nature is -that they consist of an infinite number of discrete, solid molecules, -at great distances from each other, with very little attraction among -themselves, or toward the nucleus, and having, therefore, great -mobility. Now Baron Reichenbach, having carefully examined a great -number of meteoric stones, has found them for the most part composed -of extremely minute globules, apparently cemented together. He hence -infers that they have been comets--perhaps very small ones--whose -component molecules have by degrees collected into single masses. - -2. _The Number of Aerolites._--The average number of aerolitic falls -in a year was estimated by Schreibers, as previously stated, at 700. -Reichenbach, however, after a thorough discussion of the data at -hand, makes the number much larger. He regards the probable annual -average, for the entire surface of the earth, as not less than 4500. -This would give about twelve daily falls. They are of every variety -as to magnitude, from a weight of less than a single ounce to over -30,000 pounds. The Baron even suspects the meteoric origin of large -masses of dolerite which all former geologists had considered native -to our planet. In view of the fact that from the largest members of -our planetary system down to the particles of meteoric dust there is -an approximately regular gradation, and that the larger, at least -in some instances, appear to have been formed by the aggregation of -the smaller, he asks may not the earth itself have been formed by an -agglomeration of meteorites? The learned author, from the general scope -of his speculations, would thus seem to have adopted a form of the -nebular hypothesis somewhat different from that proposed by Laplace. - -3. _Composition and mean Density of Aerolites._--A large proportion of -meteoric stones are similar in structure to the volcanic or plutonic -rocks of the earth; and _all_ consist of elements identical with -those in our planet's crust. Their mean density, moreover, is very -nearly the same with that of the earth. These facts are regarded by -Reichenbach as indicating that those meteoric masses which are daily -becoming incorporated with our planet, have had a common origin with -the earth itself. Baron Reichenbach's views, as presented by himself, -will be found at length in _Poggendorf's Annalen_ for December, 1858. - -_Stability of the Solar System._--The well-known demonstrations of -the stability of the solar system, given by Lagrange and Laplace, -are not to be accepted in an unlimited sense. They make no provision -against the destructive agency of a resisting medium, or the entrance -of matter into the solar domain from the interstellar spaces. In -short, the conservative influence ascribed to these celebrated -theorems extends only to the major planets; and even in their case it -is to be understood as applying only to their mutual perturbations. -The phenomena of shooting-stars and aerolites have demonstrated the -existence of considerable quantities of matter moving in _unstable_ -orbits. The amount of such matter within the solar system cannot now be -determined; but the term probably includes the zodiacal light, many, -if not all, of the meteoric rings, and a large number of comets. These -unstable parts of the system are being gradually incorporated with the -sun, the earth, and doubtless also with the other large planets. It is -highly probable that at former epochs the quantity of such matter was -much greater than at present, and that, unless new supplies be received -_ab extra_, it must, by slow degrees, disappear from the system. - -The fact, now well established, of the extensive diffusion of meteoric -matter through the interplanetary spaces has an obvious bearing on -Encke's theory of a resisting medium. If we grant the existence of such -an ether, it would seem unphilosophical to ascribe to it one of the -properties of a material fluid--the power of resisting the motion of -all bodies moving through it--and to deny it such properties in other -respects. Its condensation, therefore, about the sun and other large -bodies must be a necessary consequence. This condensation existed in -the primitive solar spheroid, before the formation of the planets: -the rotation of the spheroid would be communicated to the coexisting -ether; and hence, _during the entire history of the planetary system, -the ether has revolved around the sun in the same direction with the -planets_. This condensed ether, it is also obvious, must participate in -the progressive motion of the solar system. - -But again; even if we reject the doctrine of the development of the -planetary bodies from a rotating nebula, we must still regard the -density of the ether as increasing to the center of the system. The -sun's rotation, therefore, would communicate motion to the first and -denser portions; this motion would be transmitted outward through -successive strata, with a constantly diminishing angular velocity. -The motion of the planets themselves through the medium in nearly -circular orbits would concur in imparting to it a revolution in the -same direction. Whether, therefore, we receive or reject the nebular -hypothesis, the resistance of the ethereal medium to bodies moving -in orbits of small eccentricity and in the direction of the sun's -rotation, becomes an infinitesimal quantity. - -The hypothesis of Encke, it is well known, was based solely on the -observed acceleration of the comet which bears his name. More recently, -however, a still greater acceleration has been found in the case of -Faye's comet. Now as the meteoric matter of the solar system is a -_known_ cause for such phenomena, sufficient, in all probability, both -in mode and measure, the doctrine of a resisting ethereal medium would -seem to be a wholly unnecessary assumption. - - - - -CHAPTER VIII. - - DOES THE NUMBER OF AEROLITIC FALLS VARY WITH THE EARTH'S DISTANCE - FROM THE SUN?--RELATIVE NUMBERS OBSERVED IN THE FORENOON AND - AFTERNOON--EXTENT OF THE ATMOSPHERE AS INDICATED BY METEORS. - - -An analysis of any extensive table of meteorites and fire-balls proves -that a greater number of aerolitic falls have been observed during the -months of June and July, when the earth is near its aphelion, than in -December and January, when near its perihelion. It is found, however, -that the reverse is true in regard to bolides, or fire-balls. Now the -theory has been held by more than one physicist, that aerolites are -the outriders of the asteroid ring between Mars and Jupiter; their -orbits having become so eccentric that in perihelion they approach -very near that of the earth. If this theory be the true one, the earth -would probably encounter the greatest number of those meteor-asteroids -when near its aphelion. The hypothesis therefore, it has been claimed, -appears to be supported by well-known facts. The variation, however, -in the observed number of aerolites may be readily accounted for -independently of any theory as to their origin. The fall of meteoric -stones would evidently be more likely to escape observation by night -than by day, by reason of the relatively small number of observers. But -the days are shortest when the earth is in perihelion, and longest when -in aphelion; the ratio of their lengths being nearly equal to that of -the corresponding numbers of aerolitic falls. - -On the other hand, it is obvious that fire-balls, unless of very -extraordinary magnitude, would not be visible during the day. The -_observed_ number will therefore be greatest when the nights are -longest; that is, when the earth is near its perihelion. This, it will -be found, is precisely in accordance with observation. - -It has been found, moreover, that a greater number of meteoric stones -fall during the first half of the day, that is, from midnight to noon, -than in the latter half, from noon to midnight. This would seem to -indicate that a large proportion of the aerolites encountered by the -earth have direct motion. - -_Height of the Atmosphere._--The weight of a given volume of mercury is -10,517 times that of an equal volume of air at the earth's surface; and -since the mean height of the mercurial column in the barometer is about -thirty inches, if the atmosphere were of uniform density its altitude -would be about 26,300 feet, or nearly five miles. The density rapidly -diminishes, however, as we ascend above the earth's surface. Calling -it unity at the sea level, the rate of variation is approximately -expressed as follows: - - Altitude in Miles. Density. - - 0 1 - 7 1/4 - 14 1/16 - 21 1/64 - 28 1/256 - 35 1/1024 - 70 1/1000000 - 105 1/1000000000 - 140 1/1000000000000 - etc. etc. - -From this table it will be seen that at the height of 35 miles the air -is one thousand times rarer than at the surface of the earth; and that, -supposing the same rate of decrease to continue, at the height of 140 -miles the rarity would be one trillion times greater. The atmosphere, -however, is not unlimited. When it becomes so rare that the force of -repulsion between its particles is counterbalanced by the earth's -attraction, no further expansion is possible. To determine the altitude -of its superior surface is a problem at once difficult and interesting. -Not many years since about 45 or 50 miles were generally regarded as a -probable limit. Considerable light, however, has been thrown upon the -question by recent observations in meteoric astronomy. Several hundred -detonating meteors have been observed, and their average height at the -instant of their first appearance has been found to exceed 90 miles. -The great meteor of February 3d, 1856, seen at Brussels, Geneva, Paris, -and elsewhere, was 150 miles high when first seen, and a few apparently -well-authenticated instances are known of a still greater elevation. We -conclude, therefore, from the evidence afforded by meteoric phenomena, -that the height of the atmosphere is certainly not _less_ than 200 -miles. - -It might be supposed, however, that the resistance of the air at -such altitudes would not develop a sufficient amount of heat to -give meteorites their brilliant appearance. This question has been -discussed by Joule, Thomson, Haidinger, and Reichenbach, and may now -be regarded as definitively settled. When the velocity of a meteorite -is known the quantity of heat produced by its motion through air of -a given density is readily determined. The temperature acquired is -the equivalent of the force with which the atmospheric molecules are -met by the moving body. This is about one degree (Fahrenheit) for a -velocity of 100 feet per second, and it varies directly as the square -of the velocity. A velocity, therefore, of 30 miles in a second -would produce a temperature of 2,500,000 deg.. The weight of 5280 cubic -feet of air at the earth's surface is about 2,830,000 grains. This, -consequently, is the weight of a column 1 mile in length, and whose -base or cross section is one square foot. The weight of a column of the -same dimensions at a height of 140 miles would be about 1/350000th of a -grain. Hence the heat acquired by a meteoric mass whose cross section -is one square foot, in moving 1 mile would be one grain raised 7-1/7 -degrees, or one-fifth of a grain 2500 deg. in 70 miles. This temperature -would undoubtedly be sufficient to render meteoric bodies brilliantly -luminous. - -But there have been indications of an atmosphere at an elevation of -more than 500 miles. A discussion of the best observations of the -great aurora seen throughout the United States on the 28th of August, -1859, gave 534 miles as the height of the upper limit above the -earth's surface. The aurora of September 2d, of the same year, had an -elevation but little inferior, viz., 495 miles. Now, according to the -observed rate of variation of density, at the height of 525 miles, the -atmosphere would be so rare that a sphere of it filling the orbit of -Neptune would contain less matter than 1/30th of a cubic inch of air at -the earth's surface. In other words, it would weigh less than 1/90th -of a grain. We are thus forced to the conclusion either that the law -of variation is not the same at great heights as near the surface; or, -that beyond the limits of the atmosphere of air, there is another of -electricity, or of some other fluid. - - - - -CHAPTER IX. - -THE METEORIC THEORY OF SOLAR HEAT. - - -Of the various theories proposed by astronomers to account for the -origin of the sun's light and heat, only two have at present any -considerable number of advocates. These are-- - -1. _The Chemical Theory_; according to which the light and heat of the -sun are produced by the chemical combination of its elements; in other -words, by an intense combustion. - -2. _The Meteoric Theory_, which ascribes the heat of our central -luminary to the fall of meteors upon its surface. The former is -advocated with great ingenuity by Professor Ennis in a recent work on -"_The Origin of the Stars, and the Causes of their Motions and their -Light_." It has, on the other hand, been ably opposed by Dr. Mayer, -Professor William Thomson, and other eminent physicists. A brief -examination of its claims may not be destitute of interest. - -If the sun's heat is produced by chemical action, whence comes the -necessary supply of fuel to support the combustion? The quantity of -solar heat radiated into space has been determined with at least an -approximation to mathematical precision. We know also the amount -produced by the combustion of a given quantity of coal. Now it has been -found by calculation that if the sun were a solid globe of coal, and a -sufficient supply of oxygen were furnished to support its combustion, -the amount of heat resulting from its consumption would be less than -that actually emitted during the last 6000 years. In short, _no known_ -elements would meet the demands of the case. But it is highly probable -that the different bodies of the solar system are composed of the same -elements. This view is sustained by the well-known fact that meteoric -stones, which have reached us from different and distant regions of -space, have brought us no new elementary substances. The _chemical_ -theory of solar heat seems thus encumbered with difficulties well-nigh -insuperable. - -Professor Ennis' mode of obviating this objection, though highly -ingenious, is by no means conclusive. The latest analyses of the solar -spectrum indicate, he affirms, the presence of numerous elements -besides those with which we are acquainted. Some of these may yield -by their combustion a much greater amount of heat than the same -quantity of any known elements in the earth's crust. "Every star," he -remarks, "as far as yet known, has a different set of fixed lines, -although there are certain resemblances between them. They lead to -the conclusion that each star has, in part at least, its peculiar -modifications of matter, called simple elements; but the number of -stars is infinite, and therefore the number of elements must be -infinite."[21] He argues, moreover, that in a globe so vast as the -sun there may be forces in operation with whose nature we are wholly -unacquainted. This leaving of the _known_ elements as well as the -_known_ laws of nature for _unknown possibilities_ will hardly be -satisfactory to unbiased minds. - -Again: that the different bodies of the universe are composed of -different elements is inferred by our author from the following among -other considerations: "In our solar system Mercury is sixty or eighty -times more dense than one of the satellites of Jupiter, and probably in -a much greater proportion denser than the satellites of Saturn. This -indicates a wide difference between the nature of their elements." This -statement is again repeated in a subsequent page.[22] "The densities of -the planets and their satellites prove that they are composed of very -different elements. Mercury is more than sixty times, and our earth -about fifty times, more dense than the inner moon of Jupiter. Saturn is -only about one-ninth as dense as the earth; it would float buoyantly on -water. There is a high probability that the satellites of Saturn and -Uranus are far lighter than those of Jupiter. Between the two extremes -of the attendants of the sun, there is probably a greater difference -in density than one hundred to one; and from one extreme to the other -there are regular gradations of small amount. - -"The difference in constitution between the earth and the moon is -seen in their densities: that of the moon being about half that of -the earth. The nitrogen of our globe is found only in the atmosphere, -and such substances as derive it from the atmosphere. The moon has -no appreciable atmosphere, and therefore, in a high probability, no -nitrogen." - -The statements here quoted were designed to show that the physical -constitution of the sun and planets is widely different from that of -the earth, and that the combustion of _some_ of the elements in this -indefinite variety may account for the origin of solar heat. Let us -examine the facts. - -According to Laplace the mass of Jupiter's first satellite is -0.000017328, that of Jupiter being 1. The diameter is 2436 miles. Hence -the corresponding density is a little more than _one-fifth_ of the mean -density of the earth. In other words, it is somewhat greater than the -density of water, and very nearly equal to that of Jupiter himself. -Professor Ennis' value is therefore erroneous.[23] In regard to the -densities of the Saturnian and Uranian satellites nothing is known, -and conjecture is useless. In short, Saturn has the least mean density -of all the planets, primary or secondary, so far as known. This may be -owing to the great extent of his atmospheric envelope. The density of -the moon is but three-fifths that of the earth: it is to be borne in -mind, however, that the _mass_ and _pressure_ are also much less. - -With respect to meteorites the same author remarks that "like the -moon, they are probably satellites of the earth; but being very small, -they are liable to extraordinary perturbations, and hence strike the -earth in many directions." Here, again, his _facts_ are at fault; for -(1) the observed velocities of these bodies are inconsistent with the -supposition of their being satellites of the earth; and (2) the amount -of perturbation of such bodies does not vary with their masses: a -_small_ meteorite would fall toward the earth or any other planet with -no greater velocity than a _large_ one. - - -THE METEORIC THEORY. - -It has been shown in a previous chapter that immense numbers of -meteoric asteroids are constantly traversing the planetary spaces--that -many millions, in fact, daily enter the earth's atmosphere. Reasons -are not wanting for supposing the numbers of these bodies to increase -with great rapidity as we approach the center of the system. Moreover, -on account of the greater force of gravity at the sun's surface the -heat produced by their fall must be much greater than at the surface -of the earth. It has been calculated that if one of these asteroids -be arrested in perihelion by the solar atmosphere, the quantity of -heat thus developed will be 9000 times greater than that produced by -the combustion of an equal mass of coal. There can, therefore, be no -reasonable doubt that a _portion_ of the sun's heat is produced by -the impact of meteoric matter. In considering the probability that it -is _chiefly_ so generated, the following questions naturally present -themselves: - -1. _What amount of matter precipitated upon the sun would develop -the quantity of heat actually emitted?_--This question has been -satisfactorily discussed by eminent physicists, and it will be -sufficient for our purpose to give the result. According to Professor -William Thomson, of Glasgow, the present rate of emission would be kept -up by a meteoric deposit which would form an annual stratum 60 feet in -thickness over the sun's surface. - -2. _Could such an increase of the sun's magnitude be detected by -micrometrical measurement?_--This inquiry is readily answered in the -negative. The apparent diameter would be augmented only one second in -17,600 years. - -3. _Is there any known or visible source from which this amount -of meteoric matter may be supplied?_--Thomson, Mayer, and other -distinguished writers regard the zodiacal light as the source of -such meteorites. The inner portions of this immense "tornado" must -be resisted in their motions by the solar atmosphere, and hence -precipitated upon the sun's surface. - -4. _Would this increase of the sun's mass derange the motions of the -solar system?_--To this question Prof. Ennis gives an affirmative -answer; his first objection to the theory under consideration being -stated as follows: "The constant accumulation of such materials, -during hundreds of millions of years, would increase the body of the -sun and its consequent gravity so greatly as to derange the entire -solar system, by destroying the balance between the centripetal and -centrifugal forces now acting on the planets."[24] This, it must be -confessed, would be a valid objection, if the meteoric matter were -supposed to be derived from the extra-planetary spaces. As their -source, however,--the zodiacal light--is interior to the earth's orbit, -it can have no application to any planet exterior to Venus. Most -probably the greater portion of the meteoric mass is even within the -orbit of Mercury, so that the effect of its convergence could scarcely -be noticed even in the motion of the interior planets. In pre-historic -time the zodiacal light may have extended far beyond the earth's orbit. -If so, its convergence to its present dimensions was undoubtedly -attended by an acceleration of the earth's mean motion. We can of -course have no evidence that such a shortening of the year has never -occurred. - -The second objection urged against the meteoric theory by the author -of "The Origin of the Stars" is thus expressed: "As we must believe -that all stars were lighted up by the same means, so we must believe, -according to this theory, that the present interior heat of the earth -and its former melted condition in both exterior and interior, was -caused by the fall of meteorites. But if so, they must have gradually -ceased to fall, as space became cleared of their presence, and we would -now find a thick covering of meteorites on the earth's cooled surface. -Instead of this, we find them very rarely, and in accordance with their -present very rare falls." - -To this it may be replied that the primitive igneous fluidity of the -earth and planets was a necessary consequence of their condensation--a -fact which has no inconsistency with the theory in question. - -A different _mechanical_ theory of the origin of solar heat is -advocated by Professor Helmholtz in his interesting work _On the -Interaction of Natural Forces_. In regard to the sun he says: "If we -adopt the very probable view, that the remarkably small density of so -large a body is caused by its high temperature, and may become greater -in time, it may be calculated that if the diameter of the sun were -diminished only the ten-thousandth part of its present length, by this -act a sufficient quantity of heat would be generated to cover the -total emission for 2100 years. Such a small change besides it would be -difficult to detect by the finest astronomical observations."[25] The -same view is adopted by Dr. Joel E. Hendricks, of Des Moines, Iowa.[26] - - - - -CHAPTER X. - -WILL THE METEORIC THEORY ACCOUNT FOR THE PHENOMENA OF VARIABLE AND -TEMPORARY STARS? - - -Having shown that meteor-asteroids are diffused in vast quantities -throughout the universe; that according to eminent physicists the -solar heat is produced by the precipitation of such matter on the -sun's surface; and that Leverrier has found it necessary to introduce -the disturbing effect of meteoric rings in order fully to account -for the motion of Mercury's perihelion; we now propose extending the -meteoric theory to a number of phenomena that have hitherto received no -satisfactory explanation. - - -VARIABLE AND TEMPORARY STARS. - -No theory as to the origin of the sun's light and heat would seem to -be admissible unless applicable also to the sidereal systems. Will the -meteoric theory explain the phenomena of variable and temporary stars? - -"It has been remarked respecting variable stars, that in passing -through their successive phases, they are subject to sensible -irregularities, which have not hitherto been reduced to fixed laws. In -general they do not always attain the same maximum brightness, their -fluctuations being in some cases very considerable. Thus, according -to Argelander, the variable star in _Corona Borealis_, which Pigott -discovered in 1795, exhibits on some occasions such feeble changes of -brightness, that it is almost impossible to distinguish the maxima -from the minima by the naked eye; but after it has completed several -of its cycles in this manner, its fluctuations all at once become -so considerable, that in some instances it totally disappears. It -has been found, moreover, that the light of variable stars does not -increase and diminish symmetrically on each side of the maximum, nor -are the successive intervals between the maxima exactly equal to each -other."--_Grant's History of Physical Astronomy_, p. 541. - -Of the numerous hypotheses hitherto proposed to account for these -phenomena we believe none can be found to include and harmonize all -the facts of observation. The theories of Herschel and Maupertius fail -to explain the irregularity in some of the periods; while those of -Newton and Dunn afford no explanation of the periodicity itself.[27] -But let us suppose that among the fixed stars some have atmospheres -of great extent, as was probably the case with the sun at a remote -epoch in its history. Let us also suppose the existence of nebulous -rings, like those of our own system, moving in orbits so elliptical -that in their perihelia they pass through the atmospheric envelopes -of the central stars. Such meteoric rings of varying density, like -those revolving about the sun, would evidently produce the phenomena -of variable stars. The resisting medium through which they pass in -perihelion must gradually contract their orbits, or, in other words, -diminish the intervals between consecutive maxima. Such a shortening of -the period is now well established in the case of _Algol_. Again, if a -ring be influenced by perturbation the period will be variable, like -that of _Mira Ceti_. A change, moreover, in the perihelion distance -will account for the occasional increase or diminution of the apparent -magnitude at the different maxima of the same star. But how are we -to account for the variations of brightness observed in a number of -stars where no order or periodicity in the variation has as yet been -discovered? It is easy to perceive that either a single nebulous ring -with more than one _hiatus_, or several rings about the same star, may -produce phenomena of the character described. Finally, if the matter of -an elliptic ring should accumulate in a single mass, so as to occupy a -comparatively small arc, its passage through perihelion might produce -the phenomenon of a so-called temporary star. - -Recent researches relating to nebulae seem in some measure confirmatory -of the view here presented. These observations have shown (1) a change -of position in some of these objects, rendering it probable that in -certain cases they are not more distant than fixed stars visible to -the naked eye; and (2) a variation in the brilliancy of many small -stars situated in the great nebula of Orion, and also the existence -of numerous masses of nebulous matter in the form of tufts apparently -attached to stars,--facts regarded as indicative of a physical -connection between the stars and nebulae.[28] - - - - -CHAPTER XI. - -THE LUNAR AND SOLAR THEORIES OF THE ORIGIN OF AEROLITES. - - -Besides the _cosmical_ theory of aerolites which has been adopted in -this work, and which is now accepted by a great majority of scientific -men, at least four others have been proposed: (1) the _atmospheric_, -according to which they are formed, like hail, in the earth's -atmosphere; (2) the _volcanic_, which regards them as matter ejected -with great force from terrestrial volcanoes; (3) the _lunar_, which -supposes them to have been thrown from craters in the moon; and (4) -the _solar_ hypothesis, according to which they are projected by some -tremendous explosive force from the great central orb of our system. -The first and second have been universally abandoned as untenable. The -third and fourth, however, are entitled to consideration. - - -THE LUNAR THEORY. - -The theory which regards meteoric stones as products of eruption in -lunar volcanoes was received with favor by the celebrated Laplace: "As -the gravity at the surface of the moon," he remarks, "is much less -than at the surface of the earth, and as this body has no atmosphere -which can oppose a sensible resistance to the motion of projectiles, -we may conceive that a body projected with a great force, by the -explosion of a lunar volcano, may attain and pass the limit, where -the attraction of the earth commences to predominate over that of the -moon. For this purpose it is sufficient that its initial velocity in -the direction of the vertical may be 2500 meters in a second; then in -place of falling back on the moon, it becomes a satellite of the earth, -and describes about it an orbit more or less elongated. The direction -of its primitive impulsion may be such as to make it move directly -toward the atmosphere of the earth; or it may not attain it, till after -several and even a great number of revolutions; for it is evident that -the action of the sun, which changes in a sensible manner the distances -of the moon from the earth, ought to produce in the radius vector of a -satellite which moves in a very eccentric orbit, much more considerable -variations, and thus at length so diminish the perigean distance of the -satellite, as to make it penetrate our atmosphere. This body traversing -it with a very great velocity, and experiencing a very sensible -resistance, might at length precipitate itself on the earth; the -friction of the air against its surface would be sufficient to inflame -it, and make it detonate, provided that it contained ingredients proper -to produce these effects, and then it would present to us all those -phenomena which meteoric stones exhibit. If it was satisfactorily -proved that they are not produced by volcanoes, or generated in our -atmosphere, and that their cause must be sought beyond it, in the -regions of the heavens, the preceding hypothesis, which likewise -explains the identity of composition observed in meteoric stones, by an -identity of origin, will not be devoid of probability."--_Systeme du -Monde_, t. ii. cap. v. - -Knowing the masses and volumes of the earth and moon, it is easy to -estimate the force of gravity at their surfaces, the distance from each -to the point of equal attraction, and the force with which a projectile -must be thrown from the lunar surface to pass within the sphere of the -earth's influence. It has been calculated that an initial velocity -of about a mile and a half in a second would be sufficient for this -purpose--a force not greater than that known to have been exerted by -terrestrial volcanoes. The _possibility_, therefore, that volcanic -matter from our satellite may reach the earth's surface seems fairly -admissible. - -Since the time of Laplace, several distinguished European astronomers -have regarded the lunar hypothesis as more or less probable. It was -advocated as recently as 1851 by the late Prof. J. P. Nichol, of -Glasgow. This popular and interesting writer, after describing Tycho, a -large and well-known lunar crater, from which luminous rays or stripes -radiate over a considerable part of the moon's surface, expresses the -opinion that that immense cavity was formed by a single tremendous -explosion. "Reflecting," he remarks, "on the probable suddenness and -magnitude of that force, or rather of that _explosive_ energy one of -whose acts we have traced, as well as on the immense mass of matter -which seems to have been thus violently dispersed, is not the inquiry -a natural one, _where is that matter now_? It is a mass indeed which -cannot well have wholly disappeared. It filled a cavern 55 miles in -breadth, and 17,000 feet deep--a cavern into which even now one might -cast Chimborazo and Mont Blanc, and room be left for Teneriffe behind! -Like rocks flung aloft by our volcanoes, did this immense mass fall -back in fragments to the surface of the moon, or was the expulsive -force strong enough to give it an outward velocity sufficient to resist -the attractive power of its parent globe? The moon, be it recollected, -is very small in _mass_ compared with the earth, and her attractive -energy greatly inferior accordingly. Laplace has even calculated that -the force urging a cannon-ball, increased to a degree quite within -the limits of what is conceivable, could effect a final separation -between our satellite and any of its component parts. It is _possible_ -then, and, although not demonstrable, very far from a chimera, that -the disrupted and expelled masses were, in the case of which we are -speaking, driven conclusively into space; but if so, where are they -now? where their new residence, and what their functions? In the -emergency to which I refer, such fragments would necessarily wander -among the interplanetary spaces in most irregular orbits, and chiefly -in the neighborhood of the moon and the earth. Now, while the planetary -orbits are so nicely adjusted that neither confusion nor interference -can ever occur, it is not at all likely that the same order could be -established here; nay, it is next to certain, that in the course of its -orbital revolution our globe would ever and anon come in contact with -these lunar fragments; in other words, STONES _would fall occasionally -to its surface, and apparently from its atmosphere_."--_Planetary -System_, pp. 301, 302. - -We have preferred to give the views of these eminent scientists in -their own language. Olbers, Biot, and Poisson, who adopted the same -theory, estimated the _initial_ velocity which would be necessary in -order that lunar fragments might pass the point of equal attraction, -and also the _final_, or acquired velocity on reaching the earth's -surface. The several determinations of the former were as follows: - - According to Olbers 1.570 miles a second. - " Biot 1.569 " " - " Laplace 1.483 " " - " Poisson 1.437 " " - -The mean being almost exactly a mile and a half. The velocity on -reaching our planet, according to Olbers, would be about six and a half -miles. At the date of these calculations, however, the true velocity -of aerolites had not been in any case satisfactorily determined. Since -that time it has been found in numerous instances to exceed _twenty -miles a second_--a velocity greater than that of the earth's orbital -motion. This fact of itself would seem fatal to the theory of a lunar -origin. - -At the meeting of the American Association for the Advancement of -Science, in 1859, Dr. B. A. Gould read a paper on the supposed lunar -origin of aerolites, in which the hypothesis was subjected to the test -of a rigid mathematical analysis. We will not attempt even an abstract -of this interesting memoir. It amounts, however, to a virtual disproof -of the lunar hypothesis. - - -THE SOLAR THEORY. - -The theory which ascribes a solar origin to meteorites is not of recent -date, having been held by Diogenes Laertius and other ancient Greeks. -Among the moderns its advocates have been much less numerous than those -of the lunar hypothesis. The late Professor Charles W. Hackley, of New -York, regarded shooting-stars, aerolites, and even comets, as matter -projected with enormous force from the solar surface. The corona seen -during total eclipses of the sun he supposed to be the emanations of -this matter through the intervals of the luculi.--(See the Proceedings -of the American Association for the Advancement of Science, Fourteenth -Meeting, 1860.) An ingenious theory, differing in its details from that -of Professor Hackley, though somewhat similar in its general features, -has lately been advocated by Alexander Wilcocks, M.D., of Philadelphia, -in a memoir read before the American Philosophical Society, May 20th, -1864, and published in their Proceedings. In regard to this hypothesis -it seems sufficient to remark that it fails to give a satisfactory -account of the annual periodicity of meteoric phenomena. - - - - -CHAPTER XII. - -THE RINGS OF SATURN. - - -Until about the middle of the present century the rings of Saturn were -universally regarded as solid and continuous. The labors, however, of -Professors Bond and Pierce, of Cambridge, Massachusetts, as well as the -more recent investigations of Prof. Maxwell, of England, have shown -this hypothesis to be wholly untenable. The most probable opinion, -based on the researches of these astronomers, is, that they consist of -streams or clouds of meteoric asteroids. The zodiacal light and the -zone of small planets between Mars and Jupiter appear to constitute -analogous _primary_ rings. In the latter, however, a large proportion -of the primitive matter seems to have collected in distinct, segregated -masses. These meteoric zones have probably presented--what are not -elsewhere found in the solar system--cases of commensurability in the -planetary periods. The interior satellites of Saturn are so near the -ring as doubtless to exert great perturbative influence. Unfortunately, -the elements of the Saturnian system as determined by different -astronomers are somewhat discordant. This, however, is by no means -surprising when we consider the great distance of the planet and the -small magnitude of some of the satellites. For convenience of reference -the mean apparent distances of the satellites, together with their -periodic times, are given in the following table. The former are taken -from Hind's _Solar System_; the latter from Herschel's _Outlines of -Astronomy_. - - -TABLE I.--THE SATELLITES OF SATURN. - - +-----------+------------------------+---------------+ - | | | MEAN APPARENT | - | NAME. | SIDEREAL REVOLUTION. | DISTANCE. | - +-----------+------------------------+---------------+ - | | _d._ _h._ _m._ _s._ | '' | - | Mimas | 0 22 37 22.9 | 26.78 | - | Enceladus | 1 8 53 6.7 | 34.38 | - | Tethys | 1 21 18 25.7 | 42.57 | - | Dione | 2 17 41 8.9 | 54.54 | - | Rhea | 4 12 25 10.8 | 76.16 | - | Titan | 15 22 41 25.2 | 176.55 | - | Hyperion | 22 12? | 213.3? | - | Japetus | 79 7 53 40.4 | 514.52 | - +-----------+------------------------+---------------+ - -The late Professor Bessel devoted much attention to the theory of -Titan, whose mean distance he found to be 20.706 equatorial radii of -the primary. Struve's measurements of the ring are given in the second -column of the following table. Sir John Herschel, however, regards -the Russian astronomer's interval between the rings as "somewhat too -small."[29] This remark is confirmed by the measurements of Encke, -whose results are given in column third. The fourth contains the -_mean_ of Struve's and Encke's measurements; and the fifth, the same, -expressed in equatorial radii of Saturn. - - -TABLE II.--THE RINGS OF SATURN. - - +---------------------+---------+---------+----------+------------+ - | | | | | IN | - | | STRUVE. | ENCKE. | MEAN. | SEMI-DIAM. | - | | | | | OF SATURN. | - +---------------------+---------+---------+----------+------------+ - | Equatorial radius | '' | '' | '' | | - | of the planet | 8.9955 | | | | - | Ext. semi-diameter | | | | | - | of exterior ring | 20.047 | 20.2225 | 20.13475 | 2.23830 | - | Int. semi-diameter | | | | | - | of exterior ring | 17.644 | 18.0190 | 17.83150 | 1.98230 | - | Ext. semi-diameter | | | | | - | of interior ring | 17.237 | 17.3745 | 17.30575 | 1.92380 | - | Int. semi diameter | | | | | - | of interior ring | 13.334 | 13.3780 | 13.35600 | 1.48470 | - | Breadth of interval | 00.407 | 00.6445 | 00.52575 | 0.05844 | - +---------------------+---------+---------+----------+------------+ - - The period of a satellite revolving at - the distance, 1.9238, the interior - limit of the interval =10h. 50m. 16s. - One-sixth of the period of Dione =10 56 53 - One-third " Enceladus =10 59 22 - One-half " Mimas =11 18 32 - One-fourth " Tethys =11 19 36 - And the period of a satellite at the - distance, 1.9823, the exterior - limit of the interval =11 28 3 - -The interval, therefore, occupies precisely the space in which the -periods would be commensurable with those of the four members of the -system immediately exterior. Particles occupying this portion of the -_primitive_ ring would always come into conjunction with one of these -satellites in the same parts of their orbits. Such orbits would become -more and more eccentric until the matter moving in them would unite -near one of the apsides with other portions of the ring. _We have thus -a physical cause for the existence of this remarkable interval._ - - - - -CHAPTER XIII. - -THE ASTEROID RING BETWEEN MARS AND JUPITER. - - -The mean distances of the minor planets between Mars and Jupiter vary -from 2.20 to 3.49. The breadth of the zone is therefore 20,000,000 -miles greater than the distance of the earth from the sun; greater -even than the entire interval between the orbits of Mercury and -Mars. Moreover, the _perihelion_ distance of some members of the -group exceeds the _aphelion_ distance of others by a quantity equal -to the whole interval between the orbits of Mars and the earth. The -_Olbersian_ hypothesis of the origin of these bodies seems thus -to have lost all claim to probability.[30] Professor Alexander's -theory of the disruption of a primitive discoidal planet of great -equatorial diameter, is less objectionable; still, however, it requires -confirmation. But whatever may have been the original constitution -of the ring,[31] its existence in its present form for an indefinite -period is unquestioned. Let us then consider some of the effects of -its secular perturbation by the powerful mass of Jupiter. - -_Portions of the ring in which the periods of asteroids would be -commensurable with that of Jupiter._--The breadth of this zone is -such as to contain several portions in which the periods of asteroids -would be commensurable with that of Jupiter. As in the case of the -perturbation of Saturn's ring by the interior satellites, the tendency -of Jupiter's influence would be to form gaps or chasms in the primitive -ring. - - The mean distance of an asteroid whose period - is 1/2 that of Jupiter =3.2776 - - That of one whose period is 1/3 of Jupiter's =2.5012 - " " 2/5 " =2.8245 - " " 2/7 " =2.2569 - " " 3/7 " =2.9574 - " " 4/9 " =3.0299 - -For the purpose of facilitating the comparison of these numbers with -the mean distances of the asteroids and of observing whether any order -obtains in the distribution of these mean distances in space, we have -arranged the minor planets, in the following table, in the consecutive -order of their periods: - - -Periods and Distances of the Asteroids. - - +------------+-------------+-----------+---------+ - | ORDER OF | NAME. | DISTANCE. | PERIOD. | - | DISCOVERY. | | | | - +------------+-------------+-----------+---------+ - | 8 | Flora | 2.2014 | 1193 d | - | 43 | Ariadne | 2.2034 | 1194.6 | - | 72 | Feronia | 2.2654 | 1245.4 | - | 40 | Harmonia | 2.2677 | 1247.3 | - | 18 | Melpomene | 2.2956 | 1270.4 | - | 80 | Sappho | 2.2971 | 1271.6 | - | 12 | Victoria | 2.3342 | 1302.6 | - | 27 | Euterpe | 2.3468 | 1313.2 | - | 4 | Vesta | 2.3613 | 1325.3 | - | 84 | Clio | 2.3618 | 1325.8 | - | 30 | Urania | 2.3655 | 1328.9 | - | 51 | Nemausa | 2.3657 | 1329.0 | - | 9 | Metis | 2.3858 | 1346.0 | - | 7 | Iris | 2.3863 | 1346.5 | - | 60 | Echo | 2.3931 | 1352.2 | - | 63 | Ausonia | 2.3949 | 1353.8 | - | 25 | Phocea | 2.4008 | 1358.8 | - | 20 | Massilia | 2.4144 | 1365.5 | - | 67 | Asia | 2.4217 | 1376.5 | - | 44 | Nysa | 2.4234 | 1378.0 | - | 6 | Hebe | 2.4244 | 1379.0 | - | 83 | Beatrice | 2.4287 | 1382.5 | - | 42 | Isis | 2.4400 | 1392.2 | - | 21 | Lutetia | 2.4411 | 1393.0 | - | 19 | Fortuna | 2.4416 | 1393.5 | - | 79 | Eurynome | 2.4437 | 1395.3 | - | 11 | Parthenope | 2.4519 | 1402.4 | - | 17 | Thetis | 2.4737 | 1421.1 | - | 46 | Hestia | 2.5262 | 1466.5 | - | 89 | | 2.5498 | 1487.2 | - | 29 | Amphitrite | 2.5544 | 1491.2 | - | 5 | Astraea | 2.5772 | 1511.2 | - | 13 | Egeria | 2.5775 | 1511.4 | - | 14 | Irene | 2.5860 | 1519.0 | - | 32 | Pomona | 2.5868 | 1519.6 | - | 91 | | 2.5958 | 1527.5 | - | 56 | Melete | 2.5959 | 1527.7 | - | 70 | Panopea | 2.6129 | 1543.0 | - | 53 | Calypso | 2.6188 | 1548.0 | - | 78 | Diana | 2.6236 | 1555.3 | - | 23 | Thalia | 2.6280 | 1568.0 | - | 37 | Fides | 2.6414 | 1570.0 | - | 15 | Eunomia | 2.6436 | 1572.6 | - | 85 | Io | 2.6466 | 1573.0 | - | 50 | Virginia | 2.6491 | 1575.0 | - | 88 | Thisbe | 2.6553 | 1580.0 | - | 26 | Proserpina | 2.6561 | 1581.1 | - | 66 | Maia | 2.6635 | 1587.8 | - | 73 | Clytie | 2.6666 | 1590.5 | - | 3 | Juno | 2.6707 | 1594.2 | - | 75 | Eurydice | 2.6707 | 1594.2 | - | 77 | Frigga | 2.6719 | 1595.3 | - | 64 | Angelina | 2.6805 | 1603.0 | - | 34 | Circe | 2.6865 | 1608.3 | - | 58 | Concordia | 2.7014 | 1622.0 | - | 54 | Alexandra | 2.7123 | 1631.6 | - | 59 | Elpis | 2.7131 | 1632.3 | - | 45 | Eugenia | 2.7218 | 1640.1 | - | 38 | Leda | 2.7401 | 1656.8 | - | 36 | Atalanta | 2.7458 | 1662.0 | - | 71 | Niobe | 2.7501 | 1665.8 | - | 82 | Alcmene | 2.7547 | 1670.0 | - | 55 | Pandora | 2.7591 | 1674.0 | - | 41 | Daphne | 2.7657 | 1679.9 | - | 1 | Ceres | 2.7663 | 1681.0 | - | 2 | Pallas | 2.7696 | 1683.5 | - | 39 | Laetitia | 2.7740 | 1687.6 | - | 74 | Galatea | 2.7777 | 1690.9 | - | 28 | Bellona | 2.7785 | 1691.6 | - | 68 | Leto | 2.7836 | 1696.3 | - | 81 | Terpsichore | 2.8591 | 1765.7 | - | 33 | Polyhymnia | 2.8653 | 1770.6 | - | 47 | Aglaia | 2.8812 | 1786.4 | - | 22 | Calliope | 2.9092 | 1812.4 | - | 16 | Psyche | 2.9233 | 1826.0 | - | 69 | Hesperia | 2.9707 | 1871.1 | - | 61 | Danae | 2.9837 | 1882.4 | - | 35 | Leucothea | 3.0040 | 1904.2 | - | 49 | Pales | 3.0825 | 1976.6 | - | 86 | Semele | 3.0909 | 1984.7 | - | 52 | Europa | 3.1000 | 1993.6 | - | 48 | Doris | 3.1094 | 2002.7 | - | 62 | Erato | 3.1297 | 2022.3 | - | 24 | Themis | 3.1431 | 2035.3 | - | 10 | Hygeia | 3.1512 | 2043.2 | - | 31 | Euphrosyne | 3.1513 | 2044.6 | - | 57 | Mnemosyne | 3.1565 | 2048.4 | - | 90 | Antiope | 3.1576 | 2049.4 | - | 76 | Freia | 3.3864 | 2276.2 | - | 65 | Cybele | 3.4205 | 2310.6 | - | 87 | Sylvia | 3.4927 | 2384.2 | - +------------+-------------+-----------+---------+ - - -REMARKS ON THE FOREGOING TABLE. - -1. The first two members of the group, Flora and Ariadne, have very -nearly the same mean distance. Immediately exterior to these, however, -occurs a wide interval, including the distance at which seven periods -of an asteroid would be equal to two of Jupiter. - -2. On the _outer_ limit of the ring Freia, Cybele, and Sylvia have also -nearly equal distances, and are separated from the next interior member -by a wide space including the distance at which two periods would be -equal to one of Jupiter, and also that at which five would be equal to -one of Saturn. - -3. Besides these extreme members of the group, our table contains -eighty-six minor planets, all of which are included between the -distances 2.26 and 3.16; the mean interval between them being 0.0105. -The distances are distributed as follows: - - 2.26 to 2.36 6 minimum. - 2.36 to 2.46 19 maximum. - 2.46 to 2.56 4 minimum. - 2.56 to 2.66 16 } - 2.66 to 2.76 16 } maximum. - 2.76 to 2.86 8 - 2.86 to 2.96 4 } minimum. - 2.96 to 3.06 3 } - 3.06 to 3.16 10 maximum. - -The clustering tendency is here quite apparent. - -4. The three widest intervals between these bodies are-- - - (_a_) between Leucothea and Pales 0.0785, - (_b_) " Leto and Terpsichore 0.0755, - (_c_) " Thetis and Hestia 0.0525; - -and these, it will be observed, are the three remaining distances, -indicated on a previous page, at which the periods of the primitive -meteoric asteroids would be commensurable with that of Jupiter. Now, -if the original ring consisted of an indefinite number of separate -particles moving with different velocities, according to their -respective distances, those revolving at the distance 2.4935--in -the interval between Thetis and Hestia--would make precisely three -revolutions while Jupiter completes one. A planetary particle at this -distance would therefore always come in conjunction with Jupiter in -the same parts of its path: consequently its orbit would become more -and more eccentric until the particle itself would unite with others, -either exterior or interior, thus forming an asteroidal nucleus, while -the primitive orbit of the particle would be left destitute of matter, -like the interval in Saturn's ring. - -5. If the distribution of matter in the zone was originally nearly -continuous, as in the case of Saturn's rings, it would probably break -up into a number of concentric annuli. On account, however, of the -great perturbations to which they were subject, these narrow rings -would frequently come in collision. After their rupture, and while -the fragments were collecting in the form of asteroids, numerous -intersections of orbits and new combinations of matter would occur, so -as to leave, in the present orbits, but few traces of the rings from -which the existing asteroids were derived. A comparison, however, of -the elements of Clytie and Frigga shows a striking similarity; and -Professor Lespiault has pointed out a corresponding likeness between -the orbits of Fides and Maia. For these four asteroids the nodal -lines and also the inclinations are nearly the same; while the periods -differ by only a few days. It is probable, therefore, that they are all -fragments of the same narrow ring. Finally, as they all move nearly in -the same plane, they must at some future time approach extremely near -each other, and perhaps become united in one large asteroid. - - - - -CHAPTER XIV. - -ORIGIN OF METEORS--THE NEBULAR HYPOTHESIS. - - -In regard to the physical history of those meteoric masses which, -in such infinite numbers, traverse the interplanetary spaces, our -knowledge is exceedingly limited. Such as have reached the earth's -surface consist of various elements in a state of combination. It -has been remarked, however, by a distinguished scientist[32] that -"the character of the constituent particles of meteorites, and their -general microscopical structure, differ so much from what is seen -in terrestrial volcanic rocks, that it appears extremely improbable -that they were ever portions of the moon, or of a planet, which -differed from a large meteorite in having been the seat of a more or -less modified volcanic action." As the celebrated nebular hypothesis -seems to afford a very probable explanation of the origin of those -bodies, whether in the form of rings or sporadic masses, its brief -consideration may not be destitute of interest. We will merely premise -that the existence of true nebulae in the heavens--that is, of matter -consisting of luminous gas--has been placed beyond doubt by the -revelations of the spectroscope. - -As a group, our solar system is comparatively isolated in space; the -distance of the nearest fixed star being at least seven thousand times -that of Neptune, the most remote known planet. Besides the central or -controlling orb, it contains, so far as known at present, ninety-nine -primary planets, eighteen satellites, three planetary rings, and nearly -eight hundred comets. In taking the most cursory view of this system we -cannot fail to notice the following interesting facts in regard to the -motions of its various members: - -1. The sun rotates on his axis from west to east. - -2. The primary planets all move nearly in the plane of the sun's -equator. - -3. The orbital motions of all the planets, primary and secondary, -except the satellites of Uranus and Neptune, are in the same -_direction_ with the sun's rotation. - -4. The direction of the rotary motions of all the planets, primary and -secondary, in so far as has been observed, is identical with that of -their orbital revolutions; viz., from west to east. - -5. The rings of Saturn revolve about the planet in the same direction. - -6. The planetary orbits are all nearly circular. - -7. The _cometary_ is distinguished from the _planetary_ portion of the -system by several striking characteristics: the orbits of comets are -very eccentric and inclined to each other, and to the ecliptic at all -possible angles. The motions of a large proportion of comets are _from -east to west_. The physical constitution of the latter class of bodies -is also very different from that of the former; the matter of which -comets are composed being so exceedingly attenuated, at least in some -instances, that fixed stars have been distinctly visible through what -appeared to be the densest portion of their substance. - -None of these facts are accounted for by the law of gravitation. The -sun's attraction can have no influence whatever in determining either -the _direction_ of a planet's motion, or the eccentricity of its orbit. -In other words, this power would sustain a planetary body moving from -east to west, as well as from west to east; in an orbit having any -possible degree of inclination to the plane of the sun's equator, no -less than in one coincident with it; or, in a very eccentric ellipse, -as well as in one differing but little from a circle. The consideration -of the coincidences which we have enumerated led Laplace to conclude -that their explanation must be referred to the _mode_ of our system's -formation--a conclusion which he regarded as strongly confirmed by -the contemporary researches of Sir William Herschel. Of the numerous -nebulae discovered and described by that eminent observer, a large -proportion could not, even by his powerful telescope, be resolved into -stars. In regard to many of these, it was not doubted that glasses -of superior power would show them to be extremely remote sidereal -clusters. On the other hand, a considerable number were examined which -gave no indications of resolvability. These were supposed to consist -of self-luminous, nebulous matter--the chaotic elements of future -stars. The great number of these irresolvable nebulae scattered over -the heavens and apparently indicating the various stages of central -condensation, very naturally suggested the idea that the solar system, -and perhaps every other system in the universe, originally existed -in a similar state. The sun was supposed by Laplace to have been an -exceedingly diffused, rotating nebula, of spherical or spheroidal -form, extending beyond the orbit of the most distant planet; the -planets as yet having no separate existence. This immense sphere of -vapor, in consequence of the radiation of heat and the continual -action of gravity, became gradually more dense, which condensation was -necessarily attended by an increased angular velocity of rotation. At -length a point was thus reached where the centrifugal force of the -equatorial parts was equal to the central attraction. The condensation -of the interior meanwhile continuing, the equatorial zone was detached, -but necessarily continued to revolve around the central mass with -the same velocity that it had at the epoch of its separation. If -perfectly uniform throughout its entire circumference, which would be -highly improbable, it would continue its motion in an unbroken ring, -like that of Saturn; if not, it would probably collect into several -masses, having orbits nearly identical. "These masses should assume a -spheroidal form, with a rotary motion in the direction of that of their -revolution, because their inferior articles have a less real velocity -than the superior; they have therefore constituted so many planets in a -state of vapor. But if one of them was sufficiently powerful to unite -successively by its attraction all the others about its center, the -ring of vapors would be changed into one spheroidal mass, circulating -about the sun, with a motion of rotation in the same direction with -that of revolution."[33] Such, according to the theory of Laplace, is -the history of the formation of the most remote planet of our system. -That of every other, both primary and secondary, would be precisely -similar. - -In support of the nebular hypothesis, of which the foregoing is a -brief general statement, we remark that _it furnishes a very simple -explanation of the motions and arrangements of the planetary system_. -In the first place, it is evident that the separation of a ring would -take place at the equator of the revolving mass, where of course the -centrifugal force would be greatest. These concentric rings--and -consequently the resulting planets--would all revolve _in nearly the -same plane_. It is evident also that the central body must have a -revolution on its axis _in the same direction with the progressive -motion of the planets_. Again: at the breaking up of a ring, the -particles of nebulous matter more distant from the sun would have -a greater absolute velocity than those nearer to it, which would -produce the observed _unity of direction in the rotary and orbital -revolutions_. The motions of the satellites are explained in like -manner. The hypothesis, moreover, accounts satisfactorily for the fact -that the orbits of the planets are all nearly circular. And finally, -it presents an obvious explanation of the rings of Saturn. It would -almost seem, indeed, as if these wonderful annuli had been left by the -Architect of Nature, as an index to the creative process. - -The argument derived from the motions of the various members of the -solar system is not new, having been forcibly stated by Laplace, -Pontecoulant, Nichol, and other astronomers. Its full weight and -importance, however, have not, we think, been duly appreciated. That a -common physical cause has determined these motions, must be admitted -by every philosophic mind. But apart from the nebular hypothesis, -no such cause, adequate both in mode and measure, has ever been -suggested;--indeed none, it seems to us, is conceivable. The phenomena -which we have enumerated _demand_ an explanation, and this demand -is met by the nebular hypothesis. It will be found, therefore, when -closely examined, that the evidence afforded by the celestial motions -is sufficient to give the theory of Laplace a very high degree of -probability. - -A comparison of the facts known in regard to comets, falling-stars, -and meteoric stones, seems to warrant the inference that they are -bodies of the same nature, and perhaps of similar origin; differing -from each other mainly in the accidents of magnitude and density. The -hypothesis of Laplace very obviously accounts for the formation of -planets and satellites, moving in the same direction, and in orbits -nearly circular; but how, it may be asked, can the same theory explain -the extremely eccentric, and in some cases retrograde, motions of -comets and aerolites? This is the question to which we now direct our -attention. - -After the nuclei of the solar and sidereal systems had been established -in the primitive nebula, and when, in consequence, immense gaseous -spheroids had collected around such nuclei, we may suppose that about -the points of equal attraction between the sun and neighboring -systems, portions of nebulous matter would be left in equilibrio. -Such outstanding nebulosities would gradually contract through the -operation of gravity; and if, as would sometimes be the case, the solar -attraction should preponderate, they would commence falling toward our -system. Unless disturbed by the planets they would probably move round -the sun in parabolas. Should they pass, however, near any of the large -bodies of the system, their orbits might be changed into ellipses by -planetary perturbation. Such was the view of Laplace in regard to the -origin of comets. - -It seems probable, however, that many of these bodies originated -_within_ the solar system, and belong properly to it. The outer rings -thrown off by the planets may have been at too great distances from the -primaries to form stable satellites. Such masses would be separated -by perturbation from their respective primaries, and would revolve -round the sun in independent orbits. Again: small portions of nebulous -matter may have been abandoned as primary rings, at various intervals -between the planetary orbits. At particular distances such rings would -be liable to extraordinary perturbations, in consequence of which -their orbits would ultimately assume an extremely elliptical form, -like those of comets, and perhaps also those of meteors. It was shown -in Chapter XIII. that several such regions occur in the asteroid zone -between Mars and Jupiter. We may add, in confirmation of this view, -that there are twelve known comets whose periods are included between -those of Flora and Jupiter. Their motions are all direct; their orbits -are less eccentric than those of other comets; and the mean of their -inclinations is about the same as that of the asteroids. These facts -certainly appear to indicate some original connection between these -bodies and the zone of minor planets. - -The nebular hypothesis, it is thus seen, accounts satisfactorily for -the origin of comets, aerolites, fire-balls, shooting-stars, and -meteoric rings; regarding them all as bodies of the same nature, moving -in cometary orbits about the sun. In this theory, the zodiacal light is -an immense swarm of meteor-asteroids; so that the meteoric theory of -solar heat, explained in a previous chapter, finds its place as a part -of the same hypothesis. - - - - -CONCLUSION. - - -Some of the prominent results of observation and research in meteoric -astronomy may be summed up as follows: - -1. The shooting-stars of November, August, and other less noted epochs, -are derived from elliptic rings of meteoric matter which intersect the -earth's orbit. - -2. Meteoric stones and the matter of shooting-stars coexist in the -same rings; the former being merely collections or aggregations of the -latter. - -3. The most probable period of the November meteors is thirty-three -years and three months. Leverrier's elements of this ring agree so -closely with Oppolzer's elements of the comet of 1866 as to render it -probable that the latter is merely _a large meteor_ belonging to the -same annulus. - -4. The spectroscopic examination of this comet (of 1866) by William -Huggins, F.R.S., indicated that the nucleus was self-luminous, that -the coma was rendered visible by reflecting solar light, and that "the -material of the comet was similar to the matter of which the gaseous -nebulae consist." - -5. The time of revolution of the August meteors is believed to be about -105 years. M. Schiaparelli has found a striking similarity between the -elements of this ring and those of the third comet of 1862. The same -distinguished astronomer has shown, moreover, that a nebulous mass of -considerable extent, drawn into the solar system _ab extra_, would form -a _ring_ or _stream_. - -6. The aerolitic epochs, established with more or less certainty, are -the following: - - 1. February 15th-19th. - 2. March 12th-15th. - 3. April 10th-12th. - 4. April 18th-26th. - 5. May 8th-14th; or especially, 12th-13th. - 6. May 19th. - 7. July 13th-14th. - 8. July 26th. - 9. August 7th-11th. - 10. October 13th-14th. - 11. November 11th-14th. - 12. November 27th-30th. - 13. December 7th-13th. - -About one-half of this number are also known as shooting-star epochs. - -7. The epoch of November 27th-30th corresponds with that of the earth's -crossing the orbit of Biela's two comets. The aerolites of this epoch -may therefore have been moving in nearly the same path. - -8. A greater number of aerolitic falls are observed-- - - 1. By day than by night. - 2. In the afternoon than in the forenoon. - 3. When the earth is in aphelion than when in perihelion. - -The first fact is accounted for by the difference in the number of -observers; the second indicates that a majority of aerolites have -direct motion; and the third is dependent on the relative lengths of -the day and night in the aphelic and perihelic portions of the orbit. - -9. The observed velocities of meteorites are incompatible with the -theory of their lunar origin. - -10. If the meteoric swarm of November 14th has a period of thirty-three -years, Biela's comet passed very _near_, if not actually _through_ it -toward the close of 1845, about the time of the comet's separation. Was -the division of the cometary mass produced by the encounter? - -11. The rings of Saturn may be regarded as dense meteoric masses, and -the principal or permanent division accounted for by the disturbing -influence of the interior satellites. - -12. The asteroidal space between Mars and Jupiter is probably a wide -meteoric ring in which the largest aggregations are visible as minor -planets. In the distribution of the mean distances of the known members -of the group a clustering tendency is quite obvious. - -13. The meteoric masses encountered by Encke's comet may account for -the shortening of the period of the latter without the hypothesis of an -ethereal medium. - - - - -APPENDIX. - - -A. - -The Meteors of November 14th. - -The _American Journal of Science and Arts_ for May, 1867 (received by -the author after the first chapters of this work had gone to press), -contains an interesting article by Professor Newton "On certain recent -contributions to Astro-Meteorology." Of the five possible periods of -the November ring, first designated by Professor N, it is now granted -that the longest, viz., 33-1/4 years, is most probably the true one. -The results of Leverrier's researches in regard to the epoch at which -this meteoric mass was introduced into the solar system, are given in -the same article. This distinguished astronomer supposes the group of -meteors to have been thrown into an elliptic orbit by the disturbing -influence of Uranus. The meteoric stream, according to the most -trustworthy elements of its orbit, passed extremely near that planet -about the year 126 of our era; which date is therefore assigned by -Leverrier as the probable time of its entrance into the planetary -system. This result, however, requires confirmation. - -Although the earliest display of the November meteors, so far as -certainly known, was that of the year 902, several more ancient -exhibitions may, with some probability, be referred to the same epoch. -These are the phenomena of 532, 599, and 600, A.D., and 1768, B.C. (See -Quetelet's Catalogue.) The time of the year at which these showers -occurred is not given. The _years_, however, correspond very well -with the epochs of the maximum display of the November meteors. The -intervals arranged in consecutive order, are as follows: - - From B.C. 1768 to A.D. 532, 69 periods of 33.319 years each. - " A.D. 532 to " 599.5, 2 " 33.750 " - " " 599.5 to " 902, 9 " 33.614 " - " " 902 to " 934, 1 " 32.000 " - " " 934 to " 1002, 2 " 34.000 " - " " 1002 to " 1101, 3 " 33.000 " - " " 1101 to " 1202, 3 " 33.667 " - " " 1202 to " 1366, 5 " 32.800 " - " " 1366 to " 1533, 5 " 33.400 " - " " 1533 to " 1698, 5 " 33.000 " - " " 1698 to " 1799, 3 " 33.667 " - " " 1799 to " 1833, 1 " 34.000 " - " " 1833 to " 1866, 1 " 33.000 " - -The first three dates are alone doubtful. The whole number of intervals -from B.C. 1768 to A.D. 1866 is 109, and the mean length is 33.33 years. - -The perturbations of the ring by Jupiter, Saturn, and Uranus, are -doubtless considerable. It is worthy of note that-- - - 14 periods of Jupiter are nearly equal to 5 of the ring. - 9 " Saturn " " 8 " - 23 " Uranus " " 58 " - -This group or stream has its perihelion at the orbit of the earth; its -aphelion, at that of Uranus. (See diagram, p. 24.) It must therefore -produce star-showers at the latter as well as at the former. Our -planet, moreover, at each encounter appropriates a portion of the -meteoric matter; while at the remote apsis of the stream Uranus in all -probability does the same. The matter of the ring will thus by slow -degrees be gathered up by the two planets. - - -B. - -Comets and Meteors. - -The recent researches and speculations of European astronomers in -regard to the origin of comets and of meteoric streams, have suggested -to the author the propriety of reproducing the following extracts from -an article written by himself, in July, 1861, and published in the -_Danville Quarterly Review_ for December of that year: - -"Different views are entertained by astronomers in regard to the -_origin_ of comets; some believing them to enter the solar system _ab -extra_; others supposing them to have originated within its limits. The -former is the hypothesis of Laplace, and is regarded with favor by many -eminent astronomers. It seems to afford a plausible explanation of the -paucity of large comets during certain long intervals of time. In one -hundred and fifty years, from 1600 to 1750, sixteen comets were visible -to the naked eye; of which eight appeared in the twenty-five years from -1664 to 1689. Again, during sixty years from 1750 to 1810, only five -comets were visible to the naked eye, while in the next fifty years -there were double that number. Now, according to Laplace's hypothesis, -patches of nebulous matter have been left nearly in equilibrium in the -interstellar spaces. As the sun, in his progressive motion, approaches -such clusters, they must, by virtue of his attraction, move toward -the center of our system; the nearer portions with greater velocity -than the more remote. The nebulous fragments thus introduced into our -system would constitute comets; those of the same cluster would enter -the solar domain at periods not very distant from each other; the forms -of their orbits depending upon their original relative positions with -reference to the sun's course, and also on planetary perturbations. On -the other hand, the passage of the system through a region of space -destitute of this chaotic vapor would be followed by a corresponding -paucity of comets. - -"Before the invention of the telescope, the appearance of a comet was -a comparatively rare occurrence. The whole number visible to the naked -eye during the last three hundred and sixty years has been fifty-five; -or a mean of fifteen per century. The recent rate of telescopic -discovery, however, has been about four or five annually. As many of -these are extremely faint, it seems probable that an indefinite number, -too small for detection, may be constantly traversing the solar domain. -If we adopt Laplace's hypothesis of the origin of comets, we may -suppose an almost continuous fall of primitive nebular matter toward -the center of the system--the _drops_ of which, penetrating the earth's -atmosphere, produce _sporadic_ meteors; the larger aggregations forming -comets. The disturbing influence of the planets may have transformed -the original orbits of many of the former, as well as of the latter, -into ellipses. It is an interesting fact that the motions of some -luminous meteors--or _cometoids_, as perhaps they might be called--have -been decidedly indicative of an origin beyond the limits of the -planetary system. - -"But how are the phenomena of _periodic_ meteors to be accounted for, -in accordance with this theory? - -"The division of Biela's comet into two distinct parts suggests several -interesting questions in cometary physics. The nature of the separating -force remains to be discovered; 'but it is impossible to doubt that it -arose from the divellent action of the sun, whatever may have been the -mode of operation.' - -"'A signal manifestation of the influence of the sun,' says a -distinguished writer, 'is sometimes afforded by the breaking up -of a comet into two or more separate parts, on the occasion of its -approach to the perihelion. Seneca relates that Ephoras, an ancient -Greek author, makes mention of a comet which before vanishing was -seen to divide itself into two distinct bodies. The Roman philosopher -appears to doubt the possibility of such a fact; but Keppler, with -characteristic sagacity, has remarked that its actual occurrence was -exceedingly probable. The latter astronomer further remarked that there -were some grounds for supposing that two comets, which appeared in the -same region of the heavens in the year 1618, were the fragments of a -comet that had experienced a similar dissolution. Hevelius states that -Cysatus perceived in the head of the great comet of 1618 unequivocal -symptoms of a breaking up of the body into distinct fragments. The -comet when first seen in the month of November, appeared like a round -mass of concentrated light. On the 8th of December it seemed to be -divided into several parts. On the 20th of the same month it resembled -a multitude of small stars. Hevelius states that he himself witnessed a -similar appearance in the head of the comet of 1661.'[34] Edward Biot, -moreover, in his researches among the Chinese records, found an account -of 'three dome-formed comets' that were visible simultaneously in 896, -and pursued very nearly the same apparent path. - -"Another instance of a similar phenomenon is recorded by Dion Cassius, -who states that a comet which appeared eleven years before our era, -separated itself into several small comets. - -"These various examples are presented at one view, as follows: - - "I. Ancient bipartition of a comet.--_Seneca, Quaest. Nat._, - _lib. VII. cap. XVI._ - - "II. Separation of a comet into a number of fragments, 11 - B.C.--_Dion Cassius._ - - "III. Three comets seen simultaneously pursuing the same orbit, - A.D. 896--_Chinese records--Comptes Rendus_, tom. xx. 1845, p. - 334. - - "IV. Probable separation of a comet into parts, A.D. - 1618.--_Hevelius_, _Cometographia_, p. 341.--_Keppler_, _De - Cometis_, p. 50. - - "V. Indications of separation, 1661.--_Hevelius_, - _Cometographia_, p. 417. - - "VI. Bipartition of Biela's comet, 1845-6. - -"In view of these facts it seems highly probable, if not absolutely -certain, that the process of division has taken place in several -instances besides that of Biela's comet. May not the force, whatever -it is, that has produced _one_ separation, again divide the parts? And -may not this action continue until the fragments become invisible? -According to the theory now generally received, the periodic phenomena -of shooting-stars are produced by the intersections of the orbits of -such nebulous bodies with the earth's annual path. Now there is reason -to believe that these meteoric rings are very elliptical, and in this -respect wholly dissimilar to the rings of primitive vapor which, -according to the nebular hypothesis, were successively abandoned at -the solar equator; in other words, that the matter of which they are -composed moves in _cometary_ rather than _planetary_ orbits. May not -our periodic meteors be the _debris_ of ancient but now disintegrated -comets, whose matter has become distributed around their orbits?" - - -C. - -Biela's Comet and the Meteors of November 27th-30th. - -At the close of Chapter IV. it was suggested that the meteors of -November 27th-30th might possibly be derived from a ring of meteoric -matter moving in the orbit of Biela's comet. Since that chapter was -written similar conjectures have been started in the _Astronomische -Nachrichten_[35] by Dr. Edmund Weiss and Prof. d'Arrest. The latter -attempts to show that the December meteors may be derived from the same -ring. The question will doubtless be decided at no distant day. - - -D. - -The First Comet of 1861 and the Meteors of April 20th. - -Recent investigations render it probable that the orbit of the first -comet of 1861 is identical with that of the meteors of April 20th. The -orbit is nearly perpendicular to the ecliptic. - - - - -FOOTNOTES: - - -[1] For a full description, see Silliman's Journal for January and -April, 1834 (Prof. Olmsted's article). Also a valuable paper, in the -July No. of the same year, by Prof. Twining. - -[2] Physique du Globe, Chap. IV. - -[3] Professor Olmsted estimated the number of meteors, visible at New -Haven, during the night of November 12th-13th, 1833, at 240,000. - -[4] Conde says, "there were seen, as it were lances, an infinite number -of stars, which scattered themselves like rain to the right and left, -and that year was called 'the year of stars.'" - -[5] In 1202, "on the last day of Muharrem, stars shot hither and -thither in the heavens, eastward and westward, and flew against -one another like a scattering swarm of locusts, to the right and -left; this phenomenon lasted until daybreak; people were thrown -into consternation, and cried to God the Most High with confused -clamor."--Quoted by Prof. Newton, in Silliman's Journal, May, 1864. - -[6] Am. Journ. of Sci. and Arts, May and July, 1864. - -[7] The stream or arc of meteors is several years in passing its node. -The first indication of the approach of the display of 1866 was the -appearance of meteors in unusual numbers at Malta, on the 13th of -November, 1864. The great length of the arc is indicated, moreover, by -the showers of 931 and 934. - -[8] Silliman's Journ. for Sept. and Nov., 1861. - -[9] The numerical results here given are those found by Professor -Newton. See Silliman's Journ. for March, 1865. - -[10] The diameters of the asteroids are derived from a table by Prof. -Lespiault, in the Rep. of the Smithsonian Inst. for 1861, p. 216. - -[11] "It appears probable, from the researches of Schreibers, that 700 -fall annually."--Cosmos, vol. i. p. 119 (Bohn's Ed.). Reichenbach makes -the number much greater. - -[12] New Concord is close to the Guernsey County line. Nearly all the -stones fell in Guernsey. - -[13] Cosmos, vol. i. p. 120. - -[14] Leverrier's Annals of the Observatory of Paris, vol. i. p. 38. - -[15] "This is a remarkable example of a stone arriving on the earth -with a temperature approaching that of the interplanetary spaces. -Aerolites containing much iron, a substance which conducts heat well, -get thoroughly heated by their passage through the atmosphere. But the -stony aerolites, containing less iron, conducting heat badly, preserve -in their interior the temperature of the locality from which they fall; -their surface only is heated, and generally fused. When the stones are -large, the _excessive cold_ of their interior portion, which must be -nearly that of interplanetary space, is remarked; but when small, they -remain hot for some time."--_Dr. Phipson._ - -[16] Silliman's Journal, September, 1864. - -[17] The same explanation is given by T. M. Hall, F.G.S., in the -Popular Science Review for Oct. 1866. - -[18] This list contains nothing but _aerolites_. In the Edinburgh -Review for January, 1867, we find the following statements: "Out of -the large number of authentic aerolites preserved in mineralogical -collections, two only--one on the 10th of August, and one on the 13th -of November--are recorded to have fallen on star-shower dates. On the -other hand, five or six meteorites, on the epoch of the 13th-14th of -October, belong to a date when star-showers, so far as is at present -known, do not make their appearance." The inaccuracy of the former -statement is sufficiently apparent. In regard to the latter we remark -that Quetelet's Catalogue gives one star-shower on the 14th of October, -and another on the 12th. - -[19] The date of this remarkable occurrence is worthy of note as a -probable aerolite epoch. From the 12th to the 15th of March we have the -following falls of meteoric stones: - - 1. 1731, March 12th. At Halstead, Essex, England. - 2. 1798, March 12th. At Sales, France. - 3. 1806, March 15th. At Alais, France. - 4. 1807, March 13th. At Timochin, Russia. - 5. 1811, March 13th. At Kuleschofka, Russia. - 6. 1813, March 13th-14th. The phenomena above described. - 7. 1841, March 12th. At Grueneberg, Silesia. - -Numerous fire-balls have appeared at the same epoch. - -[20] The innermost or semi-transparent ring of Saturn appears to be -similarly constituted, as the body of the planet is seen through it -without any distortion whatever. - -[21] Origin of the Stars, p. 173. - -[22] Origin of the Stars, p. 184. - -[23] Since the above was written Prof. Ennis has informed the author -that, without making any estimate of his own, he adopted the density of -Jupiter's first satellite as given in Lardner's _Handbook of Astronomy_. - -[24] Origin of the Stars, p. 77. - -[25] Youman's Correlation and Conservation of Forces, p. 244. - -[26] Iowa Instructor and School Journal for November, 1866, p. 49. - -[27] A recent hypothesis in regard to the temporary star of 1572 has -been proposed by Alexander Wilcocks, M.D., of Philadelphia. See Journ. -Acad. Nat. Sci. of Phila. for 1859. - -[28] Gautier's Notice of Recent Researches relating to -Nebulae.--Silliman's Journal for Jan. 1863, and March, 1864. - -[29] Outlines of Astronomy, Art. 442. - -[30] A learned and highly interesting examination of this hypothesis -will be found in a memoir "On the Secular Variations and Mutual -Relations of the Orbits of the Asteroids," communicated to the Am. -Acad. of Arts and Sciences, April 24th, 1860, by Simon Newcomb, Esq. - -[31] For an explanation of the origin of the asteroids according to -the nebular hypothesis, see an article by David Trowbridge, A.M., in -Silliman's Journal for Nov. 1864, and Jan. 1865. - -[32] H. C. Sorby, F.R.S. - -[33] Harte's Trans. of Laplace's Syst. of the World, vol. ii., note vii. - -[34] Grant's Hist. of Phys. Astr., p. 302. - -[35] Nos. 1632 and 1633. - - - - -PUBLICATIONS OF J. B. 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