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diff --git a/43715-0.txt b/43715-0.txt new file mode 100644 index 0000000..e4006b3 --- /dev/null +++ b/43715-0.txt @@ -0,0 +1,3770 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 43715 *** + +[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 Brahé, 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° to 100° 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° 14´), and between 46° and 82° +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° toward the north and south. In an amplitude of 60° 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°, and all exceeded 25° or 30°.... 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°. 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°, and +its latitude 8° 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° 25´ 60° 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'étoiles 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° + 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° 38´ 344° 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 Göttingen, 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 Böotes. + +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 Ægos 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° 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° 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° or 25° + 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 Göttingen. + +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° and 44° +north latitude, and is about 25° 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 Göttingen 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 Mässing, 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 château 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° after I saw +it. Height above the northern horizon about 50°. 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 maculæ, 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 Mädler, 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, Vouillé, France. + +(_f_) May 13th, 1855, Oesel, Baltic Sea. + +(_g_) May 13th, 1855, Bremevörde, 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 _resumé_ +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°. 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° 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 nebulæ 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 nebulæ.[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."--_Système 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 | Astræa | 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 | Lætitia | 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 | Danaë | 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 nebulæ 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 +nebulæ 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 nebulæ 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, +Pontécoulant, 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 +nebulæ 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, Quæst. 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 Salés, 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 Grüneberg, 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 +Nebulæ.--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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Price $1.00. + + +_LIPPINCOTT'S PRONOUNCING GAZETTEER OF THE WORLD_, + +OR GEOGRAPHICAL DICTIONARY. + +Revised Edition, with an Appendix containing nearly ten thousand new +notices, and the most recent Statistical Information, according to the +latest Census Returns, of the United States and Foreign Countries. + + +Lippincott's Pronouncing Gazetteer gives-- + + I.--A Descriptive notice of the Countries, Islands, Rivers, + Mountains, Cities, Towns, etc., in every part of the Globe, + with the most Recent and Authentic Information. + + II.--The Names of all Important places, etc., both in their + Native and Foreign Languages, with the PRONUNCIATION of the + same--a Feature never attempted in any other Work. + + III.--The Classical Names of all Ancient Places, so far as they + can be accurately ascertained from the best Authorities. + + IV.--A Complete Etymological Vocabulary of Geographical Names. + + V.--An elaborate Introduction, explanatory of the Principles of + Pronunciation of Names in the Danish, Dutch, French, German, + Greek, Hungarian, Italian, Norwegian, Polish, Portuguese, + Russian, Spanish, Swedish, and Welsh Languages. + + Comprised in a volume of over two thousand three hundred + imperial octavo pages. Price, $10.00. + +FROM THE HON. HORACE MANN, LL.D., + +_Late President of Antioch College_. + + I have had your Pronouncing Gazetteer of the World before me + for some weeks. Having long felt the necessity of a work of + this kind, I have spent no small amount of time in examining + yours. It seems to me so important to have a comprehensive + and authentic gazetteer in all our colleges, academies, and + schools, that I am induced in this instance to depart from my + general rule in regard to giving recommendations. Your work has + evidently been prepared with immense labor; and it exhibits + proofs from beginning to end that knowledge has presided over + its execution. The rising generation will be greatly benefited, + both in the accuracy and extent of their information, should + your work be kept as a book of reference on the table of every + professor and teacher in the country. + + + + +Transcriber's Notes: + + +Punctuation and spelling were made consistent when a predominant +preference was found in this book; otherwise they were not changed. + +Simple typographical errors were corrected; occasional unbalanced +quotation marks retained. + +Ambiguous hyphens at the ends of lines were retained. + +Text uses both "star shower" and "star-shower"; not changed here. + +"Keppler" is spelled that way in this text. + + + + + + + + +End of the Project Gutenberg EBook of Meteoric astronomy, by Daniel Kirkwood + +*** END OF THE PROJECT GUTENBERG EBOOK 43715 *** |