The Music of the Spheres/Chapter 12
CHAPTER XII
THE CHILDREN OF THE SUN
The Planets
We have just obtained a close view of one of the stars of the Galaxy,—the nearest star, our own sun,—and have gazed in admiration at the pearly setting of its corona, the turbulent waves of its crimson atmosphere, its black spots and moving belts, and our admiration increases as we visualize in our mind's eye, the eight fine planets which swing unceasingly around in its beautiful light.
In comparison with the sun, these planets are very small; either the earth, Mars, Venus or Mercury could be dropped into an average-sized sun-spot, or all four into an extra large sun-spot, while a thousand globes huge as Jupiter would scarcely balance the globe of the sun. Indeed, it has been computed that if the total mass of the whole solar system, with the exception of the sun, were called I, then the mass of the sun on the same scale would be 744.
All of the planets of the solar system roll as if on a great shield, one orbit set within the other at widely separated intervals. These orbits are not round but elliptical, with the sun shining at one focus of each elliptical orbit.
An unseen force called gravitation holds the planets in their pathways, always just so near and just so far from the sun. This is the same force that holds the stars in a Galaxy and keeps the objects on the earth from sliding off into space. Since the attractive power of the sun is tremendous, the planets must travel around their pathways at a tremendous rate in order to develop enough centrifugal force to offset the gravitational pull, and the closer the planet the faster it must fly._-_figure_141.jpg)
The orbits of the four outer planets, Neptune, Uranus, Saturn and Jupiter, and the orbits of Mars and the Earth, drawn to scale. (Within the orbit of the Earth would appear the orbits of Venus and Mercury, too small to be shown in this drawing.) Mercury, for instance, travels at a rate of 35 miles a second while Neptune, seventy-five times as far off, has an orbital velocity of only 3.4 miles a second. The following table shows the distances of each planet from the sun and the time it takes it to complete its journey around its orbit, beginning with Mercury, the nearest planet to the sun, and continuing outward.
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Mercury, Venus, Earth and Mars are sometimes called the inner planets because they form a group nearest the sun but more frequently are called the Terrestrial Planets because they all have solid crusts like the earth.
Jupiter, Saturn, Uranus and Neptune, forming a group called the outer or major planets, are more or less in a gaseous condition and are very huge in comparison to the first four.
The orbit of Neptune, the farthermost planet, encloses the orbits of all the other planets, and is so very large that it requires 165 years for Neptune to travel around it. This is quite a contrast to the time consumed by little Mercury who flies so close to the sun that he travels around it in 88 days. This, of course, means the length of the year on each of these planets.
Since the planets shine by light reflected from the sun, half of their globes are always bright,—and the other half is always hidden in the darkness of the shadow which trails behind. Each planet, however, rotates on its axis, which gives each side in turn a night and day. Exception to this must be made in the case of Mercury and Venus, their rotation with respect to the sun having been destroyed by the powerful tidal actions of the sun eons ago. Hence only one hemisphere in each of these planets is warmed by the light of the sun; the other forever faces the darkness and the cold of outer space.
The period of a planet's rotation is determined by watching its markings, just as the period of the sun's rotation was determined by watching its spots. The larger planets rotate much more swiftly than the smaller ones; a "day" on Jupiter or Saturn is not half as long as on Mars or on Earth.
The seasons of a planet depend on the angle at which its axis is tipped. The axis of the earth tips over at an angle of 23½ degrees from the perpendicular to the plane of its orbit, so its seasons are fairly well divided. Jupiter leans only 3 degrees and has little seasonal change but poor Uranus is inclined about 98 degrees and is subjected to the direst extremes. Since the year of Uranus consists of 84 of our years, each hemisphere has 42 years of darkness and 42 years of light.
The four inner planets are quite solid in comparison to the four outer ones, which are largely gaseous._-_figure_142.jpg)
The Axis of the Earth tips from the Perpendicular to the Plane of its Orbit. Mercury is the most solid planet of all, being more like metal than the earth; neither Jupiter nor Saturn have stable surface crusts while Saturn is so light that it would float on water.
Following are the diameters of the planets starting from Mercury, nearest to the sun, to Neptune, the farthest away.
Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
3,030 miles | |
Venus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7,700 miles“ | |
Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7,927 miles“ | |
Mars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
4,230 miles“ | |
Jupiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
88,300 miles“ | |
Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
73,700 miles“ | |
Uranus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
32,000 miles“ | |
Neptune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
35,000 miles“ | |
The planets that are relatively near the sun have few or no satellites, Mercury and Venus having none, Earth one, Mars two; those farther distant have a goodly number, Uranus possessing four, Jupiter nine and Saturn ten.
Mars has been studied in much detail and, of all the planets, has excited the most popular interest. Conditions are such that markings, mysterious at this distance, and colorful details, may be studied with comparative ease. The other planets that have been studied are too far away, too close to the sun, or are obscured by too cloudy atmospheres to permit detailed observations. The great planet Jupiter forms a magnificent picture, his broad face striped by colored bands which occasionally vary. This planet may be seen to turn completely around in 9 hours and 50 minutes, while four of its moons revolve about it in close attendance. Saturn is even more superbly magnificent than Jupiter, for the great, flat, shining ring which encircles this planet is the wonder of the whole solar system.
Because the planets are so much closer than the stars, they may be seen to change their places against the background of the constellations. An almanac will tell which of these worlds are visible in the evening during the different months and where they may be found. Since they lie nearly in the same plane as the orbit of the earth, they are always found within the boundaries of a pathway 16 degrees wide. This pathway circles the sky and is marked by the sun in the daytime and the moon at night. All the planets except Mars, Venus and Mercury travel nearly in the middle of this path which in ancient times was named the zodiac.
The constellations which lie along the pathway of the sun, moon and planets are called the constellations of the zodiac. The following are the Latin names of the signs of the twelve parts of the zodiac, with their English equivalents:
| Spring: | Aries, the Ram ♈︎ |
Summer: | Cancer, the Crab ♋︎ |
| Autumn: | Libra, the Scales ♎︎ |
Winter: | Capricornus, the Goat ♑︎ |
When the winter months begin, the sun is in the constellation of Sagittarius, in the beginning of spring in the constellation of Pisces, in the beginning of summer, in Gemini, and at the commencement of autumn, in the constellation of Virgo. The zodiacal constellations are very important, and to the people in the olden days, the sun's position in front of them was a way to tell the season of the year. The words of Chaucer
Hath in the Ram his halfe cours y-ronne"
meant to any ploughboy in old England that it was April because during the first half of April the sun traverses the last half of Aries, the constellation of the Ram. Chaucer, by the way, wrote a book to teach "litel Lewis" his son, "to knowe every time of the day by the light of the sonne, and every time of the night by the starres fixed."
To locate a planet in modern days one has only to look up its position in the almanac or on a monthly sky map and then find it similarly located in the same constellation in the sky. The Monthly Evening Sky Map, an eight page journal for the amateur published by Leon Barritt, 150 Nassau St., New York, contains not only a map of the sky for every month, but also current astronomical news. With such aid, after becoming familiar with the belt of zodiacal constellations—which are easily learned by the following verse, it is not difficult to find the nearest planets.
And next the Crab, the Lion shines
The Virgin and the Scales.
The Scorpion, the Archer and He-goat,
The Man that holds the Watering-pot,
The Fish with glittering tails."
Both Venus and Jupiter are brighter than first magnitude stars and will be recognized with but little difficulty. Mars and Saturn are as bright as first magnitude stars, although Saturn is not so easy to find unless its location is definitely known. Venus is a very white star, Jupiter a bright yellow, Saturn a pale orange, and Mars a fiery red. Mars wanders farther south than any other planet seen in the evening skies. Mercury may sometimes be seen after sunset in the spring or before sunrise in the fall, but only for a few days at a time and hence will seldom be seen by one who does not know just when, as well as where, to look for it. Uranus and Neptune are too far away and the planetoids too small to be of much interest to amateurs.
If examined with a glass the planets will show a bright round disk while a star is no more than a point of light. Mercury and Venus show phases just as our moon for their orbits lie between the earth and the sun. Venus is particularly beautiful as a crescent and is best seen in the west near the setting sun. Jupiter ranks second in popularity for even a field-glass discloses his round shining face and four of his principal moons.
The Planetoids
The Miniature Worlds of the Solar System
Between Mars and Jupiter lies an immense lane of over 300,000,000 miles. This lane had been considered vacant until a century and a quarter ago, and since it was an exception to the general law of planetary distances, it had long been of interest to astronomers. Mercury, Venus, Earth and Mars are distant 35,750,000; 66,750,000; 92,500,000 and 141,000,000 miles, respectively, from the sun; then came this wide vacancy, with the order for the distances between the planets again resumed beyond Jupiter. When the great Kepler suggested that there must be an invisible planet revolving in this gap, many thought that the idea was only a dream of a great mind, for a planet so close would have been discovered long ago. Yet the suggestion was often considered, for the space had been to astronomers as a false note is to a musician, and they knew that if there were only a planet circling here, the spaces between every world would "increase with regularity in proceeding outward from the sun" and the solar kingdom would then be laid out in perfect harmony. The matter was left at this stage for many years, indeed it was not until 200 years after the suggestion was made that astronomers banded together, divided up the zodiac into twenty-four parts and, distributing them among an equal number of observers, began a systematic search. It is quite likely that during the 200 years previous to 1801, when the search began, not an astronomer lived but who had at some time wished to participate in such a search. Astronomers were, however, so few, the heavens so wide and life so short, that there was more than a load already on each of those earnest workers among the star fields.
Why is it, by the way, that more people are not curious about the sky? It sometimes happens that those who have stars for a hobby, a rocking-horse Pegasus, unexpectedly find themselves transported by the Winged Horse to regions above. Thus, Piazzi, at Palermo on the island of Sicily, happened across the first of the little planets, or "planetoids," quite by accident, delighting not only himself but every scientist in the world, for order was now established in the solar system. Although this newly discovered planet was so tiny that its whole surface was no more than equal to the area of the United States, the very fact of its existence in what had seemed a wasted space, probably gave as much satisfaction as the discovery of Uranus ten years before. At the request of Piazzi, the new planet was named Ceres after the tutelary Goddess of Sicily, and as a symbol was appropriately given the sign of the sickle: .svg){kind=small}
But a year later, Dr. Olbers, a physician at Bremen in Lower Saxony, discovered a second planetoid in the same region, with a mean distance and a periodic time so nearly identical with that of Ceres that they were almost within hailing distance. This second planetoid, which was named Pallas, was not greeted as joyously as the first, for now a situation was created that was harder to explain than the great vacant gap. But this was not all. In 1804, still another little globe was discovered, which was called Juno, and another in 1807, which was named Vesta,—four little planets in less than six years! Subsequent discoveries have brought the number almost up to 1000. An explanation by Olbers suggested that these minute bodies might be fragments of an exploded planet, but since they do not lie in the same plane nor do their orbits have a common point of intersection, this theory was discarded. It was then thought that the great attractive force of Jupiter would not allow a planet to form in the space. This theory was also discarded, and even now, a century and a quarter later, no one theory bearing on the origin of the little worlds has found general acceptance.
Following the custom of the ancients, the planetoids were given the names of Greek divinities, the next four being named Astræa, Hebe, Iris and Flora. But the names of Greek divinities at last ran out, and the planetoids were christened with more common names. Astronomers do not bother with any of these names, however, except in the case of a few. The rest they refer to by inclosing its number in a circle.
Although these little globes are very small, many of them have been found to possess distinct individuality. Vesta, for instance, is exceedingly bright, while Ceres, in contrast, is gray and dull. An explanation is that Ceres may be composed "of rugged and sombre rock, unclothed by any vestige of air, while Vesta displays a brilliant shell of clouds." Ceres is the largest of the planetoids, although even Ceres is less than 500 miles in diameter. Eros, which comes closer to the earth than any other known celestial body with the exception of the moon, exhibits a rapid variation in the brilliancy of its light. It is thought that this may be due to a rough, uneven surface with unequal reflecting power, for Eros is no more than a huge rock only 20 miles across. It has also been suggested that perhaps Eros consists of two bodies revolving close together so that one body eclipses the other in certain parts of its orbit, or again, it may be an angular body, not round at all! Many of the planetoids are smaller than Eros, some being only a few miles across.
Thus a thousand mysterious little worlds of assorted shapes and sizes roll along on their individual pathways in the great space between the orbit of Mars and the orbit of the earth. The bright light of Vesta, the dull glow of Ceres and the variable brilliancy of Eros lightly suggest the interest with which further observations and study may invest each tiny planet, as larger and more powerful telescopes are constructed.
Comets and Meteors
Comets
"Jove brandishing a star which men a comet call."
A comet, in olden times, was an object of terror and dread and was regarded as an omen of pestilence and war. Searching through ancient records, incidents without number could be narrated to show that the malicious influence of some comet had caused—
Hard times, need and hunger's scathe,
Great heat, drought, and barren Nature,
War, murder, riots, fire and slaughter,
Frost, cold, storms, and want of water."
Josephus tells us that the destruction of Jerusalem in 69 A.D. was caused by no less than the sword shaped comet which pierced the heavens above the city!
A story is sometimes told of the great consternation caused in Europe in 1456 at the appearance of Halley's comet. This great shaft of light moving across the sky so disturbed the equanimity of Pope Calixtus that he instituted a form of prayer ("Lord, deliver us from the devil, the Turk and the comet") as a protection against its baleful influence. But the comet remained, and, with his people mightily afraid, the pope himself was forced "to interfere, exorcise and expell" the malignant one from the skies.
Halley's comet has always been a most interesting comet. The last time that it appeared, in 1910, the earth rolled right through its beautiful, highly diffused tail, and although the experience was of interest to astronomers, it affected not a whit the affairs of the populace; indeed, but few people knew about it.
In 1680, Halley, an English astronomer and mathematician, while on a passage to France, was the first to observe this great comet, and later made observations with Cassini at Paris, where he observed its appearance with great care and painstakingly computed the elements of its orbit. From the nature of its orbit, he predicted that it would return at regular intervals of 75 years. He even traced this comet back on his historical table of comets, and found that the comets of 1607, 1531 and 1456 had the same orbit as the one which had appeared in 1680. Seventy-five years after, true to his prediction, the comet returned, thus proving that comets may travel in elongated orbits and appear periodically. Halley has the honor of being the first to predict the return of a comet.
It is now known that some comets require hundreds and even thousands of years to perform a revolution around the sun; Donati's comet, one of the most famous comets, which appeared in 1858 "like a plume of fire, shaped like a bird of paradise," travels on such a long circuit that it returns only every 2000 years. The brilliant comet of 1811, which remained visible for nearly ten months, has a period estimated as being around 3000 years. But the orbits of some comets are even longer than this, some traveling so far into space that they not only over-leap the boundary of Neptune but fly to a turning-post so distant that we may never see them return. More than 30 short period comets have been discovered and these have their orbits entirely within the solar system. Encke's comet, with a period of 3½ years, has the shortest period known.
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Although it was discovered to the relief of mankind that comets have no influence upon the earth, it was also discovered that some of the planets with great mass and strong gravitational power, can exert considerable influence on a comet, in fact, enough influence to attract many of these celestial bodies out of their courses and force them to make their outer turn around a point near that planet's orbit. Jupiter has a larger family of comets than any other planet. If a planet once captures a comet it is his captive forever, unless the near approach of some planet of greater mass pulls the comet away and forces it to enclose its new master in the outer end of its orbit.
_-_figure_144.jpg)
A large comet first appears among the stars as a dim spot of light. It may appear from any direction, for, although comets are considered members of the solar system, their orbits do not lie in the same plane as the planets. As it sweeps toward the sun with terrible velocity, which increases hourly, a long streamer of luminous gas gradually develops and floats backward from its head. A small comet often has no tail, but a large comet usually possesses a long and beautiful one, and has been known to possess two, and even half a dozen. This tail, or tails, are at their best when close to the sun, although at all times swung carefully away from the terrific flames of that luminary. Scientists almost hold their breath sometimes at the close call of comets, for the Great Comet of 1843 almost grazed the surface of the sun and many another has passed right through the outstretched banners of the corona. After darting swiftly around this brilliant center, the comet again heads into fathomless space, its long, bright tail gradually disappearing and its fierce speed relaxing as it escapes farther and farther from the sun's control.
The word comet means a "long-haired" star. The star-like nucleus of the comet is called the head and the long nebulous streamer which trails behind, the tail. The head may be colossal, or it may be a mere shred; the head of Donati's comet would have more than filled the space between the earth and moon, while that of the comet of 1811 was considerably larger than the sun itself. The length of a comet's tail is equally amazing for it extends often for millions of miles. The comet of 1882 had 100,000,000 miles of tail while that of 1483 had one twice as long. The comet of 1680 extended below the horizon when its head touched the zenith.
The mean density of a comet is very small. Young states that it is nothing more than a sandbank—a swarm of solid particles of unknown size and widely separated. This light and airy object darts through space at a most hectic speed, often at the rate of a number of hundred miles per second, when close to the sun. It is of such flimsy construction that its light does not even obscure the stars although there have been comets so bright that they were visible in the daytime.
It is now believed that a comet derives its light, except that portion which is reflected sunlight, from electrical discharges between its particles. By some influence emanating from the sun, gas is emitted from the scattered swarm of meteoric particles which compose the head, and these stream out "like smoke from a locomotive" in a magnificent luminous trail. This only occurs when in the vicinity of the sun. Each time the comet comes back to the sun, it loses some of its beauty and its mass decreases—yet like a moth to a flame, it always returns. Newcomb describes the way in which a comet gradually loses itself in the following manner:
"Altogether a good idea of the operations going on in a comet may be obtained if we conceive of a nucleus (or head) to be composed of water or other volatile fluid which is boiling away under the heat of the sun, while the tail is a column of steam rising from it. We do not see the same tail of the comet all the time because the matter which makes up the tail is constantly streaming outwards and constantly being replaced by new vapor rising from the nucleus."
In the course of time, the whole comet becomes disintegrated and its pathway scattered with debris. Astronomers now look upon meteors as the remains of worn out comets, for meteoric swarms follow along the same orbits as many of the comets. When the earth crosses the orbit of a disintegrated comet, or meteoric swarm, the fragments come in contact with our atmosphere where they blaze into incandescence and are seen as shooting stars.
The Biela comet is often mentioned as furnishing the best example of comet disintegration. This comet, which was discovered in 1826, had a period of 6.6 years. In 1846, after a lapse of twenty years, it was noticed to be considerably more elongated than usual and a month later it had separated into two comets, each developing a tail of its own. Before long these twin comets had become separated by 200,000 miles. On its next return, in 1852, the two halves of Biela appeared for the second time, with the distance between them increased to 1,500,000 miles. Once again they flew around the sun, but it was a farewell tour, for one streak of light followed the other out into space, grew fainter and fainter and finally disappeared, never to be seen again. But just here is the best part of the story, for although the comets have completely vanished, in their place every year comes a radiant display of meteors! _-_figure_145.jpg)
COMET 1910a.
Photograph with 6-inch Bruce Lens by Yerkes Observatory.These meteors—the Andromids, coming on the 27th of November regularly—are believed to be the "fragments of the lost comet of Biela"! Thus, Serviss, with a touch of art, gives the shivery atmosphere of Poe to such an uncanny proceeding.
Although comets have here been placed with planets and planetoids under the heading of "The Children of the Sun," we are not sure, as yet, of the origin of comets. There is one theory which suggests that comets may be the waste material of the solar system; the left-overs, as it were, after the planetary system was formed. Again, perhaps, a great comet may be material drawn in from outside space, perhaps flying back and forth between two stars until it becomes so exhausted that one of the stars is able to capture it. At least we know that the solar system now possesses a great number of comets who bow to the mastery of our star and never wander beyond the orbits of his planets. If these are not true children of the sun they are at least his adopted ones, and there is nothing that will ever lure them from his magnetic personality.
Meteors
Meteoric showers are popularly called "shooting stars." At least one shooting star may be seen every ten minutes but at certain times of the year they appear in showers. Three of the most profuse of these "star" showers appear from the
13th to 15th of November—Leo
27th to 29th of November—Andromeda
The Perseids, radiating from a point in the constellation of Perseus, are best seen about three o'clock in the morning. These meteors are called the "Tears of Saint Lawrence" and are noted in ancient legends as the "fiery tears" of this saint who was cruelly persecuted and burned at the stake. His festival is celebrated on the 10th of August, but his "tears" fall for three whole nights.
The Leonid star shower radiates from the vicinity of the star γ in the Sickle of Leo and rains most thickly in the early morning hours. On an average of every 33 years the earth's orbit seems to cut through a denser portion of this meteoric swarm which causes especially beautiful displays. There is a record of this spectacular performance for a thousand years back, although it was not until after the brilliant displays of 1799, 1833 and 1866 that astronomers began a vigorous investigation of the subject of shooting stars. On the night of November 13th, 1833, "the stars fell like flakes of snow, varying in size from a moving point or phosphorescent line to globes of the moon's diameter." A witness of the spectacle wrote for the Christian Advocate and Journal of the following month, 1833, the following enthusiastic description:
"It seemed as if the whole starry heavens had congregated to a point near the zenith, and were simultaneously shooting forth, with the velocity of lightning, to every part of the horizon; and yet they were not exhausted; thousands swiftly followed in the track of thousands, as if created for the occasion."
This shower was particularly well observed in the eastern part of North America. One eye-witness in the Southern States says that the negroes on the plantations were so unnerved that they "lay prostrate on the ground, some speechless and some with the bitterest cries, but with their hands upraised, imploring God to save the world and them." Another witness of the scene in the vicinity of Niagara Falls says that "no spectacle so terribly grand and sublime was ever before beheld by man as that of the firmament descending in fiery torrents over the dark and roaring cataract." Comstock tells of one illiterate observer being anxious to see how the heavens would appear the next evening, for he believed that there would be no stars left. In 1866 this shower was also a wonderful spectacle commencing "about 11:30 P. M., with the appearance at brief intervals of single meteors; then they came in twos and threes, steadily and rapidly increasing in number till 1 h. 13 min. A. M. on November 14th, when no fewer than 57 appeared in one minute. From this time the intensity of the shower diminished gradually, wholly ceasing about 4 A. M. The total number of meteors which at that time came within the limits of the earth's atmosphere was estimated at about 240,000." This was not as brilliant a spectacle as when in 1833 the meteors fell like snowflakes, but it must have been very fine for, to continue with the description of an observer who witnessed it from Great Britain: "The great majority were white, with a bluish or yel_-_figure_146.jpg)
METEORIC SHOWER OF NOVEMBER 13, 1833.
Like tears they poured adown creation's face."
—Bailey.
The third shower listed, the Andromids, radiate from the orange-gold star on the foot of Andromeda during the last week in November. These are best seen during the evening. They are also called the Biela meteors and bring to mind the interesting history of the late Biela comet.
Many hundreds of these radiant points have now been discovered. The meteors which appear in a direct line to the eye, appear as points or stars; those appearing farthest from the center, other things being equal, appear to have the longest trails but their paths are all parallel. The illustration in perspective of the trains coming forward from a point on the horizon of a desert illustrates this clearly.
Meteors, which represent the wreckage which comets strew along their orbits, are not visible until they strike our atmosphere, which causes them to glow. They "glow" because they become white-hot, and they become white-hot because they have been rushing through space at planetary speed, and striking our atmosphere is like striking a match against a stone wall. The friction thus engendered causes the smaller particles to burst into flame and melt in a streak of fire, although the larger ones only melt on the outside, which is thrown off in a streaming tail of incandescent matter, the remainder of the meteor falling to the earth like a heavy rock. Thunders and visible explosions sometimes are heard as an accompaniment of the falling meteor. The meteors which fall to the ground are called "meteorites," or "aerolites," a literal translation of the latter term being "airstone." On an average, however, the individual bodies of a meteor swarm are very small, being represented by "a cloud of silver dimes each about 250 miles from its nearest neighbor." The smaller and lighter meteors called shooting stars which are consumed in our atmosphere probably number from 10 to 20 million daily.
Occasionally a meteorite found is very large, a few weighing several tons, but this is most unusual. The one brought by Commander Peary from Greenland is 11 feet long and 5 feet wide and weighs 36 tons. This is now on display in the Museum of Natural History in New York City. At Ensisheim, in Alsace, during the 15th century, a stone weighing 260 pounds which had descended from the sky was ordered by Emperor Maximilian to be suspended in the church where it hung for 300 years. A shower of nearly 3000 stones of various sizes occurred in Normandy within an elliptical area seven miles long and three miles wide. Nearly all the inhabitants of a large district saw the cloud and witnessed the rain of the stones.
The Greeks and Romans thought that casting stones upon the earth was some sort of pastime indulged in by the Gods and the Romans incorporated in a temple a shower of stones which fell on Alban Mount near Rome. A stone from Heaven was also reverenced in the masonry of the great Mosque of Mecca where it is annually kissed by thousands of pilgrims who begin holy rites by walking seven times around the Kaaba starting from the corner where the black stone is fixed. The great stone in the pyramid of Cholula, in Mexico, and a black stone at Emesa, in Syria, have also been regarded with religious veneration. In India, the residence of a soul in heaven is believed to be proportionate to its charities on earth, and when its allotted period is over, it falls to earth as a meteorite.
If picked up soon after it falls, a meteoric stone is found to be very hot on the outside while the inside is cold. One constant characteristic by which it may be identified is the fused, black, thin and glossy crust, somewhat like varnish, which coats the surface of the meteoric stone. This surface crust is thin and sharply defined from the inner mass.
The predominating element in one class of meteorites is iron, generally combined with a small amount of nickel. Copper, tin, cobalt and other substances are also found, but never silver or gold. Stony meteorites are, however, more common than iron meteorites.
The velocity of meteors, or shooting stars, varies from 12 to 40 miles a second. Herschel estimates their average height above the earth at the time of their appearance as 73 miles, and 52 miles at the time of their disappearance.