Concerning this apparently wild hypothesis, Sir John Herschel offered the following remarkable apology: “This may serve as a specimen of the dreams in which astronomers, like other speculators, occasionally and harmlessly indulge.”
The dream, wild as it appeared, has been realised now. Sir John, in the fifth edition of his Outlines of Astronomy, published in 1858, tells us:
Whatever may be thought of such a speculation as a physical hypothesis, this conclusion has been verified to a considerable extent as a matter of fact by subsequent discovery, the result of a careful and minute examination and mapping down of the smaller stars in and near the zodiac, undertaken with that express object. Zodiacal charts of this kind, the product of the zeal and industry of many astronomers, have been constructed, in which every star down to the ninth, tenth, or even lower magnitudes, is inserted; and these stars being compared with the actual stars of the heavens, the intrusion of any stranger within their limits cannot fail to be noticed when the comparison is systematically conducted. The discovery of Astræa and Hebe by Professor Hencke, in 1845 and 1847, revived the flagging spirit of inquiry in this direction; with what success, the list of fifty-two asteroids, with their names and the dates of their discovery, will best show. The labours of our indefatigable countryman, Mr. Hind, have been rewarded by the discovery of no less than eight of them.
FIRE-BALLS AND SHOOTING STARS.
Humboldt relates, that a friend at Popayan, at an elevation of 5583 feet above the sea-level, at noon, when the sun was shining brightly in a cloudless sky, saw his room lighted up by a fire-ball: he had his back towards the window at the time, and on turning round, perceived that great part of the path traversed by the fire-ball was still illuminated by the brightest radiance. The Germans call these phenomena star-snuff, from the vulgar notion that the lights in the firmament undergo a process of snuffing, or cleaning. Other nations call it a shot or fall of stars, and the English star-shoot. Certain tribes of the Orinoco term the pearly drops of dew which cover the beautiful leaves of the heliconia star-spit. In the Lithuanian mythology, the nature and signification of falling stars are embodied under nobler and more graceful symbols. The Parcæ, Werpeja, weave in heaven for the new-born child its thread of fate, attaching each separate thread to a star. When death approaches the person, the thread is rent, and the star wanes and sinks to the earth.—Jacob Grimm.
THEORY AND EXPERIENCE.
In the perpetual vicissitude of theoretical views, says the author of Giordano Bruno, “most men see nothing in philosophy but a succession of passing meteors; whilst even the grander forms in which she has revealed herself share the fate of comets,—bodies that do not rank in popular opinion amongst the external and permanent works of nature, but are regarded as mere fugitive apparitions of igneous vapour.”
METEORITES FROM THE MOON.
The hypothesis of the selenic origin of meteoric stones depends upon a number of conditions, the accidental coincidence of which could alone convert a possible to an actual fact. The view of the original existence of small planetary masses in space is simpler, and at the same time more analogous with those entertained concerning the formation of other portions of the solar system.
Diogenes Laertius thought aerolites came from the sun; but Pliny derides this theory. The fall of aerolites in bright sunshine, and when the moon’s disc was invisible, probably led to the idea of sun-stones. Moreover Anaxagoras regarded the sun as “a molten fiery mass;” and Euripides, in Phaëton, terms the sun “a golden mass,” that is to say, a fire-coloured, brightly-shining matter, but not leading to the inference that aerolites are golden sun-stones. The Greek philosophers had four hypotheses as to their origin: telluric, from ascending exhalations; masses of stone raised by hurricanes; a solar origin; and lastly, an origin in the regions of space, as heavenly bodies which had long remained invisible: the last opinion entirely according with that of the present day.
Chladni states that an Italian physicist, Paolo Maria Terzago, on the occasion of the fall of an aerolite at Milan, in 1660, by which a Franciscan monk was killed, was the first who surmised that aerolites were of selenic origin. Without any previous knowledge of this conjecture, Olbers was led, in 1795 (after the celebrated fall at Siena, June 16th, 1794), to investigate the amount of the initial tangential force that would be required to bring to the earth masses projected from the moon. Olbers, Brandes, and Chaldni thought that “the velocity of 16 to 32 miles, with which fire-balls and shooting-stars entered our atmosphere,” furnished a refutation to the view of their selenic origin. According to Olbers, it would require to reach the earth, setting aside the resistance of the air, an initial velocity of 8292 feet in the second; according to Laplace, 7862; to Biot, 8282; and to Poisson, 7595. Laplace states that this velocity is only five or six times as great as that of a cannon-ball; but Olbers has shown that “with such an initial velocity as 7500 or 8000 feet in a second, meteoric stones would arrive at the surface of our earth with a velocity of only 35,000 feet.” But the measured velocity of meteoric stones averages upwards of 114,000 feet to a second; consequently the original velocity of projection from the moon must be almost 110,000 feet, and therefore 14 times greater than Laplace asserted. It must, however, be recollected, that the opinion then so prevalent, of the existence of active volcanoes in the moon, where air and water are absent, has since been abandoned.
Laplace elsewhere states, that in all probability aerolites “come from the depths of space;” yet he in another passage inclines to the hypothesis of their lunar origin, always, however, assuming that the stones projected from the moon “become satellites of our earth, describing around it more or less eccentric orbits, and thus not reaching its atmosphere until several or even many revolutions have been accomplished.”
In Syria there is a popular belief that aerolites chiefly fall on clear moonlight nights. The ancients (Pliny tells us) looked for their fall during lunar eclipses.—Abridged from Humboldt’s Cosmos, vol. i. (Bohn’s edition).