« AnteriorContinuar »
when these terrific exhibitions burst on earth's inhab tants unheralded and unannounced ? Here then way an investigation, not prompted by curiosity alune, but involving the peace and security of man in all coming ages. We cannot doubt that the causes of the solar eclipse were first detected. It was observed, that no cclipse of the sun ever occurred, when the inoon was visible. Even during a solar eclipse, when the sun's light had entirely faded away, and the stars and planets stole gently upon the sight in the sombre and unnatural twilight, the moon was sought for in vain; she was never to be seen. This fact excited curiosity and gave rise to a careful and critical examination of the place in which the moon should be found, imrnediately after a solar eclipse; and it was soon discovered that on the night following the day of eclipse, the moon was seen in her crescent shape very near to the sun and but a short distance from the sun's path. By remarking the moon's place, next before a solar eclipse and that immediately following, it was seen that at the time of the occurrence of the eclipse, the moon was actually passing from the west to the east side of the sun's place, and finally a little calculation showed that a coincidence of the sun and moon in the heavens took place at the precise time at which the sun had been eclipsed. The conclusion was irresistible, anel the great fact was announced to the world, that the sun's light was hidden by the interposition of the dark boily of the moon. Having reached this important result with en
certainty, the explanation of the moon's phases foilowed in rapid succession. For it now became manifest, that the moon shone with borrowed light
and that her brilliancy came from the reflected beams of the sun. This was readily demonstrated by the following facts. When the moon was so situated what the side next to the sun, (the illuininated one), was turned from the eye of the observer, (as was the case in a solar eclipse), then the moon's surface next to the observer, was always found to be entirely black Pursuing her journey from this critical point, the moon was next seen near the sun, in the evening twilight, a: a slender thread of light, a very small portion of her illuminated surface being now visible. Day after day this visible portion increases, until finally the moon rises as the sun sets, full orbed and round, being directly oppo site the sun, and turning her entire illuminated surface towards the eye of the observer. By like degrees she loses her light as she approaches, and finally becomes invisible as she passes by the sun.
From this exam. ination it became evident that the moon was a globular body, non-luminous, and revolving in an orbit, com: prehended entirely within that described by the sun, and consequently, nearer to the earth than the sun. Having ascertained this fact, it was concluded that among all the moving heavenly bodies, the periods of revolution indicated their relative distances from the earth. Hence Mars was regarded as more distant than the sun, Jupiter more remote than Mars, and Sat urn the most distant, as it was the slowest moving of all the planets.
After reaching to a knowledge of the causes pro ducing the eclipses of the sun and the phases of the moon, it remained yet to resolve the mystery of the lunar eclipse. It was far more difficult to render a satisfactory account of this phenomenon than either of
the preceding. The light of the moon was not inter cepted by the interposition of any opaque body between it and the eye of the observer. No such body existed, and long and perplexing was the effort to explain this wonderful phenomenon. Finally it was observed that all opaque bodies cast shadows, in directions opposite to the source of light. Was it not possible that the light of the sun, falling upon the earth, might be intercepted by the earth, and thus produce a shadow which might even reach as far as the moon ? So soon as this conjecture was made, a series of examinations were commenced to confirm or destroy the theory. It was at once seen that in case the conjecture was true, no lunar eclipse could occur except when the sun, earth, and moon, were situated in the same straight line; a position which could never occur, except at the full or new of the moon. soon discovered that, it was only at the full, that lunar eclipses took place, thus confirming the truth of the theory, and fixing it beyond a doubt that the shadow of the earth falling on the moon, was the cause of her eclipse. The moon had already been shown to be non-luminous, and the moment the interposition of the earth, between it and its source of light, the sun, cut off its light, it ceased to be visible, and passed through an eclipse. The sphericity of the earth, which had been analogically inferred from that of the heavens was now made absolutely certain--for it was remarked, that as the moon entered the earth's sha that the track of this dark shadow across the bright surface of the moon was always circular, which was quite impossible, for every position, except the
earth, which cast this circular shadow, should be of a globular form.
Having now attained to a clear and satisfactory explanation of the two grand phenomena, solar and lunar eclipses, the question naturally arose, why was not the sun eclipsed in each revolution of the moon? and how happened it that the moon in the full, did not always pass through the earth's shadow ? An examination of the moon's path among the fixed stars gave to these questions a clear and positive answer. It was found that the sun and moon did not perform their revolutions in the same plane. The moon's route among the stars crossed the sun's route under a certain angle, and it thus frequently happened, that at the new and full, the moon occupied some portion of her orbit too remote from that of the sun to render either a lunar or solar eclipse possible.
Rapidly have we traced the career of discovery. The toil and watching of centuries have been condensed into a few moments of time, and questions requiring ages for their solution have been asked, only to be answered. In connexion with the investigations just developed, and as a consequence of their successful prosecution, the query arose whether in case science had reached to a true exposition of the causes producing the eclipse of the sun, was it not possible to stretch forward in time, and anticipate and predict the coming of these dread phenomena?
To those who have given but little attention to the subject, even in our own day, with all the aids of modern science, the prediction of an eclipse, seems sufficiently mysterious and unintelligible. How then it was possible, thousands of years ago, to accomplish the same great object, without any just views of the structure of the system, seems utterly incredible Follow me, then, while I attempt to reveal the train of reasoning which led to the prediction of the first cclipse of the sun, the most daring prophecy ever made by human genius. Follow in imagination. this bold interrogator of the skies to his solitary mountain summit-withdrawn from the world-eurrounded by his mysterious circles, there to watch and ponder through the long nights of many-many years. But hope cheers him on, and smooths his rugged pathway. Dark and deep as is the problem, he sternly grap ples with it, and resolves never to give over till victory crowns his efforts.
He has already remarked, that the moon's track in the heavens crossed the sun's, and that this point of crossing was in some way intimately connected with the coming of the dread eclipse. He determines to watch and learn whether the point of crossing was fixed, or whether the moon in each successive revolution, crossed the sun's path at a different point. If the sun in its annual revolution could leave behind him a track of fire marking his journey among the stars, it is found that this same track was followed from year to year, and from century to century with undeviating precision. But it was soon discovered, that it was far different with the moon. In case, she too could leave behind her a silver thread of light sweeping round the heavens, in completing one revolution, this thread would not join, but would wind around among the stars in each revolution, crossing the sun's fiery track at a point west of the previous crossing. These points of crossing were called the