assist in the recurrence to this important circle, a brazen circle was at length devised, and fastened permanently to another brazen circle of equal size, under an angle exactly equal to the inclination of the equator to the ecliptic. Circles, perpendicular to the equator, and passing through the solstices and equinoxes, completed the second astronomical instrument, the sphere. Having constructed this simple piece of machinery, it was mounted on an axis passing through its centre, and perpendicular to its equator, so as to revolve as did the heavens, whose motions it was intended to represent. Having so placed the axis of rotation that its prolongation would pass through the north star, this rude sphere came to play a most important part in the future investigations of the heavens. Its brazen equator and ecliptic were each divided into a certain number of equal parts, by reference to which the motion of the heavenly bodies might be followed with far greater precision than had ever been previously obtained.

Armed with a new and more perfect instrument, the astronomer resumes his great investigation. Finding it now possible to mark out the sun's path in the heavens with certainty by means of his brazen ecliptic, he discovers that the moon and planets in each revolution pass across the sun's track, and spend nearly an equal amount of time on the north and south sides of the ecliptic. This discovery led to a more accurate determination of the periods of revolution of the planets. The interval was noted from one passage across the ecliptic to the next on the same side, and these intervals marked with accuracy the planetary periods. It now became possible to fix with greater certainty, the relative positions of the sun and moon, and problems were once more resumed which had thus far baffled every effort of human genius. The phases of the moon, the very first point of investigation, had never yet yielded up its hidden cause; and those terrific phenomena, solar and lunar eclipses, which had long covered the earth with terror and dismay, were wrapped in mystery, and their explanation had resisted the sagacity of the most powerful and gifted intellects.

No one has ever witnessed the going out of the sun in dim eclipse, even now when its most minute phenomena are predicted with rigorous exactitude, without a feeling of involuntary dismay. What then must have been the effect upon the human mind in those ages of the world, when the cause was unknown, and when these terrific exhibitions burst on earth's inhabitants

unheralded and unannounced? Here then was an investigation, not prompted by curiosity alone, 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 eclipse of the sun ever occurred when the moon 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 immediately 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, and the great fact was announced to the world, that the sun's light was hidden by the interposition of the dark body of the moon.

Having reached this important result with entire certainty, the explanation of the moon's phases followed 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 that the side next to the sun (the illuminated 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, as 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 qualem primo qui

opposite the sun, and turning her entire illuminated surface or the roug
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 examination it became evident

D

that the moon was a globular body, non-luminous, and revolving in an orbit, comprehended 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 Saturn the most distant, as it was the slowest moving of all the planets.

After reaching to a knowledge of the causes producing 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 intercepted 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. It was 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, as the moon entered the earth's shadow, 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 connection 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 an 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 eclipse 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, surrounded 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 is the problem; he sternly grapples with it, and resolves never to give over till victory crown 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 moon's nodes. At each revolution the node occurred farther west, until after a circle of about nineteen years, it had circulated in the same direction entirely round the ecliptic. Long and patiently did the astronomer watch and wait; each eclipse is duly observed, and its attendant circumstances are recorded; when at last the darkness begins to give way, and a ray of light breaks in upon his mind. He finds that no eclipse of the sun ever occurs unless the new moon is in the act of crossing the sun's track. Here was a grand discovery. He holds the key which he believes will unlock the dread mystery, and now, with redoubled energy, he resolves to thrust it into the wards and drive back the bolts.

To predict an eclipse of the sun, he must sweep forward from new moon to new moon, until he finds some new moon which should occur while the moon was in the act of crossing from one side to the other of the sun's track. This certainly was possible. He knew the exact period from new moon to new moon, and from one crossing of the ecliptic to another. With eager eye he seizes the moon's place in the heavens, and her age, and rapidly computes where she will be at her next change. He finds the new moon occurring far from the sun's track; he runs round another revolution; the place of the new moon falls closer to the sun's path, and the next yet closer, until, reaching forward with piercing intellectual vigour, he at last finds a new moon which occurs precisely at the computed time of her passage across the sun's track. Here he makes his stand, and on the day of the occurrence of that new moon, he announces to the startled inhabitants of the world that the sun shall expire in dark eclipse! Bold prediction! Mysterious prophet! with what scorn must