CHAP. I.

Of the Astronomy of the Ancients; till the Foun dation of the Alexandrine School.

THE view of the firmament must at all times have fixed the attention of mankind, and more particularly in those happy climates, where the serenity of the air invited them to observe the stars. Agriculture required that the seasons should be distinguished and their returns known. It could not be long before it was discovered that the rising and setting of the stars, when they plunge themselves in the Sun's rays, or when they again disengage themselves from his light, might answer this purpose. Hence we find that among most nations, this species of observations may be traced back to such early times, till their origin is lost. But

some rude remarks on the rising and setting of the stars, could not constitute a science. Astronomy did not commence till observations being registered and compared, and the celestial motions examined with greater care, some attempt was made to explain their motions and their laws.

The motion of the Sun in an orbit inclined to the equator; the motion of the Moon, its phases and eclipses, the knowledge of the planets and their revolutions, and the sphericity of the Earth, were probably the objects of this ancient astronomy, but the few monuments that remain of it are insufficient to ascertain either its epoch or its extent. We can only judge of its great antiquity, by the astronomical periods which it has transmitted to us, by some just notions which the Egyptians and Chaldeans seem to have had of the system of the world, and by the exact relation of the ancient measures to the circumference of the Earth, Such has been the vicissitude of human affairs, that the

arts by which alone the events of past ages can be transmitted in a durable manner, being of modern invention, the remembrance of the first inventors in the arts and sciences, has been entirely effaced. Great nations, whose names are hardly known in history, have disappeared from the soil which they inhabited; their annals, their language, and even their cities have been obliterated, and no remnant left of their science or their industry, but a confused tradition, and some scattered ruins, of doubtful and uncertain origin.

It appears that the practical astronomy of these early ages, was confined to the observations of eclipses, the rising and setting of the principal stars, with their Occultations by the Moon and planets. The path of the Sun was followed by means of the stars which were eclipsed by the twilights, and perhaps by the variations in the meridian shadow of the gnomon. The motion of the planets was determined by the stars which they came nearest to, in their course. To distinguish

these bodies, and recognize their various motions, the heaven was divided into constellations. And that zone from which the Sun, Moon and planets were never seen to deviate, was called the zodiac. It was divided into the twelve following constellations. Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus and Pisces. These were called signs, because they served to distinguish the seasons. Thus the entrance of the Sun into Aries, in the time of Hipparchus, marked the commencement of the spring, after which it described the other signs Taurus, Gemini, &c. but the retrograde motion of the equinoxes, changed the coincidence of the seasons; nevertheless, observers accustomed to mark the commencement of the spring. by the entrance of the Sun into the sign of Aries, have continued to mark this in the same manner, and have distinguished the signs of the zodiac from the constella tions, the first being ideal, and serving only to designate the course of the Sun in the ecliptic. Now that we endeavour to refer

our ideas to the most simple expressions, we begin no longer to use the signs of the zodiac, but mark the positions of the hea venly bodies on the ecliptic, according to their distance from the equinoctial point.

Some of the names given to the constellations of the zodiac, appear to relate to the motion of the Sun. Cancer, for example, seems to indicate the retrogradation of this body from the solstice, and the balance denotes the equality of day and night. And other names seem to refer to the climate and agriculture of those nations to whom the zodiac owes its origin. The most ancient observations that have been transmitted to us with sufficient detail, are three eclipses of the Moon, observed at Babylon in the years 119 and 720 before the Christian ærá. Ptolemy, who cites them in his Almagist, employs them in his determination of the motion of the Moon. It is certain, that neither he nor Hipparchus could obtain any that were more ancient, for the exactness of the comparison is in proportion to the