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THE

GALLERY

OF

NATURE AND ART.

PART I.

NATURE.

BOOK I.

ASTRONOMY.

CHAPTER I.

ASTRONOMY OF THE ANCIENTS BEFORE THE FOUN DATION OF THE ALEXANDRIAN SCHOOL.

A CONTEMPLATION * of the Heavens must at all times have fixed the attention of mankind; and especially in those happy climates where the serenity of the atmosphere invited them to ob. serve 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

* This chapter, extracted from La Place, is given as nearly as may be from the translation of our own Astronomer Royal; but the numerous and unac◄ countable errors of this translation have compelled us to a perpetual collation with the original, and to alterations in every page.-Editor.

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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; a knowledge of the planets and their revolutions, and of the sphericity of the earth, were probably the objects of this ancient astronomy, but the few monuments of it that remain 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 that of the arts which could alone transmit the events of past ages in a durable manner, being of modern invention, the remembrance of the first inventors 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 nothing is 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 meridiau 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 en

trance 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 motions 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 Aries, have continued to characterise this season in the same manner, and have distinguished the signs of the zodiac from the constellations, the first being ideal, and serving only to designate the course of the sun in the ecliptic. Now, however, 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 heavenly 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 Libra, or 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 719 and 720 before the Christian æra. Ptolemy, who cites them in his Almagest, 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 interval which separates the extreme observations. This consideration should diminish our regret for the loss of nineteen hundred years of observations by the Chaldeans, and of which they boasted in the time of Alexander, and which Aristotle obtained by means of Calysthenes. But they could only have discovered the period of 6,585 days, by a long series of observations. This period, called the saros, has the advantage of bringing back the moon to nearly the same period, with respect to its node, its perigee, and to the sun. Thus, the eclipses observed in one period, afford an easy method of calculating those which are to happen in the succeeding ones. The lunar-solar period of six hundred years, seems to have been known to the Chaldeans. These two periods suppose a knowledge nearly approximating to the true length of the year; it is also highly probable, that they

had remarked the difference between the sidereal and tropical year, and that they were acquainted with the use of the gnomon and surdial. And finally, some of them were led from considering the spectacle of nature, to suppose that comets, like planets, are subject to fixed periods, which are regulated by external laws.

Astronomy is not less ancient in Egypt than in Chaldea, The Egyptians were acquainted, long before the christian æra, with the excess of the year, of one quarter of a day beyond 365 days: on this knowledge, they formed the sothic period of 1460 years, which, according to them, brought back the same seasons, months, and festivals of their years, whose length was 365 days. The exact direction of the sides of their pyramids with the four cardinal points, give us a very advantageous idea of their accuracy of observation. It is probable that they had also methods of calculating eclipses. But that which reflects most honour to their astronomy, was the sagacious and important observation of the motion of Mercury and Venus about the sun. The reputation of their priests attracted to them the greatest philosophers of Greece; and, according to all appearance, the school of Pythagoras is indebted to them for the sound notions they professed relative to the system of the universe.

Among these people, astronomy was only cultivated in their temples, and by priests, who made no other use of their knowledge than to consolidate the empire of superstition, of which they were the ministers. They carefully disguised it under emblems, which presented to credulous ignorance, heroes and gods, whose actions were only allegories of celestial phenomena, and of the operations of nature; allegories which the power of imitation, one of the chief springs of the moral world, has perpetuated to our own days, and been mingled with our religious institutions. The better to enslave the people, they profited by their natural desire of penetrating into futurity, and created astrology. Man being induced, by the illusions of his senses, to consider himself as the centre of the universe, it was easy to persuade him, that the stars influenced the events of his life, and could prognosticate to him his future destiny. This error, dear to his self-love, and necessary to his restless curiosity, seems to have been co-eval with astronomy. It has maintained itself through a very long period, and it is only since the end of the last century, that our knowledge of our true relations with nature, has caused them to disappear. In Persia and in India, the commencement of

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