i CHAP. V. NATURAL PHILOSOPHY, Continued. ASTRONOMY, sketch of the history of-appearances of the heavenly bodies-division of the fixed stars-constellations-Speculations of Dr. Herschel - Solar System-Sun - Planets: Mercury-Venus- The Earth-Mars-Ceres-Pallas-Juno-Vesta-Jupiter-Saturn-Geor gium Sidus-Satellites-Moon. MOST authors fix the origin of Astronomy, either to Chaldea or Egypt. The Chaldeans boasted of their temple or tower of Belus, and of Zoroaster, whom they placed 5000 years before the destruction of Troy; and the Egyptians speak of their colleges, in which astronomy was taught, and of the monument of Oxymandyas, in which it is said there was a golden circle of 365 cubits in circumference, divided into 365 parts, corresponding to the number of days in the year. There are, on the page of history, unquestionable facts, which prove that both the Chaldeans and Egyptians were acquainted with many of the principles of Astronomical science, at a very early period. From Chaldea and Egypt, this science passed into Phoenicia, the inhabitants of which country, applied it to the purposes of navigation, steering their course by the north-polar star; and hence they became masters of the sea, and of almost all the commerce of the world. The Greeks, it is probable, derived their astronomical knowledge chiefly from the Egyptians and Phoenicians, by means of several of their countrymen who visited these nations for the purpose of learning the different sciences. Sir Isaac Newton supposes, that most of the constellations were invented about the time of the Argonautic expedition, though other writers imagine they can trace this species of knowledge to a much earlier period. Several of the constellations are mentioned by Hesiod and Homer, the two most ancient of the Greek writers, who flourished about nine centuries before the birth of Christ. Their knowledge was greatly improved by Thales, who flourished three hundred years later: this philosopher was followed by Anaximander, Anaxagoras, and especially Pythagoras, who lived five centuries and a half before the Christian æra, and taught the true system of the world, as it has been demonstrated by Copernicus and Newton in later times. Eratosthenes, about two hundred and fifty years before the birth of Christ, measured the earth by means of a gnomon: he also determined the distance between the tropics, and made the obliquity of the ecliptic to be 23° 51′. Archimedes likewise was a great cultivator of astronomy, as well as of geometry and mechanics: he determined the distances of the planets, and is said to have constructed a sort of planetarium, which represented the phenomena and motions of the heavenly bodies. Hipparchus, who flourished a century later than Eratosthenes, was the first person who applied himself to every part of Astronomy: he discovered that the orbits of the planets are not circular, but elliptic, that the moon moved slower in one part of her orbit than in another, and many other facts, of which his predecessors had no idea. But the chief work of this philosopher is his catalogue of fixed stars, to the number of more than a thousand, with their longitudes, 1 latitudes, and apparent magnitudes. From Hipparchus to Ptolemy, who flourished in the first century of the Christian æra, little or no progress is to be traced in the history of astronomy. Ptolemy made a system of his own, which, though proved in after-times to be completely erroneous, was implicitly followed for many ages by all nations. He compiled a great work entitled the Almagest, which contained the observations and collections of Hipparchus and his other predecessors in astronomy; on which account it has always been in the highest estimation with the professors of that science. This work most fortunately escaped the horrible conflagration of the Alexandrian library, was translated out of Greek into Arabic in the year 827, and from that language into the Latin in 1250. Considerable improvements were made in astronomy by the Arabians; among whom may be mentioned Arzachel, a Moor of Spain, who observed the obliquity of the ecliptic, and greatly improved Trigonometry; and Alhazen, his contemporary, who wrote upon the twilight, the phenomenon of the horizontal moon, and who first demonstrated the importance of the theory of Refractions in astronomy. By the settlement of the Moors in Spain, the sciences in general were introduced into Europe; from which period they have continued to improve, and to be communicated from one people to another, to the present time, when astronomy and all the sciences have arrived at a very eminent degree of perfection. In this outline, the names of very few of the promoters of astronomy can be mentioned in the selection, Nicolaus Copernicus must not be omitted. Early in the sixteenth century he conceived doubts respecting the Ptolemaic system, that made the earth a centre, round which the sun and planets revolved; and suspected that the sun himself must be the central body, which gave motion, as well as light and heat, to the planets. To confirm his theory, he made the most diligent observations, formed new tables, and at length, in 1580, completed a work containing these observations, and a renovation of the true : system of the universe, in which the planets are proved to be bodies revolving about the sun. This was the system of Pythagoras of old. Tycho Brahè, a noble Dane, attempted to improve upon the Copernican system; but his account of the planetary motions was involved, and very shortly fell to the ground. The labours of Tycho were, however, very important to the science of astronomy, although his system was the work of a fertile imagination only. He observed the great conjunction of Jupiter and Saturn, and he constructed, or caused to be constructed many much improved astronomical instruments. He discovered, in 1571, a new star in the chair of Cassiopeia; which induced him, like Hipparchus on a similar occasion, to make a catalogue of stars. Kepler was the next great improver of the astronomical science: he discovered several of the true laws of nature, by which the motions of the heavenly bodies are regulated. He ascertained, to a certainty, that all the planets revolve about the sun, not in circular, but in elliptical orbits, having the sun in one of the foci of the ellipses :that their motions are not equable, but varying quicker or slower, as they are nearer to, or farther from the sun :-that the arcas, described by an imaginary line drawn from the sun to the planets, are equal, in equal times, and of course proportional to the times of describing them. He also discovered by trials, that the cubes of the mean distances of the planets from the sun, are in the same proportion as the squares of the periodical times in which they revolve about the sun. e The beginning of the seventeenth century was distinguished by the invention of telescopes, and the application of them to astronomical observations. The more distinguished early observations with the telescope were made by Galileo, Huygens, and Cassini. Galileo is said to have manufactured with his own hands the telescopes with which were discovered the inequalities of the moon's surface, Jupiter's satellites, the ring of Saturn, and the spots on the surface of the sun, by means of which he discovered the revolution of that luminary round its axis. Hevelius furnished à catalogue of fixed stars more complete than that of Tycho. Huygens and Cassini discovered the satellites of Saturn, and his ring. The illustrious Newton first demonstrated from physical considerations, the laws by which the motions of the heavenly bodies are regulated. He taught upon mathematical principles, whence arose that constant and regular proportion observed both by the primary and secondary planets, in their revolutions about their central bodies. Mr. Flamsteed was appointed the first astronomer royal at Greenwich, in 1675. He kept an almost perpetual watch, for the space of forty-four years, on all the celestial phenomena, viz. on the sun, the planets, the moon, and fixed stars, of all which he gave improved theories and tables, and he formed a catalogue of three thousand stars, with their places, to the year 1689. In 1719, Mr. Flamsteed was succeeded by Dr. Halley, who gave the world the astronomy of comets, and a catalogue of stars in the southern hemisphere. On the death of Halley, in 1742, he was succeeded by Bradley, as astronomer royal, who, to the other benefits which he conferred on science, discovered the aberration of light, and the nutation of the earth's axis. This astronomer was succeeded, in 1762, by Mr. Bliss, who did not retain the office many years, and was followed by Dr. Maskelyne, who had, in the year 1761, been sent by the Royal Society at a very early age, to the island of St. Helena, to observe the transit of Venus over the sun, and the parallax of the star Sirius. The labours of Dr. Maskelyne through a long course of years, are highly estimated by all those who are capable of appreciating his merit. The discoveries of Herschel, Piazzi, Harding, and Olbers, form a new era in astronomy. The former of these gentlemen, by his great skill in the construction of large specula, has made telescopes which have opened new views of the heavens, and unfolded scenes, which cannot fail to excite our wonder, admiration, and reverence of the Creator. In March, 1781, he discovered a new primary planet, named by himself, in honour of |