HIPPARCHUS

, a celebrated astronomer among the ancients, was born at Nice in Bithynia, and flourished between the 154th and the 163d olympiads; that is, between 160 and 135 years before Christ; for in this space of time it is that his observations are dated. He is accounted the first, who from vague and scattered observations, reduced astronomy into a science, and prosecuted the study of it systematically. Pliny often mentions him, and always with great commendation. He was the first, he tells us, who attempted to count the number of the fixed stars; and his catalogue is preserved in Ptolomy's Almagest, where they are all noted according to their longitudes and apparent magnitudes. Pliny places him among those men of a sublime gen<*>us, who, by foretelling the eclipses, taught mankind, that they ought not to be frightened at these phenomena. Thales was the first among the Greeks, who could discover when there was to be an eclipse. Sulpitius Gallus among the Romans began to succeed in this kind of prediction; and he gave an essay of his skill very seasonably, the day before a battle was fought. After these two, Hipparchus improved that science very much; making ephemerides, or catalogues of eclipses, for 600 years. He admires him for making a review of all the stars, acquainting us with their situations and magnitudes; for by these means, says he, posterity will be able to discover, not only whether they are born and die, but also whether they change their places, and whether they increase or decrease. He mentioned a new star which was produced in his days; and by its motion, at its first appearance, he began to doubt whether this did not frequently happen, and whether those stars, which we call fixed, do not likewise move. Hipparchus is also memorable for being the first who discovered the precession of the equinoxes, or a very slow apparent motion of the fixed stars from east to west, by which in a great number of years they will seem to have performed a complete revolution. He endeavoured also to reduce to rule the many discoveries he made, and invented new instruments, by which he marked their magnitudes and places in the heavens; so that by means of them it might be easily observed, not only whether they appear and disappear, but likewise whether they pass by one another, or move, and whether they increase or decrease.

The first observations he made, were in the isle of| Rhodes; whence he got the name Rhodius; but afterwards he cultivated this science in Bithynia and Alexandria only. One of his works is still extant, viz, his Commentary upon Aratus's Phenomena. He composed several other works; and upon the whole it is agreed, that astronomy is greatly indebted to him, for laying that rational and solid foundation, upon which all succeeding astronomers have since built their superstructure.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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HEXACHORD
HEXAEDRON
HEXAGON
HEXASTYLE
HIPS
* HIPPARCHUS
HIRCUS
HIRE (Philip de la)
HOBBES (Thomas)
HOBITS
HOGSHEAD