HIPPARCHUS, hip-pliektis (Let., from Gk. "Irrapxos) (11. between 'Lc. 161 and 126). A Greek astronomer and mathematician. Ile was born in Nictea. Bithynia, but his astronomical work was clone on the island of Rhodes. and pos sibly also in Alexandria. Of his personal history nothing is known. lie was the founder of gen uinely scientific astronomy, and also of a part of that science which lies on the border-land of astronomy and geometry, viz. trigonometry. in this field he computed a table of chords. which. although lost, is known to us through the works of Theon of Alexandria (q.v.). who wrote about A.n. 365. it is probable, too, that this is the Hipparchus who wrote on combinatory analysis, and that the Arabs were correct in attributing to him a knowledge of the quadratic equation. Cer tain it is that Ptolemy was indebted to him for much of the Almagest (q.v.). According to Pa brieins, Hipparchus wrote nine separate works; but of these only the Commentary on stratus lies come down to us. From the Almagest we learn
that it was Hipparchus who first discovered the precession of the equinoxes, determined the place of the equinox among the stars, invented solar and lunar theories, invented the astrolabe (q.v.), and drew up a catalogue of upward of 1000 stars, determining the longitude and latitude of each (this catalogue has been preserved in the Alma gest). A.' Ptolemy was also an astronomer, there is some ditliculty in allotting to each his treed of praise for the discoveries mentioned in the Almagest, which difficulty has given rise to some discussion. Consult: Delambre. Histoire de l'astronomie aneienne (Paris, 1817) ; Berger, Die geographischen Fragmente des II ipparch (Leipzig. 1870) ; Wolf, Geschiehte der Astrono mic (Munich, 1877).