ERATOS"THENES, an eminent Greek writer, called, on account of his varied erudi tion, thephilo.7o,gist, was b. at Cyrene 278 R. c. Among his teachers were Lysanias the gram marian, and Callimachus the poet. By Ptolemy Euergetes, lie was called to Alexandria to superintend his great library. Here he died of voluntary starvation, at the age of 80, having become blind, and wearied of life. As an astronomer, E. holds an eminent rank :among ancient astronomers. He measured the obliquity of the ecliptic, and the result at which he arrived—viz., that it was 23° 51' 20"—must be reckoned a very fair obser vation, considering the age in which he lived. Hipparchus used it, and so did the cele brated astronomer Ptolemy. An astronomical work which goes under the name of E., but which is certainly not his, is still extant, and is called Katastorismoi; it contains an account of the constellations, their fabulous history, and the stars in them. It is believed, however, that E. did draw up a catalogue of the fixed stars, amounting to 675; but it is lost. A letter to Ptolemy, king of Egypt, on the duplication of the cube, is the only complete writing of his that we possess. E.'s greatest claim to distinction,
however, is as a geometer. In his attempt to measure the magnitude of the earth, he introduced the method which is used at the present day, and found the circumference of the earth to be 252,000 stadia; which, according to Pliny, is 31,500 Roman miles. But as it is not known what stadium E. used, it is possible that he came nearer the actual circumference than the above figures indicate. His work on geography must have been of great value in his times: it was the first truly scientific treatise on the subject. E. worked up into an organic whole the scattered information regarding places and coun tries related in the books of travels, etc., contained in the Alexandrian library. He also wrote on moral philosophy, history, grammar, etc. His work on the Old Attie Comedy appears, from the remains we possess, to have been a learned and very judicious per formance. Such fragments of E.'s writings as are still extant have been collected by Bernhardy in his Eratosthenica (Berlin, 1822).