A Greek Astronomer Eratosthenes, geometer, geographer, poet, and philosopher, born in Cyrene about 276 B. C, died about 196. He was variously named by his contemporaries the "cosmographer," the "measurer of the universe," the "second Plato," and the "pen-tathlete" or victor in five contests. He had for masters Ariston the philosopher, Lysanias the grammarian, and Callimachus the poet, and he completed his education in Athens. Ptolemy III. invited him to Alexandria and intrusted to his care the renowned library of that city. He is said to have died of voluntary starvation, to which he was led by regret for the loss of his sight. His most important work, the treated of the nature and form of the earth, which he supposed to be a motionless globe, of its magnitude, and of its countries, towns, lakes, rivers, and mountains. He was the founder of geodesy, and was the first to compute the magnitude of the earth by the astronomical method still in use. He is supposed to have suggested the construction of the large armilloe, or fixed circular instruments, which were long in use in Alexandria. He devised a method for discovering the prime numbers, and resolved the problem of the duplication of the cube. Among his works was one of universal chronology, the fragments of which form the basis of the system adopted by Bunsen in his work on Egypt. He also wrote verses on numerous scientific subjects, a commentary on the astronomical poem of Aratus, and treatises on comedy and on the Homeric poems. A number of other works are attributed to him upon doubtful grounds. Only a few brief fragments of his writings remain; but Strabo and other later writers made great use of his geographical works.