Sosigenes

, an Egyptian mathematician, whose principal studies were chronology and the mathematics in general, and who flourished in the time of Julius Cxsar, is represented as well versed in the mathematics and astronomy of the ancients; particularly of those celebrated mathematicians, Thales, Archimedes, Hipparchus, Calippus, and many others, who had undertaken to determine the quantity of the solar year; which they had ascertained much nearer the truth than one can well imagine they could, with instruments so very imperfect; as may appear by reference to Ptolomy’s Almagest. It seems Sosigenes made great improvements, and gave proofs of his being able to demonstrate the certainty of his discoveries; by which means he became popular, and obtained repute with those who had a genius to understand and relish such inquiries. Hence he was sent for by Julius Caesar, who being convinced of his capacity, employed him in reforming the calendar; and it was he who formed the Julian year, which begins 45 years before the birth of Christ. His other works are lost since that period. ²