 Complete the following phrase:  The third head librarian, Eratosthenes of Cyrene lived 280 194 BC, is best known today for his scientific works, but he was also a literary scholar. Eratostheness most important work was his treatise Geographika, which was originally in three volumes. The work itself has not survived, but many fragments of it are preserved through quotation in the writings of the later geographer Strabo. Eratosthenes was the first scholar to apply mathematics to geography and map-making and, in his treatise Concerning the Measurement of the Earth, he calculated the circumference of the earth and was only off by less than a few hundred kilometers. Eratosthenes also produced a map of the entire known world, which incorporated information taken from sources held in the Library, including accounts of 