It is not, then, surprising that the two great theoretical geographers next to be considered are not associated with the capital of the Roman Empire. Of the work of Marinus of Tyre nothing is known beyond what is recorded by his immediate successor, Ptolemy, who used and acknowledged his results--as far as concerned the Mediterranean fully, and in respect of other countries to a modified extent. Ptolemy, mathematician, astronomer, and geographer, was a native of Egypt, who worked at or in the neighbourhood of Alexandria in the second century. His geographical book was called _Geographike Syntaxis_. He carried mathematical geography far beyond the standard of his predecessors. He used the theoretical division of the globe into five zones by the equator and the tropics, adopted Hipparchus’s division of the equator into 360 degrees, and worked out a network of parallels of latitude and meridians of longitude, first thus applying these terms in their technical sense. In mapping the habitable world he used the Fortunate Isles, beyond the western confines of Europe and Africa, as the location of his prime meridian. The errors which resulted from the vague idea as to the position of these islands (the Canaries and Madeira), and from the fact that Ptolemy followed Posidonius’s underestimate of the circumference of the globe and made his degree at the equator equal to 500 instead of 600 stadia,[2] have been very fully analysed, but cannot be even summarized here. [2] Fifty instead of sixty geographical miles. [Illustration: PTOLEMÆUS ROMÆ 1490. Fig. 4.--The World according to Ptolemy.] [Illustration: Fig. 4. (left side)] [Illustration: Fig. 4. (right side)]