82 SCIENCE IN GRECO-ROMAN ANTIQUITY 



since the Homeric age displays true historical per- 

 ception, especially in comparison with the fantastic 

 descriptions given at the same period by certain com- 

 mentators on Homer. After having calculated mathe- 

 matically the habitable regions (78,000 stadia by 

 38,000), Eratosthenes divides them by parallels to the 

 equator and meridians into unequal rectangles. The 

 parallel which passes through Gibraltar and Rhodes is 

 in the middle and separates the northern parallels 

 (Byzantium, Borysthenes or Dnieper, Thule) from the 

 southern (Alexandria, Syene, and Meroe). The 

 extreme meridians are formed by the Pillars of 

 Hercules (Gibraltar) and the Ganges. 1 Eratosthenes 

 also measured the length of the circumference of the 

 earth by a method as ingenious as accurate. He 

 observed that at Alexandria at noon, at the time of 

 the summer solstice, the distance of the sun from the 

 zenith is one-fiftieth of the circumference of the heavens, 

 whilst at Syene at the same moment the sun is at the 

 zenith, since it lights up perpendicularly the bottom 

 of the wells. These two towns, situated on the same 

 meridian, are 5,000 stadia apart. Therefore, by 

 multiplying 5,000 by 50, the required measurement is 

 found, namely, 250,000 stadia, which is equal to about 

 44,000,000 metres, the stadium being equal to 177*4 

 metres (Cleomedes, de Motu circulari, p. 96, 21) . (Fig. 8.) 

 Although the method used is correct, the result 

 obtained is not accurate. Firstly, Syene and Alexan- 

 dria are not on the same meridian: between these two 

 towns there is a difference of longitude of 3 . 2 Further, 



1 G. Lespagnol, Geographic gindrale, Delagrave, Paris, 

 p. 83. For the authenticity and interpretation of the frag- 

 ments of Erastosthenes, see A. Thalamas, Etude bibliographique 

 de la geographie d'Eratosthene, Riviere, Paris, 1921 ; La geo- 

 graphie d'Eratosthene, Riviere, Paris, 192 1. 



2 " Astronomie, " Kultur der Gegenwart, Teubner, Leipzig, 

 1921, p. 187. 



