24 SCIENCE IN GRECO-ROMAN ANTIQUITY 



This being so, the universe is a great liquid mass, 

 which encloses a large hemispherical bubble of air 

 (Fig. 4). The concave surface of the bubble forms the 

 sky, while on the plane surface, the earth, which is 

 cylindrical, floats like a cork. The stars are boats 

 steered by divinities ; the interior of these boats is 

 luminous, but not the exterior, so that, when the stars 

 float on the diametral surface of the bubble, they are 

 invisible. The eclipses are produced every time the 

 boats of the Sun or Moon tend to overturn. 



Fig. 4; 



According to P. Tannery, this conception is funda- 

 mentally of Egyptian origin, but to Thales belongs the 

 merit of having rationalized it by interpreting it 

 according to a rudimentary natural philosophy. Thus, 

 from the beginning, Greek thought asserted at the same 

 time its dependence and its independence with regard 

 to the East. 



In another realm of knowledge it appears that Thales 

 also imported into Ionia the methods of surveying in 

 use in Egypt. Was he, however, the founder of rational 

 geometry ? It is difficult to say, although it is true 



