THE HELLENIC PERIOD 29 



and reached his " acme " * before 494 B.C., the year when 

 Miletus was conquered. He produced a work, which 

 has actually survived till the age of literary criticism. 2 

 His ideas are less daring but perhaps more thought out 

 than those of his predecessor. For him, the air was the 

 primitive boundless matter, which by condensation 

 gave birth to earth and water, and by rarefaction to 

 fire. It must not be forgotten that for the first 

 cosmologists the air was always a form of vapour, 

 darkness being another form. It was Empedocles who 

 first discovered that the air is a distinct body, differing 

 from vapour, and from empty space. It was he also 

 who showed that darkness is a shadow. Anaximenes 

 introduced several interesting theories on astronomical 

 matters, thus justifying the esteem in which he was held 

 by the Ancients. He considered the celestial vault, to 

 which the stars are fixed, as solid and turning round the 

 earth. In the interior of this vault float the sun, moon 

 and planets, upheld by the surrounding air. In this 

 way, the planets are distinguished from the stars for 

 the first time in Greek astronomy. Anaximenes also 

 supposed that dark solid bodies wander under the celes- 

 tial vault . ' ' The heavenly bodies proceed from the earth 

 whose moisture has evaporated and, by its expansion, 

 has formed fire ; the latter rises and forms the heavenly 

 bodies. In the region occupied by these, there are also 

 bodies of a terrestrial nature, carried likewise by the 

 movement of revolution " (Hippolytus : Diels, Dox, 561, 

 4) . This was a fruitful conception, for it was bound to 

 lead to the true explanation of eclipses. Indeed there 

 was but one step needed to arrive at the supposition that 

 the moon is one of these dark bodies, illuminated wholly 

 or partly by the sun, according to its position, and 

 capable of being eclipsed by the shadow of the earth. 3 



1 Epoch of full intellectual maturity ; about the age of 40. 



2 8 Burnet, Aurore, p. 77. 



3 25 Tannery, Science helUne, p. 152. 



