A HISTORY OF SCIENCE 



since the stars seem obviously brighter on dark nights, 

 Anaxagoras was but following up a perfectly logical 

 induction when he propounded the theory that the 

 stars in the Milky Way seem more numerous and 

 brighter than those of any other part of the heavens, 

 merely because the Milky Way marks the shadow of 

 the earth. Of course the inference was wrong, so far 

 as the shadow of the earth is concerned ; yet it contained 

 a part truth, the force of which was never fully recog- 

 nized until the time of Galileo. This consists in the 

 assertion that the brightness of the Milky Way is 

 merely due to the glow of many stars. The shadow- 

 theory of Anaxagoras would naturally cease to have 

 validity so soon as the sphericity of the earth was 

 proved, and with it, seemingly, fell for the time the 

 companion theory that the Milky Way is made up of 

 a multitude of stars. 



It has been said by a modern critic * that the 

 shadow-theory was childish in that it failed to note 

 that the Milky Way does not follow the course of the 

 ecliptic. But this criticism only holds good so long 

 as we reflect on the true character of the earth as a 

 symmetrical body poised in space. It is quite pos- 

 sible to conceive a body occupying the position of the 

 earth with reference to the sun which would cast a 

 shadow having such a tenuous form as the Milky Way 

 presents. Such a body obviously would not be a 

 globe, but a long-drawn-out, attenuated figure. There 

 is, to be sure, no direct evidence preserved to show that 

 Anaxagoras conceived the world to present such a 

 figure as this, but what we know of that philosopher's 

 close-reasoning, logical mind gives some warrant to 



