THE PATH OF EVOLUTION 



optics was then too limited to permit his studies 

 therein to be of much value now. He added to 

 what was then known, his discoveries as to the true 

 laws of refraction. He pointed out the fact that the 

 only rays that enter the eye of an observer from the 

 rainbow are those which, penetrating the raindrop 

 under a certain angle, are so reflected within it as to 

 become visible to the spectator. His "Theory of 

 Vortices," published in 1644 in the Philosophia 

 Priucipia, attracted the attention of the world. 

 According to it the sun and each of the fixed stars are 

 the centre of a whirlwind (Tourbillon) or Vortex of 

 finely divided matter, which causes the circulation of 

 matter still more subtile around these centres. In 

 the seventeenth century it was, wise to preserve the 

 orthodox immobility of the earth, in order to avoid 

 persecution ; therefore the vortex embraced the sun, 

 and the planets circulated around our earth. The 

 subtile matter of this first vortex constituted Des- 

 cartes' first dement, He imagined a second element 

 like the first, but in which the molecules were round ; 

 finally, a third element, formed of molecules furrowed 

 with canals, through which molecules of the other 

 two elements could circulate in all directions! If 

 Descartes in his theory of vortices had had the key to 

 the system of the world, he would not have failed to 

 prove it by calculations, as Newton did with his 



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