$$ i6 2 , 163] The Velocity of Ligfit : Descartes 209 



general statement of the first law of motion discovered 

 by Galilei (chapter vi., 130, 133), but did not support it 

 by any evidence of value. The same book contained an 

 exposition of his famous theory of vortices, which was an 

 attempt to explain the motions of the bodies of the solar 

 system by means of a certain combination of vortices or 

 eddies. The theory was unsupported by any experimental 

 evidence, and it was not formulated accurately enough to 

 be capable of being readily tested by comparison with 

 actual observation; and, unlike many erroneous theories 

 (such as the Greek epicycles), it in no way led up to 

 or suggested the truer theories which followed it. But 

 " Cartesianism," both in philosophy and in natural science, 

 became extremely popular, especially in France, and its 

 vogue contributed notably to the overthrow of the authority 

 of Aristotle, already shaken by thinkers like Galilei and 

 Bacon, and thus rendered men's minds a little more ready 

 to receive new ideas : in this indirect way, as well as by 

 his mathematical discoveries, Descartes probably con- 

 tributed something to astronomical progress. 



