THE PATH OF EVOLUTION 



distance." The originality of the conception of these 

 relations is not Newton's. Islmiael Bouillau (1605- 

 1694) from metaphysical considerations maintained 

 that the action of the sun upon the planets decreases as 

 the square of the distance ; not as Kepler had asserted 

 in the direct ratio of the distance. Jean Alphonse 

 Borelli (1608-1679) explained clearly in his book 

 on the Satellites of Jupiter (1666) how the planets 

 were held in space around the sun by a power that 

 was exactly balanced by the centrifugal force due to 

 their revolution ; and therefore there was no need of 

 the solid skies of Aristotle or the Vortices of Des- 

 cartes to prevent their flying off. 



Robert Hooke (1635-1703), who spent a large 

 portion of his life in disputing the priority of his 

 theories and discoveries with his rivals, who likewise 

 claimed them, published in 1674 an essay upon 



1st. The reciprocal attraction of the sun and all the 

 planets upon each other. 



2d. The supposition that the heavenly bodies 

 when once in motion would persist in motion in a 

 straight line until some other force would bend or 

 deflect their course into a circle, ellipse or other 

 composite curve. 



3d. That the attractive powers exercise more 

 energy in proportion as the bodies upon which they 

 act approach the centre from which they emanate. 



112 



