PRELUDE TO THE EPOCH OF NEWTON. 149 



or their deflection by the Second Law ; the two 

 main steps on the road to the discovery of the 

 true forces by which they are made to describe their 

 orbits. 



(Leibnitz, &p.) Nor does it appear that in Ger- 

 many mathematicians had attained this point of 

 view. Leibnitz, as we have seen, did not assent to 

 the opinions of Descartes, as containing the complete 

 truth ; and yet his own views of the physics of the 

 universe do not seem to have any great advantage 

 over these. In 1671 he published A new physical 

 hypothesis, by which the causes of most phenomena 

 are deduced from a certain single universal motion 

 supposed in our globe ; not to be despised either 

 by the Tychonians or the Copernicans. He supposes 

 the particles of the earth to have separate motions, 

 which produce collisions, and thus propagate 15 an 

 " agitation of the ether," radiating in all directions ; 

 and 16 , "by the rotation of the sun on its axis, concur- 

 ring with its rectilinear action on the earth, arises 

 the motion of the earth about the sun." The other 

 motions of the solar system are, as we might expect, 

 accounted for in a similar manner ; but it appears 

 difficult to invest such a hypothesis with any me- 

 chanical consistency. 



John Bernoulli maintained to the last the Carte- 

 sian hypothesis, though with several modifications of 

 his own, and even pretended to apply mathematical 

 calculation to his principles. This, however, belongs 



15 Art. 5. l6 Ib. 8. 



