12 CROONIAN LECTURES 



says the vehicle of that virtue which urges the 

 planets, circulates through the spaces of the 

 universe after the manner of a river or whirl- 

 pool (vortex), moving quicker than the planets. 

 He asserted these vortices to be an " immaterial 

 species," capable, however, of overcoming the 

 inertia of bodies. 



Thence came the vortices of Descartes, by 

 which he showed how the world must have 

 been constructed, and thence the agitation of 

 the sether of Leibnitz. 



And then follows Newton, who may rightly 

 give his name to this stage of our ideas on 

 matter and force; for Newtonian ideas on 

 matter and force have continued in consequence 

 of his authority down to the present time. 

 Even with regard to gravity, Newton refused 

 to entertain the third stage of ideas. In his 

 second letter to Bentley, 1693, he says : " You 

 sometimes speak of gravity as essential and 

 adherent to matter. Pray do not ascribe that 

 notion to me. The cause of gravity I do not 

 pretend to know, and would take more time to 

 consider of it." 



He seems to have been disposed to refer the 

 tendency of bodies to a centre to the elasticity 



