46 THE PRINCIPLES OF SCIENCE. 



million times greater than that of light ; but it does not 

 really follow that it is instantaneous ; and were there any 

 means of detecting the action of one star upon another 

 exceedingly distant star, we might possibly find an ap- 

 preciable interval occupied in the transmission of the 

 gravitating impulse. Newton could not demonstrate the 

 absence of all resistance to matter moving through 

 space, or the adamantine basis of light ; but he ascer- 

 tained by one of the most beautiful experiments with the 

 pendulum, elsewhere more fully described (vol. ii. p. 55), 

 that if such resistance existed, it was in amount less 

 than one five-thousandth part of the external resistance 

 of the air P. 



Innumerable incidents in the history of science tend to 

 show that phenomena, which one generation has failed 

 to detect, may become accurately known to a succeeding 

 generation. The compressibility of water which the Aca- 

 demicians of Florence could not prove, because at a low 

 pressure the effect was too small to perceive, and at a 

 high pressure the water oozed through their silver vessels, 

 has now become the subject of exact measurements and 

 precise calculation. Independently of Newton, Hooke 

 entertained very remarkable notions concerning the nature 

 of gravitation. In this and other subjects he showed, in- 

 deed, a genius for experimental investigation which would 

 have placed him in the first rank in any other age than 

 that of Newton. He correctly conceived that the force of 

 gravity would decrease as we receded from the centre of 

 the earth, and he boldly attempted to prove it by experi- 

 ment. Having exactly counterpoised two weights in the 

 scales of a balance, or rather one weight against another 

 weight and a long piece of fine cord, he removed his 



Laplace, 'System of the World/ transl. by Harte, vol. ii. p. 322. 



P Trincipia/ bk. II. sec. 6, Prop. xxxi. Motte's translation, vol. ii. p. 108. 



1 ' Essaycs of Natural Experiments/ &c. p. 117. 



