Xrx EXPEEIMENT. 



435 



of an air-pump, as did Du Sejour. It is equally impossi- 

 ble to prove that gravity occupies no time in transmission 

 Laplace indeed, ascertained that the velocity of propagation 

 of the influence was at least fifty milUon times greate? than 

 that of lights but it does not really follow that it is in- 

 stantaneous; and were there any means of detecting the 

 action of one star upon another exceedingly distant star 

 we might possibly find an appreciable interVal occupied in 

 the transmission of the gravitating impulse. Newton 

 could not demonstrate the absence of all resistance to 

 matter moving through empty space; but he ascertained by 

 an experiment with the pendulum (p. 443) that if such 

 resistance existed it was in amount S than one five- 

 thousandth part of the external resistance of the air * 



A curious instance of false negative inference is fur- 

 nished by experiments on light. Euler rejected the cor 



mov >l 



moving with the immense velocity of IHit would 



momentum, of which there was no evidence. n 



attempted to detect the momentum of li^ht by concentrat 

 mg the rays of the sun upon a deHcately bakS body 

 Observing no result, it was considered to be proved thlt 

 light had no momentum. Mr. Crookes, however havin* 

 suspended thin vanes, blacked on one side, in a nearfc 

 vacuous globe, found that they move under 'the influence 

 )f light. It is now allowed that this effect can be ex- 

 plained in accordance with the undulatory theory of Ifrht 

 and the molecular theory of gases. It comes to this-that 

 Bennet fai ed to detect an effect which he might have 

 detected with a better method of experimenting; Ut 2 

 had found it, the phenomenon would have confirmed no? 



u 1 , g ' aS Was ex P ected > *<* 



undulatory theory. The conclusion drawn from 



falsely drawn ' but 



of science ten d ^ show 

 phenomena, which one generation has failed to dis- 



- 



T^ accuratel y * to a succeeding 

 The compressibiHty of water which the 



1 - - Ofth ! ^^ t^lated by Harte, vol. ii. p. 33, 

 " sect - 6, Prop. xxxi . Motto's translation, ol ii! 



Fi? 

 r 



