ON MATTER AND FORCE. 23 



great variety in its duration, that non constat 

 all may not have it, though for a time so short 

 that the eye cannot detect its duration. 



"If it be said that there is not sufficient 

 elasticity in ordinary matter for the transmis- 

 sion of undulations with such velocity as light 

 is known to travel with, this may be so if the 

 vibrations be supposed exactly analogous to 

 those of sound ; but that molecular motion can 

 travel with equal, and even greater, velocity 

 than light, is shown by the rapidity with which 

 electricity traverses a metal wire when each 

 particle of metal is undoubtedly affected." 



Mr. Brooke, in the Proceedings of the Royal 

 Society, 1867 (p. 412), says : " The known enor- 

 mous velocity (of probably not less than 

 250,000 miles in a second) at which electricity 

 travels through a copper conductor is complete 

 evidence that ordinary matter is capable of 

 transmitting something at a considerably greater 

 velocity than the waves of light and heat. 

 Why should not appropriate kinds of matter 

 be assumed capable of transmitting these also ? 

 and if so, the need of the interstitial presence 

 of aether ceases altogether." 



Mr. Grove sums up the arguments in favour 



