408 



MEMOIRS OF THE AMERICAN ACADEMY. 



These theoretical considerations will go far towards explaining the apparent contra- 

 dictions between the results obtained by Wheatstone, Walker, Mitchel, Gould, Fizeau 

 Faraday, Gaugain, Guillemin, Jenkin, Clark, and many others, who have experimented 

 upon the velocity of electricity, — results which range from 288,000 miles per second 

 to 800 miles per second. No two experiments are properly compared with each 

 other unless a variety of conditions is taken into the account. The enormous velocity 

 obtained by Wheatstone favors the supposition that electricity of high tension (as 

 that which exists in a charged Leyden jar) is endowed with a superior power of trans- 

 mission. But the experiments of Mr. Latimer Clark 2 (quoted by Faraday) have 

 proved that a voltaic battery might be increased from 31 cells to 500 cells, without sensi- 

 bly changing the velocity, when the current was sent through 768 miles of copper wire 



* 



covered with gutta-percha. Moreover, Wheatstone's experiment only proved that the 

 electricity went through less than a mile of wire (in addition to the air spaces where 

 the sparks occurred) at the rate of 288,000 miles a second. If many persons have 

 hastily come to the conclusion that electricity would actually move through 288,000 

 miles of the same kind of wire in a single second, they have made the assumption, 

 which neither theory nor observation warrant, that the velocity is independent of the 

 total resistance of the wire and the length to be traversed. Melloni appears to have 

 adopted this view, as an inference from Clark's experiments, already quoted. He 



says: "The equal velocity of currents of various tension offers, on the contrary 

 fine argument in favor of the opinion of those who suppose the electric current to 



i the electric current to be 

 analogous to the vibrations of air under the action of sonorous bodies. As sounds, 



© 



her or lower in pitch, traverse in air the same space in the same 



be the length or the intensity of the aerial wave formed by the vibration of the 

 sonorous body, so the vibrations, more or less rapid or more or less vigorous, of the 

 electric fluid, excited by the action of batteries of a greater or smaller number of 

 plates, are propagated in conductors with the same velocity.'* The theoretical ex- 

 aminations which have been made of the problem by Ohm, Gaugain, Kirchhoff, and 

 Thompson all point the other way. They all imply that the whole space travelled by 

 electricity is proportional to the square root of the time. A simple computation con- 

 ducts Gaugain to the conclusion that Wheatstone's experiment, when interpreted in the 

 light of the best theoretical knowledge, only proved that electricity would take one 

 second to run over 268 miles of similar wire. But Gaugain has evidently gone to 





1 London Philosophical Magazine, 1855. 



As 



Experimental Researches in Electricity, III. 577. 



