of Current and Static Effects. 163 



of the experiments, and the way in which practical difficulties 

 were avoided, Melloni says, (t It appears, then, that when the 

 electric current possesses sufficient force to overcome the sum of 

 the resistance offered by a given conductor, whatever its length 

 may be, an augmentation of its intensity ten or twentyfold does 

 not alter the velocity of its propagation. This fact is in open 

 contradiction with the general meaning attributed to the deno- 

 minations of quantity and intensity ; since the first compares the 

 mass of electricity to that of a fluid, and the second represents 

 its elasticity or tendency to motion. The equal velocity of cur- 

 rents of various tension offers, on the contrary, a fine argument 

 in favour of the opinion of those who suppose the electric current 

 to be analogous to the vibrations of air under the action of sono - 

 rous bodies. As sounds, higher or lower in pitch, traverse in 

 air the same space in the same time, whatever 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 bat- # 

 teries of a greater or smaller number of plates, are propagated 

 in conductors with the same velocity. Every one will see how 

 the hypotheses imagined by us to give a reason for natural phe- 

 nomena, will serve to suggest certain experimental investigations, 

 the results of which will test their validity or insufficiency." 



Melloni then says that he shall shortly have occasion to publish 

 facts which clearly demonstrate the errors of certain conclusions 

 admitted up to the present time respecting electro- static induc- 

 tion ; and I am aware, from written communications with him, 

 that he considered the results arrived at by Coulomb, Poisson, 

 and others since their time, as not accordant with the truth of 

 nature*. In the mean time he died, and whether his researches 

 are sufficiently perfected for publication or not, I do not know. 



The uniformity in the time and appearance of currents of 

 different intensities at the further end of the same wire in the 

 same inductive state, is a very beautiful result. It might at first 

 be supposed to be in opposition to the views I set forth some 

 years ago on induction and conduction, and the statements more 



* He says, " I deceive myself much, or else the fundamental theorem of 

 electrical induction, as we find it ordinarily announced, ought to be modi- 

 fied so as not to confound two effects completely distinct — the electric state 

 during induction, and after the contact and separation of the inducing body. 

 We know perfectly what occurs in the latter case, but not in the former," 

 &c. Again, " In my last letter I raised doubts with regard to the con- 

 sequences which have up to the present been deduced from the experiments 

 nerving as a base for the fundamental theorem of electro-static induction. 



These doubts hare passed to a state of certitude in my mind, and 



behold me at this time thoroughly convinced that the enunciation of that 

 theorem ought to he essentially modified." (July 1854.) 



M 2 



