

VARIATIONS OF ELECTRIC CURRENTS. 175 



there are helices, capable of giving strong extra currents, the oscilla- 

 tions are strong, and consequently more numerous. They may be 

 expressed by a formula which contains an exponential and, at the same 

 time, a periodical function. In rectilineal circuits they are very feeble, 

 and perhaps they do not exist at all. So much for the variable state. 

 If the extra current be separated from the principal current, and be 

 considered as an independent thing, it may be said that the inverse 

 extra current is formed of a series of alternate currents, which begin 

 by being very strong and become gradually very weak. They are 

 oscillations positive and negative. 



As to the direct extra current, it is also formed of oscillations, which 

 are even more energetic and rapid. 



Sir W. Thomson had arrived, by analysis, at the conclusion, that, 

 under certain circumstances, the current may become oscillatory. The 

 oscillations, which he discovers, have a different character from those 

 which experiment has, up to the present time, revealed. According to 

 what has as yet been experienced the fluctuations of the current, in its 

 variable period, never reach zero, whilst Sir W. Thomson proves that the 

 oscillations are positive and negative that is to say, there are contrary 

 currents. It would be very difficult to say whether the conditions, 

 under which Sir W. Thomson's beautiful analysis brings about this result, 

 could ever be practically realized, for it becomes most difficult to turn 

 these mathematical conditions into experimental ones. In any case, it 

 is interesting to see how calculation had, to a certain extent, foreseen 

 these phenomena. 



With regard to inducted currents, judging by all the results obtained 

 by experiment up to the present moment, it may be said that they are, 

 like the extra currents, formed of very numerous oscillations. The 

 exact conditions on which they depend are as yet unknown, and many 

 questions relative to them must yet be studied. It is indeed a broad 

 field that has still to be gone over. You will permit me not to enter 

 into the details of this question, regarding which there exists still much 

 difference of opinion, which will, however, disappear under the in- 

 fluence of time and research. 



I prefer rather to call your attention to an idea which readily 

 suggests itself to the mind, and which, according to my opinion, 

 deserves to be considered. It has been somewhat difficult to prove the 





