OF ELECTRO-DYNAMIC FORCES. 521 



where four electric masses occur under the conditions premised 

 to exist where two invariable and undistui'bed elements of a cur- 

 rent are concerned. Under conditions where these premises 

 do not exist, the new fundamental principle only can be ap- 

 plied for the a priori determination of the forces and phaeno- 

 mena ; and it is exactly in this way that the greater advantage of 

 the new principle, arising from its more general application, will 

 be exhibited. 



The case in which the principle of electro-dynamics laid down 

 by Ampere is inapplicable, thus occurs even when one element 

 of a current is disturbed or its intensity varies ; in addition to 

 which it may also happen, that instead of the other element of 

 he current, one element only of the conductor of a current may 

 be present, without however any current being present in it. In 

 fact, we know from experience that currents are then excited or 

 induced, and the phccnomena of these induced currents are com- 

 prised under the name of voltaic induction ; but none of these 

 phaenomena could be predicted or estimated a priori either from 

 the principle of electro-statics or the principle of electro-dynamics 

 laid down by Ampere. It will now however be shown, that by 

 means of the new fundamental principle as laid down here, the 

 laws for the a priori determination of all the phaenomena of vol- 

 taic induction may be deduced. It is evident that the laws of 

 voltaic induction deduced in this manner are correct, so far only 

 as we are in possession of definite observations. 



For the purpose of this deduction the magnitudes concerned 

 may be denoted as follows : — « and «' denote the length of two 

 elements, the former of which, a, is supposed to be at rest. This 

 supposition does not limit the generality of the consideration, 

 because every movement of the element « may be transferred 

 to a', by attributing the opposite direction to it in a'. The four 

 following electric masses are distinguished in these two elements, 

 viz. — 



+ ue, — « e, -f- «' e', — a' e'. 



The^r*^ of these masses + ote would move with the velocity 

 -I- M in the direction of the quiescent element a, which forms the 

 angle 6 with the right line drawn from « to «'. This velocity 

 during the element of time dt would alter by + du. 



The second mass — « e would move, in accordance with the 

 determinations relating to a galvanic current, in the same direc- 



VOL. v. PART XX. 2 N 



