864 ACTION OF ELECTRIC CURRENTS. [SECT. xxxn. 



inversely as the squares of the distances, the action being at 

 right angles to the direction of the current, it is found that 

 the attraction and repulsion of a current of indefinite length 

 on the elementary portion of a parallel current at any distance 

 from it, is in the simple ratio of the shortest distance between 

 them. Consequently the reciprocal action of electric currents 

 is reduced to the composition and resolution of forces, so that 

 the phenomena of electro-magnetism are brought under the 

 laws of dynamics by the theory of M. Amp&re. 



