DETERMINATION OF THE CONSTANT k. 457 



The value of the action F, of the current on unit magnetic mass 

 placed at the origin, and therefore the intensity of the field which 

 this current produces at the point where is the element, is expressed 

 by IG, where I is the electromagnetic intensity of the current (466), 

 and its components are 



z=-ic "'^-^ 



-I 



The three components d%, dtj, d, of the action d$ of the 

 circuit on the element ds' may then be written 



Mi'ds 1 



from which is deduced 



It follows from this that the two forces F and d$ are perpendicular 

 to each other. 



As the x axis is the only one which is defined, we may choose 

 the two others in such a way that the magnetic action F of the 

 current is in the plane xz\ we have then- 



Y = 0, B = 0, 



X = Fcosa, A = Gcosa, 



Z=Fsina, C=Gsina, 



a being the angle which the force F on the straight line G makes 

 with the x axis. 



