7IO INDUSTRIAL APPLICATIONS. 



If the current has had the time to establish itself in the closed 

 coil, the equation which defines the angle of lead is then 



CO 2 



When the magnetisation M is proportional to the current, we 

 may represent it by M = r'- , which gives 



The magnetisation only cornes then into the angle of lead as 

 a fictive increase of the resistance of a winding, which would be 

 proportional to the velocity. 



1266. The useful work may be represented by a resistance x 

 equivalent to the useful resistance and to the electromotive forces 

 overcome. The current and the angle of lead are then given by 

 the equations 



47T 



and, if the magnetism is proportional to the current, 



/{)- 



4?r R + a l + x 



It will also be observed that the coefficient / is proportional to 

 the square of the number of turns of each coil; and may be re- 

 presented by 4A/> 2 ; we have then 



a i = mnl= ^mnp^X = riPj>X. 



In order to diminish the influence of self-induction, it is 

 advantageous as much as possible to form the coils of a single 

 winding. 



