48 ELECTRIC LIGHTING. 



one to foresee a priori, and that was that the current is 

 merely temporary, for it ceases immediately, giving place to 

 another current equally transient which shows itself at the 

 instant the magnet is withdrawn from the coil. This latter 

 current has its direction opposite to that of the former, and 

 if the direction of these currents be compared with that of 

 the magnetic or voltaic current which gives rise to them, it 

 will be observed the directions are the same for the latter 

 current and opposite for the former. Hence the name of 

 direct current given to the current which shows itself in the 

 second case, and the name of inverse current given to that 

 which is produced in the first case. Thus the mere approach 

 of a permanent magnet to, and its recession from, a spirally 

 arranged circuit give rise to two opposite instantaneous cur- 

 rents which are distinctly separate. 



These instantaneous currents may, however, successively 

 appear one after the other, from one and the same movement 

 of the inducer or of the induced circuit, if this movement is 

 successive ; for at each stage of this movement there is pro- 

 duced a differential induced current which continues the 

 action of the former, and all these currents joining one to 

 .another may give rise to a current of appreciable duration, 

 which may be in one direction or the other, according as the 

 movements succeed each other in the direction of approach 

 or in that of recession. This current, however, is feebler at 

 any given instant than that which would result from the 

 same total movement suddenly effected through the same 

 space. We shall see farther on what is the effect of quicker 

 or slower movements with respect to the nature of the in- 

 duced currents developed by them ; but here it may be stated 

 that quicker or slower movements through the same space 

 affect only the tension of the induced current. 



When these principles were once recognized, it only 

 remained to mechanically combine the different elements 

 producing these temporary currents, so as to rectify them 

 and cause them to succeed each other without interruption. 



