MAINTENANCE OF ELECTRIC CURRENTS BY MECHANICAL WORK. 85 



On the other hand, the primary coil loses that part of the total current 

 which passes through the shunt; but we know that an iron core, when highly 

 magnetized, requires a great increase of current to increase its magnetism, 

 whereas its magnetism can be maintained at a considerable value by a current 

 much less powerful. In this way the diminution in resistance and self-induction 

 due to the shunt may more than counterbalance the diminution of strength in 

 the primary magnet. 



Also, since the self-induction of the shunt is very small, all instantaneous 

 currents will run through it rather than through the electromagnetic coils, and 

 therefore it will receive more of the heating effect of variable currents than 

 a comparison of the resistances alone would lead us to expect. 



