MAQiVETIZATION AND MAGNETIC CHANGE OF LENGTH. 



17 



Here H, B and W denote respectively the internal field, the 

 magnetic induction, and the hysteresis-loss, all expressed in C.G.S. 

 units. In Swedish iron, the hysteresis-loss is decreased in weak 

 inductions and increased in the strong, by cooling it in liquid air. 

 Fleming and Dewar* found no effect of cooling on the hysteresis- 

 loss of iron. In tungsten steel, nickel, cast and annealed cobalts, 

 the hysteresis-loss is always increased by cooling. These changes 

 are briefly expressed by saying that the cooling in liquid air 

 magnetically hardens the specimens. 



In comparing the hysteresis-loss of different metals, it is to 

 be observed that the hysteresis-loss in nickel is the smallest among 

 them and that those for tungsten steel and cast cobalt are greater 

 by about three times than the hysteresis-loss of Swedish iron, and 

 the same relation also holds between annealed cobalt and tungsten 

 steel. 



From the courses of the curves in Fig. 1, it is evident that 

 Steinmetz's formula giving the relation between the hysteresis-loss 

 and the maximum induction holds for nickel and annealed cobalt 

 up to an induction of 3000 C.G.S. ; it holds for cast cobalt and 



*J FiiEMiNG and Dewak, loc. cit. 



