CONTEMPORARY ADVANCES IN PHYSICS 



335 



however, the angle may be enormous — a field inclined at no more than 

 five or ten degrees to the hexagonal axis produces a magnetization 

 which, when investigated by delicate methods, seems to lie exactly 

 in the plane perpendicular to the hexagonal axis, which conse- 

 quently is known as the "plane of easy magnetization." A sphere 

 of pyrrhotine to which a bar magnet is brought up from the direction 

 in which its hexagonal axis points does not seem to realize that the 

 magnet is there, but if the approaching magnet is displaced a little 



15 000 



12 500 



10 000 

 B-H 

 7 500 



5000 



2 500 



?5 , 5.0 7.5 10.0 



5.0 

 H 



Fig. 7 — Initial curves for Swedish transformer iron at two temperatures. 

 (After D. K. Morris.) 



sidewise the ball flies over to its surface at once. It will readily be 

 seen what complications these facts introduce into the mathematics 

 of predicting or describing the magnetization of an arbitrarily-shaped 

 solid body — and in this connection it is well to remember that an 

 ordinary polycrystalline mass of metal partakes as soon as it is strained, 

 by pulling or rolling, of some of the properties of a single crystal. 



