CONTEMPORARY ADVANCES IN PHYSICS 



315 



This rather nebulous statement might be made precise by expressing 

 / as a power-series in H, after this fashion: 



I = aH + hH^ + cH^ + ..., 



and citing experimental values of the coefificients a, b, c, . . . ; from 

 this a student equipped with a measuring-instrument could determine 



12 000 



10000 



400 



B-H 

 ZOO 



0.02 



0.04 0.0& 



H 



0.08 



0.10 



F^g-. 1 — Initial curve for a permalloy, displaying the three segments. The lower 

 curve IS part of the first segment of the upper, on a larger scale. (After L W 

 McKeehan.) 



the value of // at which the terms after the first become so small 

 that with his apparatus he could not detect them. I mention this to 

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