278 jPeirce — Permeabilities and Reluctivities for Steel. 



a longer rod in the other. 



If, then, a testing coil (K) of very 

 fine wire were wound in a single layer over a centimeter or 

 two of the middle of a rod of the standard length, and a second, 

 similar, coil (L) of radius about two millimeters greater than 

 that of K, upon an extremely thin non-magnetic spool slipped 



Fig. 1. 



P 



B 



H 



Tm 



over K, it was to be expected that a knowledge of the whole 

 amounts of the currents induced in Kand L when the exciting 

 current of the yoke was reversed would determine, as in the 

 Isthmus Method, corresponding values of R and B. This 

 assumption was fully justified by experiment. The radii of 



Fig. 



the coils and the diameter of the wire were measured with the 

 help of a Zeiss comparator (No. 3196). The coil L was 

 wound upon a very dry piece of boxwood, and was carefully 

 baked in shellac. Parafnne wax is inadmissible as an insulator 

 on the wire because of its magnetic properties, and for the 

 same reason a vulcanite spool cannot be used for L. 



