Magnetic Permeability, <Jc., of Iron at Low temperatures. 89 



perature of liquid air. If, instead of plotting the hysteresis loss and 

 induction, the ordinary logarithms of these quantities are taken 

 as coordinates, the curve, as shown in fig. 4, then obtained is 



FIGK 4. 



very nearly a straight line as far as the limit of an induction 

 of about 9000, and from the inclination of this line it is clear 

 that the hysteresis loss, W, in watts per lb, per 100 cycles is 

 found to be related to the maximum induction B in C.GLS. units 



per square centimetre by the law W = -jgj B rM , or, if the hys- 

 teresis loss is reckoned in ergs per cubic centimetre per cycle - 

 W, then W = 0-002 B r56 . These results are quite in accordance 



VOL. LX. 



