Jemperature on the Hysteresis Loss in It 



127 



could be reached even when the temperature was only a few 

 degrees below the critical temperature, which in this speci- 

 men is about 776° C. 



It will be noticed that the fall in hysteresis with rise of 

 temperature decreases as the critical temperature is ap- 

 proached. This is more noticeable in the case of the 

 tungsten alloy, the corresponding curves for which are given 

 in fig. 9. 



Searle and Bedford* have studied the effect of strain on 

 the hysteresis loss of iron, and have drawn curves showing 

 the variation of hysteresis with induction for constant ranges 

 of magnetic force. Their curves for any value of H show 

 that through a considerable range of straining the hysteresis 

 is a linear function of the induction. In the case of torsion 

 the hysteresis for this part of the curve is given by 

 W = aH2B — b, where a and b are constants ; for a specimen 

 of soft iron they found that a = 0'o5, 6 = 600, and for a steel 

 rod b = 0. 



Corresponding curves can be obtained from the data given 

 in Table 13., the hysteresis and induction being varied by 

 heating. Fig. 5 gives three such curves for values of H 



Fig. 5. 



1250 









' y^* ^> 



L 



<t fOOO 



*: 



1. 750 



1 



;,500 



t 



is 



^£50 







M 









/ 



/ 



f \ 





/ 





*/ 



/ / 



/- 



yl 



/ 





/ 



/ / & 



' / / 



/ 



'// 





M 



















40C 





 B 



60C 







so 



30 



of 0'68, 1*02, and 1*36 c.g.s. respectively. It will be seen 

 that for values of B between 1800 and 5000 the points for 

 each curve lie on a straight line, and that these lines, when 



* Phil. Trans. A. vol. cxcviii. pp. 80-90 (1902). 



