718 Dr. J. R. Ashworth on the Application of 



The products on the left side of this equation are 



0*30 (for iron), 0*30 (for nickel), and 032 (for 

 cobalt) when ra = 0'92, 

 and 0-30 (for iron), 0-32 (for nickel)*, and 0*37 t 

 (for cobalt) when w = 0"60, 



numbers which are in fair agreement with O30, the approxi- 



Q 



mate decimal value of the fraction ^. The agreement, 



however, is not so good at values of m intermediate to these. 



The theoretical number — with which the experimental 



values are compared is obtained on the assumption that the 

 ferromagnetic equation is a cubic in I. 



6. The manner in which the intensity of magnetization 

 changes with rise of temperature can be traced by considering 

 the differential coefficient of I with respect to the temperature. 

 As before, we have 



dl B/ 



H being supposed constant. Now when I is large and 

 always greater than ^I the first term in the denominator is 

 negligible, and the second term, which is then negative, 

 measures the rate of change of intensity. Thus the in- 

 tensity falls at an increasing rate until I = JI . But just 

 below this value of I the second term becomes positive, 



TT JT 



Y2 being still negligible, and therefore ^- is positive, which 



indicates that the magnetic intensity has reached a state of 



instability, and a rapid fall takes place until -j- becomes 



again negative, which occurs at some very low value of I. 

 When I becomes exceedingly small the first term in the 

 denominator becomes the important one and, when large 

 enough to allow a' to be neglected, Curie's law of the inverse 

 proportionality of intensity to temperature then comes into 

 operation. Thus the equation represents broadly the chief 

 features accompanying the loss of ferromagnetism, namely, 

 at first a region of progressive and increasingly rapid loss up 



* Phil. Mag. xxiii. p. 36 (1912). 



t Honda and Shimizu, Phil. Mag. x. p. 548 (1905) ; and Stifler, 

 Phys. Kev. xxxiii. No. 4, p. 268. 



