418 Dr. J. R. Ash worth on the Theory of 



critical temperature in the approximate ratio of three to 



five, and we should therefore expect the slope of the line 



to change in the same ratio. From the reduced curve we 



o-et the following results : — 



j 



Nickel. — Beginning at air temperature 17 ~ ^ '^ 



At the critical temperature ■£ = 1"63 



Ratio 3/5 



This ratio is approximately the ratio of the specific heats at 

 these temperatures. 



Iron. — Beginning at air temperature j- = 0'72 



At the critical tetrfperature ~ = 2*15 



at 



Ratio 3/9 



And, again, this ratio is nearly the ratio ol the specific 

 heats. 



There seems little doubt that the large and increasing 

 change of resistivity up to the critical temperature- is due to 

 the increase of the specific heat ; and as this in its turn 

 depends on the mutual magnetic forces between the molecules, 

 we have an explanation of why ferro-magnetic substances 

 exhibit an abnormally large change of resistivity with rise 

 of temperature. 



10. Recapitulating, we find from the ferro-magnetic 

 equation, based as it is on a kinetic theory of magnetism, 

 that a magnet possesses an intrinsic field, and that this 

 field must be in magnitude immense if energy effects are 

 taken into account, but only very small if the effects of an 

 external applied field are considered. In short, when the 

 intensity of magnetization is treated as a function of the 

 temperature the intrinsic field must be very large, and when 

 treated as a function of the applied field the intrinsic field 

 must be very small — results which are not consistent with 

 one another. 



Further, we find from the effects of an alternating field 

 upon ferro-magnetism — more definitely its ability to lower 

 the critical temperature and at the same time its inability to 

 alter the temperature at which electrical resistivity, thermo- 

 electric power, and specific heat change abruptly — that the 



