BETWEEN LONGITUDINAL AND CIRCULAR .AFAGNETIZATIONS. 307 



from which we soe thai tho w]iol(> phciioincnon depends upon the 

 change of /; considered as function of H. 



Now we know that k increases at first, till it reaches a maxi- 

 mum, and then gradually decreases ; hence so long as the resultant 

 field H is less than the field corresponding to the maximum 

 susceptibility, the value of ^^ is always positive, so that there 

 must he increase of magnetization in the direction of/ by increas- 

 ing t. When H is greater than that field, ^y is negative, and 

 we have decrease of magnetization. When Tl becomes just equal 

 to that field, ^ ! is zero, and the value of i reaches a maxi- 

 mum. This field is determinate for a particular substance, so that 

 the value of / corresponding to the maximum value of i must 

 diminish when / is increased, such that I' + f is constant. 



Tn soft iron or nickel, ..t in weak fields is greater than 

 that for harder one ; hence increase of magnetization in weak fields 

 for the former metal is greater than that for tho latter, as 

 already remarked. 



The convexity or concavity of the curve of / plotted against 

 t will be seen from the sign of the expression 



W~~ \n) a II- + 1 IÏ7 "0 II • 



1 7, 0-7. 



From the experimental values of ^ ^ a,nd yFP' ^^'G see that 

 when I is small and less than the critical field, ^^^o is at 

 first positive, but it soon becomes negative, and when t is still 

 further increased, it again changes its sign. When / is greater than 

 the critical field, -^w. is negative at first, and passing an inflexion 

 point, it changes sign. 



