CHANGE OF VOLUME AXD OF LENGTH. 



69 



.i=zz{,4_3(.'+-^-)|;. 



Putting / = 4.67x lO"", 4.80 x lO-", and 4.8.5 x 10"" for soft iron, ordin- 

 ary steel, and wolfram steel respectively, each corresponding to a 

 pull of 0.1 Kilog. per sq. mm., we get the following results : 



\ 



It will be seen from tlie above table that tliere is an increase 

 of magnetization in low fields, till it reaches a maximum, after 

 which it gradually decreases. The decrease does not proceed 

 continuously, but reaches a maximum, whence the magnetization 

 begins to recover. Although the former result here arrived at 

 is the well-known Yillari effect, we do not know whether the 

 maximum decrease due to longitudinal stress has as yet been 

 experimentally ascertained. AVith nickel, we obtain the following 

 values for the change of magnetization due to elongation, /= 



