Length in Iron, Steel, and Nickel Ovoids by Magnetization. 329 



with the axis of H. k" is at first negative, and attaining the 

 minimum value goes on gradually increasing till it becomes 

 greater than zero, and reaches a maximum of which the exact 

 position is very vague ; ultimately the curve for k" coincides 

 with that for k' . The position of the maximum for k' and that 

 of the minimum for k" lies nearly in the same field, which is 

 greater for wolfram steel than for soft iron, while that for 

 ordinary steel occupies an intermediate position. The abso- 

 lute values of k' and k" are greater in iron than in steel. In 

 nickel, as already noticed, the values of k' and k u are far 

 greater than those for iron and steel, and, moreover, are of 

 opposite signs. The maximum of k" or the minimum of k' 

 seems to lie in a weak field ; the rate of decrease or increase 

 is quite rapid, and the curves for k' and k" soon approach the 

 axis of H. Compared with the results of our former experi- 

 ments, the absolute values of k 1 and k n are generally small for 

 iron, but far greater for nickel. This difference arises from 

 the fact that for iron the change of length in weak fields is 

 less in this case than in the former experiment, and for nickel 

 the contrary is the case. As regards the sign, these two 

 experiments show fair agreement. 



Consequences of the Theory \ 

 Effect of Longitudinal Pull. — The change of magnetization 

 produced by the elongation \ of the wire can be easily calcu- 

 lated from the formula 



Putting A, = 4- 6 7 X 10" 6 , 4'80 x 10-°, 4'85 x lO" 6 , 4'74 x lO" 6 

 for soft iron, ordinary steel, wolfram steel, and nickel respec- 

 tively, corresponding to a pull of O'l kilog. per sq. mm., we 

 obtain the following results : — 



H. 



Soft Iron. 

 SI. 



Steel. 

 81. 



Wolfram 



Steel. 



SI. 



Nickel. 

 SI. 



10 



0-92 



107 



0-83 



0-40 



024 



0-1 3 



0-04 



-0-08 



-016 



-0 26 



-0-31 



-0-28 



-022 



-0-18 



06 



0-21 



0-40 



025 



015 



007 



01 



-009 



-0-15 



-0-21 



-024 



-0-20 



-0-16 



-013 



004 



017 



0-35 



029 



025 



019 



015 



0-09 



0-06 



002 



00 



-0 04 



-004 



-0 03 



-24-6 



-18 9 

 -14-2 



- 91 



- 71 



- 60 



- 5-2 



- 2-7 



-*2-3 



- 14 



- 0-9 



- 06 



- 05 



20 



30 



60 



80 



100 



120 



160 



200 



300 



500 



800 



1200 



1600 





