of Steely Nickel, Cobalt, and Nickel- St eels. 



69 



In deducing the three formulae (A), (B), (C), we cannot, 

 strictly speaking, put k" outside the sign of integration, 

 because the strain coefficient depends on the field strength, 

 which is not uniform in a wire traversed by an electric current. 

 Hence we shall have to use a mean value to obtain a close 

 approximation. 



In order to test the consequences of the theory as regards 

 the twist produced by the joint action of circular and longi- 

 tudinal magnetizations, we have calculated the twist by 

 assuming the values of k" calculated from the changes of 

 volume and of length in iron and nickel ovoids. Graphically 

 represented (fig. 16), the fields of maximum twist by 



Fig. 16. 



40 



eo 



-20 



<z 













1 \x3 





/RON W/A 



'£ 







I l<; 



fo : -^ 



w — — L_Z§ 



|W AC 



rn— - _ ^ 











S**i 



/V/C/C£ 



L W/ffE 



















-60 



a &, a' : obs. & calc. transient currents in 10" C.G.S. uuits for iron. 

 A&A': „ „ „ „ „ for nickel. 



b &b' : obs. & calc. Wiedemann effect for iron. 

 B&B': „ „ „ for nickel. 



calculation coincide nearly with those given by experiments, 

 and the reversal of twist in iron takes place in low fields as 

 actually found by observation. The quantitative differences 

 are, however, tolerably large in iron, but in nickel the amount 

 of twist is nearly coincident with the experimental values. 

 Calculating in the same manner the quantity of the transient 

 current produced by twisting longitudinally magnetized wires, 

 we find a close coincidence between the experimental and 

 theoretical values in nickel, but the difference is tolerably 



