of Steel, Nickel, Cobalt, and Nkkel-Steeh 



47 



to the relative proportion of the magnetostriction of the con- 

 stituents, but the phenomena are of a very complex nature. 



Associated with the change o£ length and of volume comes 

 the Wiedemann effect, which is measured by the amount of 

 torsion caused by the interaction of circular and longitudinal 

 magnetizations. The measurement in cobalt must at present 

 be postponed, as the metal cannot be brought to a geome- 

 trical shape suitable for experiment on account of its brittle- 

 ness. Investigation of the effect in nickel-steel of different 

 percentages presents the phenomenon in the same aspect as 

 for the length-change, and the sense of twist is determined 

 by that of iron in weak fields. 



A singular characteristic of magnetostriction is its re- 

 ciprocity with the effect of stress on the magnetization of 

 different ferromagnetic substances. In the present instance, 

 we have specially turned our attention to cobalt .and nickel- 

 si eels. As will be expected from the nature of the length- 

 change, the former metal is characterized by the existence of 

 a minimum point closely analogous to that bearing the name 

 cf Villari for iron, while with the latter the effect of the 

 longitudinal pull always results in the diminution of mag- 

 netization. The parallel statements giving the correlation 

 between the magnetization and the effect of torsion, first 

 noticed by G. Wiedemann, can thus be extended to other effects 

 of stress and the strain resulting from the magnetization. 



§ 2. Intensity of Magnetization in Steel, Nickel, 

 Cobalt, and Nickel-Steel voids. 



In all of our experiments we noticed the change of dimen- 

 sions by magnetization and the strength of the field «£) 

 (£ = ,!£)' — N3, where fy is the external field, N the demag- 

 netizing factor, and 3 the intensity of magnetization). It 

 will therefore be not out of place to make a digression on 

 the magnetization of the ferromagnetic substances here ex- 

 amined, in order to enable us to examine the various changes, 

 considered as functions of the intensity of magnetization. 



The following table gives the dimensions as well as the 



Metal. 



a (cm.). 



c (cm.). 



v (cicm.), 



P- 



N. 



Steel 



0-493 

 0-493 

 0-493 

 0-495 

 0-494 

 0-496 

 0492 

 0-494 



10-00 

 10-00 

 10-00 

 10-02 

 1001 

 10-01 

 10-01 

 1002 



10-40 

 10-40 

 10-38 

 10-52 

 10-45 

 10 48 

 1043 

 10-40 



7-85 

 8-87 

 8-26 

 8-20 

 8-15 

 8-11 

 8-12 

 805 



oooooooo 



0000000000000000 



1 as o* oi oi ci os oi oi 



Nickel 





Annealed Cobalt 



Nicksl-Steel (46 p. cent. Ni) ... 

 „ (36 p. cent. Ni) ... 

 „ (29 p. cent. Ni) ... 

 „ (25 p. cent, Ni) ... 



