Rigidity of Ferromagnetic Substances by Magnetization, 541 



produced torsions proportional to|their respective weights, the 

 friction at the pivot does not seem to disturb our results. 



The examples tested were the same as used in the pre- 

 ceding experiment, except the nickel rod. In the present ex- 

 periments the length of each rod was reduced to 22 cms., and 

 the diameter of the cobalt bar also to 1*082 cm. The nickel 

 rod used in the last experiment was not sufficiently thick for 

 the torsion experiment, so that another nickel bar, whose 

 diameter was 1*117 cm., was substituted for it. 



Our apparatus was not suited for the absolute measurement 

 of the modulus of rigidity, and therefore its determination 

 was carried out in the usual manner with Prof. Nagaoka's 

 apparatus above referred to. The results were: — 



Metals... Soft iron. Steel. Wolfram steel. Nickel. Cobalt. 



Rigidity 7-92 xlO 11 7*89 xlO 11 8-57 X 10 11 7*41 x 10 11 6-04 xlO 11 



4. Soft Iron. — The results of observation are given in fig. 3. 



Here ordinates represent the change of twist due to mag- 

 netization given in seconds of arc, taken positive when the 

 change indicates an increase of rigidity and taken negative 

 when it indicates a decrease ; abscissae represent the effective 

 field. N is the moment of force expressed in C.G.s. units. 



From the figure we see that the untwisting o£ the rod 

 always increases with magnetizing force, its amount increas- 

 ing in the same way as the intensity of magnetization with 

 increasing magnetizing force. As the moment of force in- 

 creases the amount of untwisting increases proportionally, so 

 that the change of rigidity is fairly independent of the twist- 

 ing couple for all magnetizing fields. The form of the 

 curves is similar to that of the curves of depression in the 

 former experiment, except in very weak fields. In the pre- 

 sent case the initial minute depression of the curves was not 

 observed. 



The angle of torsion, as calculated from the applied couple 



