142 Magnetic- Elongation and Magnetic-Twist Cycles* 



tudinal field acting on the wire was gradually altered between 

 limits + H, and at suitable intervals observations of the twist 

 were made. With small range of field the hysteresis curve 

 obtained by plotting twist against field was very similar to the 

 well-known hysteresis curve of magnetization. But with 

 limiting fields stronger than the field which produced the 

 maximum twist, the hysteresis curve crossed itself twice and 

 formed three loops. A typical example is shown in the figure, 

 the magnetic-twist cycle being the Z-shaped graph with 

 the thick lines. 



/\ f S ■ 1! 



|-L00 - V 



V + Yield. 4 10 



I ■ • 



\f 



Magnetic-Twist Cycle. 



In the magnetic-elongation cycle, the change of sign of the 

 magnetizing force does not produce a change of sign in the 

 elongation. On the other hand, in the magnetic-twist cycle, 

 as the magnetizing force passes through zero from positive to 

 negative, the twist tends to do the same, though laggingly. 

 Suppose, now, that we change the sign of the twist throughout 

 one-half of the cycle. In other words, take the reflexion of 

 the one-half of the graph in the horizontal axis, as indicated 

 by the thin lines in the figure. Then round off the sharp 

 angles by the dotted lines, and we get a curve similar to 

 Mr. Nagaoka's magnetic-elongation curve, fig. 2, Plate II. 

 Or, taking Mr. Nagaoka's curves of fig. 4, Plate II., we 

 may reflect one half of each in the horizontal axis, join the 

 parts so as to have continuous flowing lines, and thus get 

 curves identical in form with those of the magnetic-twist 

 cycle (see plate iii. of my paper already referred to) . 



The magnetic-elongation curves obtained for nickel are all 

 of the simpler two-looped form, the reason being that there 

 is no maximum contraction for nickel. But with high ranges 



