EFFECT OF MAGNETIZATION ON THE PERMANENT TWIST OF NICKEL. 



331 



These reading« are plotted in curves (1) (2) (3) Fig. 2. respec- 

 tively. Curve (4) is plotted from an experiment made with a wire of 

 the same thickness, with a permanent twist of 1621°. These curves 

 shoAv that tlie untwisting on the first application (jf the magnetizing 

 foi'ce is very large. AVhen the twist is small the untwisting im- 

 mediately becomes very small, and the wire 1)egins to twist, liut the 

 further increase of the magnetizing force is of very little effect. The 

 curve, shortly after the maxinum is attained, liecomes nearly ])arallel 

 to the line of no twisting. 



This appearance is confined to those cases where the ]3ermanent 

 twist is small. With a residual torsion of 10°.6 in the same wire, the 

 curve acquires quite n différent appearance. The I'ate of increase of 

 untwisting with the increase cjf magnetizing force liecomes less, so that 

 the untwisting gradually approaches the maximum. Thereafter the 

 twisting takes place gi'adually and steadily. On removing the mag- 

 netizing force, there is at first untwisting Avhich reaches a maximum 

 in a magnetizing Held less than that corresponding to the maximum 

 untwisting on the first a])plication of the magnetizing force. The 

 wire then again begins to twist, Imt on the complete removal of the 

 magnetizing force, the Avire remains untwisted relatively to its first 

 position. The most striking difference between the curves in Fig. 1 

 and those of Fig. 2 is that the latter has a maximiun ])()int and the 

 former has none. This maximum which seems to be closely connected 

 with the amount of residual torsion occurs in weak magnetizing fields 

 when the twist is small, l)ut as the twist is increased, it occurs in 

 stronger fields. 



When the permanent twist is very large, the features of the curve 

 do not change essentially. Curves (3) (4) Fig. 2. show the state of 

 things for the twists of 861° and 1621° respectively. From these it 

 will be seen that the untwisting does not increase ])roportionally with 



