Longitudinal Stress on the Magnetization of Nickel. 121 



Twist (positive). 



Eeadings. 



Twist (negative). 



Eeadings. 



O 







24-2 



O 







3-4 



20 



35-8 



20 



-0-2 



40 



45-5 



40 



-2-0 



60 



55-8 



60 



-2-4 



80 



64-4 



80 



-2-6 



100 



71-0 



100 



-2-4 



120 



76-3 



120 



-1-9 



140 



79-8 



140 



-1-2 



160 



82-2 



160 



-0-.5 



180 



83-8 



180 



00 



160 



81-9 



160 



00 



140 



78-8 



140 



-0-2 



120 



73-5 



120 



-0-3 



100 



65-2 



100 



-1-0 



80 



51-9 



80 



-1-0 



60 



35-9 



60 



1-9 



40 



220 



40 



7-8 



20 



10-8 



20 



17-3 







3-4 







28-7 



The above readinors, reduced to absolute units, are shown 

 plotted ill fig. 1 (PL XL). The amount of load per square centi- 

 metre was 82 kilograms, and the twist of 180° corresponded 

 to that of "0785 radian per centimetre. 



Examining the figure, we see that the first effect of twisting 

 is to increase the magnetization. The rate of increase is rapid 

 at first, but gradually falls off as the magnetization attains its 

 greatest value at the maximum twist. During the process of 

 untw^isting the magnetization diminishes more rapidly than it 

 increased during twisting, so that for every position of twist 

 the magnetization during twisting is greater than the magne- 

 tization during untwisting. The diminution of magnetization 

 goes on even after the wire has passed the original position 

 from which the twisting was begun until the apparent mag- 

 netization is at length reduced to zero. This happens very 

 soon after the original position of the untwisted wire has been 

 reached, as the process of untwisting is continued as twisting in 

 the negative direction. But now as this negative twisting is 

 continued, the polarity of the wire changes sign, a very striking 

 fact indeed. As the twisting is continued on towards —180°, 

 this negative magnetization passes through an arithmetical 

 maximum, becoming finally almost zero. As the wire is being 

 brought back to the position from which it started, the mag- 

 netization gradually recovers nearly its original value, as 

 shown in the figure. 



Now, reasoning from analogy, we should expect to obtain 



