136 Messrs. Bottomley and Tanakadat^ on 



Twist. Magnetometer. 



6 805 



+ 90 830 



+ 180 823 



+ 90 512 



298 



- 45 240 



- 90 225 



-180 220 



- 90 480 



730 



Wire. free from torsion-apparatus 540 

 Wire removed, magnetometer-zero . . 498 



The series thus described having been completed, the wire 

 was replaced with the weight on as before, but the torsion- 

 apparatus was not connected to it. The wire had then a 

 negative permanent set of about 35". Left free it influenced 

 the magnetometer but little, the reading being 500. Twisting 

 a little (well within elastic limits) from this free position in 

 the positive direction produced increased southern magnetism 

 in the lower end of the wire ; twisting to the negative side 

 produced the opposite magnetic effect. 



Lastly, so far as this wire was concerned, it was twisted 

 first positively through 180°, then negatively through 180°, 

 observations being taken. The twisting in the negative direc- 

 tion was then carried through another 180^, and finally the 

 negative twist was taken out. The result of this operation 

 was to annul entirely the effect of the first positive twist (say 

 right-handed, see p. 120) and as it were to convert the former 

 positiveness of right-handed twist into negativeness, and 

 vice versa. 



Cycle of Tioisting in the Zero Magnetic Field. 



A fresh wire was now suspended, and was subjected to 

 the action of a strong uniform magnetic field obtained bv 

 means of a magnetizing-coil with secondary coils. The 

 strength of the field was 182 C.G.S. The stretching-load 

 was small ; being only 1*78 kilogs., or 91 kilogs. per square 

 centimetre, or the smallest necessary for keeping the wire 

 stretched in position. After the wire had been thus magne- 

 tized the field was reduced to zero (the earth^'s vertical force 

 being neutralized by means of the solenoid). The change of 

 residual magnetic moment was then observed. This is shown 

 in the followins series of numbers : — 



