TOKSION AND MAGNETIZATION. 271 



Here 6 denotes the angle of torsion and Q the time-integral 

 of the transient current expressed m C.G.S. units. The resistance 

 of the whole circuit was 4.5 ohms. The nickel wire here used was 

 made of the same specimen as the nickel prism used in our former 

 experiments. 



As is w^ell known, the direction of the transient current, 

 and therefore that of the circular magnetization, is opposite in 

 iron and nickel. The current for constant amount of twist in- 

 creases with the strength of the longitudinal field ; it, however, 

 soon reaches a maximum, whence it gradually diminishes. In 

 nickel, the transient current attains asymptotic values in strong 

 fields without changing its direction, while in iron, it is reversed 

 in a field of about 200 C.G.S. units, when the twist is small. 

 The increase after the reversal is not pronounced, but becomes 

 finally asymptotic. 



§ 3. Longitudinal magnetization produced by twisting 

 a circularly magnetized wire. 



The longitudinal magnetization produced by twisting a cir- 

 cularly magnetized wire presents the same character as the tran- 

 sient current above described. The experiment is very difficult 

 on account of the heating of the wire. To avoid the rise of 

 temperature, the iron or nickel wire to be tested was covered with 

 urushi (Japan lac) which has the special property of being a very 

 good insulator while, at the same time, the melting temperature 

 is comparatively high. The wire thus insulated was stretched 

 in the axial line of a secondary coil whose diameter was 1.5 cm. 

 and wdiose total number of turns was 540, and the current of 

 cold water was kept fiowing about it to keep the temperature 



