Brown — 3lechanical Stress and Magnetisation of Nickel. 505 



It will be seen that eacli of the three curves rises quickly to a maximum 

 and diminishes more gradually ; and the longitudinal magnetic field in which 

 the maximum twist occurs changes with the value of the longitudinal load 

 on the wire.' 



The longitudinal magnetic field in which the maximum twist occurs, for 

 a given load, is tlie same for all the wires, though they are of different 

 degrees of hardness, that is, in a field of 13 units for the small load, in a field 

 of 35 units for the large load, and in a field of about 20 units for the 

 middle load of 1'5 x 10* grammes per sq. cm. In Table II the maximum 

 twists are indicated by means of heavy-faced tyi3e. Again, for all tiie wires of 

 different degrees of hardness, the curves cross each other in the same longi- 

 tudinal magnetic field ; thus the curves obtained with loads (0'5 x 10') and 

 (1-5 X 10*) cross in a magnetic field of 13 units, under loads (0"5 x 10*) and 

 (3 X 10*) in a field of 18-5 units, and under loads (1-5 x 10*) and (3 x 10*) they 

 cross in a magnetic field of 23 units ; these relations hold for wires of different 

 lengths as well as for wires of different tempers. 



O 20 4-0 60 



Magnetic Field H. 

 Fig. 2. — 'Wires of diiferent tempers and tlie load constant. 



Taking from Table II the results for wires of the same length (226 ems.) 

 and with the same longitudinal load on the end (1'5 x 10* grammes per sq. 

 em.), but of different degrees of temper or magnetic softness, and plotting as 



' Nagaoka, Phil. Mag., 1908, vol. xxis., j). 123 (using a nickel wire 30 cms. long, and 1 mm. 

 diameter), found the maximum transient current produced in the wire (when the free end was twisted 

 through 60°) to take place in a longitudinal magnetic field of 2.5 units with no load on the wire, and 

 in fields of J.j and 70 when the loads on the wire were ?)'S2 x 10-' and 7'64 x 10° grammes persq. cm. 

 respectively. 



