.328 



PROFESSOR J. A. EWING AND MR. G. C. COWAN 



ANNEALED Nickel Wire. 



In this case the greatest susceptibility was 23'5, when $ was 9 '5. This gives 302 

 as the maximum value of /*.* These numbers are just about one-tenth of what they 

 would be for an iron wire annealed in the same way. The residual magnetism is 284, 

 or 71 per cent, of the induced, and the coercive force is 7 '5, or a good deal less than 

 half of what it was before the wire was annealed. The energy of the cycle of double 

 reversal of magnetism (J %d$) is 11,200 ergs. 



The broken lines in fig. 2 show a magnetising cycle performed on another piece, cut 

 from the same coil of nickel wire, which, after being softened in a Bunsen flame, was 

 mechanically hardened by being stretched enough to give it some permanent extension 

 (namely, from a length of 26'6 cm. to 27 cm.). Here the maximum susceptibility is 

 only 8 '3, the coercive force is 18, and the highest value of 3, reached by applying a 

 force of 117, is only 340. The cycles for annealed and hardened nickel differ in much 

 the same way as the corresponding cycles for annealed and hardened iron. 



Effects of Stress on the Magnetic Susceptibility and Retentiveness of Nickel. 



The effects of stress, consisting of longitudinal pull, were examined (1) by magne- 

 tising wire from which a constant load of greater or less amount was hung, and (2) 

 by loading and unloading wire which was exposed to a constant magnetising force of 

 greater or less intensity. The same pieces of wire that served for the experiments in 

 cyclic magnetisation were tested for effects of stress, both before and after annealing, 

 and after being hardened by stretching. 



While still in the hard-drawn original condition the wire of fig. 1 was tested for 

 induced and residual magnetism under varying magnetising forces : first, when not 

 exposed to stress, then when under a longitudinal pull of 2 kilogrammes, and lastly 

 when under a pull of 12 kilogrammes. The observations were made by applying 

 magnetising force, noting the induced value of 3, reducing the magnetising force to 



* ROWLAND (loe. cit.) gives 302 as the maximum of fi in a specimen of cast nickel. 



