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XLVlIL On the Magnetic Change of Length and Electrical 

 Resistance in Nickel. By W. E. Williams, B.Sc* 



IT is well known that the length of a nickel wire is 

 diminished, while its electrical resistance is increased, 

 by longitudinal magnetization. The first of these effects has 

 been investigated by Bidwellj, Nagaoka J, and Taylor Jones §, 

 and the second by Tomlinson|| and Barlow If. 



If these effects are represented in curves showing the 

 change of length, or resistance, as a function of the magne- 

 tizing field, it will be found that the two curves bear a very 

 striking resemblance to ench other. This is well shown by 

 the similarity in form of the hysteresis curves of the two 

 effects given by Nagaoka and Barlow. 



It was suggested by Prof. Taylor Jones that I should in- 

 vestigate further the relation between these two effects, and 

 the experiments described below were undertaken for that 

 purpose. 



As both effects vary considerably for different specimens 

 and even for the same specimen at different times, it was 

 thought necessary to measure both changes in the same pi< j ce 

 of wire, as nearly as possible at the same time and under the 

 same conditions. 



Apparatus.— The magnetizing field was furnished by a 

 solenoid 1 metre long, giving a field of 50 C.G.s. units per 

 ampere, the maximum field used being 420 units. This coil 

 was fixed vertically in a wooden framework. 



The experiments were made on a nickel wire *12 mm. 

 diameter and 80 cms. long. Its ends were soldered to two 

 thick brass rods, the lower of which was firmly clamped to the 

 wooden plank on which the coil rested, the other being held 

 up by means of a lever. The tension of the wire could be 

 altered by placing weights on the other end of this lever. 



Between the brass rods and the inner tube of the solenoid 

 were placed two brass tubes, which formed the terminals of 

 the copper ware used for comparison of resistance, this wire 

 also being within the solenoid. The coil w as provided with a 

 water-jacket through which a current of cold water was kept 

 constantly flowing. The wires were further protected from 

 the heating effect of the current by means of a glass tube, in 

 which they were inclosed. The wires and terminals were, of 

 course, well insulated from each other and from the coil, and 



* Communicated by Prof. E. Tavlor Jones. 



t Bidwell, Proc. Roy. Soc. vol ly. p. 228. 



X Nagaoka, PhiL Mag. vol. xxxvii. p. 131. 



§ Tavlor Jones, PhiL Trans. 1897. || Tomlinson, ibid. 1883. p. 1. 



^[ Barlow, Proc. Roy. Soc. 190:2. 



