On the Magnetic Deformation of Nickel. 47 



tion at high fields. Change of temperature, therefore, seems to have 

 similar effects on the magnetisation and contraction curves. Of 

 course this comparatively small difference of temperature, 35 C., 

 would have but a small effect on the magnetisation curve, but as the 

 contraction seems to depend on rather high powers of the magnetisa- 

 tion, it might be expected that the effect would be more noticeable 

 in the change of length than in the magnetisation. 



Measurements were next made of the magnetisation and the effect 

 of change of tension on the magnetisation, in order to calculate the 

 quantity 



0-123 0-00587 



which was shown in the former paper to be the value of the 

 elongation, <>Z/Z, of the wire deduced from Kirchhoff's theory. For 

 these measurements a coil of 611 turns of No. 40 double silk-covered 

 and shellacked copper wire was wound en the nickel wire near the 

 middle, and connected in series with a ballistic galvanometer, and 

 with the secondary of a standardising solenoid. The magnetisation 

 was determined by reversing a measured magnetising current, and the 

 galvanometer standardised by reversing a current in the solenoid, 

 the deflections being observed in the two cases. The galvanometer 

 was standardised before and after each set of readings. 



Since the resistance in circuit with the galvanometer changed 

 when the temperature of the coil on the nickel wire changed, care was 

 taken that the temperature indicated by the coil thermometers was 

 the same in the magnetisation and standardising experiments. By 

 using a series of different currents in the standardising coil, it was 

 verified that the " quantity of electricity " flowing through the 

 galvanometer was proportional to the sine of half the deflection of 

 the needle. The deflections were observed by a telescope and scale 

 at a distance of 124 cm. 



In observing the influence of tension on magnetisation, galvano- 

 meter readings were taken first with a load of 1'4 kg. on the wire, 

 then after an additional weight of 7 kg. was applied. The mag- 

 netising current was reversed several times and the load ap- 

 plied and removed several times before readings were taken. This 

 was repeated for various field strengths, ranging between 30 and 

 320 C.G.S., and with the coil at 10 C. and 55 C. Then the mag- 

 netisation curve of increasing reversals was determined for the 

 mean load 4'9 kg. at both temperatures, after which the coil was 

 removed from the nickel wire, and observations made with load 

 4'9 kg., and at the same two temperatures, of the magnetic contrac- 

 tion at a number of increasing field strengths, each field being 

 reversed several times before readings were taken. 



