of Steel, Nickel, Cobalt, and Nickel- Steels, 53 



fields, but the elongation is less than in 46 per cent. Ni. 

 After this stage is over the ovoid goes on elongating at an 

 almost constant rate, which is greater than for the 4(5 per 

 cent. Ni. Although the field at which the curves for 46 per 

 cent, and 36 per cent. Ni intersect has not yet been reached, 

 we can easily infer that if the field be sufficiently increased, 

 the elongation in 36 per cent. Ni *, which is the least expan- 

 sible by rise o£ temperature, will exceed that for 46 per cent. 

 Ni. The contrast between 46 per cent, and 36 per cent. Ni 

 is similar to that between 36 per cent, and 29 per cent., so 

 that what has just been remarked with respect to the two 

 former alloys equally applies to the relation between the two 

 latter. It is also remarkable to observe that the 29 per 

 cent. Ni, which will apparently indicate the largest increase 

 of length if the field be made sufficiently strong, is the least 

 susceptible of the three nickel-steels. With the 25 per cent. 

 Ni we could not detect any change which is within the scope 

 of measurement now attainable with the present arrangement. 



The nickel-steel wires in the annealed state present similar 

 changes of length to the o voids. In the hard drawn state 

 the change is decidedly less than for the annealed. 



The curves of the length-change in iron or nickel, placed 

 side by side with those in nickel-steel, present a singular 

 contrast. As is well known, nickel contracts instead of 

 elongating like iron, the amount of contraction being several 

 times that of iron. The feature here presented by nickel- 

 steel is similar to nickel as regards the amount and the 

 character of the change, but as to the sense of elongation it is 

 similar to iron in weak fields, increasing instead of diminish- 

 ing as in nickel. It thus appears that the length-change by 

 magnetization is not of a simple nature, and not to be easily 

 determined from the percentages of the constituent metals. 



(e) Nickel- Steel wires in low fields. 



Urged by the question of the practical utility of the metal 

 we made special investigation into the change of length in low 

 fields, such as may habitually occur in the neighbourhood of 

 electric installations or in the terrestrial magnetic field. The 

 question will be of great importance in deciding the effect of 

 the terrestrial field ; as one instance, we may mention that 

 in using Jaderin's wire of nickel-steel in geodetic measure- 

 ments. One may suspect, from what has already been 

 described, that the effect of the magnetic field will not be 



* The expansion-coefficients a for nickel-steel are as follows : — 

 For 29 per cent. Ni : a =0-000010. 

 „ 36 per cent. Ni : a= 0-C0000 1 . 

 „ 46 per cent. Ni : a=0000009. 



