MAGNETIZATION AND MAGNETIC CHANGE OF LENGTH. 



61 



The above manner, in which the magnetization is changed 

 by temperature, is common to all other irreversible nickel steels. 

 As the percentage of nickel decreases, the concave portion of the 

 ascending branch becomes fainter and fainter ; and with 24.409^ 

 and 24.049^ Ni, it almost vanishes for strong fields. Apparently, 

 the forms of the two curves for nickel steels of 29.249^ and 

 24.04?^^ Ni, are widely different from each other ; but if we 

 compare the forms of the curves of two consecutive nickel steels, 

 we can trace transition stages from one form to the another. 



The critical temperatures of the alloys for H =400 C.G.S. 

 are given in the following table : — 



Thus in the ascending branch, the critical temperatures of 

 these irreversible nickel steels are nearly equal, except with the 

 last but one. The above numbers fairly coincide with those ob- 

 tained by M. Osmond, except with 24.40^ Ni. AVith this alloy, 

 the critical temperatures are greater, in our case, by about 50°C 

 for the ascending branch and 100°C for the descending, than in 

 the experiment by Osmond. The values given by L. Dumas for the 

 first four of these alloys are considerably less than those obtained 

 by us ; but for the remaining alloys, the contrary is the case. 

 These discrepancies may probably be due to the previous history 

 of the alloys. 



It remains to mention a singular phenomenon. If at a point 

 in an ascending branch of the temperature-cycle, the temperature 

 be reduced to the ordinary, the path is utterly different from the 



