of Steel, JVickelj Cobalt, and Nickel-Steels. 59 



graphical representation, is the approximate proportionality 

 of the effect to the magnetizing force. 



The magnitude of the change is, however, not directly 

 proportional to the intensity of magnetization, as the 46 per 

 cent. Ni shows a smaller effect than the 29 per cent. Ni, which 

 is the least magnetizable among the specimens with the 

 exception of 25 per cent. Ni, whose magnetization is scarcely 

 to be detected by ordinary means. In fields of 1600 c.G.s. 

 units the change amounts to 



13 



= 3-8 x 10~ 6 for 46 per cent. Ni. 



= 22-0 



xl0~ 6 



»J 



36 



7J 



= 48-9 



xlO- 6 



5? 



29 



» 



= 0-2 



xlO- 6 



V 



25 



ii 



= 1-2 



XlO" 6 



•)"> 



soft 



iron. 



The difference between steels containing different per- 

 centages of nickel is indeed remarkable, as the changes here 

 noted far exceed that hitherto observed in simple ferro- 

 magnetic substances. The change in 29 per cent. Ni is 

 nearly 40 times greater than in soft iron ; in fact, the motion 

 of the capillary meniscus can be easily followed by the naked 

 eye, as the displacement, which takes place almost instan- 

 taneously w T ith the making of the current, is nearly 5 mm. 

 in the capillary tube of 0*4 mm. diameter in the strongest 

 field at our disposal. Even the 25 per cent. Ni shows a 

 volume-change which, in spite of the minute magnetizability, 

 is distinctly visible with a microscope. 



From the above result, it follows that there is a certain 

 alloy, whose percentage content will lie somewhere between 

 25 per cent, and 36 per cent., that will indicate greatest change 

 of volume ; the change will indeed be the greatest that we 

 can observe in the ferromagnetic substances of common 

 occurrence. 



AVhen we consider that the alloys of nickel and iron show 

 increase of volume, we at once perceive that the sense of the 

 change is not common to both the constituent metals. When 

 we further consider the magnitude of the change and compare 

 it with that observed in iron or nickel, we are struck with 

 the immensity of the effect, which is not shared in such 

 an extraordinary degree by either of the constituents of the 

 alloy. A similar remark applies to the magnetizability of the 

 different specimens ; that the alloy of two strongly magnetic 

 substances should give rise to an almost neutral body is in no 

 way a matter for surprise, when considered in the same light 



