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BELL SYSTEM TECHNICAL JOURNAL 



netized curve, the greater will be the anomaly in expansion. For the 

 alloy invar the Curie point occurs at about 200° C. and the transition is 

 so rapid that the magnetic effect nearly cancels the normal expansion. 



100 200 300 400 500 600 700 SCO 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 34 — Coefificients of expansion for iron-nickel alloys versus temperature. 



Figure 35 shows a curve for the thermal expansion of an iron-nickel 

 alloy containing 36.5 per cent Ni, corresponding to Fig. 33c. The 

 flat region implies an expansion coefficient of nearly zero. 



Griineisen's law is definitely violated by metals having expansion 

 effects of the sort associated with ferromagnetic changes. Griineisen's 

 law, it will be recalled, states that the thermal expansion coefficient is 

 proportional to the specific heat. For all ferromagnetic transforma- 



