8 Mr. R. L. Wills on the Effects of Temperature 



T dT p c in } i5 ° 26 °° 367 ° 43 °° 482 ° 592 ° 645 ° 735 ° 748 ° 767 ° 



/* 1299 2788 4320 5305 5743 7250 7805 6300 5579 473 



In this case the second stage is just entered upon before 

 any heat is applied, the permeability consequently increases 

 as shown immediately the temperature is raised. At about 

 650° C. the prejudicial effect of temperature becomes stronger 

 and the permeability falls. 



With a magnetizing force of 0*688 C.G.S. the results 

 were: — 



T d<r p c l i5 ° i74 ° 26 °° 367 ° 482 ° 592 ° 645 ° 735 ° 748=i 767 ° 



H 814 1180 1315 2228 4208 8204 9999 9315 8375 733 



As the magnetizing force is reduced the increase in per- 

 meability during the earlier stages of heating gets less ; but 

 at the higher temperatures the permeability increases more 

 rapidly, and the change from the magnetic to the non-mag- 

 netic state becomes more and more abrupt. This is because less 

 of the third stage of the magnetizing process is entered upon 

 before the critical temperature is reached ; and consequently 

 the rate of increase of permeability at high temperatures will 

 be greater. 



Reducing the magnetizing force still more, the maximum 

 permeability obtained in each case and the temperature at 

 which it occurs increase, until with a force of 0'172 C.G.s. 

 the maximum permeability is practically 17,000 at a tempe- 

 rature of about 750° C. 



The values of the permeability at different temperatures 

 with this magnetizing force were: — 



T |™ P in ] 15° 174° 260° 367° 482° 592° 045° 735° 748° 767° 

 ^ 461 542 597 759 1085 1790 2985 14852 17228 2632 



shown graphically in fig. 4. 



Corresponding curves were drawn for lower magnetizing 

 forces. The temperature at which the rapid rise in per- 

 meability begins increases as the magnetic force is reduced, and 

 the maximum permeability obtained in each case diminishes. 

 This is just what we should expect, seeing that with weaker 

 fields the temperature necessary to bring on the second stage 

 is higher, and therefore less of this stage is entered upon 

 before the critical temperature is reached. 



