6 



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



Various magnetizing forces were afterwards used and curves 

 plotted showing the relation between permeability and tempe- 

 rature corresponding to heating and cooling. In each case 

 the permeability reaches the same maximum value during 

 cooling as on heating, and for each magnetizing force the 

 heating and cooling curves are very similar. 



The ring was afterwards examined in successive experi- 

 ments at different temperatures, the magnetic force was 

 varied while the temperature was kept constant, and from 

 these results permeability -temperature curves were drawn 

 for various magnetizing forces. The curves obtained com- 

 pare satisfactorily with those given by Hopkinson * for cor- 

 responding fields. 



A few special cases will be given here to show the effect of 

 heat on the permeability as the magnetizing force is varied 

 between two values, the larger of which brings on the second 

 or third stage before any heat is applied, while the smaller is 

 unable to bring on the second stage before the critical tempe- 

 rature is reached. 



In each experiment the observations were repeated several 

 times with reversed directions of magnetizing force, and after 

 each experiment the ring was demagnetized by reversals as 

 explained above. 



A magnetizing force of 4*3 c.G.s. gave the following values 

 for the permeability at the temperatures noted : — 



T dS P c n } 15 ° 174 ° 260 ° 367 ° 430 ° 482 ° 592 ° 645 ° 735 ° 748 ° 767 ° 

 li 2606 2693 2719 2769 2744 2744 2593 2568 1682 1477 122 



shown graphically in fig. 2. 



Fig. 2. 



3000 

 2500 



2000 



f — 





H=4 



■3 C.G 



S. 



+ 



























\ 



\ 

















\ 

















\ 

































■ 





100J 200° [300° 400° 500° 600° 700° 800° 

 Temperature in Degrees Centigrade. 



* Phil. Trans, vol. clxxx. plate xiv. (1889). 



