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



until the temperature is rather high, owing to the gradient of 

 the curve of magnetization in the third stage being small. 

 With a field slightly above 1 C.G.s. the second stage is just 

 entered upon while the metal is cold, and a small increase in 

 the strength of the field makes a very considerable increase in 

 the permeability. In this case the first effect of heating is 

 to bring on more of the second stage; consequently the per- 

 meability rises as in fig. 3. In the first stage the gradient of 

 the curve of magnetization is again small ; and therefore with 

 weak fields the permeability increases but slightly throughout 

 a wide range of temperature as in the case of a moderately 

 strong field. 



Fk. 5. 



18000 

 16000 

 14000 

 12000 

 10000 

 8000 



6000 

 4000 

 2000 









1 













\ 





1 









\ 













\ 





'/ 











\ 



r 











\ 



I 











\ 



























\r 















c N, 



7 



6H 



5 



4 



3 



2 



1 



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

 Temperature in Degrees Centigrade. 



Fig. 5 is drawn to show the maximum permeability and 

 the temperature at which it occurs for different magnetizing 

 forces. In this figure the ordinates to the curves marked A 

 and B represent the magnetizing force and maximum per- 

 meability respectively, and the abscissa? the temperature at 

 which the permeability begins to fall. 



To make this clear, let us consider the case of a magnetic 

 force of 1 C.G.s. represented by RQ, the maximum permea- 

 bility obtained with this field is given by the ordinate PQ, 

 and is reached at a temperature represented by OQ. The 

 scales of magnetic force and permeability are given on the 

 right and left of the figure respectively. 



We have seen that the successive stages of the magnetizing 

 process are brought on with values of the magnetic force 



