608 Prof. Richardson and Mr. Lownds on the Magnetic 



§ V. Connexion between Hysteresis Loss and 

 Temperature. 



It had been observed in the earlier experiments that the 

 curve connecting the maximum induction reached at each 

 reversal and the temperature for a given value of the field- 

 strength altered to some extent after the specimen had been 

 heated to a high temperature. This was also found to be the 

 case witlrthe specimen containing 5'44 per cent, of aluminium. 

 In the case of the other two specimens investigated, how- 

 ever (the one containing 9*89 and the other 18'47 per cent, of 

 aluminium), this was not the case, unless the temperature 

 reached was much higher than the temperature of minimum 

 permeability. 



For the alloy containing 9*89 per cent, of aluminium the 

 curve was quite constant under all conditions, unless the 

 specimen was raised to a temperature of 670° C. (i. e. 220° 

 above the temperature of minimum permeability), in which 

 case a new curve of the same general shape as the original 

 curve was obtained. 



The change in this case may be due to the specimen reaching 

 the melting-point of aluminium. That conclusion, however, 

 is not borne out by the experiments on other specimens, as in 

 general a noticeable change takes place at a temperature 

 considerably lower than this. 



In order to obtain comparable results, the loops were taken 

 in the order of increasing temperature : the temperature on 

 any day on which an experiment was made being higher than 

 that reached in the preceding experiment. 



The experiments were conducted under the following 

 conditions : — 



At about 10 a.m. the heating current necessary to produce 

 the required temperature was started in the heating circuit. 



A steady temperature was, in general, reached at about 



3 P.M. 



The specimen was kept at this temperature till about 5 p.m., 

 to ensure a uniformity of temperature when a loop was taken. 



The specimen was then allowed to cool, and the process of 

 re-heating was commenced on the following day*. 



In some cases several loops were taken in one day. When 

 this w r as so, the higher temperatures were obtained without 

 first cooling the specimen to the temperature of the room. 



The standardising throw was taken before and after the 

 observations for each hysteresis-loop. 



The loops obtained are shown on Plate VI. 

 * This method is spoken of as the method of successive heatings. 



