(302 Prof. Hichardson and Mr. Lownds on the Magnetic 



thought it desirable to undertake further experiments on the 

 magnetic behaviour of these specimens. 



Experiments were accordingly made in the first instance to 

 ascertain in what way the hysteresis-loss, between given limits 

 of the field strength, was connected with the temperature for 

 the specimen containing 3*64 per cent, of aluminium. 



As will be seen later, these experiments show that the 

 hysteresis-loss attains a maximum value at a temperature con- 

 siderably higher than the temperature of maximum induction. 

 An account is also given of some experiments on the changes 

 produced in the magnetic properties of the alloy by heating to 

 a high temperature and subsequently cooling. It is shown 

 that the magnetic properties depend largely on the previous 

 history of the specimen ; successive curves connecting the 

 maximum induction obtained for any given value of the field- 

 strength and the temperature differing from one another to 

 some extent when the heating has been carried to a high 

 temperature. This difference has been found to be greater 

 for weak than for strong fields. 



There does not, however, appear to be any essential differ- 

 ence between the behaviour of this alloy during heating and 

 cooling (except near the temperature of minimum permea- 

 bility, e. g. critical temperature). 



Similar results have been obtained for the specimen 

 containing 5*44 per cent, of aluminium. For the speci- 

 men containing 9*89 per cent, of aluminium, however, no 

 change in the magnetic properties could be detected due 

 to heating and cooling unless the heating was continued to 

 about 670° C, which temperature is about 220° higher than 

 the temperature of minimum permeability for this specimen 

 (e.g. 450° C). In addition an account is given of some 

 experiments on the abrupt change in the permeability that 

 takes place at a temperature of 052° C. (vide p. 139, Phil. 

 Mag. Jan. 1900). 



The Ballistic method was used for determining the hysteresis- 

 loss; and the Balance method (vide Parti.) for obtaining the 

 smaller values of the induction when the specimen was near 

 the temperature of minimum permeability. 



The specimen in the form of a ring was wrapped round 

 with asbestos-paper. Next to this was twisted the ther- 

 mometer-wire which consisted of platinum wire of '2 millim. 

 diameter. This wire was connected to platinum leads of 

 •5 millim. diameter. 



Compensating leads, cut from the same specimen of wire, 

 passed out along with these between the primary and 

 secondary winds. 



