832 



Miss M. B. Moir on Magnetic Properties of a 



readings in each case were found to differ appreciably, thus 

 showing the want o£ homogeneity of the specimen. The 

 results of the tests carried out with the specimen in this 

 condition are therefore of comparatively little importance, 

 and are not included in the tables of results. 



The effect of annealing the specimen from 900° C. is to 

 remove the internal strains, and bring it into a standard 

 homogeneous condition. In annealing the specimens, a 

 Fletcher gas-furnace, capable of giving temperatures up to 

 900° C, was used, and each specimen, before being placed in 

 the furnace, was carefully wrapped in copper foil to exclude 

 air and prevent oxidation. 



Each specimen after being annealed was tested mag- 

 netically in the usual way, and was then, as before, changed 

 end for end and the test repeated. In the case of each 

 specimen the two tests gave identical results, showing that 

 the material was now homogeneous. The specimen was 

 next immersed in liquid air and tested at the temperature 

 — 190° C. To bring the specimen to that temperature the 

 arrangement shown in fig. 1 below was employed. The 



Fijr. 1. 



Te 



Bi 



Ej 



[n 





m 



: f'- 



El 



specimen A was enclosed in a glass tube BCD, of which the 

 end B was closed with a cork and the end D was open and 

 bent up. Cork bungs F, F were fitted on the tube so as to 

 bring the axis of the specimen into coincidence with that of 

 the solenoid EE, inside which the tube was slipped. A third 

 bung F, or a pad of cotton-wool, was used to prevent access 

 of warm air into the interior of the solenoid, and a covering 

 of cotton-wool wound closely round the tube prevented 

 conduction of heat to the specimen. The liquid air was 

 poured in at the bent end of the tube D, and the specimen 

 kept completely immersed in it for long enough to ensure 

 its temperature being reduced to —190° C. before a magnetic 

 test was made. 



In order to make quite certain that the specimen was in 

 exactly the same position when tested at room-temperature 

 and at the temperature of liquid air, it was inserted in the 

 tube before the test at room-temperature, and not moved 

 between that test and the test at —190° C. The specimen 



