834 



Miss M. B. Moir on Magnetic Properties of a 



Table I. (Fig. 2.) 



1 per cent. Cr. 





Annealed at 900° C. 



Quenched at 900° C. 











15° C. 



-190° C. 



15° C. 



-190° C. 





H. 



I. 



I. 



I. 



I. 



5 



190 



130 



16 



10 



10 



460 



480 



60 



40 



20 



680 



708 



210 



143 



40 



844 



878 



588 



504 



60 



940 



978 



796 



762 



100 



1040 



1082 



960 



944 



150 



1117 



1159 



1076 



1060 



It is to be noticed that this latter curve starts below the 

 former, as was to be expected, but crosses it very early in 

 the range, the value of the magnetizing force at the crossing- 

 point being only about 8 C.G.s. units. Thereafter the curve 

 at —190° G. lies entirely above the curve taken at room- 

 temperature, and the improvement in magnetic quality 

 becomes more marked as the field is increased in value. 

 The results of the next test, made after the specimen had 

 again reached room-temperature, are not included in the 

 table nor in the diagram, The curve belonging to this test, 

 however, almost coincides with the previous curve taken at 

 room-temperature, lying only very slightly below it at the 

 beginning of the range and slightly above it later on, the 

 crossing of the curves in this case also being in the neigh- 

 bourhood of H = 8. That is to say, the effect on the specimen 

 of immersion in liquid air is to give it a permanent set 

 magnetically in the direction of its condition at — 190° C. 

 The change in susceptibility is, however, very small. 



The other two curves, the dotted curves marked II and II', 

 belong to tests 3 and 4 in Table I., and show the results 

 obtained on testing the specimen in the quenched condition. 

 II is the curve taken at ordinary temperature, II' is the 

 curve belonging to —190° O. In this case the liquid-air 

 curve lies everywhere below the curve taken at room-tem- 

 perature, and the form of the curves shows that crossing will 

 only occur for a very high value of the magnetizing force. 

 The third test, made when the specimen had again reached 

 room-temperature, gives a curve which exactly coincides 

 with curve II, showing that in the quenched condition the 

 lowering of the temperature of the specimen to — 190° C. 

 does not permanently affect its magnetic quality. 



