10 



On Magnetic Testing. 



temperature of liquid air. On being tested at this temper- 

 ature it gave results which are shown in curve J I. Finally 



Fk 







//A 





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H IN C.G.5. UNITS. 



the specimen was submitted once more to a process of re- 

 versals and retested, care being taken to keep ihe temperature 

 at —190° C. throughout. The results shown in curve III. 

 were then obtained. 



Curves I. and III. are the true magnetization curves for the 

 material at room temperature and at —190° C. respectively; 

 it is these curves, and not curves I. and II., which must be 

 employed in contrasting the magnetic properties of the 

 materials at the two temperatures. If, for any reason, it is 

 desired to obtain curve II., it is evident that a method of 

 experimenting must be employed which does not involve 

 reversal of the magnetizing force. Tests carried out by the 

 method of reversals upon a specimen in the condition brought 

 about by the cooling alone would yield neither curve II. nor 

 curve III. 



In carrying out the tests which furnish the magnetization 

 curve for the specimen at the temperature of liquid air, it is 

 necessary that not only the tests, but also the neutralization 

 process, should be carried out at that temperature. This is 



