Hackett — The Twist and Magnetisation of a Steel Tube. 421 



of observations could not be taken for the higher fields, as the circular current 

 was limited to 60 amperes. 



Inspection of the graphs demonstrates that the linear relation required 

 holds approximately within the region under investigation. As we increase 

 the intensity of the resultant field the graph becomes slightly curved. This 



20 



is 



!5 



10 



10 



Sin 2a. 

 Fig. 2. 



suggests some minor departures from the ideal conditions of magnetization 

 postulated by the theoretical investigation. We require, therefore, to examine 

 the actual state of magnetization of the tube under these special conditions. 

 The results of the investigation are given in the second section of the paper. 



