1907-8.] Sensitive State induced in Magnetic Materials. 241 
specimen; the dotted line shows the condition after demagnetisation by 
reversals. It will be observed that the change is most pronounced at the 
steep part of the curve, whilst for fields greater than 60 c.G.S. units the 
susceptibility is practically unaltered. In subsequent work attention was 
therefore directed to field strengths below this value. 
It was found that reannealing at 900° C. resulted in the specimen being 
restored to the magnetic condition defined by the continuous line. 
Nature of the “ Sensitive State ” — As the enhanced magnetic quality of 
the steel induced by the thermal treatment was removed in the process of 
demagnetising by the method of reversals, it follows that if a specimen in 
the sensitive state is magnetised by a field H = H / , for which 1=1', and if 
H is now reduced to — IT and then increased to + IT, the final value of I 
should be less than I'. That is to say, a cyclic alteration in H should not 
VOL. xxviii. 16 
