1912-13.] Sensitive Magnetic State induced in Various Ways. 243 
XXII. — The Effect of Thermal Treatment and the Effect of Longi- 
tudinal Strain in inducing a Sensitive State in certain 
Magnetic Materials. By Margaret B. Moir, M.A., B.Sc., Carnegie 
Research Fellow in the University of Glasgow. Communicated by 
Professor A. Gray, F.R.S. 
(MS. received March 13, 1913. Read May 26, 1913.) 
It has been pointed out by several experimenters, notably by Ewing,* and 
Gray and Ross,f that a specimen of steel freshly annealed is in a peculiar 
magnetic condition. Thus, if a specimen, thoroughly demagnetised, is 
annealed and then tested, a certain I-H curve is obtained. If it be then 
demagnetised, and tested again, a second I-H curve is obtained which lies 
definitely below the first; and any further tests after demagnetisation 
produce a repetition of the second curve, which is characteristic of the 
specimen. To obtain the first curve again, the specimen has to be annealed 
from the same temperature as before, and a test made before demagnetisa- 
tion. It has been shown also that this “ sensitive state ” of the material, 
as it has been called, can be induced not only by heating to a high 
temperature, but, to some extent at least, by any change of temperature, 
and that it is while the temperature is actually changing, not while it 
remains constant at any value, that it is induced. 
Though much has been done by previous experimenters, there still 
remains a wide field for further investigation, and, at the suggestion of 
Dr J. G. Gray, the author began in January 1911 a detailed examination 
of a number of steels, with a view to finding how they compared with one 
another when subjected to similar thermal treatment, and how differing 
thermal treatment affected the same specimen. 
After considerable progress had been made in this research, it was 
suggested by Dr Gray, with a view to obtaining further information about 
the nature of the “ sensitive state,” that the effect of strain in inducing it 
should also be investigated. That the “ sensitive state ” could be induced 
by application or removal of longitudinal stress had already been pointed out 
by Ewing, J but no attempt had been made to compare the amounts of sensi- 
tive state induced under different circumstances and in different materials. 
* J. A. Ewing, “ Experimental Researches in Magnetism,” Trans. Roy. Soc ., clxxvi. p. 630. 
t Proc. Roy. Soc. Edin ., xxviii. pp. 239 and 615 (1908). 
f Trans. Roy. Soc., clxxvi. p. 580 et seq. 
