621 
1907-8.] Sensitive State in Magnetic Materials. 
the solenoid, and gradually reduced from a large value to zero. The specimen 
in this demagnetised condition was allowed to rise gradually to about 10° C., 
and then once more cooled to — 190 ° C. with liquid air. When it had assumed 
this temperature throughout its mass, a cjmle was taken, the specimen de- 
magnetised by reversals, and the magnetometric test repeated. For a field 
of 12 C.G.S. units the intensity of magnetisation in the first test exceeded 
that in the second by nearly 4 per cent. Three specimens in all were tested 
in this manner, and gave results in very close agreement. Similar tests 
were made with the hard steel and showed only a very feeble indication of 
a “sensitive state” — about 0*5 per cent, for a field of 10 C.G.S. units. 
This production of a “ sensitive state ” by employment of low tempera- 
tures pointed to a very important fact. Since specimens which have been 
demagnetised do not improve in quality with time at ordinary room tem- 
perature, it follows that the “ sensitive state ” induced by raising the speci- 
men from — 190° C. to 10° C. and lowering it again was acquired whilst the 
temperature was changing, and not during the period when the temperature 
was constant at 10°. Tests were therefore made to measure the enhance- 
ment of magnetic quality produced (1) by heating the specimen from 
— 190° C. to 10° C., and (2) by cooling from 10° C. to —190° C., testing, it 
is to be noticed, after each variation of temperature, and wiping out the 
sensitive state before imposing the next variation. The results obtained^are 
given in Table VI., and are contrasted with those obtained in the previous test. 
Table VI. — Sensitive State with Liquid Air. 
Percentage Sensitive State. 
Thermal Treatment. 
— 
Steel wire 
Hard steel 
H = 12. 
H = 10. 
From - 190° to 10°, and then to - 190° C. . 
3*5 
0-5 
From - 190° C. to 10° C 
15- 
IP 
From 10° C. to - 190° C 
24- 
6- 
From 10° to - 190°, and then to 10° C. 
3- 
1-5 
