1912-13.] Sensitive Magnetic State induced in Various Ways. 2,45 
The specimen was then, while in its position in the solenoid, raised by 
means of the electric furnace -to a temperature of about 50° C., put through 
a magnetic test, demagnetised by reversals to remove the sensitive state, 
and tested again. The difference between the first and second readings is 
a measure for any field strength of the sensitive state induced by the 
previous thermal treatment. The specimen was then demagnetised once 
more, and the temperature raised another 50° C., and the process repeated, 
and this continued till a temperature of about 600° C. was reached. This 
enables the amount of sensitive state induced by a rise of about 50° C. at 
different parts of the temperature scale to be determined. 
The same process was then repeated at intervals of 100° C. instead of 
50° C., and tests were also made to determine the effect of a rise of 
temperature from room temperature to about 100°, 200°, 300°, 400°, 500°, 
and 600° C., the effect of fall of temperature from these temperatures to 
room temperature, and also the effect of rise and fall of temperature with- 
out intermediate demagnetisation. 
The values of the sensitive state are expressed in the usual manner as 
the percentage by which the magnetic intensity for the specimen in the 
sensitive condition exceeds the normal value, and the figures for each 
specimen are taken for the particular field for which for that specimen the 
effect is about a maximum. 
The effects produced by successive rises of 50° C. and 100° C. are shown 
graphically by ordinates erected at the temperature points at which 
readings are taken. This method was adopted as showing more clearly 
than a continuous curve could do exactly what measurements were obtained, 
and also because the successive rises were not in every case exactly 
the same, and therefore the process could hardly be described as a con- 
tinuous one. 
The other effects, however — of rise of temperature, of fall of temperature, 
and of rise and fall of temperature — are all shown graphically in curve form 
with the temperatures as abscissae and the percentage sensitive state as 
ordinates. 
Discussion of Results. 
Medium Carbon Steel. — Fig. 1 (i.) shows the effect of successive rises of 
temperature of about 50° C., and illustrates very clearly how greatly the 
effect of a certain rise of temperature depends on its position on the 
temperature scale; for while a rise from 100° C. to 150° C. produces a 
sensitive state of nearly 40 per cent., a rise from 200° to 250° C. has an 
entirely negligible effect. The most susceptible part of the temperature 
