654 
Proceedings of the Royal Society of Edinburgh. [Sess. 
was no temperature gradient, the wire was covered with asbestos and put 
through a cycle of heating and cooling, but there was no difference in the 
results. 
Soft Iron. 
A wire from a different coil, but of the same gauge as in the first 
experiment, was taken. The modulus was determined at the temperature 
of the room, and found to be 18T4 x 10 11 , which was lower than the value 
in the first wire. A weak current was then passed through it, which 
raised the temperature slightly, and this was accompanied by a decrease 
in the modulus. On strengthening the current the modulus rose in value, 
and continued to rise as the current was increased until the temperature 
was a little over 50° C. After the maximum had been reached there was 
a gradual diminution, the rate of which was fairly uniform up to a 
temperature of about 110° C. Beyond this the rate of fall diminished. 
On decreasing the current there was at first a further slight fall in the 
modulus, but as the temperature continued to fall a minimum was reached, 
and the increase that ensued went on to a temperature a little over 60° C. 
This maximum with the diminishing current has a lower value, and is 
reached at a higher temperature, than that with the increasing current. 
Beyond this point, as the current becomes less, the modulus falls, and 
finally reaches a value lower than what it had when the current was 
started. After cooling to the temperature of the room, the modulus had 
a higher value than before any current was passed through the wire. 
This was the behaviour of the wire during the first cycle, and these results 
are quite the same as those described in my former paper. 
As the wire had not returned to the same state as when the current 
was started, the cycle was repeated and readings taken as before. There 
were slight changes, the value being always higher than at the correspond- 
ing temperature in the first cycle. The value at a temperature only 
slightly above that of the room was still lower than what it was with a 
commencing current at the same temperature, and it was not till the fifth 
cycle had been completed that the steady state was reached. 
After the steady state was reached, the value was higher than at the 
same temperature in any of the preceding cycles. It is to be noted that 
the change is greatest with a diminishing current when the temperature is 
below 50° C. The same effect, viz. an increase in the modulus, was found 
when no current was being carried by the wire. The value was higher 
after the cyclically steady state had been reached than under the same 
conditions in any of the preceding cycles. 
