1907-8.] Young’s Modulus under an Electric Current. 
667 
Platinum. 
In this case the wire was that used in the first experiment, and the first 
cycle is, with a few trifling exceptions, practically identical with that 
experiment. When the modulus was determined at the temperature of the 
room, the value was 13'55 X 10 11 , and then when a weak current was passed 
the value fell. Here there is a difference from the first experiment, for in 
it the first effect of the current was to increase the modulus. In the two 
experiments, however, the modulus had the same value when the current 
was weak. Now, in the first experiment the effect of the cycle was to 
increase the modulus when the wire had cooled to the temperature of the 
room, so that some of this effect must have remained in the wire ; for, while 
the value is lower than the final determination at the room temperature in 
the first experiment, it is higher than the initial value. 
The modulus was then determined at various temperatures with a 
gradually increasing current, with the results as shown in the graph. It 
will be seen how closely this agrees with the first experiment. The 
maximum is at about 108° C., and the modulus falls more rapidly than it 
rose. On decreasing the current there is at first a fall, then a rise, which 
at about 125° C. increases in rate until a maximum is reached at about 
85° C. The subsequent fall is at first fairly rapid, then the rate gradually 
diminishes down to the lowest temperature at which a reading was taken. 
After cooling to the temperature of the room, there was an increase in the 
modulus. 
As the wire had not returned to its original state, the cycle was repeated, 
and the results were as shown in the graph. With an increasing current 
the value was a little greater than at the corresponding stage in the pre- 
ceding cycle until a temperature of about 107° C. was reached, at which 
point the graphs intersect. Beyond this, until a temperature of about 
143° C. was reached, the second cycle was lower than the preceding. At 
this point they crossed again, and the second did not diminish so rapidly as 
the first. On decreasing the current there was again a fall, but the values 
with the diminishing current were still higher than those with the preceding 
cycle. The two graphs then run closely side by side until near the maximum 
with a decreasing current, when it was found to be lower than that which 
preceded it. Beyond this point the rate of fall is at first almost the same 
as previously; then, at about 77° C. , the rate of decrease becomes greater 
than at the same stage, and continues increasing until, on being brought 
back to the temperature produced by a weak current at the beginning of 
