1906-7.] Variation of Young’s Modulus under Electric Current. 351 
was next increased, with the result that the value rose until a maxi- 
mum was reached about 34°, after which there was a regular decrease 
until the temperature was 108°, this being the highest temperature 
reached. Throughout the latter part of this curve the rate of decrease 
in the modulus was less than that of increase when the value was 
rising. 
The current was then diminished, with the result that the modulus rose 
until the temperature had fallen to 57°, the maximum at this point being 
higher than that got with the increasing current. Throughout this stage 
the rate of increase was higher than the rate of fall with the increasing 
current. Below this temperature the modulus diminished along with the 
temperature, the rate of fall being greater than that at the same tempera- 
ture with the increasing current, so that the graph cuts at about 41° ’5. 
The fall was then quite regular to 25°, this having been the last reading 
taken with a current. The value was finally determined at the tempera- 
ture of the room without a current, and found to be higher than what 
it was before any current had been passed. There was therefore a 
permanent increase in the value of the modulus. 
Copper Wire. 
The modulus was determined at the temperature of the room, and when 
a weak current was passed it produced a fall in its value. As the current 
was increased, there was a rapid increase in the modulus, which continued 
until the temperature had risen to about 45°, when a maximum was reached. 
Above this temperature there was a diminution which was fairly rapid at 
first, but the rate was not so great as that of the increase before the 
maximum. The rate of fall began to alter about 60°, and after 80° it was 
fairly uniform up to 127°, beyond which point the readings were not 
continued. 
The current was then diminished, with the result that the modulus 
increased in value till the temperature had fallen to about 60°, and through- 
out this stage the value was higher than at the same temperatures with the 
increasing current. Until the temperature had fallen to 80°, the rate of 
increase in the modulus was greater than that of decrease for the increasing 
current ; but at lower temperatures the rate of increase became less than 
that of decrease, and the two curves cut at about 57°. Further, the 
maximum with the diminishing current was not so high as that obtained 
when the current was increasing. The modulus still kept on falling, the 
rate also being less than that with the increasing current, until the 
