664 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Copper. 
A piece of wire of the same gauge was used as in the first experiment. 
First, a measurement at the temperature of the room was made, the value 
being 11 '21 x 10 11 . On strengthening the current there was a rapid increase 
in the modulus, the maximum being at about 45° C. There was then a 
diminution, somewhat rapid at first, but the rate of which gradually fell 
away, until at about 95° C. it had become fairly uniform. When the 
current was diminished there was an increase in the modulus, which con- 
tinued until a maximum was attained at about 57° C. This maximum was 
lower than that with the increasing current, and the value fell gradually 
until it was the same as when the current started. In this case, then, the 
cyclically steady state was reached in the course of the first cycle. On 
cooling to the temperature of the room, the modulus had a value somewhat 
higher than its original value before any current was passed through the 
wire, so that there was a permanent increase produced by the current. 
In this experiment the wire was loaded with *8 kilo, that is, 12'8 kilos 
per sq. mm. The wire was then loaded with 1*6 kilos, that is, 25'6 kilos 
per sq. mm., and the graph was a straight line, the values being as shown 
in the diagram. 
The same wire was next heated in the ordinary way, as in the other two 
cases, and here again the graph was a straight line. 
The results for copper are, generally speaking, similar to those for iron 
and steel, the differences being in degree rather than in kind. For example, 
the fall in the modulus from the value it had before any current was passed 
to its value when there was a weak current, also the rise in the modulus at 
the end of the cycle after the wire had cooled to the temperature of the 
room, were both smaller than the corresponding changes with iron and 
steel. Again, the difference between the values obtained by the ordinary 
heating and the electric heating with the wire under greater tension is less 
than in the two preceding cases. 
When the two straight lines are produced they intersect at about 
180° C. ; and since the graph for electric heating with a load of '8 kilo has 
become at 120° C. nearly a straight line, in which the rate of fall is greater 
than in the other graphs, they will all finally intersect one another. There- 
fore it is possible in this case also that the three may ultimately coincide. 
