209 
1910-11.] Young’s Modulus under an Electric Current. 
higher than before any current was passed through the wire, and also that 
the value when the load was T5 kilos, was greater after the cyclic state had 
been reached than during the first cycle. The other curves give the results 
that were obtained after the cyclic state had in each case been reached. 
Before commencing each of the other cycles the wire was demagnetised, 
and the loads were 2*2, 2’9, 8*5, and 4 kilos. It will be seen from fig. 11 that 
as the weight is increased the modulus falls in value, that the hysteresis 
diminishes with increase of load, and that with the greatest load the 
modulus diminishes uniformly, the curve being a straight line. 
At the conclusion of these cycles the wire was again demagnetised, and 
the modulus determined at the temperature of the room without any 
current. It was found to be higher than the first determination, so that 
the current had produced a permanent increase in the modulus. 
Another piece of wire from the same coil was next passed through the 
double-walled tube, and the modulus determined for ordinary heating at 
the same temperatures as before by this method of heating — viz. that of 
the air, 35° C., 78° C., 100° C., and 130° C. As was to be expected, the graph 
was a straight line, showing the modulus diminishes uniformly when the 
wire is heated in this manner. 
Finally, as stated in the general outline of the course at the beginning 
of this paper, the current was kept constant while the load was varied. 
The curves are shown in figs. 12 and 13, and it is at once evident that they 
are very similar to those for iron. 
In order to eliminate any effect of torsion which might be produced by 
the wire hanging over the pulley, I attached the scale-pan to the wire by a 
string which was passed over the wheel. 
On looking at the curves of fig. 11, we see that the effect of the current is 
first to produce an increase in the modulus, a maximum is reached, after 
which it begins to diminish. Next, as the load is increased the value of 
the modulus diminishes until, with the greatest load used, the decrease is 
uniform. It will also be seen that as the load is increased the maximum 
is reached in weaker fields, and that the curve for diminishing current 
always lies below the one for increasing current. 
VOL. XXXI. 
14 
