1910-11.] Youngs Modulus under an Electric Current. 
221 
Cobalt. 
The specimen of cobalt I used was a rectangular strip, as I had found 
it impossible to obtain a rod of a suitable size. 
In the first place, the cobalt was heated in the ordinary way in the 
double-walled tube, the temperatures being the same as in the previous 
cases. The graph was a straight line, and the results are represented 
in fig. 15. 
It was then passed through the glass tube preparatory to being heated 
by the current, and the modulus again determined at the temperature of 
the room. It was found to be higher, so that heating it to 130° C. had 
produced an increase in the modulus, a result similar to what was obtained 
by Shakespear and Gray, Blyth and Dunlop, in their experiments on 
Young’s Modulus. 
A weak current was then passed, with the result that the modulus was 
still further increased. On continuing to increase the current, the modulus 
also increased, until a maximum was reached at about 57° C., after which 
increase of current caused the modulus to diminish. The heating was 
continued until the temperature was nearly 160° C. When the current 
was diminished the modulus rose, and had at first a higher value than at 
the corresponding stage with increasing current. A maximum was reached 
at about 80° C., and it was lower than that with the increasing current. 
This was the first cycle, and the curve did not return into itself, so that 
the cyclic state had not been reached. The cycle was repeated, with the 
result that all through the value was a little higher than in the first ; and 
it was not until the fourth cycle had been completed that the metal attained 
the cyclic condition. The first and last of these experiments are given in 
fig. 14, the weight being 15 kilos., or 13 kilos, per sq. mm. 
The cycles were repeated with increasing loads, these being 20, 25, 30, 
35, and 40 kilos., that is, 17'3, 21*6, 26‘0, 30 3, and 34’6 kilos, per sq. mm. 
respectively. The results are shown in fig. 15, and the curves show in each 
case the values for the final cycle only. 
Finally, the current was kept constant while the load was varied, and 
the results of this series of experiments are shown in figs. 16 and 17. 
These curves are also found to be similar in form to those for iron and 
nickel. As they display no marked peculiarity, it is needless to enter into 
any detailed discussion of them. We find at first the same increase in the 
value as the current is raised, that a maximum is reached, and thereafter 
increase of current causes the modbus to diminish. 
