672 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Discussion of Results. 
In this paper, as already stated, the new results are — the reaching of 
the cyclically steady state with a small load, the effect when the load is 
increased, and the heating by the ordinary method. 
With the copper the steady state was reached during the first cycle, 
but with the other three more than one cycle of operations had to be 
completed before this was accomplished. In all four, the heating by the 
ordinary method gave values that were a little higher than those by the 
electric heating with the greater load on, but in all cases the temperature 
coefficient of decrease of modulus was greater with the ordinary heating 
than with the other. This, of course, means that at some temperature, if 
the coefficients do not alter, the lines will intersect. Again, the modulus 
with the electric heating and smaller weight had in all cases settled down 
to a fairly uniform rate of decrease, these rates being such that it seems 
probable that all the graphs would intersect, but the current at my disposal 
was not sufficient to heat the wires to the temperature necessary to test 
this. Now, the straight-line graphs are inclined, in each case, to one 
another at a small angle ; and quite a slight change in the coefficients 
would be sufficient to produce such a change in the slope of the lines, for 
the coefficients may not be absolutely constant, that after meeting they 
coincide, and then the values by the two methods of heating would be the 
same. In all cases, too, it might be that the same would be true of the 
modulus when the wire is heated by the current and loaded with the 
smaller weight. 
There has not been much investigation of the effect of a current 
through a wire, that is, of a circular magnetic field, on elasticity, but there 
has been a good deal of research on the effect of a longitudinal field. 
In a paper by Stevens and Dorsay,* the effect of a longitudinal field on 
Young’s modulus is investigated. The method was that of flexure, a 
mirror being attached to the middle of the rod, and the deflections read by 
the movements of interference bands. The apparatus was arranged so that 
the rod was not heated. It passed through an inner tube, in the annular 
space surrounding this tube a current of water at a constant temperature 
was kept flowing, and on the outside of this the coil was wound. As the 
temperature of the rod did not rise, their results give the effect of the 
magnetic field alone. 
In their experiments, which were performed on steel and wrought iron, 
* Phys. Rev., vol. ix., p. 116. 
