652 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XL. — The Variation of Young’s Modulus under an Electric Current. 
By Henry Walker, M.A., B.Sc. Communicated by Professor J. G. 
MacGregor, F.R.S. 
Part II. 
(MS. received July 13, 1908. Read same date.) 
In my first paper on this subject * the behaviour of soft iron, steel, copper, 
and platinum was examined. In this paper the experiments have been 
carried a stage further, viz. 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. 
As the behaviour of the wire when heated by the current was some- 
what complicated, I considered it necessary, for purposes of comparison, 
to heat the wire in some other manner. To effect this, a double-walled 
tube of tinned iron was made, through the inner tube of which the wire 
was passed, and the ends plugged with cotton- wool. The wire was hori- 
zontal, and measurements were made with the microscopes as in the other 
experiments. As the turning values of the modulus were all found at 
comparatively low temperatures, it was not sufficient to determine the 
modulus at the temperature of the air and at 100° C., and then assume 
that the decrease was uniform between these two temperatures. To get 
suitable intermediate temperatures, steam, and the vapours of boiling 
sulphuric ether, ethyl -alcohol, and amyl-alcohol were passed through the 
annular space between the two tubes. In this way temperatures of about 
35° C., 78° C., 100° C., and 130° C. were obtained. Marks were made on the 
wires as near to the ends of the tube as it was possible to place them, so 
as to be in the field of the microscope. Except for these small lengths, 
which did not exceed 1 centimetre at each end, the part of the wire 
measured was at the temperature of the inner tube. The marks were 
observed in the microscopes, and no reading was taken until a short time 
after the wire had ceased expanding, the temperature being taken by a 
platinum thermometer, as recommended by Gray, Blyth, and Dunlop.f 
The results of these experiments gave in every case graphs which were 
straight lines. 
* Proc. R.S.E., vol. xxvii., p. 343, read June 1907. 
t Proc. R.S . , vol. lxvii., p. 180. 
