1906-7.] Variation of Young’s Modulus under Electric Current. 343 
XXXIV. — 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. 
(MS. received May 20, 1907. Read June 24, 1907.) 
Object of the Investigation. 
This investigation was carried out for the purpose of extending to other 
substances an inquiry into the effect of an electric current on Young’s 
Modulus, which was carried out by Miss Noyes on a steel wire at Cornell 
University, and described in the Physical Review , No. 4, vol. ii. In 
the investigation of Miss Noyes, the wire under examination was heated 
by a coil, the current being supplied by a storage battery. To vary the 
method of heating, the current was also sent through the wire with the 
expectation that the same effects would be obtained as when the wire 
was heated by the coil. This, however, was found not to be the case, and 
Professor Nichols, under whose superintendence the investigation was 
carried out, in his Laboratory Manual of Physics , vol. ii. p. 293, states 
that an extension of the inquiry to other materials than iron would be of 
interest. 
In the present series of experiments the behaviour of steel, soft iron, 
copper, and platinum was examined when a current was passed through 
the wires. 
General Plan of the Experiments. 
The wire to be tested was mounted horizontally on a solid block of wood 
and carefully adjusted so as to be parallel to lines ruled on it. Care was 
also taken to see that the wire was horizontal. It was placed in a glass 
tube of about 4 cms. diameter for protection against air-currents. This 
tube was 130 cms. long, and two holes were drilled in it, whose centres 
were 98 cms. apart, through which the positions of two marks on the wire 
were observed by microscopes. To prevent currents of air, the ends of the 
tube were stopped with cotton-wool. The temperature of the wire was 
determined by its electrical resistance. 
The microscopes employed had micrometers in the eye-pieces which 
were intended to be •01 mm. between each division ; but on carefully 
measuring them it was found that in the right-hand microscope each 
