938 Prof. Trouton and Mr. Rankine: Stretching and 
atom ; and is so small that he was led to believe it to be an 
atom of resinous electricity unloaded with ponderable matter, 
It is also very interesting to know from J. J, Thomson’s 
experiments and from a continuation of them by H. A. 
Wilson *, that the virtual mass of the particles of the torrent 
from the kathode, was the same whether the metal of the 
kathode was aluminium, platinum, copper, iron, lead, silver, 
tin, or zinc. This strongly corroborates Thomson’s original 
conclusion that Varley’s+ ‘“‘attenuated particles of matter 
“* projected from the negative pole by electricity in all directions,” 
are atoms of resinous electricity. \ 
§ 12. It is very much to be desired that careful experiments 
with the very highest obtainable vacuum should be made to 
ascertain the greatest steady, measured, difference of poten- 
tials; that can "be maintained with or without ¢ any measurable 
electric current between two metals separated by a very short 
length of vacuous space. 
LIL. On the Str Bs and Torsion of bade Wire , eee 
the Elastic Limit.. By Prof. Trouton, F.R.S., and 
A. O. Ranxinet. . 
[Plates XIV. & XV.] 
HE behaviour of wires or rods when stressed longitu- 
dinally or torsionally beyond the elastic limit is of a 
complicated nature. The general character of the effects 
observed on the application of such a stress is as follows. 
First there is the immediate effect followed by an increase 
with time. The latter initially may be considerable, but 
gradually diminishes with time to what appears to be a small 
constant amount. It is convenient to refer to the first as the 
primary strain, to the final constant rate as the viscous flow, 
and the remaining intermediate effect as the secondary strain. 
What follows refers mostly to the. secondary strain. 
The method of procedure in investigating this question 
has apparently always been to apply a constant stress and to 
observe the rate of change in the resulting strain. Or after- 
wards to remove the stress and examine the rate of recovery. 
This method has been adopted for instance in the investigation 
of: torsional strains in wires. We also have used it, but in 
addition we have used the method in which a constant strain 
* H. A. Wilson, Proc. Camb. Phil. oe, xi. p. 179 (1901). 
_ + “Some Experiments on the Discharge of Electricity through Rar efied 
Media and the Atmosphere,” by Peomwell Fleetwood Varley, “Proc. R.S. 
Oct. 5, 1870. td 
i Communicated bythe Authoys, oii. 24 50: ew ef iF 
