24 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
apparently affected in a similar manner by stress and strain whether these latter be 
due to mechanical force, to magnetization, or to change of temperature. 
The influence of rest on the wire, whether the metal is left loaded or unloaded, is 
also very noticeable in the case of iron, and less but sufficiently so with the other 
metals ; thus we see in a that in the case of iron after 10 turns of permanent torsion 
the amount of twist for 8 kilogs. is five minutes after the permanent torsion, 8 
divisions, 14 divisions after a rest of half-an-hour, and 22'5 divisions after a rest of 
16 hours. 
Torsional Eigidity. 
The torsional rigidity of the wires was determined by the method of vibrations. The 
vibrators were similar to those employed by Sir W. Thomson in his experiments on 
the rigidity and viscosity of metals," namely, thin cylinders of sheet brass, supported 
by a thin, flat rectangular bar. The wire to be tested passed perpendicularly through 
a hole in the middle of the bar, and was there soldered. The other end of the wire 
was soldered into a stout iron bar, firmly held in a vice attached to a rigid support. 
Effects of Permanent Torsion and Elongation on the Modulus of Eigidity. 
Thomson has provedt that the rigidity of a wire is diminished both by permanent 
longitudinal extension and by permanent twist. As it seemed desirable to ascertain 
whether rest would restore any of the rigidity thus lost, and also whether the influences 
of permanent extension and torsion would be greater on vibrations through large arcs 
than through small ones, a series of experiments was begun of which the following 
are examples. 
Experiment XIV. 
An iron wire was considerably stretched, and the times of vibration ascertained 
to be— 
Number of minutes 
after stretching.! 
Time of vibration. 
5 
Seconds. 
3-040 
25 
3-025 
35 
3-019 
45 
3-015 
1440 
3-000 
2880 
2-996 
* Proc. Roy. Soc., vol. xiv., p. 289. 
f ‘ Brit. Encyc.,’ Art.: “Elasticity,” §§ 78, 81. 
X The vibrations were generally counted in each trial for about 10 minutes, and the times are reckoned 
from the commencement of each trial. The initial arc of vibration was in each case 10°, 
