26 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
afterwards vibrated once in 6’431 seconds through small arcs, and in 6'58 seconds 
when started with a twist of three revolutions. The difference between the two 
times is now T49 second or twice the former difference. After a rest of 24 hours 
the two times became respectively 6'370 and 6'474, and the difference T04 second. 
Experiment XIX. 
An iron wire, feet in length, was vibrated through different arcs for 30 seconds 
in each of several trials, and the means of these taken as the time of vibration. 
Number 
of degrees in initial 
arc of vibration. 
Mean time of 
oscillation. 
Seconds = t. 
l°0 
1-200 
90 
1-250 
180 
1-244 
90 
1-228 
10 
1-200 
360 
1-210 
180 
1-188 
720 
1-250 
360 
1-245 
180 
1-220 
90 
1-182 
10 
1-200 
Previous to these trials the wire had received 10 turns of permanent torsion, which 
had had the effect of diminishing the rigidity. 
Vibrating the wire caused, in this instance, as it does in all cases wdiere the metal 
has received permanent torsion, a certain amount of untwisting depending upon the 
amplitude of the arc of vibration.* 
Experiment XX. 
A piano-steel wire was vibrated several times, for about 30 seconds each time, 
through 1080°, and the time of vibration was found to diminish on each trial until 
the fourth, when it became constant. It was then vibrated through smaller and 
smaller arcs with the following results :— 
O 
Initial arc of vibration. 
Time of vibration. 
Seconds = t. 
1080t 
1-647 
720 
1-662 
360 
1-677 
10 
1-706 
* In consequence of this untwisting the vibrations were, in experiments of this kind, counted from the 
beginning of the swing, and not, as is usual, from the position of equilibrium, 
f The elasticity of the wire was perfect for this degree of torsion. 
