830 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS AND 
Load in kilos. 
Logarithmic 
decrement due to 
internal friction. 
Remarks. 
14 
•001017 
After a rest of 24 hours and a very large number 
of previous oscillations. 
10 
•001089 
Ditto. 
6 
•001109 
Ditto. 
2 
•001307 
Ditto. 
The above experiment suffices to show the great extent to which the internal friction 
can be diminished by the permanent molecular strain resulting from loads which are 
not sufficient to cause any appreciable permanent extension. For we see that even 
with a load of 15 kilos, the permanent extension was only about 0'4 per cent., whereas 
a load of half this was sufficient to cause a permanent molecular strain which reduced 
the friction to less than one-half of the original amount. 
The Effect of Permanent Strain on the Torsional Rigidity. 
I have already pointed out in Experiments XVI., XVII., and XVIII. that when very 
sensible permanent molar deformation is produced, either by traction or torsion, the 
torsional rigidity is decreased,* so that we need only now consider the effect of stress 
which, without producing sensible molar deformation, suffices to cause molecular 
permanent strain. 
Experiment XX. 
An annealed copper wire 602 centims. in length and 0T622 centim. in diameter. 
The mass of the vibrator attached to the wire was 1554 grammes, and the determina¬ 
tions of the logarithmic decrements were all made with only the vibrator. When, 
however, it was necessary to strain the wire, a pan was suspended from the bar of the 
vibrator, and on this pan weights were placed which were suffered to remain for some 
time. The pan and weights were then removed, and 24 hours after the removal the 
testing, preceded by a large number of preliminary vibrations, began. The temperature 
ranged from 15° C. to 20° C. 
Load in kilos, used to 
produce the permanent 
strain. 
Number of days 
during which the load 
acted before removal. 
Couple in dyne- 
centimetres required to 
twist the wire through 
one radian. 
1-554 
0 
41477 
1-554 
8 
44373 
21-554 
6 
48158 
* Sir W. Thomson had previously shown this to be the case (‘ Encycl. Bint.,’ 9th edit., Art. 
“ Elasticity,” § 81). 
