828 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS AND 
Experiment XVII. 
An annealed copper wire 602 centims. in length and 0'960 centim. in diameter was 
provided with a vibrator whose mass was 430 grammes, and after resting for several 
days was tested ; the logarithmic decrement proving to be '000297. The wire was 
now permanently lengthened 2'67 per cent., and ten minutes after it had been 
shortened to its original length and re-suspended was again tested, with the following- 
results : — 
Logarithmic 
decrement due to 
internal friction. 
Remarks. 
•000717 
•000496 
Mean value for tbe first 100 vibrations 
Mean value for tbe next 200 vibrations 
After a rest of two days. 
•000262 
Mean value for 400 vibrations 
Thus we see that, though the permanent extension increased considerably the 
internal friction, when the wire was vibrated shortly after the strain had been pro¬ 
duced, the effect was rapidly lessened by rest, so that after two days the logarithmic 
decrement became slightly less than it was before the extension. The time of 
vibration was, before the extension, 5'125 seconds, and after the extension 5'275 
seconds. If we allow for the diminution of section, caused by the strain, there 
results from extension a diminution * of the torsional rigidity of about 0'7 per cent. 
Experiment XVIII. 
The same wire was now twisted through twenty complete revolutions, of which six 
came out, leaving a permanent torsion of fourteen revolutions ; ten minutes after¬ 
wards the wire, which had been kept vibrating, was again examined, with the 
following results :— 
Time of vibration 
in seconds. 
Logarithmic 
decrement due to 
internal friction. 
Remarks. 
5-475 
•001175 
Mean value for tbe first 100 vibrations 
5-440 
•001051 
Mean value for tbe next 200 vibrations 
After a rest of 24 hours. 
5-425 
•000461 
Mean value for 400 vibrations 
* Observe that diminution of torsional rigidity is not always attended by increase of internal friction. 
