114 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
The mode of experimenting adopted was as follows : X and Y having been placed 
in position and the air chamber covered with its baize jackets, the balance between the 
two wires was observed, and the thermometer having been pulled sufficiently far out 
of the cork to enable one to take the reading of the temperature, was afterwards 
replaced. The water in W was then boiled, and in about half an hour the air in the 
chamber was found to be at 100° C., and was allowed to remain so for another half an 
hour, when X and Y were again balanced. The burner was next taken from under AV, 
when a vacuum was formed in the upper part of the boiler by the steam condensing; 
this vacuum was at once filled by the atmospheric pressure forcing water from K, and 
when the space between the two brass cylinders had in a short time become filled 
with the water from K, the cork E was removed from the boiler, and a siphon action 
allowed to continue from K which was kept supplied with cold water. The jackets 
were then removed, and the cork E having been replaced, the whole arrangement was 
suffered to rest for two hours, when the thermometer indicating the temperature of 
the air chamber to be within a degree or so of the original temperature, the balance 
between X and Y was once more determined. As the processes of hammering and 
stretching by increasing the length of X might possibly have caused an error by 
making the lower portion of the wire to occupy a lower position in the chamber than 
the corresponding portion of Y,'“ the former wire was from time to time shortened to 
the same length as the latter. Also, since with all the wires it was found impossible, 
even by using the greatest care in annealing, to find two pieces of the same wire 
which would agree exactly in their co-efficients of increase of resistance, these were 
compared before X was subjected to strain of any sort. The following experiments 
illustrate the nature of the results obtained :— 
Experiment XL. 
An annealed copper wire, '095 centim. in diameter, was stretched by hand per¬ 
manently to different extents, and after each stretching tested for alteration of 
resistance from change of temperature. 
Percentage 
increase of length. 
Percentage of average temporary 
superior increase of resistance 
of stretched wire over unstretched 
for 1° C. between 20° C. and 100° C. 
+ signifies superior increase of 
stretched wire on rise of temperature. 
Percentage of average 
permanent decrease 
of resistance for 1° C. 
between 20° C. and 
100° C. of 
stretched wire. 
5-83 
--00046 
•00104 
11-40 
--00074 
•00107 
22-27 
--00045 
•00354 
32-73 
4--00378 
•00190 
* I have found it very difficult even with such an arrangement as the above to get an exactly uniform 
temperature, except in the central portion of the chamber. 
