DE. JOULE ON SOME THEEMO-DTNAMIC PEOPEETIES OF SOLIDS. 
105 
each series, this circumstance does not affect the conclusion that the action of tension on 
a band of vulcanized india-rubber sensibly diminishes its specific gravity. 
46. In my experiments on the thermal effects of stretching vulcanized rubber, a piece 
about fths of an inch square, and weighing 1452 grs. to the foot, was employed. The 
upper end was made fast, and to the lower, weights could be applied and removed at 
pleasure. A thermo-electric junction of thin copper and iron wires was inserted in a 
slit made in the direction of the length of the thong and near its middle. Also pins 
were stuck into the rubber at 4 inches distance from each other, in order to measure its 
length under various tensile forces. The following is a Table of results : — 
Stretching 
weight in 
pounds. 
Length of measured 
part, under tensile 
force, in inches. 
Deflection of 
thermo-multiplier. 
Thermal effect 
indicated by 
the deflection. 
0 
4 
O / 
0 
O 
0 
2 
4-06 
— 1*4 
-0*003 
4 
4*12 
-2 
-0*004 
7 
4-3 
— 2*4 
-0*004 
14 
4-8 
— 0*5 
-0*001 
21 
5-21 
7-9 
0*014 
28 
5-87 
29-1 
0*053 
35 
6-6 
51-9 
0*095 
42 
7-25 
1 15-7 
0*137 
49 
7-75 
1 39-3 
0*180 
47. The data for turning the deflections in the third column into the thermal 
in the fourth, were obtained by immersing the rubber, to a point above the place 
the thermo-electric junction was inserted, in water of different temperatures. 
48. These experiments developed the following facts : — 1st. That the effect of 
on the weights was not sensibly different in quantity from the reverse effect of removing 
them. 2nd. That with light weights and a low temperature there was a slight cooling 
effect on the application of tensile force, which, first increasing with the weights laid on, 
ultimately changed into a heating effect, increasing much more rapidly than the stretch- 
ing weight. 
49. The temperature of the thong during the experiments was 7°'8. I found that at 
temperatm'es a few degrees higher, the reverse action with weak tensile forces did not 
take place, but that there was, on the contrary, a very slight heating effect. 
50. Professor Thomson suggesting to me that in those circumstances in which the 
rubber was heated by being stretched, it would contract its length under tension when 
its temperature was raised, I arranged the same piece with which the foregoing experi- 
ments were made in the manner already described in the case of common india-rubber. 
The method pursued was to observe the lengths at several temperatures successively 
raised, and then at similar temperatures descending. The necessity for this arose from 
the circumstance that a gradual elongation took place, particularly at the higher tem- 
peratures, and by taking the mean of the ascending and descending Series, I hoped to 
eliminate the error thus arising. I give the following experiments in the order in which 
they were made : — 
effects 
where 
laying 
