DE. JOrLE ON SOME THEEMO-DYNAMIC PEOPEETIES OF SOLIDS. 
125 
287 124 1 1 1 
1390 1660 ^ ^ ^ *77 
0°-05. 
The excess of the actual result may be attributed to the central part, in which the junc- 
tion was placed, bearing an undue share of pressure in consequence of the bulging of 
the waist of the pillar. 
116. On examining the above Table, it will be remarked that the thermal effect 
increases more rapidly than the pressure. This is owing partly to the influence of a rise 
of temperature in increasing the elasticity of rubber under strain, to which we have 
ah’eady alluded, and partly to the unequal distribution of pressure to which I have just 
adverted. The longitudinal expansion of a pillar of vulcanized India rubber, 2-21 inches 
long and 1'44 inch in diameter, under various pressures, was found to be 
Pressure in pounds. 
0 
55 
135 
Expansion per degree Cent, 
on the length under pressure. 
1 
5 7 00 
1 
3730 
L_ 
2 2 2 8 
117. Being desirous of ascertaining the thermal effects of higher pressures, I made 
the experiments tabulated below, on a pillar 1-7 inch long and 2-5 inches in diameter. 
Pressure applied or 
removed, in pounds. 
Heat on applying 
pressure, or cold on 
removing it, in degrees 
Centigrade. 
Length of the pillar 
when under pressure. 
Length of the pillar 
after the pressure was 
removed. 
70 
0-011 
1-7 
113 
0-015 
134 
0-029 
162 
0-036 
242 
0-052 
275 
0-078 
386 
0-114 
547 
0-130 
1-43 
1426 
0-384 
1-00 
2742 
0-750 
•72 
4058 
0-885 
-64 
6692 
1-192 
-51 
1-66 
11958 
1-463 
22400 
1-426 
-36 
1-68 
118. After a few experiments with the last pressure the rubber burst, being ruptured 
in a singularly symmetrical manner at the four quadrants of its circumference. Placed 
in hot water, it almost immediately regained its original shape. 
119. I have collected in the following Table the results of the foregoing experiments 
on the thermal effects of pressing pillars. In reckoning the mean, the last result in each 
of the series for wrought iron, cast iron, copper, and lead is rejected on account of having- 
been obtained with a pressure nearly up to the limit of strength, and after the form and 
structure of the pillar had been changed by the force to which it had been subjected. 
MDCCCLIX. 
s 
