DE. JOULE ON SOME THEEMO-DYNAMilC PEOPEETlES OF SOLIDS. 
119 
likewise of heat, on removing the tensile force. There could be no doubt that in 
this instance the imperfect elasticity of the moist wood caused a considerable quantity 
of heat to be generated frictionally. It may therefore be safely concluded that the 
thermal effect, considered apart from the result of friction, was, as in the case of india- 
rubber, one of heat on the application of tension^ and cold on its removal. Its actual 
value would be over-estimated by — ^^^^ = 0°-0Q3, on account of the set communi- 
cated by tension being always greater than that taken out when the tension is removed. 
The approximate theoretical result is 
H= 
277 
1390 
-200 
X— p— X 
1 _ 1 _ 1 
2000000 ^ 768 ^ - 0476 “ 
0°-0006. 
93. For the sake of ready comparison I have collected in the following Table the 
results of the foregoing experiments on the thermal effects of tension, placing by their 
side the results of Professor Thomsojst’s theory. 
Material. 
Experiment. 
Theory. 
Theoretical thermal effect of 
1 lb. tension on a prism 
weighing 1 lb. to the foot, 
at the temperature 0° Cent. 
Iron 
— •115 
—•no 
1 
Iron 
— 124 
—•no 
1 —-0000220 
Iron 
— •101 
—•107 
Hard steel 
—•162 
— •125 
— •0000235 
1 --0000168 
Cast iron 
— 160 
— •112 
Cast iron 
— •148 
—•115 
Copper 
— 174 
— •154 
— •0000355 
1 — -0001847 
Lead 
— •053 
—•040 
Lead 
— •076 
-•028 
—•055 
Gutta percha 
—•031 
1 --0000769 
Gutta percha 
—•052 
-•066 
Vulcanized india-rubber 
-b-114 
+ •137 
Pine wood 
—•017 
—•023 
— •0000021 
Bay wood 
— •059 
— •060 
— •0000028 
Pine, cross-erained 
-•006 
— •009 
—•0000213 
Wet bay wood 
-f -003 
+ •001 
+ •00000015 
On the Thermal Effects of Longitudinal Compression on Solids. 
94. Wrought Iron. — A pillar 2 inches long and one-quarter of an inch in diameter 
had a fine hole bored through it, in which a thermo-electric junction of fine copper and 
iron wires was inserted, as described in § 18. It was placed under the lever which had 
served for the tension experiments, the weight of which alone gave a pressure of 50 lbs. 
When, in addition to this, a pressure of 1060 pounds was applied, a deflection of 2I'-3, 
indicating heat, was produced; and a like deflection in the opposite direction, indicating- 
cold, was produced by removing the pressing weight. The value of the deflection, 
ascertained by immersing the pillar, in water of various temperatures, to within one- 
eighth of an inch from the thermo-electric junction, was 0°T517. The theoretical result is 
__ 28 ^ 
1390 ^ 
1060 
X 
1 
81200 
1 
^• 1491 ~ 
0°-1645. 
R 2 
1 
