128 DE. JOULE ON SOME THBBMO-DYN AJHC PEOPEETIES OP SOLIDS. 
aspring be such that a slight elevation of temperature weakens it, and the foil strength 
is r— d again with the primitive temperature, work done agamst that sprang by 
beirding or working in whatever way must cause a cooling effect. e quantify o co 
e^cted was excessively smaU, yet I hoped to measure it by taking the mean of a large 
number of observations with the thermo-multiplier. I took a spual of tempeie s e 
wire ith of an inch thick, of which each convolution was 1* mch in diametei and one 
quarter of an inch distant from its neighbour. A thermo-electric junction was attached 
to one of the convolutions, and means were provided to compress or extend the sp ^ 
at pleasure without approaching it. In the case of a spual stretched by a weight him, 
to ft the application of heat causes, as we have seen, a considerable elongation, in con- 
seqtncf of diminution of elasticity ; but in the case of a sph-al compressed by a we^vh. 
laid on the top of it, the effect of the same cause is to dimmish its length. Hence e 
the pulling out or the compression of the spiral must cause the absorption of 
the letum of the spiral to its normal state must be accompanied by the evolution of h 
123 The above thermal effects of bending a spring are evidently proportional the 
squfit of the pressing or tensile force; for if these be increased, the e astic spimg and 
ralteration f f lenj^h by rise of temperature wiU be also ^ pui- 
124. Having arranged the thermo-multiplier so as to give one srag m 30 I p 
• follows • A weight of 7 lbs. was laid on the top of the ^punl 
sued t e ^ ^ elapsed, the change in the position of the needle was 
Lndmd such experiments were tried alternately. Afteixvai-ds I made another senes of 
“ndred experiments, on the effect of stretching and removing the stretc ling foice 
The results are placed in the following Table, in which the signs and - distmguis, 
deflections indicating evolution and absorption of heat. 
