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VI. On the Thermal Effects of Compressing Fluids. By J. P. Joule, LL.B., F.B.S., 
F.C.S., Hon. Mem. Phil. Soc. Cambridge., Vice-President of the Lit. and Phil. Soc. 
Manchester, Corresp. Mem. R.A. Sc. Turin, &c. 
Eeceived October 9, — -Bead November 25, 1858. 
Peofessoe William Thomson has published* a theoretical investigation of the subject 
of the present paper, in which he arrives at the formula 6= j£, where 6 is the increase 
of temperature, T the temperature from absolute zero, e the expansibility by heat, p the 
pressure in pounds on the square foot, J the mechanical equivalent of the thermal unit 
in foot-pounds, and K the capacity for heat in pounds of water, of a cubic foot of the 
fluid employed. He has also given a Table of theoretical results for the compression of 
water and mercury. The investigation being established on the basis of well-ascertained 
principles and facts, the correctness of the Table could not be reasonably doubted. 
Nevertheless, believing that an experimental inquiry would be interesting if not im- 
portant, I have ventured to oflfer the following to the notice of the Royal Society. 
The only previous experiments on the subject of which I am aware are those of 
M. Regnault. To his memoir on the Compressibihty of Liquids, he appends a notef 
on the heat disengaged by the compression of water. The method employed by this 
celebrated physicist, though less delicate, is similar to that which I have adopted. One 
set of the junctions of a thermo-electric pile was placed in a copper vessel filled with 
water, to which a pressure of ten atmospheres could be instantaneously communicated 
by means of a reservoir of compressed air. The ^-th of a degree Centigrade could be 
detected by his thermo-multipher. Nevertheless the conclusion arrived at was the 
negative one, that “ the heat disengaged by a sudden pressure of ten atmospheres on 
water is unable to raise its temperature g^th of a degree Centigrade.” 
In the absence of any statement to the contrary, we may consider that the tempera- 
ture of the water compressed by Regnault was not above an ordinary one of the atmo- 
sphere, say 18° Centigrade. Thomson’s formula gives a thermal effect of 0°-013 for a 
pressure of ten atmospheres at this temperature; and therefore the conclusion of 
Regnault above cited is strictly correct : indeed it is so as regards any temperature 
below 30°. It is to be regretted that he did not pursue his experiments a little further, 
for had he done so he would without fail have solved this, as he has done so many other 
more ditficult problems, by showing the minute but nevertheless appreciable thermal 
* Proceedings of the Eoyal Society, June 18, 1857, vol. viii. No. 27, p. 566. 
t M^inoires de I’Acaddmie Boyale des Sciences, xxi. p. 462. 
T 
xVIDCCCLIX. 
