Page:Scientific Memoirs, Vol. 1 (1837).djvu/359

 VOL. I.— PART III.

XV.

questions are more worthy of fixing the attention of geometers and natural philosophers than those which relate to the constitution of gases and vapours: the functions they exercise in nature, and the advantages which industry derives from them, account sufficiently for the numerous and important labours of which they have been the object: this vast question, however, is far from being exhausted. The law of Mariotte and that of Gay-Lussac, which establish the relations existing between the volume, the pressure, and the temperature of a given quantity of any gas, have both long since obtained the assent of scientific men. The experiments recently made by MM. Arago and Dulong leave no doubt of the accuracy of the first of those laws within very extended limits of pressure; but these important results give no information respecting the quantity of heat which the gases contain, and which is disengaged by pressure or diminution of temperature,—they do not give the law of the specific calorics when the pressure and the volume are constant. This part of the theory of heat, however, has been the object of profound researches, among which we may cite those of MM. La Roche and Bérard on the specific caloric of gases. Lastly, M. Dulong, in a memoir which he published under the title of Recherches sur la Chaleur Spécifique des Fluides Elastiques, has established by experiments free from all objection, that equal volumes of all elastic fluids at the same tempeature and under the same pressure, being suddenly compressed or dilated by the same fraction of their volume, disengage or absorb the same absolute quantity of heat. Rh