Page:Reflections on the Motive Power of Heat.djvu/268

244 We will not enter into the details of the calculation necessary to determine these quantities. It is sufficient to say that the following values,

satisfy fairly well the prescribed conditions, so that the equation

expresses very nearly the relation which exists between the volume of the vapor and its temperature. We may remark here that the quantity B'  is positive and very small, which tends to confirm this proposition—that the specific heat of an elastic fluid increases with the volume, but follows a slow progression.

.—Were we to admit the constancy of the specific heat of a gas when its volume does not change, but when its temperature varies, analysis would show a relation between the motive power and the thermometric degree. We will show how this is, and this will also give us occasion to show how some of the propositions established above should be expressed in algebraic language.

Let r be the quantity of motive power produced by the expansion of a given quantity of air passing