Note 27 — Chapter VI · General Rules for the Construction of the Conception.

For if θ be the temperature of the inclosure, and t the excess of temperature of the hot body, it appears, by this law, that the radiation of heat is as aθ. And hence the quickness of cooling, which is as the excess of radiation, is as aθ + t − aθ; that is, as aθ(at − 1) which agrees with the formula given in the last note. The whole of this series of researches of Dulong and Petit is full of the most beautiful and instructive artifices for the construction of the proper formulæ in physical research.