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Article VI.
On the Mathematical Theory of Heat; by S. D. Poisson, Member of the Institute, &c [1]
From the Annales de Chimie et de Physique, vol. lix. p. 71 et seq.
The work which I have just published under the title of The Mathematical Theory of Heat (Théorie Mathematique de la Chaleur), forms the second part of a treatise on Mathematical Physics (Physique Mathématique), the first of which is the New Theory of Capillary Action (Nouvelle Théorie de l'Action Capillaire), which appeared four years ago. It contains twelve chapters, preceded by some pages in which I recapitulate in a few words the first applications of the calculus which have been made to the theory of heat, and the principal researches of geometers upon that subject, which have been made of late years, namely, since the first Memoir presented by Fourier to the Institute in 1807. I will here transcribe the contents of the Preface, on the important question of the heat of the earth.
"In applying to the earth the general solution of the problem of a sphere at first heated in any manner whatever, Laplace was led to participate in the opinion of Fourier, which attributes to the primitive heat of the earth the increase in temperature which is observed in descending from the surface, and the amount of which is not the same in all localities. This hypothesis of a temperature proceeding from the original heat of the globe (la chaleur d'origine), and which must rise to millions of degrees in its central layers, has been generally adopted; but the difficulties it presents appear to me to render it improbable. I have proposed a different explanation of the increasing temperature which has long since been observed at all depths to which man has penetrated.
"According to this new explanation the phænomenon depends on the inequality of temperature of those regions of space which the earth successively passes through in its translatory motion, and which are common to the sun and all the planets. It would be indeed opposed to all probability that the temperature of space should everywhere be the same; the variations to which it is subject from one point to another, separated by very great distances, may be very considerable, and ought to produce corresponding variations in the temperature of the earth, ex-
- ↑ The work of which this article is an analysis, is described as a quarto volume of more than 500 pages, with a plate; published by Bachelier, Quai des Augustins, Paris.
