122 
ArTIcLE VI. 
On the Mathematical Theory of Heat ; hy S.D. Poisson, 
Member of the Institute, &c.* 
From the Annales de Chimie et de Physique, vol. u1x. p. 71 et seq. 
Tur work which I have just published under the title of The Mathe- 
matical Theory of Heat ( Théorie Mathématique de la Chaleur), forms 
the second part of a treatise on Mathematical Physics (Physique Mathé- 
matique), the first’ of which is the New Theory of Capillary Action 
(Nouvelle Théorie de 0 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 caleulus 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. Iwill here transcribe the contents of the Preface; on the im- 
portant 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 par- 
ticipate in the opinion of Fourier, which attributes to the primitive heat 
of the earth the increase in temperature which is observed in descend- 
ing from the surface, and the amount of which is not the same in all lo- 
calities. This hypothesis of a temperature proceeding from the original 
heat of the globe (la chaleur dorigine), and which must rise to millions 
of degrees in its central layers, has been generally adopted; but the dif- 
ficulties it presents appear to me to render it improbable. I have pro- 
posed a different explanation of the increasing temperature which has 
long since been observed at all depths to which man has penetrated. 
“ According tothis new explanation the phenomenon depends on-the 
inequality of temperature of those regions of space which the earth suc- 
cessively passes through in its translatory motion, and which are com- 
mon to the sun and all the planets. It would be indeed opposed to all pro- 
bability that the temperature of space should everywhere be the same; 
the variations to which it is subject from one point to another, sepa- 
rated 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 Augus- 
tins, Paris. 
