78 REPORT—1840. 
though for convenience it is distinguished from the direct. solar 
heat measured by an actinometer; secondly, the proper low 
temperature of the higher atmosphere which is communicated 
to the earth by radiation through the inferior strata. M. Pois- 
son contents himself with supposing that these two causes neu- 
tralize one another, or that the latter rather preponderates*, 
for which he assigns, I think, no sufficient reason ; on the con- 
trary, from what we have just stated (110.) of the action of the 
atmosphere, which lets more heat enter than can directly escape, 
we conceive that the heating effect of the atmosphere is essen- 
tially positive. 
. M. Poisson having thus estimated the direct solar effect 
on the climate of Paris at 24° cent., and the atmospheric in- 
fluence as nothing relatively to the existing temperature, assigns 
the temperature which remains, namely, 11°, the actual mean 
temperature of Paris, diminished by 24°, or — 13° (=8°6 Fahr.) 
for the heat of space, or the temperature which our globe would 
take were the sun permanently extinguished. 
113. This result must certainly be considered as a very start- 
ling and improbable one. That the temperature which our globe 
would take did the sun not heat at all should be actually higher 
than the mean temperature of many points of its surface exposed 
to the solar rays during a great part of the year, and nearly 80° 
of Fahr. above a degree of natural cold actually observedy, 
is a paradox to which M. Arago drew attention, and which M. 
Poisson we think did not succeed in rendering plausible{. Fou- 
rier was distinctly of opinion that the temperature of space must 
be lower than the mean of any point of the earth’s surface, 
though he admits that local causes might produce a temporary 
depression §. The only explanation, indeed, which it can admit 
of, is that to which M. de la Rive has shown that Poisson’s rea- 
soning necessarily leads, viz. that the atmosphere is an inde- 
pendent source of heat|| (or cold, which is the same thing), a 
conclusion nowhere distinctly admitted by the author. Now 
this conclusion surely will be very reluctantly adopted, seeing 
that, even supposing the direct solar influence could be success- 
fully estimated, the remaining temperature must be derived from 
(what is called) the heat of space and the heat of the atmosphere. 
Experiments are, I apprehend, totally wanting which can se- 
* «Ta partie (namely, of the heat not directly received from the sun by any 
part of the earth’s surface) provenant de l’atmosphére ne nous est pas connue ; 
nous pouvons seulement présumer qu’elle est négative.’’— Théorie, p. 520. 
t Viz.—70° Fahr., by Captain Back. 
+ Comptes Rendus (Paris), i nN. OV. 
§ Mem. de l'Institut, vii. 582. || Bib. Univ., Dec. 1835. 
