32 
FIFTH REPORT -1835. 
feet on the superficial temperature insensible for 2000 years. It 
is calculated, moreover, that, from the rate of increase of tem¬ 
perature in descending, the quantity of central heat which 
escapes in a century through a square metre of the earth’s sur¬ 
face would melt a column of ice having this metre for its base, 
and three metres for its height*. 
(c.) The remaining subject, the Heat of the Planetary Spaces, 
is one on which the scientific world has hardly yet had time to 
form a sage and stable opinion. Fourier has assertedf that, 
without the effect of this heat, the diminution of temperature in 
proceeding from the equator to the pole would be much greater 
than it is found to be; that the variations of distance of the sun 
at different parts of the year would be felt in changes of tempe¬ 
rature ; that the alternate heat and cold of days and nights 
would produce oscillations of temperature more violent than 
those which occur. He infers that there exists a cause which 
moderates the temperatures at the surface of the globe, and 
which produces a fundamental temperature independent of the 
sun and of the central heat. This cause he holds to be the heat 
of the planetary spaces, and he ascribes this heat to the radiation 
of the fixed stars in every part of the universe. Fourier was 
led by his reasoning to fix the temperature of the planetary 
spaces at about 50 degrees (centigrade) below freezing. It is 
curious that Svanberg has been led by a wholly different line of 
reasoning to nearly the same result as to the degree of tempe¬ 
rature of the void spaces of our system. 
Fourier says that his conclusion results from the mathema¬ 
tical examination of the question ; but the mathematical part of 
his reasoning on this subject has not, so far as I am aware, been 
published. Sir John Herschel has, I believe, dissented from 
the opinion that such an effect could result from the radiation of 
the fixed stars; but his memoir also is as yet unpublished. 
Thus there appears to be still some uncertainty on the sub¬ 
ject of what we may call cosmical heat. Indeed the extension 
of our thermotical laws to cosmical cases appears to be at¬ 
tended with great difficulty. The laws of motion were first 
strictly proved by experiments made with bodies capable of ma¬ 
nipulation ; but they were immediately applied to the expla¬ 
nation of cosmical phenomena of which the laws had long been 
ascertained by observation. It should be the aim of other sci¬ 
ences to make similar applications of their results. But in most 
cases the difficulty of observation of phenomena at a distance 
from us is very great. We can observe the effects of mecha¬ 
nical force in the remotest regions of the universe into which 
* Mem. Inst., tom. vii. p. 593. t p. 580. 
