80 REPORT—1840. 
of temperature, far from getting clearer, are perhaps now more 
unfixed than ever; and what would be the result of a condition of 
which we can form no very definite physical conception (a body 
placed in an envelope deprived of heat), it is perhaps too bold to — 
conjecture. But that the planetary spaces are not exactly in 
this condition, is not improbable. A body (be it a thermometer 
ora planet) placed in space may take a temperature, by contact, 
from a fluid by which it is surrounded, or by radiation from 
distant stars (being shaded from the sun) ; the latter, we under- 
stand to be the meaning usually assigned by philosophers to the 
term Temperature of Space*. This influence may change from 
age to age, and be variable in different regions of the globe, de- 
pending on their exposure. M. Poisson supposes that the in- 
crease of temperature with depth in the earth indicates the effect 
of an at-one-period-more-intense stellar radiation, and con- 
sequently that it does not necessarily extend beneath a depth 
which the epoch of the oscillations of external influence would 
determine. This is no doubt perfectly unanswerable, as a mat- 
ter of bare possibility; but it seems hardly worth maintaining 
an opinion which a million of years will scarcely show to be 
feasible or the reverset. 
116. We have formerly stated {, that Fourier had arrived at the 
conclusion that the flux of heat from the interior to the surface 
of the globe did not raise the temperature of the latter above 
sith of a centigrade degree§, or would melt annually a stratum 
of ice =3,th of an English inch in thickness ; and in this estimate 
Poisson nearly coincides ||. The influence of internal heat is 
quite irrespective of any theory as to the state of the nucleus, 
and depends only on the rate of increase as we descend, a cir- 
cumstance which M. de la Rive seems to have overlooked in 
urging his objections against Poisson’s theory. We proceed to 
state some important additions which have been made to our 
knowledge of Facts respecting the thermometric condition of 
the accessible part of the earth’s crust. 
* See an interesting notice by Sir J. F. W. Herschel, read to the Royal 
Astronomical Society, 10 Jan. 1840; Atheneum, Feb. 15; where, as well as 
in a paper in the third volume of the Geological Transactions, New Series, 
on Astronomical Causes affecting Geological Theories, are some important sug- 
gestions on these intricate subjects. 
+ On the subject of the thermometric state of the globe, seea popular article 
by M. Arago (Annuaire, 1834), and the Eloge of Fourier, by the same author. 
In the Annales de Chimie, a few years since, Libri has given some results as to 
the rate of cooling, and the contraction of the earth’s crust, within historic 
times, chiefly with a view to the supposed explanation which it affords of certain 
geological phenomena. 
¢~ Last Report, p. 221. § Mém. de lV Institut, vii. 590. 
|| Théorie, &c., p. 424. 
