REPORT ON METEOROLOGY. 
221 
tion for a decrease of 1° cent. This however is at variance with 
the only direct observation we have on the subject. Captain 
Parry found in latitude 69° 2V, by means of a kite, that the 
thermometer indicated no diminution of temperature at a height 
of 400 feet; it stood at —24°. Much however cannot be inferred 
from a single observation. 
Some observations have recently been made by M. KupfFer 
in the range of the Caucasus, by means of the temperature of 
springs, but too few to admit of any satisfactory conclusions*. 
We must now touch upon a point of the greatest importance, 
and which daily increases in interest,—I mean the proper tem¬ 
perature of the globe itself. We have already pointed at the 
fine views of Baron Fourier relating to this subject; and from 
the experimental confirmation which they receive every year, 
there is little doubt that they will soon be established on an 
immoveable basis. He considers the globe as a mass in the pro¬ 
cess of cooling from an intense temperature. He has proved 
that the heat may be very intense at a short distance from the 
surface, and yet, from the extremely bad conducting power of 
the crust, that it may exert no sensible influence on the climate : 
he actually computes it as not amounting to ^th of a centigrade 
degree. Towards the centre the heat may be of the most ex¬ 
treme intensity, and the phasnomena of earthquakes and volca¬ 
noes may be imputed to its influence. The process of cooling, 
though at first of course comparatively rapid, may now be con¬ 
sidered to have reached an asymptotic condition. It is well 
known that the influence of the seasons, or the total difference of 
the effect of solar radiation in summer and winter, affects the 
temperature of the soil to a comparatively minute depth. Expe¬ 
riments with thermometers, sunk to different depths, have been 
made at Zurich by M. Ott, near Edinburgh by Mr. Ferguson, 
and at Strasbourg by M. Herrenschneider j~. The influence of 
the solar rays decreases rapidly ; and it is probable, from expe¬ 
riments made at Paris J, that at about 30 metres, or 100 feet, it 
is almost extinct. The position where this takes place is called 
by Fourier the “ couche invariable,” or invariable stratum ; all 
variations above this plane are imputed to the influence of ra¬ 
diation, all below to the native or primaeval heat of the globe. 
A successive influx and efflux of heat is constantly going on 
* Voyage au Mont Elbrontz, 4to, Petersburg. 
f See a resume of these experiments by M. Pouillet, Elemens de Physique, 
ii. 642. 
X The excellent observations regularly made in the caves under the Obser¬ 
vatory are regularly published in the Annales de Chimie et de Physique . 
