S74 Scientific Intelligence. — Geology . 
nal heat contained in s a spherical mass of equal dimensions with 
the earth, diminishes much more rapidly at the surface than in 
the parts situated at a great depth. These preserve almost all 
their heat during an immense time ; and there is no doubt re- 
garding the truth of the consequences, because we have calcu- 
lated these times for metallic substances, which are better com 
ductors of heat than the matters of which the globe consists. 
But, it is evident that theory alone cannot inform us what are the 
laws to which the phenomena are subjected. There remains to 
examine, if, in the strata of the globe to which we can penetrate, 
there is found any indication of this central heat. It would re- 
quire to be proved, for example, whether, beneath the surface, 
at distances at which the diurnal and annual variations have en- 
tirely ceased, the temperatures of the points of a vertical line 
prolonged into the solid earth, augment with the depth. Now, 
all the observations which have been collected and discussed by 
the most learned naturalists of our days, shew that this increase 
does exist ; it has been estimated at about a degree for 30 or 40 
metres. The experiments with which the Academy have late- 
ly been furnished, and which relate to the heat of springs, con- 
firm the results previously obtained. It is easy'to conclude, and 
it results, besides, from an accurate analysis, M. Fourier says, 
that the increase of the temperature in the direction of the depth 
cannot be produced by the prolonged action of the rays of the 
sun. The heat which emanates from this star is accumulated in 
the interior of the globe ; but the progress has almost entirely 
ceased ; and if the accumulation still continued, we should ob- 
serve the increase in a direction precisely the contrary of that 
which we have indicated. The cause which produces a higher 
temperature in the deeper beds is, therefore, an internal source 
of constant or variable heat, placed beneath points of the globe 
to which we have penetrated. This cause raises the tempera- 
ture of the earth’s surface above the value which the action of 
the sun alone would give it. But this excess of the temperature 
of the surface has become almost insensible ; and we are assured 
of it, because there exists a mathematical relation between the 
value of the increase by measure, and the quantity by which the 
temperature of the surface still exceeds that which would take 
place, if the internal cause in question did not exist. It is the 
