Temperature of the Terrestrial Globe. 7 
We ought likewise to observe respecting all the numerical values 
mentioned in this memoir, that they are presented here only as ex- 
amples of the calculus. ‘The meteorological observations proper for 
furnishing the necessary data, those which would show the capacity 
for heat and the permeability of the substances which compose the 
globe, are too uncertain and too limited, to enable us, by the cal- 
culus to deduce accurate results. But we mention these numbers to 
show, how formulas ought to be applied: and however much th 
may differ from true results, these values are much more suitable 
for giving a correct idea of the phenomena, than general expressions 
without their numerical application. 
In those parts of the crust nearest the dlirhive: the thermometer 
rises and falls during each day. These diurnal variations cease to 
be sensible at the depth of two or three meters. Below this we can 
perceive only annual variations, and these again become insensible 
at a still greater depth. 
If the rapidity of the motion of the earth around its axis were to 
be infinitely increased, and the same were supposed to take place 
respecting its motion round the sun, the diurnal and annual variations 
would no longer be observed, the points of the surface would have 
acquired and would preserve the fixed temperatures of places at a 
great depth. In general the depth which we must reach in order 
that the variations may become insensible, has a very simple ratio 
to the duration of the period which reproduces the same effects at 
the surface. This depth is exactly proportional to the square root 
of the period. It is for this reason that the diurnal variations pene- 
trate only to one nineteenth of the depth at which the annual varia- 
tions are observed. The question of a periodical motion of the 
solar heat was examined for the first time, and resolved in a separate 
paper, submitted to the French Institute in October, 1809. I again 
brought forward this solution in a paper submitted at the close of 
1811, and printed in the collection of our memoirs. 
The same theory furnishes the means of measuring the quantity 
of heat which in mg course of a year determines the succession of 
the seasons. 
The design of site example of the application of formulas is to 
show that there exists a necessary relation between the laws of peri- 
odical variation and the whole quantity of heat which effects this 
variation : so that this law being known by observations made in a 
given climate, we can determine the quantity of heat which pene- 
