Temperature of the Terrestrial Globe. 1 



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 they 

 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 surface, 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 the course of a year determines the succession of 

 the seasons. 



The design of this 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- 



