Temperature of the Terrestrial Globe. 5 



It is equally probable, that in respect to most of the planets, the 

 temperature of the poles is little above that of the surrounding space, 

 with respect to the temperature which each of these bodies owes to 

 the sun, it is not known ; because it may depend on the pressure of 

 an atmosphere and the condition of the surface. We can only ap- 

 proximate to the truth in assigning the mean temperature which the 

 earth would have acquired situated in the place of the planet. 



After this exposition, we shall examine successively, the different 

 parts of this question. We would first make a remark which has a 

 relation to all these parts, because it is founded upon the nature 

 of differential equations of the motion of heat. It is this : the effects 

 of each of the three causes we have mentioned, may be calculated 

 separately, as if it had no connection with the others. It is suffi- 

 cient afterwards to unite these partial effects : Us se superposent li- 

 brement comme les dernieres oscillations des corps. 



We shall describe in the first place the principal results of the 

 prolonged action of the solar rays upon the terrestrial globe. 



If a thermometer is placed at a considerable depth below the sur- 

 face of the solid earth, forty meters for example, the instrument in- 

 dicates a fixed temperature. This fact is observed in every part of 

 the globe. This temperature of deep places is always the same in 

 the san(ie place ; but it is not the same in different climates. It 

 generally decreases as we advance towards the poles. 



If we observe the temperature of points much nearer the surface 

 of the earth, for example, at the depth of one, five, or ten meters, 

 we see very different effects. The temperature varies during a single 

 day or year. But we can suppose the crust or envelop in which 

 these variations take place, to be removed, and consider the fixed 

 temperatures of the points of the new superficies of the globe. 



We can conceive that the state of the mass has varied continually 

 in proportion to the heat received from the origin of heat itself. 

 This variable state of internal temperature has changed by degrees, 

 and has approached nearer and nearer to a final state, which is sub- 

 ject to no change. Then each point of the solid sphere has acquir- 

 ed, and preserves, a temperature, a fixed temperature, which de- 

 pends only on the situation of the point itself. 



The final state of the mass, the heat of which has penetrated all 

 its parts, can very justly be compared to that of a vessel which re- 

 ceives by openings at the top, liquid from some constant source, and 

 permits exactly an equal quantity to escape by orifices. 



