SUPPLY OF HEAT. 



283 and 175 Fahr. At what point between these limits the 

 real temperature lies, is not yet satisfactorily ascertained, but 

 M. Pouillet thinks that it cannot differ much from 224 Fahr. 



52. It is proved from these results, that the quantity of heat 

 imparted to the earth in a year, by the radiation of the celestial 

 space, is such as would liquefy a spherical shell of ice, covering 

 the entire surface of the earth, the thickness of which would be 

 85 feet, and that forty per cent, of this quantity is absorbed by 

 the atmosphere. 



Thus the total quantity of heat received annually by the earth 

 is such as would liquefy a spherical shell of ice 185 feet thick, of 

 which 100 feet are due to the sun, and 85 feet to the heat which 

 emanates from the stellar universe. 



The fact that the celestial spaces supply very little less heat to 

 the earth annually than the sun, may appear strange, when the 

 very low temperature of these spaces is considered, a temperature 

 180 lower than the cold of the pole during the presence of the 

 sun. It must, however, be remembered that while the space 

 from which the solar radiation emanates, is only that part of the 

 firmament occupied by the disc of the sun, that from which the 

 celestial radiation proceeds is the entire celestial sphere, the area 

 of which is about five million times greater than the solar disc. 

 It will therefore cease to create surprise, that the collective effect 

 of an area so extensive should be little short of that of the sun. 



The calorific effect due to the solar radiation, according to the 

 calculations and observations of M. Pouillet, exceeds that which 

 resulted from the formulae of Poisson. These formulae were 

 obtained from the consideration of the variation of the temperature 

 of the strata of the earth at different depths below the surface. 

 M. Pouillet thinks that the results proceeding from the two 

 methods would be brought into accordance if the influence of the 

 atmosphere on solar heat, which, as appears from what has been 

 explained, is very considerable, could be introduced in a more 

 direct manner into Poisson's formulae. 



53. In fine, therefore, the researches of M. Pouillet give the 

 following results, which must be received as mere approximations 

 subject to correction by future observation : 



1st. That the sun supplies the earth annually with as much 

 heat as would liquefy 100 feet thick of ice covering the entire 

 globe. 



2nd. That the celestial spaces supply as much as would liquefy 

 85 feet thick. 



3rd. That forty per cent of the one and the other supply is 

 absorbed by the atmosphere, and sixty per cent received by the 

 Httfa. 



85 



