1/2 On the Diffusion of Heat 



and at last a uniform distribution of it through the whole mass, 

 would inevitably be the consequence. It appears that the at- 

 mosphere does present such a barrier, and the consequence, 

 therefore, necessarily follows*. 



This is true, at least, so far as relates to any ponder of the 

 atmosphere to convey heat. There is still to be considered, 

 however, another mode in which caloric may be supposed to be 

 discharged from our planet, — that by radiation. Rays possessed 

 of heating power are thrown off from a body at a high tempera- 

 ture, and by the discharge of these its temperature is reduced. 

 But various considerations show, that this would be a very in- 

 adequate source of the escape of heat from the interior part of 

 the earth. 



Tlius the radiation of caloric is inconsiderable, except from a 

 body which is heated; and the quantity radiated increases as 

 the temperature rises in a much higher ratio than the increase 

 of temperature itself. At low temperatures, therefore, it must 

 be extremely small. At 100^ it is scarcely apparent, from ex- 

 periment ; and at 50' is not sensible. Not only, too, does 

 the quantity diminish rapidly with the temperature, but the 

 projectile force of the ravs emitted becomes less, so that tiiose 

 which are discharged at low temperatures are incapable of pe- 

 netrating media such as glass, which those at high temperatures 

 penetrate with facility. And as even the latter are, to a certain 

 extent, intercepted by the atmospheric air, the former must be 

 more comjiletely arrested. At 50% therefore, the medium tem- 

 perature of the glvobe, and which prevails over so large a portion 

 of its surface, we have no reason to believe that a discharge of 

 caloric by radiation, into remote space, can take place to any 

 extent. 



At the parts of the surface of the earth which are at still loner 

 temperatures, and at those where intense cold prevails, the sup- 

 position of any radiation is of course still more precluded, and 

 the negative even may be proved. When a solid body, and the 

 surrounding elastic medium, are at the same temperature, there 



* If the sphere from the centre of which heat is supposed to be diffused, 

 be not exposed to an uner|iial external source of heat, the heat will be com- 

 municated equally at its ciicunit'(;rei)ce tu ihe incuinbtiit atmosphere, and 

 produL-fc ascent and descent of the air, >vith little of that circulation of it 

 from o!ie palt to another, which is the consequence of inequality of tem- 

 perature lit the surlacc of the solid. Hut still the same changes of capacity 

 for heat will accompany the ascent and descent oi' the aerial mass, and the 

 princijjal efiVrt will hr-, to accumulate teiiperature at the surface. The 

 condition is one, hmtver, which need not to be taken into account, as it is 

 one which has never existed with regard to our planet; and the arijument 

 remains as is slated alove, \< hile there is inequality in the distribution 

 of heat over the circumference of the globe. 



seems 



