l/S On the Diffusion of Heat 



will remain stationary, or nearly so, as no increase can take plac« 

 without the abstraction both by the atmosphere and by radiation 

 becoming proportionally greater. 



This is aided by another effect, that with regard to the dif- 

 fusion of heat through the solid mass itself. This diffusion from 

 the surface proceeds in part towards the centre, or each layer, 

 as the surface is receded from, receives a portion of heat from 

 the exterior one, and this continues onwards, though with a 

 j;radual diminution. But there must be at the same time a dif- 

 fusion more nearly horizontal, proceeding through these layers 

 from the equator towards the poles, while there can be none in 

 the opposite direction to counteract this effect. 



The ocean, too, serves to convey a considerable portion of 

 heat from the warmer to the colder regions of the earth, by the 

 movement of currents, somewhat similar to those which exist in 

 the atmosphere, and the course of which it is even possible to 

 trace. 



Thus, by these various arrangements, whatever excess of heaj 

 may be received by this planet from the sun, and retained at the 

 surface, will be permaneiitly accumulated towards the poles, and 

 the temperature there will increase. In all the portions of the 

 intermediate space, between the poles and the equator, the same 

 law will operate, though with decreasing force ; and over the 

 whole surface, there is a tendency to equality of temperature, 

 which, however slow the progression to it may be, must, as the 

 result of general causes constant in their operation, be finally 

 established. 



The speculations, then, on which some have dwelt, — that the 

 northern parts of our globe have suffered a gradual refrigeration, 

 and which Bailly, in particular, applied to the fanciful system 

 which he supported with so much ingenuity, — that civilization 

 and science have descended from the elevated regions of the 

 north of Asia, — have probably no foundation. It is always in- 

 teresting to trace the succession of opinions which mark the pro- 

 gress of knowledge, and to observe how far what at one period 

 is considered as established, is at another rendered doubtful, or 

 proved to be false. The refrigeration of the gloi)e from the loss 

 of its interior heat, is a fact, says the author just referred to, of 

 which there can be no doubt ; and this refrigeration, he adds, 

 must have been principally towards the poles, partly from the 

 flattening of the sphere there, in consequence of which the heat 

 from the centre must escape sooner, but still more from the un- 

 equal action of the solar rays, which is more intense towards the 

 equator. Hence the countries round the poles must have been 

 tiie first that were habitable, and this gradual cooling has caused 



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