428 ON THE DIFFUSION OF HEAT 



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 pos- 

 sible to trace. 



Thus, by these various arrangements, whatever excess of 

 heat may be received by this planet from the sun, and retain- 

 ed at the surface, will be permanently 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 equa- 

 lity 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 refri- 

 geration, and which Railly, in particular, applied to the fan- 

 ciful system which he supported with so much ingenuity, — 

 that civilization and science have descended from the eleva- 

 ted regions of the north of Asia, — have probably no foundation. 

 It is always interesting to trace the succession of opinions 

 which mark the progress 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 globe 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 



