in Fluids. 



13 



support greater changes of temperature than others, but 

 the extremes of Heat and of Cold are alike fatal to all. 



As the rays of the sun are the immediate cause of the 

 Heat on the surface of the globe, and as the length of 

 the days in high latitudes is so very different in summer 

 and in winter, it is evident that, in order to render those 

 regions habitable, some contrivance vv^as necessary to 

 prevent the consequences which this great inequality of 

 the Heat generated by the sun in summer and in winter 

 would naturally tend to produce ; or, in other words, to 

 equalize the Heat, and moderate its extremes in these 

 two seasons. 



Let us see how far Water is concerned in this opera- 

 tion, and then let us examine how far the remarkable 

 law which has been found to obtain in its condensation 

 by cold tends to render it well adapted to answer that 

 most important purpose. 



The vast extent of the ocean, and its great depth, but 

 still more its numerous currents, and the power of water 

 to absorb a vast quantity of Heat, render it peculiarly 

 well adapted to serve as an equalizer of Heat. 



On the retreat of the sun after the solstice, it is closely 

 followed by the cold winds from the regions of eternal 

 frost, which are continually endeavouring to press in to- 

 wards the equator. As the power of the sun to warm 

 the surface of the earth and the air diminishes very fast 

 in high latitudes on the days growing shorter, it soon 

 becomes too weak to keep back the dense atmosphere 

 which presses on from the polar regions, and the cold 

 increases very fast. 



There is, however, a circumstance by which these 

 rapid advances of winter are in some measure moderated. 

 The earth, but more especially the ""juater^ having imbibed 



