376- PHYSIOGRAPHY. [chap. 



been said about that vast body, more than ninety millions of 

 miles away, around which the earth is constantly circling. 



The Thames is fed, directly or indirectly, by rain ; 

 and the rain is condensed from vapour, which has been 

 raised into the atmosphere by means of solar heat. With- 

 out the sun, therefore, there could neither be rain nor 

 rivers ; and hence it is not too much to say that the origin 

 of the Thames is ultimately to be traced to the sun. Rain 

 is dependent for its distribution upon currents in the atmo- 

 sphere, but these currents are due to disturbances of equili- 

 brium which are brought about by means of solar heat. 

 Without the sun, then, there could be no winds. The 

 currents of the sea engaged attention in another part of our 

 work ; but here again the sun is the prime mover. Whatever 

 view be taken of the origin of such currents, — whether they 

 are due to the immediate action of winds, or to variations 

 of temperature in the water, or to the excess of evaporation 

 in one place, over that of another — it is clear that the sun 

 is the real agent in the formation of ocean-currents. 



In another chapter, attention was directed to the phenomena 

 which are presented by cold, and especially to the formation 

 of glaciers ; here, if anywhere, it might have been supposed 

 that the sun certainly had no part to play. Yet, it must be 

 remembered, that the ice of. a glacier is water which has 

 been distilled by the sun's heat, and that the descent of 

 snow in one place connotes the evaporation of water 

 in another locality. Without the sun, therefore, there could 

 be no glaciers. 



Considerable attention was given, in several chapters, to 

 the phenomena of life, so far as they bore upon the subject 

 under discussion. But every one knows that heat and light 

 are such necessary conditions for the manifestation of hfe, 

 that the earth would become lifeless, if sunshine were 



