106 PHYSICAL GEOGRAPHY OF THE SEA. AND ITS METEOROLOGY. 



all be regarded as belonging to one liydrograpbic basin, for a 

 canoe may pass inland from any one to either of the others with- 

 out portage. Of these hydiographic basins, three, including an 

 area of o,91G,000 square miles, are American; six, which con- 

 tain an area of 3,772,000 square miles, belong to Asia, one to 

 Africa, and none to Europe. The three largest rivers of Asia, 

 the Yenisei, Obi, and Lena (2,104,000 square miles), discharge 

 their waters into the Arctic Ocean ; their outlets are beyond the 

 reach of the commercial world ; consequently they do not pos- 

 sess the interest which, in the minds of men generally, is at- 

 tached to the rest. The three others of Asia drain 1,068,000 

 square miles, and run into the Pacific ; while the whole Ameri- 

 can system feed with their waters and their commerce the 

 Atlantic Ocean. These rivers, with their springs, give drink to 

 man and beast, and nourish with their waters plants and rep- 

 tiles, with fish and fowl not a few. The capacity of their basins 

 for production and wealth is without limits. These streams are 

 the great arteries of inland commerce. Were they to dry up, 

 political communities would be torn asunder, the harmonies of 

 the earth would be destroyed, and that beautiful adaptation of 

 physical forces to terrestrial machinery, by which climates are 

 regulated, would lose its adjustment, and the seasons would run 

 wild, like a watch without a balance. 



271. Heat required to lift vapour for tliese rivers. — We see these 

 majestic streams pouring their waters into the sea, and from the 

 sea we know those waters must come again, else the sea would 

 be full. We know, also, that the sunbeam and the sea-breeze 

 suck them up again ; and it is curious to fancy such volumes of 

 water as this mighty company of ten great rivers is continually 

 marching down to the sea, taken up by the winds and the sun, 

 and borne away again through the invisible channels of the air 

 to the springs among the hills. This operation is perpetually 

 going on, yet we perceive it not. It is the work of that in- 

 visible, imponderable, omnipresent, and wonderful agent called 

 heat. This is the agent which controls both sea and air in their 

 movements and in many of their offices. The average amount 

 of heat daily dispensed to our planet from the source of light in 

 the heavens is enough to melt a coating of ice completely en- 

 casing the eai-th with a film 1^ in. in thickness.* Heat is the 

 agent that distils for us fresh water from the sea. It pumps up 

 * Deduced from the experiments of Pouillet. 



