THE OCEAN 351 



the continents, so far as they stay at the surface, and in the lati- 

 tudes where they occur, the winds blow from them to the sea, rather 

 than to land. 



3. The ocean is the great source of the water for rain and snow, 

 and its precipitation from the air furnishes the conditions necessary 

 for life on the land. 



4. Through its effect on rainfall, snowfall, and temperature, 

 the ocean has an important effect on the erosion of the land. 



The total amount of rainfall for the earth is not accurately known. 

 If it is as much as forty inches per year on the average, for the 

 whole earth, and if all this were derived directly from the ocean, 

 an amount equal to all the water in the ocean would be evaporated 

 in about 3,000 years. Since most of the water evaporated from 

 the ocean falls again into the sea as rain, or runs to it in rivers, or 

 comes out beneath it as springs, the amount of the ocean water does 

 not grow less, so far as we know. 



5. The ocean yields a large amount of food-stuff every year, 

 and a large amount of other material useful to man. Thousands 

 of people are constantly employed in getting these useful tilings 

 from the ocean. 



6. The oceans play an imporant part in the commerce of the 

 world, by serving as a great highway. 



Oceans were formerly great obstacles to quick communication 

 between the continents separated by them; but during the last 

 half century several cables have been laid connecting Europe and 

 America, so that all the important news of one continent is known 

 in the others almost as soon as it is at home. The work of laying 

 cables across the Pacific has already been begun. 



REFERENCES 



1. WILD, Thalassa: Marcus Ward & Co., London. 



2. All standard text-books on Physical Geography, Physiography, and 

 Geology. 



3. MURRAY, Articles in Geog. Jour., Vol. XII, pp. 113-137, and Vol. XIV, 

 pp. 34-50 and 426-44 1; and Scot, Geog. Mag., Vol. XV, pp. 505-522. 



