Jdly 18, 1913] 



SCIENCE 



69 



moisture obtained by evaporation from the 

 land. At least it must form a larger part 

 than the water which was obtained directly 

 by evaporation from the oceans. 



The vapor brought by the prevailing 

 winds from the ocean is many times turned 

 over or reinvested before it is returned 

 again to the ocean through the rivers. 



If we could reduce the surface run-off, 

 and at its expense increase the evaporation 

 from the land, we should thereby increase 

 the moisture of the passing air currents, 

 and in this way contribute to the precipi- 

 tation of that region into which the pre- 

 vailing winds blow. This conclusion is al- 

 most axiomatic, and there can be no dis- 

 pute about it. 



"continental" and "ocean" vapor 



For a long time it has been accepted 

 without any question that all the vapor 

 that is condensed in the form of rain or 

 snow over the land surface is furnished by 

 the evaporation of water from the oceans. 



The part which vapor from the ocean 

 plays in the precipitation over land has 

 been altogether exaggerated, and it is 

 hardly possible, therefore, to agree with 

 Professor Moore when he says that "the 

 precipitation over the eastern part of the 

 United States is derived entirely from the 

 evaporation from the Gulf of Mexico and 

 the Atlantic Ocean." 



A noted European meteorologist. Pro- 

 fessor Bruckner, author of a classical work 

 on the climatic fluctuations, has computed 

 the amount of water evaporated from the 

 ocean surface, land surface and the amount 

 of water which is returned to the oceans 

 and the land in the form of precipitation. 

 The balance sheet of the circulation of 

 water on the earth's surface is made up as 

 follows : 



CIRCULATION OF WATER ON THE EARTH'S SURFACE 

 BALANCE SHEET 



The continental vapor which is fed from 

 the periphery of the land surface is thus 

 about 21,000 cubic miles. It plays, there- 

 fore, an important part in supplying the 

 moisture to the air, even a more important 

 part than the vapor directly fed from the 

 ocean. The peripheral regions of the con- 

 tinents, i. e., the regions tributary to oceans, 

 are capable of supplying seven ninths of 

 their precipitation by evaporation from 

 their own areas. The moisture which is 

 carried by the winds into the interior of 

 vast continents, thousands of miles from 

 the ocean, is almost exclusively due to con- 

 tinental vapors and not to evaporation 

 from the ocean. 



'I. e., the difference between the amount of 

 vapor that escapes from land to the ocean and 

 from the ocean to land. 



