MEMOIRS AND ADDRESSES 



EELATIONS OF AIR AND WATER TO TEMPERATURE AND 



LIFE 



BY 



HONORABLE GARDINER G. HUBBARD 

 PRESIDENT OF- THE NATIONAL GEOGRAPHIC SOCIETY 



Circulation of Air and Water. 



It was said in olden times, " The wind blowetli where it listeth, 

 and thou- hearest the sound thereof, but canst not tell whence it 

 cometh and whither it goeth." 



That which was unknown, science hath revealed. The wind 

 in its currents is governed and directed by laws as fixed as those 

 of the solar system. If a moisture-laden wind passes over the 

 country it leaves the land fruitful; but a dry wind leaves it 

 barren. The currents of air are among the most important fac- 

 tors in the physical geography of our earth, affecting not only 

 soil and climate but also vegetal and animal life. 



The winds obtain their moisture through evaporation, Avhich 

 goes on everywhere and at all times; in the equatorial and 

 polar oceans, from the rich cultivated soil and the arid desert, 

 from the valley and the snow-clad mountain. Reclus tells us 

 that the evaporation from the equatorial ocean is from 13 to 16 

 feet a year. This estimate is confirmed by the United States 

 Geological Survey, which found the evaporation from the south- 

 ern Colorado river to be 102 inches, or nearly 9 feet in a year. 

 The quantity of water evaporated from the land must be very 

 large, as only about two-fifths of the rainfall is returned by the 

 rivers to the ocean. A great part, probably more than one-half 

 of this quantity, is reevaporated to fall the second and third 

 time as rain. 



The movements of the atmosphere depend either directly or 

 indirectly on differences of temperature ; without these differ- 



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