CHAP. ix. THE IMPORTANCE OF DUST. 79 



the earth's surface became super-saturated with aqueous 

 vapor, dew would be continuously deposited, especially 

 on every form of vegetation, the result being that every- 

 thing, including our clothing, would be constantly drip- 

 ping wet. If there were absolutely no particles of solid 

 matter in the upper atmosphere, all the moisture would 

 be returned to the earth in the form of dense mists, and 

 frequent and copious dews, which in forests would form 

 torrents of rain by the rapid condensation on the leaves. 

 But if we suppose that solid particles were occasionally 

 carried higher up through violent winds or tornadoes, 

 then on those occasions the super-saturated atmosphere 

 would condense rapidly upon them, and while falling 

 would gather almost all the moisture in the atmosphere 

 in that locality, resulting in masses or sheets of water, 

 which would be so ruinously destructive by the mere 

 weight and impetus of their fall that it is doubtful 

 whether they would not render the earth almost wholly 

 uninhabitable. 



The chief mode of discharging the atmospheric vapor 

 in the absence of dust would, however, be by contact 

 with the higher slopes of all mountain ranges. Atmos- 

 pheric vapor, being lighter than air, would accumulate 

 in enormous quantities in the upper strata of the atmos- 

 phere, which would be always super-saturated and ready 

 to condense upon any solid or liquid surfaces. But the 

 quantity of land comprised in the upper half of all the 

 mountains of the world is a very small fraction of the 

 total surface of the globe, and this would lead to very 

 disastrous results. The air in contact with the higher 

 mountain slopes would rapidly discharge its water, which 

 would run down the mountain sides in torrents. This 



