ATMOSPHERIC AQUEOUS VAPOUR. 9 



other parts of the world ; as well as the occurrence of 

 these extraordinary waterspouts, so common in America 

 and South Africa, when incredible volumes of water 

 fall in the course of a few hours, or even minutes, 

 so that at times they create fearful floods, which sweep 

 everything before them. * During our late visit to the 

 interior of South Africa, quite a number of these rain- 

 bursts were reported as occurring in different parts of 

 the country within a few days of each other, and in 

 some instances considerable damage was done : roads, 

 loaded waggons, etc., being swept away completely. 



Now the existence of all this water in some form 

 of atmospheric vapour presupposes, as we conceive, a 

 much greater amount being held in suspension by the 

 air than is indicated by i or 2 per cent, of vapour, 

 in the lowest stratum of say the first 10,000 feet above 

 the earth ; while a second stratum of similar magnitude, 

 reaching to the altitude of 20,000 feet, will take us up 

 very considerably above the limits of eternal snows, 

 even upon the equator : where presumably (according 

 to our present lights) the intensity of the constant cold 

 will have wrung the air dry of all, or nearly all its 

 moisture. If this be so, it follows that there must be 

 other sources of water-supply existing in the atmo- 

 sphere, in some form perhaps entirely unknown to us, 

 which are capable of supplying the difference between 

 the known and the unknown mediums for replenishing 

 the terrestrial waters. 



For example, in the highly rarefied atmosphere known 

 to exist at great elevations, there might be a large ad- 

 mixture of hydrogen gas, which from its extreme 



* See Vol. i., Chapter iv. on " Climates and Temperatures," where several 

 such instances are cited. 



