210 MOUNTAIN MISTS. 



pices) that lie bleaching in the desert, but too truly 

 and emphatically proclaim. 



But though the clouds which form there produce 

 effects so disastrous and fatal, it is probable that 

 they could not find their way down through the 

 mass of atmosphere that lies between that elevation 

 and a low plain ; but they show that the atmosphere 

 can act as powerfully at those heights as in any 

 other situation, more so indeed than upon the sur- 

 face of a level country, and more especially of a 

 country covered with trees or other tall vegetation. 

 There is a resistance to the wind by friction, as it 

 passes over these; but the swell of the air comes 

 full and uninterrupted upon the mountain, and as those 

 temporales prove, the loss of weight may be more 

 than made up by increase of velocity. 



There is also little doubt that the mountain draws 

 the atmosphere and the atmospheric moisture 

 towards it, notwithstanding that it is cold, and that 

 the general motion of the air on the surface is 

 towards the warm place. Over white snow, the air 

 when Che sun shines is warm, very warm as com- 

 pared with that over a vast and black surface at a 

 much smaller elevation. Of course the air ascends 

 in consequence ; and the very snow on the mountain 

 has a self-maintaining property, though it is contin- 

 ually refreshing the lower places with springs and 

 streams. 



But though the atmosphere over high mountains, 

 warmed as it is by the heat reflected from the snow 

 raises moisture higher than the atmosphere does 

 over plains, yet it is less able, in cases of change of 

 temperature, to sustain that moisture. If the moun- 

 tain is so high that the air has only half the density 

 that it has at the mean level of the earth, then the 

 same volume of it will support only half the weight, 

 whether of cloud or of any thing else. Thus the 

 very same texture of cloud which is a fog over the 

 city, or a creeping and even a dry mist in the valley, 



