AIR OVER MOUNTAINS. 209 



matter, whatever it may be in appearance as light, 

 there may be a perpetual formation of clouds, not 

 one of which may be able to find its way through 

 the denser and warmer air below. In those high 

 regions of the air there must indeed be an action of 

 heat in the atmosphere much greater than that 

 which takes place on the earth, otherwise there 

 could not be snow on the summits of the loftiest 

 mountains. On some of those mountains there is con- 

 tinual frost, except in the direct rays of the sun, and 

 evenalower temperature than that at which, under or- 

 dinary circumstances, water freezes. It is true, that 

 as the whole, or at least the greater part, of the sun- 

 beams is reflected back into the atmosphere by the 

 white snow, the air around those lofty summits must 

 be warmer while the sun is shining than air at the 

 same elevation over plains. That is the reason why 

 travellers who have ascended the Andes and other 

 mountains of great elevation have described them- 

 selves as being above the clouds ; and they no doubt 

 have been above the clouds of the plain and the val- 

 ley, just as a man on Highgate Hill or Hampstead 

 Heath is often above the London fog ; but if they 

 had dwelt for months at even the highest point that 

 the human foot has trodden, they would have found, 

 though they might not have survived to tell; that 

 they were not above the clouds and storms of the 

 mountains. The inhabitants of South America, of 

 Chili in particular, have roads, and also work mines 

 in the Andes, far above the limit of perpetual frost. 

 But elevated and cold as they are, and rare as is the 

 atmosphere upon those dreary heights, they by no 

 means enjoy a peaceful sky. The "temporales" 

 which rage there are perhaps more violent, both in 

 the fury of the wind and the thickness of the snow, 

 than in any other part of the world, as the number 

 of crosses set up at death-spots, and the number of 

 bones (of those who have been blown over the preci- 

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