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Show 208 METEORS AND 1\lETEORJC STONES. As we descend downwards from that limit of ex.· treme atmospheric rarity and gravit~:ion, and co~esion becomes more and more senswle, the motwn produced by the same variation of temperature must gradually become less and less i but t~e ~tmosp~ere is so rare even where densest, that It IS probably more sensible to changes of heat than even our sense of muscular resistan?e ; and. therefore we cannot even feel it to any tlung ?ear Its ho~ndary. Thus even at moderate elevatwns,_ elevatiOns :not greater than the summits of our lo~tlest mountams, the atmosphere may be thrown mto very great action by very slight causes ; . and the very first ·1 of the morning li<Tht which streams .upon an ~~~~~Isphere thick enough for dividing that hght, a~d sending down the extreme viol~t. of the spectrum m a lim mer of dawn to us, may, m the red and more en~rgetic part, give to. that light air a degree of motion which shall send It completely ro~nd the atmos here before the other part of the Iay can rea?h u~ fro~ probably not the thousandth part of the dis-ta~~ t though, in those upper p_arts of the atmo4 s here there is the least matter In the same spac~, Je mu~t. not on that account suppo~e that na.ture IS there least active. We have notl?ed, agam and . th t matter is the clog of motwn ; and as tho ~~~~'actfve substances that mingle with the a.tm?s here have the greatest tendency to ascend m It, p rna ro erly suppose that they occupy the ;peper p~rfs 0~ it; and that their motions and oppositions are not only perfec-tly adequate to the prod f on of all the luminous meteors that appear t~c ~ but also of forming out of the scattered mat~ri~~ ~hich float at that airy height, the meteo_rl~ stones of which so many are recorded as havmo fallen to the ground. · fi th t ·t Lower than that., but still in atr so ne . a I will float nothing that can be visible to our sight as 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 continual frost, except in the direct rays of the sun, and even a lower tern perature than that at which, under ordinary circumstances, water freezes. It is true, that as the whole, or at least the greater part, of the sunbeams is reflected back into the atmosphere by the white snow, the air arotmd 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 themselves as being above the c1ouds ; and they no doubt have been above the clouds of the plain and the valley, 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. 2S |