THE CAUSE OF PERPETUAL SNOW.

Inangahua Times, Volume II, Issue II, 17 December 1880, Page 2

THE CAUSE OF PERPETUAL SNOW.

:■ »■ ■" Dr Jjmes Croll, in the current number of the American Journal of Science and Arts, says the reason why snow-at great elevations does not melt but remains permanent, i« <*win£ to the fact that the heat received from the sun is thrown off into stellar space so rapidly by radiation and reflection that the sun fails to raise the temperature of the snow to the melting point ; the snow evaporates, but is does not melt. The summits of the Himalayas, for ex* ample, must receive more than 10 times the amount of heat necessary to melt all the snow that falls on them, yet in spite of thi* the snow is not melted. Notwithstanding the strength of the sun and the ckycess of the air at those altitpdes, evaporation is insufficient to melc the snow. At ]o-.v elevations, where the snowfall is probably greater, and the amount of heat : received even les9, the snow melts and 'disappears. This, Dr. Croll believes, must be attributed to tne influence of ■aqueous vapor. At high elevations the air is dry and allots 'the heat raiia'ed from the snow to pass into .space, hut; at low elevations a very considerable amount ot the heat radiated from the snow is absorbed by the aqueous vapor in ■'♦.he atmosphere. A considerable portion of the heat thus absorbed is radiated 1 bick on the snow, and, being of the same quality as that which the snow itself radiates, is for that reason : absorbed by the latter. The conseqience is that the heat thus absorbed accumulates in the oiiow till this is melted. Were the amount of aqueous vapor possessed by the atmosphere sufficiently dimin-ahed, perpetual sdow would cover our globe clown to the sea shore. ]n a like manner- the dryness of the air will, ia a great measure, | account lor the present accumulation j lo!" .-ipw. aud itfj on.Oreealaad. and on I

the Antarctic connuent. These regions are comp'etely covered with anow and ice. not because the quantity of enow falling, on them is great, but because . the quantity melted w small. And the reason why the snow does not melt is not because the amount of beat received during the year » not; equal to to the work of melting the ice, but mainly because of the dryoess of the air, the snow is prevented from rising to the melting point. In place like Feugoand South Georgia, where tbe snowfall is considerable, perennial snow and ice are produced by diametrically opposite means, namely, by the sun's heat bmg cut off by clouds and dense fogs. In the first place, the upper surfaces of toe clcuds act 83 reflectors, throwing back tbe sun's rays into stellar space, and in tbe secood pace, of the heat which the clonda and fog 3 absorb, more than one- \ oUalffo. not raduted^^wnwajd on the i tlie • comparatiyely small portion of j heat which manages to reach the | ground and be available in melting the t snow is insufficient to clear off tbe winter's accumulation.