Discussions on climate and cosmology / by James Croll.

  • Croll, James, 1821-1890.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: Discussions on climate and cosmology / by James Croll. Source: Wellcome Collection.

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    would not take place. The heat liberated by freezing is therefore what may be termed low-grade heat— heat incapable of melting snow or ice; while the heat absorbed while ice or snow is melting is high-grade heat, such as is capable of melting snow and support- ing vegetable growth. Moreover, the low-grade heat liberated in the formation of snow is usually liberated high up in the atmosphere, where it may be carried off by winds to more southern latitudes; while the heat absorbed in melting the surface of snow and ice is absorbed close to the earth, and is thus prevented from warming the lower atmosphere which is in con- tact with vegetation. The two phenomena, therefore, by no means counterbalance or counteract each other, as it is so constantly and superficially asserted that they do (Island Life, p. 140). The Fundamental Misconception.—I come now to a misapprehension which more than any other has tended to prevent a proper understanding of the causes which lead to the conservation by snow. Whatever the ec- centricity of the earth's orbit may be, the heat received from the sun during summer is more than sufficient to melt the snow of winter. Consequently, it is assumed no permanent accumulation of snow can take place. This objection, as expressed by Mr. Hill, is as follows: We have no reason to suppose that at present, in the northern hemisphere, more snow or ice is anywhere formed in winter than is melted in summer. With greater eccentricity, less heat than now would be received in winter, but exactly as much more in summer. More snow would therefore be formed in the one half of the year, but exactly as much more be melted in the other half. The colder winter and the warmer summer would exactly neutralize each other's effects, and on the average of years no accu-