~ mis eae 
296 COSMICAL ASPECTS OF GEOLOGY. [Boor I. _ 

that rays from snow and ice are, of all others, those which it absorbs | 
best. The humid air will absorb the total radiation from the snow 
and ice, but it will allow the greater part of, if not nearly all, the 
sun’s rays to pass unabsorbed. But during the day, when the sun 
is shining, the radiation from the snow and ice to the air is 
negative ; that is, the snow and ice cool the air by radiation. The 
result is, the air is cooled by radiation from the snow and ice (or 
rather, we should say, to the snow and ice) more rapidly than it is 
heated by the sun; and as a consequence, in a country like Green- 
land, covered with an icy mantle, the temperature of the air, even 
during summer, seldom*rises above the freezing-point. Snow is a 
good reflector, but as simple reflection does not change the character 
of the rays, they would not be absorbed by the air, but would pass 
into stellar space. Were it not for the ice, the summers of North 
Greenland, owing to the continuance of the sun above the horizon, 
would be as warm as those of England; but instead of this, the 
Greenland summers are colder than our winters. Cover India with 
an ice sheet, and its summers would be colder than those of England. _ 
“ Second, Another cause of the cooling effect is that the rays which ~ 
fall on snow and ice are to a great extent reflected back into space. 
But those that are not reflected, but absorbed, do not raise the tem- 
perature, for they disappear in the mechanical work of melting the 
ice. For whatsoever may be the intensity of the sun’s heat, the 
surface of the ground will be kept at 32° so long as the snow and 
ice remain unmelted. 
“ Third, Snow and ice lower the temperature by chilling the air 
and condensing the vapour into thick fogs. The great strength of 
the sun’s rays during summer, due to his nearness at that season, 
would, in the first place, tend to produce an increased amount of 
evaporation. But the presence of snow-clad mountains and an icy 
sea would chill the atmosphere and condense the vapour into thick 
fogs. The thick fogs and cloudy sky would effectually prevent the — 
sun’s rays from reaching the earth, and the snow, in consequence, 
would remain unmelted during the entire summer. In fact, we have 
this very condition of things exemplified in some of the islands of 
the Southern Ocean at the present day. Sandwich Land, which is 
in the same parallel of latitude as the north of Scotland, is covered 
with ice and snow the entire summer; and. in the island of South 
Georgia, which is in the same parallel as the centre of England, the 
perpetual snow descends to the very sea-beach. Captain Sir James’ 
toss found the perpetual snow at the sea-level at Admiralty Inlet, 
South Shetland, in lat. 64°; and while near this place the thermo- 
meter in the very middle of summer fell at night to 28° F, The re- 
duction of the sun’s heat and lengthening of the winter, which 
would take place when the eccentricity is near to its superior limit 
and the winter in aphelion, would in this country produce a state of 
things perhaps as bad as, if not worse than, that which at present 
exists in South Georgia and South Shetland. 
