134 Mr. J. Croll on the Physical Cause of the 



fiftieth part of the snow of Norway is liquefied by the rain of 

 summer. 



The conditions necessary to the formation of glaciers would 

 be secured by a state of things the reverse of what produced the 

 climate of the coal-period, viz., by winter occurring when the 

 earth was in the aphelion of its orbit, at the time of greatest 

 excentricity. 



We have already seen that the direct heat during winter 

 would, under these conditions, be nearly one-fifth less than at 

 present. This would no doubt bring our mean winter tempe- 

 rature below the freezing-point. The low temperature of the 

 winter would not only prevent the melting of the ice and snow, 

 but would cause the entire moisture of the air to be precipitated, 

 not in the form of rain as at present, but as snow. It is also 

 more than probable that a diminution of one-fifth in the total 

 quantity of heat received from the sun during the winter months, 

 would lower the temperature to such an extent as would freeze 

 our British seas. It is quite true that the direct heat of the sun 

 during the summer would be one-fifth greater than at present. 

 But it is questionable whether the summers would on this ac- 

 count be warmer than they are at present. The temperature of 

 the summer is not always proportionate to the quantity of heat 

 directly received from the sun. In the Straits of Magellan, in 

 53° S. lat., where the direct heat of the sun ought to be as great 

 as in the centre of England, MM. Churruca and Galeano have 

 seen snow fall in the middle of summer ; and though the day was 

 eighteen hours long, the thermometer seldom rose above 42° or 

 44° F., and never above 51°*. 



The great strength of the sun's rays during summer, due to 

 its nearness at that season, would, in the first place, tend to pro- 

 duce 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 consequence would be that the snow 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 Scot- 

 land, 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. The following is Capt. Cook's description of this dismal 

 place: — "We thought it very extraordinary," he says, "that 

 an island between the lat. of 54° and 55° should, in the very 

 * Edinburgh Philosophical Journal, vol. iv. p. 266. 



