128 



ISLAND LIFE. 



[part I. 



surplus heated water of the tropics to the temperate and even 

 to the polar regions, while colder water flows from the poles to 

 ameliorate the heat of the tropics. An immense quantity of 

 sun-heat is also used up in evaporating water, and the vapour 

 thus produced is conveyed by the aerial currents to distant 

 countries, where, on being condensed into rain, it gives up much 

 of this heat to the earth and atmosphere. 



The power of water in carrying away heat is well exhibited 

 by the fact of the abnormally high temperature of arid deserts 

 and of very dry countries generally ; while the still more power- 

 ful influence of moving air may be appreciated, by considering 

 the effects of even our northern sun in heating a tightly-closed 

 glass house to far above the temperature produced by the 

 vertical sun of the equator where the free air and abundance of 

 moisture exert their beneficial influence. Were it not for the 

 large proportion of the sun's heat carried away by air and 

 water the tropics would become uninhabitable furnaces — as 

 would indeed aif^y part of the earth where the sun shone brightly 

 throughout a summer's day. 



We see, therefore, that the excess of heat derived from the sun 

 at any place cannot be stored up to an important amount owing 

 to the wonderful dispersing agency of air and water; and 

 though some heat does penetrate the ground and is stored up 

 there, this is so little in proportion to the whole amount received, 

 and the larger part of it is so soon given out from the surface 

 layers, that any surplus heat that may be thus preserved during 

 one summer rarely or never remains in sufficient quantity to 

 affect the temperature of the succeeding summer, so that there 

 is no such thing as an accumulation of earth-heat from year to 

 year. But, though heat cannot, cold can be stored up to an 

 almost unlimited amount, owing to the peculiar property water 

 possesses of becoming solid at a moderately low temperature ; 

 and as this is a subject of the very greatest importance to our 

 inquiry — the whole question of the possibility of glacial epochs 

 and warm periods depending on it — we must consider it in 

 some detail. 



Effects of Snow on Climate. — Let us then examine the very 

 different effects produced by water falling as a liquid in the 



