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 ti e 
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 any 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 
