. The mastery of water. R II. The Waters Under the Earth. Man probably welcomes the river, the lake, and the seaas means of freshening his body before or after thelabours of the day ; but for drinking he prefers the clear,crystal spring which gushes from the hillside. For onething, the water is generally colder, and in warm weatherwhen thirst is keener this is an advantage. If you haveread the volume on the Mastery of Earth, you maywonder why spring water is often so cold, although the 2—(927) 10 THE MASTERY OF WATER. temperature of the earth increases as one goes down-wards. But this increase
. The mastery of water. R II. The Waters Under the Earth. Man probably welcomes the river, the lake, and the seaas means of freshening his body before or after thelabours of the day ; but for drinking he prefers the clear,crystal spring which gushes from the hillside. For onething, the water is generally colder, and in warm weatherwhen thirst is keener this is an advantage. If you haveread the volume on the Mastery of Earth, you maywonder why spring water is often so cold, although the 2—(927) 10 THE MASTERY OF WATER. temperature of the earth increases as one goes down-wards. But this increase is very small; and at moderatedistances below the surface the ground is nearly alwayswarmer in winter and colder in summer than the airabove. Spring water is clear because aU the suspended particleshave been filtered out in its passage through the ground ;and it is often sparkling because of the gas which it hasdissolved at great depths under pressure, and which isliberated in minute bubbles as the water escapes from. HOW SPRINGS ARE FORMED. its rocky prison. Bu^ before we go into a question ofthis kind it will be well to consider how springs rain falls upon the land, some of it sinks throughthe surface, some is evaporated and carried away by thewind, some is sucked up by the roots of plants, andsome runs off into a river and so into the sea. Whatproportion goes in each direction is very important, andno doubt it varies very considerably in different engineer who proposes to supply a town with waterwants exact information on the matter. From measure-ments which have been carried out recently, it has beenshown that about fifty per cent, sinks into the ground, THE WATERS UNDER THE EARTH. 11 ten per cent, is evaporated or absorbed by plants, andforty per cent, runs back to the sea. We shall follow upthat which sinks into the ground. The rocks of which the earths crust is composed aremore or less porous, so that water can sink throughthem. This is, of co
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