The power actually at work at present in producing rain, and so, indirectly, in levelling the earth’s surface, is enormous. I have shown that the amount of heat required to evaporate a quantity of water which would cover an area of 100 square miles to a depth of one inch would be equal to the heat which would be produced by the combustion of half a million tons of coals, and that the amount of force of which this consumption of heat would be the equivalent corresponds to that which would be required to raise a weight of upwards of one thousand millions of tons to a height of one mile.[45] When we remember that the land surface of the earth amounts to about fifty millions of square miles, we perceive how enormous must be the force-equivalent of the annual rainfall of our earth. We are apt to overlook when contemplating the silent and seemingly quiet processes of nature—such as the formation of the rain-cloud or the precipitation of rain—the tremendous energy of the forces really causing these processes. “I have seen,” says Professor Tyndall, “the wild stone-avalanches of the Alps, which smoke and thunder down the declivities with a vehemence almost sufficient to stun the observer. I have also seen snow-flakes descending so softly as not to hurt the fragile spangles of which they were composed; yet to produce from aqueous vapour a quantity which a child could carry of that tender material demands an exertion of energy competent to gather up the shattered blocks of the largest stone-avalanche I have ever seen, and pitch them to twice the height from which they fell.” _ANCIENT BABYLONIAN ASTROGONY._