I. Water, as already hinted, is an element of vast account in the economy of nature, and is a recreation to the heart and a delight to the eye of both man and beast. To have a plentiful supply of it is one of the greatest blessings of God to the creature, and to be able to bestow it wisely and employ it usefully is one of the most serviceable of human arts. It is too valuable a servant to suffer to go idle, and many are the offices it might do us, if, as it travels from the mountains to the sea-board, we caught it in its course, harnessed it to our chariot, and guided it to our aim. We should turn it to account every inch of its progress, and compel it, as it can, to minister to our requirements by its irresistible energy. Its merely mechanical power is immense, and this is due in great part to its incompressibility; for it is in virtue of this quality alone we can, by means of it, achieve feats not otherwise feasible. How else could we have raised to its sublime height that stupendous bridge which spans the Menai Straits, and which is the wonder of the beholder, as it is the boast of the designer? It stands where it does by the help of some mechanism indeed, but the true giant that lifted it on his shoulders and bore it to its airy elevation was the incompressible force of water, a fluid which is, strangely, the simple product of the combination of two elastic transparent gases, oxygen and hydrogen, neither of which apart has the thew and sinew of its offspring. Nay, it is this single element, which, acted on by heat or acting through machinery, fetches and carries for us over the wide globe, and is fast weaving into one living web the far-scattered interests of the world. Water was in primitive times utilised into a motive power by the help of a mechanism of rude design, which yet is hardly out of date, and might recently be seen in its original, still more in modified form, in certain back-quarters of civilisation. A stream, guided by a sluice, was made to play upon four vertical paddle-blades, attached to a shaft which they caused to revolve, and which moved a millstone, resting upon another through which it passed. It was a primitive mill, which superseded the still more primitive hand-mill, or quern; and I myself have seen it at work in the Shetland Islands, and even the north of Scotland, though it is now done away with even there, still more farther south, and its place supplied and its work done by overshot and under-shot wheel-gear, and improved machinery attached, of less or more complexity. One of the most recent improvements is the Turbine, a sort of Barker's mill; it is of great power, small compass, and acts under a good fall with a minimum expenditure of water-power.