; the water is brought from the Crawley Springs — natural sources issuing from a bank of gravel ; they are collected in a stone reservoir, called the Fountainheads, at an elevation of 564 feet above the sea, at Leith, and 230 feet above Castle Hill. The distance from the source to the Castle Hill reservoir, in a direct line, is six miles and a quarter, but, by the line of the aqueduct, eight and a half miles. The water is conducted the whole distance through iron pipes, varying in diameter from fifteen to twenty inches, and in thickness from half an inch to one inch and a quarter — in lengths of nine feet — and formed by spigot find faucet, that is, the end of each pipe is widened, in order to receive within it the intrant end of the preceding pipe, which is called the spigot, the joints being then made tight, in the usual way, by a caulking of oakum or clay, and molten lead. The pipes were all proved by the forcing pump, before they were laid. The process is simple : the pipe is filled with water, and firmly plugged at both ends, leaving at one end a communication with the forcing pump. In this state the pipe exhibits no leak, but after a few minutes' working with the forcing pump, creating a pressure of from ten PRELIMINARY ESSAY. 61 to twenty tons upon every part of the pipe, if the casting be not perfect, water is seen to transude, and if very faulty, the pipe bursts. In either case the pipe is useless. It is remarked in the account of the works from which we derive these particulars, " that the shaking of pipes by carting, effectually tries them — for that of two similar parcels of pipes, equally well cast at first, that which has been carted twenty miles before it was proved, will exhibit a greater number of defective pipes than that which has been proved at the manufactory. Hence pipes should always be proved at the place where they are delivered, and not where they are made." The whole supply from the Fountainhead, is conveyed in a single line of pipes, commencing at twenty, and tapering off, as the descent increases, to fifteen inches ; the daily delivery is estimated at about 1,600,000, gallons. Mr. Telford, the engineer, com- putes the full supply for a town, at nine gallons for each inhabitant. The population of Edinburgh and Leith, at the time these works were completed, was about 153,000, of whom those in the country parts, intervening between Edinburgh and Leith, and on the outskirts of both, derived water from wells, springs, and rivulets. The remarkable features of this aqueduct, are : First. A large and beautiful compensation reservoir, formed by constructing a vast mound, 450 feet in thickness, 120 feet high, and 300 in length, across a valley, in order to collect and store up the flood waters of the valley, and subsequently to distribute them to the mills below, in compensation for the water of the Crawley Springs, diverted from their former destination. Second. Its tunnels : the first of them, in the city, passed under Watson's and Heriot's hospital, at the depth of 70 or 80 feet below the surface. The second, at the Castle Wynd, which passes obliquely through the solid rock of the castle, emerging at the west side of the mound. This tunnel is 700 feet long, and passes under the reservoir (which, nevertheless, is supplied by a pipe from it, ascending on the outside of the rock.) at the depth of 120 feet, Glasgow, more populous than Edinburgh, is supplied by steam power from the waters of the Clyde. The peculiarity of the principal works of this city, for there are two — the Glasgow works of which we are first to speak, and the Cranston Hill Works — is, that the channels and reservoirs into which the water, percolating through a sandy soil, passes from the river, are on the left, or south bank of the Clyde, while the most of the machinery, and the city itself, are on the other bank ; of course the water for the engine well must be conducted across the river. The difficulty of such a transmission, at first sight so great, was obviated by the genius of Watt, to whom application was made. 16 62 PRELIMINARY ESSAY. " This celebrated engineer devised a flexible main of iron pipes, so connected as to adapt its form to the bottom of the river. That part laid across the bed of the river, consisted of pipes, nine feet in length, exclusive of the joints, and having a diameter of 15 inches. Some of the joints were formed in the