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 itwas 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