(Fig. 8) is a section of the common plug, with a canvas dam or cistern over it, as used in London. The cistern is made of No. 1 canvas, 15 inches deep, extended at top and bottom by 5/8-inch round iron frames, a double stay is hinged on the top frame at each end. When the cistern is used the top frame is lifted up, and the stays put into the notches, in two pieces of hoop iron, fixed to the bottom frame. There is a circular opening 9 inches diameter in the canvas bottom, two circular rings of wash-leather, about 2 inches broad, are attached to the edges of the opening in the canvas, so as to contract it to 4 inches or 5 inches diameter; the plug being opened, the cistern is placed over it; the wash-leather is pressed down to the surface of the road by the water, and a tolerably water-tight cistern, with about 12 inches or 14 inches of water in it, is immediately obtained. [Illustration: FIG. 9. Plug, with Standcock.] (Fig. 9) is a plug with a standcock in it, to which hose may be attached. (Fig. 10) is a common single firecock with a round water-way 2-1/2 inches diameter. [Illustration: FIG. 10. Single Firecock.] (Fig. 11) is a double firecock, as laid down in Her Majesty's Dockyards. [Illustration: FIG. 11. Double Firecock, used at the Royal Dockyards.] It will be observed, that the short piece of pipe between the main and this firecock is not curved to the current of the water, but merely opened a little; this is done with a view of increasing the supply by steam power, and as the steam engines are, in most cases, situated in a different direction from the tanks or reservoirs, therefore the curve that would have assisted the current in one direction would have retarded it in the other. It has been objected to these firecocks, that the opening does not run through the centre of the key, therefore only one side of the key covers the opening in the barrel, while in the common firecock both sides are covered. [Illustration: FIG. 12. Double Firecock, used at the British Museum.] (Fig. 12) is a double firecock, as laid down at the British Museum. This has a very good delivery, and is certain to be always tight, if well made, as the pressure of the water forces the key into the barrel; this also renders the cock somewhat difficult to be opened and shut, if the pressure be great; but as a lever of any length may be used, and the key, from its perpendicular position, may be loosened by a blow, this objection is in a great measure obviated. In Figs. 10 and 11 the openings in the street are large enough to admit of the levers for opening the cock to be fixed, that no mistake may occur from the lever being mislaid; but with those at the British Museum, it was not thought necessary to have fixed levers, as a crow-bar, or anything that could be introduced into the eye of the spanner, would open them. The plug and firecock have both certain advantages and disadvantages, which are now described.