Such being the case, the attention of Engineers has for some time been directed to the best means for overcoming this difficulty. The building of a house upon a rock has ever been considered the proof of wisdom, whilst the erection of it on the sands has been held the proof of folly. But the advances of science prove that a house may be built even upon the sands, when proper care is taken in its construction—and the erection of lighthouses on this foundation is held to be a triumph in engineering. This remarkable result has been accomplished chiefly by means of Mitchell’s screw mooring, which consists of an immense screw, very similar to that of the corkscrew, with flat cutting spirals. It is a spiral or screw round a cast-iron spindle, having a square head, upon which a large key is placed (like the key of a watch), and the screw is turned by enormous leverage, and it is then forced into the ground, and can be carried to a great depth. This instrument was thought to be applicable to the establishment of Lighthouses upon sands; and, accordingly, a series of experiments was undertaken, and a lighthouse was speedily erected on the verge of the Maplin Sand, situated at the mouth of the Thames, about twenty miles below the Nore. The foundation was formed of seven screw piles, six occupying the six angles of a hexagon, and the seventh being placed in the centre. From each screw proceeded a pile fifteen feet in length, at the upper end of which was another screw for securing a wooden column. These columns were prepared of Baltic timber: the one in the centre was fifty-six feet, and each of the remainder forty-six feet in length, firmly bound together with iron hoops, and coated with pitch. The platform upon which the house stands is firmly secured round the centre column, and to the heads of the outer columns by means of hollow cast-iron capitals let down on the heads of the columns, and secured with screw bolts. To give lateral strength to the building, round iron angle traces were applied, by which means a resisting power, equal to at least three-hundred-and-fifty tons is presented in every direction. The platform upon which the house stands is twenty-seven feet in diameter and nine feet high; it has an outside door and three windows, and is divided into two apartments—one having a fire-place. The floor is tiled, and the walls are ceiled, lathed, and stuccoed; access to the platform is secured by means of a Jacob’s ladder to one of the columns. From the summit of the house rises the lanthorn: it is twelve sided, and is ten feet in feet in diameter and eight feet high. The light is elevated about forty-six feet above low water level, and is bright, steady, and uniform—ranging over an horizon of eight miles and visible at the distance of ten miles from a coaster’s deck. During foggy weather a bell is tolled by machinery. Tide time for vessels of twelve feet draught is also denoted by signals.