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.
This admirable and useful structure was erected in two of the shortest day months of the year, during which time daylight did not occur at any low water period; the workmen, therefore, had to depend upon torches and moonlight; and what is quite as extraordinary, it can be taken down and erected on another site in a month, should circumstances render it necessary.
The Old Abbeys and Castles of England.
In a former chapter I mentioned something about Old Abbeys. I am now about to say something concerning the Old Castles of England, for few things are more interesting to young people than the stories connected with them. There is scarcely any part of England but has ruins of old castles; some of these ruins are very picturesque, and, when we look at them, the mind is carried back to the times of superstition—of religious bondage—of knighthood and chivalry—and of intestine war. Happily, these times are gone for ever, and we now enjoy peace, freedom, and religious happiness, such as ancient times never did, and never could produce; and we ought to be grateful to Almighty God that we live in such blessed times.
According to Dr. Johnson, a Castle is a strong house fortified, but this gives little more information than the saying, according to law, “Every man’s house is his castle.” A Castle, properly so called, is a fortress or fortification of stone, surrounded by high and thick walls of defence, with different walls and lines of circumvallation, consisting of the Barbican, the Moat, the wall of the outer Ballium, the outer Ballium, the Artificial Mount, the wall of the inner Ballium, the inner Ballium, and the Keep or Dungeon.