Page:Royal Naval Biography Marshall v4p1.djvu/35

 height of twenty-seven feet above the surface of the summer water of the river. It is also made to me about two feet in the centre, and is finished on each side with a cornice of fifteen inches in depth.

“The roadway is suspended from the catenarian or main chains by circular rods of iron, which measure one inch in diameter. These perpendicular rods are wedged into caps or pieces of cast-iron, called saddles, which are placed at the distance of five feet apart, and are made to rest upon the shackles or joints of the chains. The attachment of the lower ends of these rods to the beams of the platform which they pass through, is by their embracing a bar of iron which runs along the whole extent of the bridge under the beams of the roadway on each aide. These bars measure three inches in depth, and they are connected with the suspending rods by a spear or bolt, which, in a very simple manner, completes the connection of the roadway with the perpendicular suspending rods, and chains.

“The chains of this bridge are twelve in number, ranged in pairs; the one pair being placed over the other, between the points of suspension on each side of the bridge. These chains, and indeed the whole of the ironwork, is made of the best Welsh iron. The chains are worked into a circular form, and measure about two inches in diameter. The links, as they may be termed, consist of rods of fifteen feet in length, and have bolt-holes, which are strongly welded, and neatly finished at each end. These links or rods are connected together by strong shackles, and a bolt is passed through them, which is of an oval form, measuring 2¼ by 2½ inches. At each joint of the three tiers of the catenarian chains respectively, one of the saddle pieces of cast-iron is introduced. The first saddle-piece, with its suspending rod, for example, on either side of the bridge, may be conceived as resting on the upper pair of chains; the next saddle-piece in the longitudinal direction of the roadway, rests upon the middle pair of chains, and the third upon the lower pair, and so on alternately, throughout the whole extent of the bridge. By this means all the chains bear an equal strain, and the joints are arranged in so precise and orderly a manner, that a saddle-piece and perpendicular suspending-rod occurs at every five feet, so that the distance between each pair of suspending-rods forms a space of five feet. The spaces of five feet between the suspending rods are formed into meshes of six inches square, to the height of five feet on each side of the bridge, and answer the purposes of a parapet wall for the safety of passengers.

“Though the timber roadway is only about 361 feet in length, yet the chord-line of the main-chains measures no less than 482 feet between the points of suspension, with which they make an angle of about 12&deg;, and in forming the catenarian curve-drop, at the rate of one perpendicular to about seven feet in the length of chain, the versed sine of the middle pair of chains being about twenty-six feet. The twelve main-chains, with their apparatus, weigh about five tons each, and the weight of the whole bridge, between the points of suspension, has been estimated at 100 tons.

