Then it occurred that the Hungerford Suspension Bridge was to be removed to make way for the Charing Cross Railway Bridge, so the chains were purchased at a comparatively small cost, and the work at Clifton proceeded, and was finally completed. Three chains on either side suspend long wrought-iron girders, which help to stiffen the platform; and cross girders between support the floor. The chains pass over rollers on the piers, and are ultimately anchored to plates bedded in brickwork abutting on rock. The platform is hung by upright rods from the chains, and hand-railing is used with lattice-work, to assist in rendering it rigid. The roadway, twenty feet wide, is made of creosoted wood, five inches thick, while the pathways on either side are made with wood half as thick. Between the piers the weight of the structure, including the chains, amounts to nearly a thousand tons. In all these suspension bridges, however large, the principles are much the same. The platform, or roadway, is hung from chains or cables, which pass over piers and are anchored fast at the ends. Some are stiffened with girders and bracing to prevent undue undulation. The chains take a graceful and definite curve, that of the Menai Bridge dipping fifty-seven feet. The strain is the greatest at the lower part, and is increased, should the chain be drawn flatter over the same space. These bridges became widely adopted. But there came a time when none of the bridges in vogue seemed to give what was required. A new principle was wanted. Where was it to be found? CHAPTER IV. THE GREATEST BRIDGE IN THE WORLD. “Have you heard the news? The Tay Bridge is blown down!” “Yes. A terrible disaster. I should think they would give up their scheme of bridging the Firth of Forth after that.” “Not they! The scheme may be altered, but bridge it they will. Engineers never give in.” The comments of these newspaper readers were right. The Tay Bridge, the longest in the world, had been blown down one wild December night in 1879, and girders, towers, and the train which was rushing over it, were suddenly hurled into the surging flood. At that time a scheme was in hand to bridge the Forth for the North British Railway system, and Sir Thomas Bouch had proposed two suspension bridges hung by steel chains. But ultimately a new design altogether was adopted, the plan being by Sir Benjamin Baker and Sir John Fowler. It was the new principle—or, rather, a remarkable development of an old principle—for which the bridge-making world was waiting: the principle, namely, of the cantilever. A cantilever is, in fact, a bracket; and Sir Benjamin Baker has described it as such. It is a strong support, built out from a firm base, and is like a powerful and magnified bracket upholding a shelf. In the Forth Bridge there are two huge spans, 1700 feet wide, crossed by these cantilevers; bridging channels of some 200 feet deep.