reach, he would adopt, instead of retaining walls, an open viaduct, placing all the piers edgeways to the force of the sea, and allowing the waves to break upon a natural slope of beach. He was ready enough to admit the errors he had committed in the original design of this work; but he said he had always gained more information from studying the causes of failures and endeavouring to surmount them than he had done from easily-won successes. Whilst many of the latter had been forgotten, the former were indelibly fixed in his memory. But by far the greatest difficulty which Robert Stephenson had to encounter in executing this railway, was in carrying it across the Straits of Menai and the estuary of the Conway, where, like his predecessor Telford when forming his high road through North Wales, he was under the necessity of resorting to new and altogether untried methods of bridge construction. At Menai the waters of the Irish Sea are perpetually vibrating along the precipitous shores of the strait; rising and falling from 20 to 25 feet at each successive tide; the width and depth of the channel being such as to render it available for navigation by the largest ships. The problem was, to throw a bridge across this wide chasm—a bridge of unusual span and dimensions—of such strength as to be capable of bearing the heaviest loads at high speeds, and at such a uniform height throughout as not in any way to interfere with the navigation of the Strait. From an early period, Mr. Stephenson had fixed upon the spot where the Britannia Rock occurs, nearly in the middle of the channel, as the most eligible point for crossing; the water-width from shore to shore at high water there being about 1100 feet. His first idea was to construct the bridge of two cast-iron arches, each of 350 feet span. There was no novelty in this idea; for, as early as the year 1801, Mr. Rennie prepared a design of a cast-iron bridge across the Strait at the Swilly rocks, the great centre arch of which was to be 450 feet span; and at a later period, in 1810, Telford submitted a design of a similar bridge at Inys-y-Moch, with a single cast-iron arch of 500 feet. But the same objections which led to the rejection of Rennie’s and Telford’s designs, proved fatal to Robert Stephenson’s, and his iron-arched railway bridge was rejected by the Admiralty. The navigation of the Strait was under no circumstances to be interfered with; and even the erection of scaffolding from below, to support the bridge during construction, was not to be permitted. The idea of a suspension bridge was dismissed as inapplicable; a degree of rigidity and strength, greater than could be secured by any bridge constructed on the principle of suspension, being considered an indispensable condition of the proposed structure. [Picture: Britannia Bridge]