an arm of the sea in North Wales, separating the island of Anglesea from the county of Carnarvon, and extending from N.E. to S.W. to a length of about 14 miles, with a breadth varying from 200 yards to 2 miles. The navigation of this strait was formerly impeded by dangerous rocks, many of which, however, have been removed, and ships, especially those with a tonnage of less than 100 tons, now pass through in safety. The Menai Strait is chiefly remarkable for the two bridges by which it is spanned. The Menai Suspension Bridge, by Telford, was begun in 1819 and opened in 1826. It is of a very elegant form, and is supported by two piers, the distance between which is 550 feet, and the whole roadway, which is carried over four arches on one side and three on the other, has a length of 1000 feet, and a breadth of 30 feet. The height of the bridge above the level of high-water is 100 feet, and the total suspending power of the bridge, exclusive of its own weight, is calculated at 1527 tons. The cost of the erection was L120,000. The Britannia Tubular Bridge is a still more wonderful erection. It was built for the Chester and Holyhead Railway by Stephenson, and was completed in 1850, after having been in the course of construction for four years. Owing to the necessity that it should be 100 feet above the water throughout, it was impossible to construct the bridge in the usual way with arches; and on account of the vibration to which it would be liable, the suspension principle was not employed. It was therefore constructed of tubular beams of iron, by means of which the greatest amount of strength with the least weight was obtained. These beams form eight large tubes, which rest upon three towers in the sea and an abutment on the land on each side. The whole length of the roadway is 1841 feet, and its height above high-water is 101 feet, while the total height of the central tower is 230 feet. The weight of all the tubes is nearly 11,000 tons, being more than that of four line-of-battle ships fully equipped; and the cost of the whole was L621,865. (See IRON BRIDGES, vol. xii., p. 607.)