The general principle of the construction of girder bridges is easily explained by considering a simple case, which is almost within everybody's experience. Public attention was first strongly drawn to suspension bridges by the engineer Telford, who, in 1818, undertook to throw such a bridge across the Menai Straits, and the work was actually commenced in the following year. The Menai Straits Suspension Bridge has been so often described, that it will be unnecessary to enter here into a lengthy account of it, especially as space must be reserved for some description of other bridges of greater spans. The approaches, on the Brooklyn side 971 feet, on the New York side 1,563 feet, are carried on stonework arches, which are utilised as warehouses, but where these approaches cross streets, iron bridges are thrown over. In relation to subject of wide-spanning bridges, the erection has been contemplated of structures which would surpass in magnitude and boldness any of those yet named.