[161] The advantages of this system of trussing are described by a practical authority, as follows: “Running fore and aft, and constituting the frame of the sides of the ship, are two arched trusses of wood and iron, of the most ingenious construction. The vertical depth, from the crown of the truss down to the level of the keel, is about 53 feet. In the truss is also interwoven a counter arch, the trusses, therefore, not only prevent the sinking of the two extremities and rising of the middle, but they likewise prevent any rising of the extremities, and sinking of the middle of the ship, and thus effectually prevent any tendency to bend or break in the direction up or down in a fore and aft vertical plane; and, by a most perfect system of lateral trussing interwoven with the tiers of beams, she is prevented from bending or breaking in the direction of a horizontal plane, running fore and aft through the ship. Where strain by tension or pulling is exerted, wrought iron is to be used, and where thrusts or compression is exerted, wood is used, and where both compression and extension are felt, wood and iron together are used.”—Address by Captain T. J. Cram, delivered at the Board of Trade Room, Philadelphia, July 11th, 1860. [162] So far as regards the stability of the proposed vessel, Captain Cram, who was a member of the United States’ Corps of Topographical Engineers, remarks, in the lecture on her, delivered in 1860 at Philadelphia, as follows: “She is to be a four-storey ship. Commencing at the bottom and going upwards we have the first storey, a hold, 16 feet high in the clear, with ample room for the machinery, boilers, and coals, and for a large quantity of freight besides. All this great weight of engines, boilers, coals, and dead weight freight, which is to be stowed in the very bottom of the ship, will act as ballast placed in the right position to insure stability and to relieve the ship from that dangerous topheaviness usually observed in many sea-going steamers.”