Of the very ingenious innovations in the structure of vessels contrived by Sir R. SEPPINGS, by which knees and crooked timber might nearly be superseded, we can only say, the practice is not followed, and, at least in private building-yards, not likely to be so;—that the demand for fine crooked timber, comparatively, is, and will continue to be, as great as ever. Should our war navy, from the introduction of steam impulse and bomb cannon, be reduced to fleets of strong gun-boats, the demand for crooked timber, instead of lessening, will greatly increase,—the building of frames of straight timber being more expensive, and less suitable, in small than in large vessels; and should war occur, in the hurry of the formation of a new war navy under a different principle, the speediest and simplest mode of construction will be followed. Nearly two-thirds of the timbers of a vessel consist of the curves and bends _a_, _b_, _c_, _d_, _e_, _f_; the other third is of straighter timber, and easily obtained. {17} All timbers require to be straight in one way—in the plane of their side, and the sides generally to be square. The under measures embrace timbers of appropriate size for vessels from 50 to 500 tons register; it is seldom that merchantmen are required under or above this size. Of course, large war-vessels require timbers of larger dimension. The corresponding timbers of vessels of different size are nearly similar figures, and the length of their respective lines not far from being in the ratio of the cube root of the tonnage—a little deeper and thicker in the smaller vessels. When timbers are formed of larch or pine, they require to be a little more in diameter than when of oak. {18} [Illustration: Fig. _a_, Flat floor, from 9 1/2 to 18 feet long (that is, 9 1/2 for a vessel of 50 tons, and 18 for one of 500), and from 9 to 16 inches deep at middle; thickness 1/4th less than depth, the diameter increasing in proportion to the length. When fillings such as _s_ are used, flat floors are cut from straight logs. _b_, Rising floor shorter, and same depth and thickness as former. _c_, _c_, High rising floors, from 4 to 8 feet in length of wing, and a little deeper, and same thickness as former. From the difficulty of procuring this bend, the wings are often used of unequal length, according as the timber turns out, the shorter wing to exceed 3 feet, and more when of considerable diameter. Floors are of every rise from _a_ to _c_, being flattest at midships, and rising gradually as they approach the bow and stern. In all timbers, it is necessary, for strength, that the fibre of the wood extend from one end to the other without much cross grain. See lines on high rising floor, _c_. _d_, First foot-hook, from 7 to 13 feet long, and from 7 to 14 inches deep; thickness 1/5th less than depth.