The boat-carriage complete consists of a wooden slide bound together in front and rear by iron plates, and a composite carriage made up of a wooden bed surmounted by an iron bed-plate and bracket-frames for the trunnions. Two buffers are put at the rear of the slide to take an over-recoil. The elevating-gear is the simple screw and hand-wheel. The compressor is a brass-faced block whose upper side takes in undercut spaces in the slide. The block is held up and tightened by a screw and hand-clamp. For transporting the boat-carriage and gun together a small block-cart is used, which is nothing more than a heavy, flat, wooden body provided with an axle and two gun-trucks. [Illustration: Boat-Carriage.] _Field-Carriages._ The field-carriage is of the ordinary type, consisting of two straight iron brackets, strengthened along the upper edge by angle-irons, and curved to form a sole at the bottom. To this a trunnion socket-frame is bolted. The brackets are braced by transoms and by two side rods. An iron axle bolts to the under side of the brackets just in rear of the trunnion-holes. The wheels are wooden with brass hub-boxes and iron tires. The elevating-gear is of the plain screw and hand-wheel pattern. A limber is provided with this carriage which carries two ammunition-boxes, each of which holds six rounds of shell and the corresponding cartridges (not fixed to the projectile). The carriage itself also carries two ammunition-boxes of the same size. [Illustration: Field-Carriage.] GUNPOWDER. [Illustration] The gunpowder used for the majority of naval guns is of the kind known as prismatic powder. Of this there are two classes. The first, for use with the heaviest calibres, is solid; that for medium calibres is pierced with holes longitudinally—for the high calibres with one central hole, and for the medium with seven. Large-grained cannon-powder is used in shell-guns, whilst the usual classes of small-grained powder is used with small-arms and for shell-charges. Prismatic powder is invariably used for battering-charges in all calibres, the gradation with regard to time of burning being obtained by the holes pierced through the grains: slow powder, solid; medium, one hole; quick, seven holes. PROJECTILES.