To facilitate the service of heavy guns and mortars, and to insure accuracy of fire. 3. Mention the kinds of platforms in general use in the service. Fixed platforms for casemate and barbette batteries in fortifications, which are constructed with the works; the siege-platform for guns and howitzers; and the siege-platform for mortars; the rail-platform; and the ricochet-platform. 4. What properties should wooden platforms possess? Strength and portability. [Sidenote: 119]] 5. Are the pieces composing siege-platforms of the same or different dimensions? All of the same dimensions, viz: 9 feet long, 5 inches wide, and 3½ inches thick; except the sleepers, which in the mortar-platform are one foot less in length. 6. What is the weight of each piece? About fifty pounds. 7. What is the number of pieces in the siege-platform for guns and howitzers? Forty-nine in all, one being used as a _hurter_ on the front part of the platform to prevent the carriage from running too far forward; and twelve for sleepers. 8. Describe the method of laying a platform for a siege-gun or howitzer. First establish the centre line of the embrasure, and stretch a cord on this line from the middle of the embrasure to the rear. This is the _directrix_ of the platform. Lay the two outside sleepers parallel to this _directrix_, their outside edges being fifty-four inches distant from it. The four other sleepers are laid parallel to these, the edge of each fifteen and a half inches from the edge of the next. The upper surface of the front ends of these sleepers to be fifty inches on a vertical line below the sole of the embrasure. [Sidenote: 120]]