By Successive Pontons

—The location of the bridge having been selected, the ponton-wagons are brought as near the river-bank as practicable, with the rear of the carriage toward the stream. The pontons are unlashed and slid from the wagon-bed into the water; cables are attached to the anchors; one of the former is coiled in the bow of each ponton with its anchor on the top, the flukes projecting over the gunwale. Those pontons which cast up-stream anchors are moored above the approach to the bridge, and the others below. A trench about 1 foot in width and depth is excavated to receive the abutment sill; this should be laid horizontally, and exactly perpendicular to the axis of the bridge; it is secured by four pickets, two driven in front and two in rear, about 8 inches from each end. A ponton is brought up opposite to the abutment, and close to the shore. The ponton is then pushed off and adjusted in its place by means of shore-lines, which are made fast to mooring-posts. As soon as the first set of balks is laid, a che is placed on edge in the trench above mentioned, and in contact with the ends of the balks. Its upper edge should be 1 1 ⁄ 2 inches above the balks. Earth is rammed behind it, crowding it firmly against the balks. The che is then laid on. The ponton which has cast the first up-stream anchor, having dropped down to the head of the bridge, is entered by the pontoniers. Five balks are then brought up and delivered to the lashers in the second ponton, which is pushed off; the shore ends of the balks are delivered to the lashers in the first ponton, who place them on the down-stream side, and in contact with those of the first set, their cleats against the outside of the interior gunwale. They lash the balks firmly together and to the lashing-hooks at both gunwales, and then step into the third ponton. When a bay is covered with che , the side-rails are laid. They are placed directly over the outside balks, to which they are lashed at three points,—at the middle and immediately over the axis of each ponton, at which point the two side-rails and balks of two bays lap and are all lashed together. In constructing a ponton-bridge there are two points that require particular attention: the anchorage, and the lashing; the men who are intrusted with their execution should be selected from the most intelligent and experienced pontoniers in the command.