=Single Lock.=--This is suitable for spans not exceeding 30 feet, measured between the footing of the frames. The slope of the frames when in position must not exceed four on seven. 1st. Prepare footings 18 inches wider apart on one side than the other. They must be correctly squared or the frames will not lock. 2d. Measure the gap and lay out section of it on the ground with a line and pickets, allowing for camber. 3d. Lay out the standards in the section, and chalk-mark them at the proper positions for lashing ledgers and transoms. 4th. Lash the frames in position on either side of the gap; butts of standards towards the bank, ledger lashed on the top of standards, about two feet from the butts, but position varied according to nature of footings, transom lashed underneath. The splay of legs in a frame is not so great as in a two-legged trestle, one foot difference between transom and ledger generally sufficing; the transom of narrow frame 18 inches wider than the width of roadway in the clear between ribbands. Square the frames carefully before lashing the braces; see that the distance apart of the butts corresponds to the footings, broad frame to be 18 inches wider than the narrow. Drive pickets or large piece of timber (bollard) for guys and foot-ropes. 5th. Attach fore and back guys and foot-ropes to each frame, the latter fastened with a timber-hitch round the standards below the ledgers. 6th. Pass across the fore guys, passing those of the narrow frame between the horns of the broad frame. 7th. Launch and lock the frames. 8th. Send out temporarily two road-bearers and by their means and with the aid of two men working on the crutch of the bridge get the fork-transom in position. 9th. Send out remainder of road-bearers, resting the whole on the fork-transom. 10th. Place planks (chesses); rack down; put up hand-rail. ESTIMATE OF TIMBER. ------------+------+------+--------------+--------------------------- Kind of |No. of|Length|Diam. in Ins. | Purpose. Bridge. |Spars.|in Ft.| | | | +-------+------+ | | |At Tip.| Mean.| ------------+------+------+-------+------+--------------------------- Single-lock | 4 | 24 | 7 | |Standards. (30-ft. | 1 | 15 | | 10 |Fork-transoms. Span). | 2 | 15 | | 6 |Transoms. | 4 | 15 | |4 to 6|Ledgers and shore-transoms. | 4 | 20 | 3 | |Diagonal braces. | 10 | 20 | | 6 |Balks. | 4 | 20 | 3 | |Ribbands. ------------+------+------+-------+------+--------------------------- If the stores are at hand and ready for use, 1 non-commissioned officer and 16 men on each side should complete the bridge in a little more than an hour.