fall at the word to swing, each oarsman having a relief under cover near him ready to seize the oar in case of any casualty. While the balks are being lashed a minimum number of anchor-boats on the outer side are held ready, with good crews, with anchors from say two not adjacent boats, and are kept head outward on the gentlest strain of their cables. At the word to move, the strain of the oars should be strong on the chord of the are of movement, as the carelessness which permits these boats to come athwart this line very greatly obstructs and delays the swinging of the bridge. In the rapid passage of the moving end of a long bridge, it is best that the outer or farther anchor-boats should be simply towed alongside the end boat of the raft.
While this work is being executed, a special squad can prepare the hither abutment, and, if no opposition is expected, another such squad can cross with two or three pontoons to complete the opposite or farther abutment.
And as soon as the squads on the raft shall have taken their position, and the officers are all in the boats, if opposition is expected, the oarsmen, at the word, should drop and ply their oars together, at the wheeling flank strongly, near the middle gently, and at the pivot very slightly; in these last cases a constant watch must be kept by the officers and men, not to advance their portions too much. With care at these parts the bridge may be carried round and kept very nearly straight, and of course with the least strain or injury to it, though I was surprised to find no damage of consequence resulted from a cramping of the pivot end of the bridge by which it was curved into about a quarter circle of a radius of not more than 150 to 200 feet. To avoid this the pivot end should always move on a small circle, well clear of the abutment.
As the bridge nears its proper position, the up-stream anchors direct from the pontoons of the bridge should be thrown, first from near the pivot end, to aid in judging of the position, for which range poles on the proper line or distance above the intended position of the bridge should be placed upon the shore. And as the bridge comes between the abutments, previously placed, the connection for vehicles is made at once, while the anchor boats with the down-stream or steadying anchors move off to drop them in position. Or if opposition is expected or is offered, the farther abutment of course not being placed, the bridge is held by its upper anchors as a raft, until the storming column of those concealed in the boats, and as many others as shall be required from our shore, shall have passed over it.
I have the pleasure of inclosing you, for the further explanation of the method of laying these bridges, some photographic views taken during the progress of construction. *
Numbers 1. shows the pontoons ready with the material, and the boat squads ready for the construction (at foot of East Fifteenth street).
Numbers 2. shows the progress of construction of the raft after four to five minutes' labor.
Numbers 3 shows the progress of the bridge raft after six to seven minutes' labor.
Numbers 4 shows the bridge completed, with the bridge squads formed ready to march off. Parts of a trestle and canvas pontoon bridge across a cove along the shore are in view here.