EXPEDIENTS FOR BOAT BRIDGES.
Anchors may be extemporised from forked branches of trees—the harder and heavier the better. These should have stones or iron lashed to them, in order to give weight. Several forks should be left on the main stem, and pointed to insure their holding. If charred in the fire, so much the better, as their durability and strength are much increased by the process. If there is but one fork, care must be taken so to balance the anchor with the stone below and the cable above, or a stock lashed across, that this fork or arm shall be sure to take the ground. The bridge may be also shored against the stream by branches, with their forks taking the beams, while their lower ends, weighted by stones, rest against the bed of the river. Stones are of no use as anchors, as they lose so much of their specific gravity when immersed; but if a heavy stone can be dropped beyond a cleft in the rock, as in our sketch, it will hold well.
If no anchors or substitutes can be had, the cables may be made fast to a stout tree as far up the stream as possible; and being brought in upon the inner bow of each boat, she will take the stream upon that side and be forced outward. The rudder, if she has one, will assist in this, but it is not material, as she can be kept at the proper angle by making the foremost beam a little longer than the after one.
If the bridge is constructed so low down the river as to be within the ebb and flow of the tide, anchors are indispensable, and each boat must be moored head and stern, as shown in one of the examples in our illustration; or, if there be but one cable to hold her against the ebb, shores may be set so as to counteract the influence of the flood, unless a great rise and fall, or violent rush at the turn of the tide, should render it unsafe to use them. If boats cannot be had, two or three large casks, placed end to end and firmly lashed to poles laid parallel to their length, may be used at each junction of the beams; or if a number of small ones can be obtained, they may be collected within a triangular frame of poles; but in any case each float must be sufficiently buoyant to keep the bridge at least 3ft. clear of the water, if there is any current; if there is none, the platform may even touch the water, and be partially sustained by it. In our sketch we have omitted all but a small portion of the planking, in order to show more clearly the manner of connecting the framework.
BAMBOO CARRYING FRAME AND PARBUCKLING LOG.
Carrying, rolling, and parbuckling heavy spars.
In some parts of India and China very heavy weights are carried by an ingenious framework of bamboo. A stout pole is crossed at its ends by two lighter ones, and each of these again by two others, each of which is again crossed by smaller ones 2in. or 3in. in diameter and 6ft. or 8ft. long; the sixteen ends of these are raised on the shoulders of as many men; the weight is slung to the centre of the larger beam, and borne with ease and comfort on the elastic frame. In our illustration (p. 352), two gangs of coolies are represented carrying a tree, but more could be employed if requisite. For rolling, the tree should be cleared of projecting stumps as much as possible; long skids should be placed under it, and if the ends from which the tree is to be rolled can be elevated by wedges or otherwise, so as to make an inclined plane for it to roll down so much the better; at all events, get the thick end under the tree and let the thin end be in the direction that you wish to roll it. Parbuckling is effected by making fast the end of a line to a stump or other holdfast in the required direction, then bringing the end of the line under the log, and taking one or more clear turns, bringing the end back over it and hauling on. A few hands judiciously using handspikes or levers will greatly assist this operation.
Ladders.