Chapter V (2)

Very neat and effective bridges may be made on the rafter principle, which our engraving at p. 303 will sufficiently illustrate. The roadway, either horizontal, as in Fig. 1, or with more or less rise in the centre, as in Fig. 3, being supported by the king-posts, a tolerably broad river may be spanned by a bridge supported on latticed-worked sides, like a number of XXXX's set up without intervening spaces; but this would require skilled workmanship and secure fastening. Arches of great strength may be made of thin planks laid one upon another; a dozen inch planks would thus give an arched beam 1ft. in thickness, and when properly clamped, or bound together, exceedingly strong. This beam may be easily lengthened, no joining or scarping of the individual planks is required, their ends may simply butt against each other; but care must be taken that no two joints come even nearly together, or much of the strength will be thrown away.

Many Chinese bridges are constructed with slabs of stone, set up much in the manner of those at Stonehenge. A number of bridges of this description, formed entirely of granite, are to be seen on the Cornish moors.

An Indian army was once sent to act against an enemy accustomed to a colder clime. A broad river checked the advance of the Indians, who had to remain day after day shivering from cold which their enemies bore with impunity; but their leader observed that ice was forming on the river, and, though the strong current kept the centre clear, he found a place some miles below the hostile camp where it had nearly united. By pushing forward poles and faggots into the water he made a nucleus on which fresh ice was formed, and before morning he had sufficiently bridged the river to allow of the passage of a few men who held their position till the rest could cross.

{Hints on fording rivers.}

In fording deep and rapid streams, the tendency of the body to float greatly diminishes the power to resist the force of the current. We have seen a short and compactly built man, struggling against this difficulty, when a couple of tall aborigines came to his assistance, and with mistaken zeal put their hands under his arms to hold him up, till he explained that he wanted them rather to press upon his shoulders and keep him down. A detachment of our troops found themselves before a ford where the stream was deep and strong, and while they hesitated, the tall guide picked up a heavy stone, placed it on his head, and walked safely through. It is to be remembered, however, that the ford which is safe for the first man is not always so for the last. An ancient general attempted the passage of a river, but the trampling of the men and horses loosened the sand, the stream swept it away, reinforcements were unable to come up, the advance was beaten, and in attempting to recross the river, numbers were drowned, owing to the increase in the depth of water.

In most countries native paths will lead to the practicable fords, and very frequently villages will be established near them, so that information and guides may generally be obtained. In the Cape colony, people who live near the drifts or fords of large rivers frequently keep spans or teams of powerful oxen for the sole purpose of drawing the waggons of travellers across, and these are generally led by some stout young fellow on a horse that is also well accustomed to the locality. It will often happen in the course of exploration that the traveller will have to find the shallow places for himself. Reefs, or edges of strata, running across the river are, of course, obvious enough, but to find moderate shallows in a river of more even depth is not quite so easy; the best way, therefore, is to follow the windings, bearing in mind generally it is better to seek up the river than down where fresh tributaries increase it. In all the hollows where the stream impinges strongly upon the banks they are generally very steep, with considerable depth of water, while the points will be found to slope downward with shoals extending from them, and there is generally an eddy or return current on the upper side; therefore, if a point can be found, with another somewhat below it on the other side, a ford may reasonably be looked for, especially if the width between the points seems greater than usual. A ford seldom leads straight across a river, and there is little use in looking for one in a hollow or under a steep bank.

{Abyssinian mule platforms.}

Mr. Percival, who has travelled much in Abyssinia, tells us that he used what he calls portable inclines to facilitate the passage of his long and heavily-laden mule trains over difficult places, especially such as the perpendicular edges of stratified rock 2ft. or 3ft. in thickness, which to laden mules would be as impassable as precipices of a thousand times the height. To obviate this difficulty, he employed one or more mules in carrying roughly-made platforms of stout poles about 10ft. long, with others lashed across them, ladder fashion, so as to present a surface of about 10ft. by 2ft. It would be the duty of the drivers of these mules to have, at least, one of them well to the front in anticipation of any difficulty; the platform would then be laid down, the train would walk over it and pass on, leaving it in the rear to be loaded up again and brought on, while one of the other platform mules would pass to the front in order to be ready for the next difficulty.

The length of these would depend on the height of ledge of rock to be mounted. Suppose the strata were 3ft. in thickness, then a platform of 4ft. 6in. would present a surface lying at an angle of 45°, while one of 7ft. 6in. would lie at 22°; this, for short distances, would not be at all a difficult incline either to descend or to climb, and platforms of 10ft. would give plenty of spare end to rest on the supporting edges, and would not be very inconvenient in carriage. Mr. Percival says he has made them of wattled or hurdle work from 12ft. or 15ft. up to 24ft. in length, and yet so light that one mule has carried two of them; and in following what are called the torrent roads, at the bottom of deep ravines, these would come into requisition at every few hundred yards.

It was in such ravines as these that most disastrous events were anticipated by travellers who knew the difficulties of the country, without being at the same time aware of the skill and resources of our military engineers.

In native warfare an army might be watched into a place from which escape is hopeless, and in the dry season the grass would be then fired at the entrance and the exit; or in the rains, some small river might be partially dammed up so as to accumulate a quantity of water, which being let loose at the proper moment by the dragging out of a pole that serves as a trigger to let go the rest of the impediments, would sweep down upon and overwhelm the helpless enemy.

{Natural bridges.}

Besides the modes of crossing rivers or ravines before described, there are various methods of passing over comparatively narrow impediments to the onward journey. A chance tree, storm felled across the stream or gully, not unfrequently affords the requisite footway without the expenditure of labour. There are, however, localities in which old hollow logs, cast in this manner across water, are to be looked on with some degree of suspicion, as the following incident of travel will serve to show: An old friend of ours chanced one day to arrive much fatigued at the brink of a tropical stream, which had one of these natural bridges thrown by some storm across it. Before passing over, he lit his fire, cooked his food, and indulged in a quiet smoke; happening to cast his eye along the fallen tree trunk, he perceived something of rather sinister appearance, in slow motion, on its surface. On looking more closely, he saw a huge python, half in and half out of a hole in the log, apparently enjoying the rays of the mid-day sun. The bark of the tree near to the bank, on which our friend was sitting, was worn quite smooth by the passage of numerous animals, and there is no doubt that this formidable toll collector had long enjoyed the monopoly of his tree bridge. Our friend selected another crossing place less carefully guarded. Small streams, or the narrow channels of swamps, may be easily and expeditiously crossed by the aid of the leaping pole. {Leaping poles.} Tall bamboos or tough, straight, well-grown poles are suitable for the purpose. In soft fen ground, it is a good plan to shoe the bottom of the pole with a piece of flat, strong wood, formed somewhat after the manner of a half ball, with a hole in the middle for the reception of the end of the pole. In exploring the cliffs at the edges of ravines, the metal seeker not unfrequently swings himself from ledge to ledge by the aid of a rope attached above, as shown in the accompanying engraving. The cliff climbers, who search for the eggs of sea-fowl, roam about at times in much the same manner. In descending from points of danger, where a leap for life affords the only hope of escape, advantage may be taken of the contrivance which was used by the rebels at Kotah, in India, during the mutiny. They, on being pushed hard by our troops, who had gained possession to the approaches to their fortified works within the town, bolted like rabbits in a warren, and made for an embrasure, or rather casemate, in one of the bastions of the outer wall; from this they thrust out a strong, but flexible bamboo pole, from the end of which a rope depended. The inner end of the bamboo was secured by heavy weights being placed on it. The fugitives worked their way out by clinging under the pole, until they in turn reached the rope at the end, when they slid down to the end, and then dropped off into the dry ditch. Judging from the immense height of the bastion, and the rocky nature of the ground, we should have had but faint hopes of escape with life; but there is little doubt that many who braved the peril of the fall escaped more or less injured. {Makeshift ladders.} We had no means at hand of measuring the bamboo, but should judge it roughly at 40ft. The illustration on p. 347 will serve to show the manner in which it was made use of. Not far from the bastion just referred to, we found a number of Indian scaling ladders. They were much in appearance like large bamboo hurdles. The canes composing them were bound at their intersections with strips of twisted cane. They were, for their size, remarkably light; and the nature of the material of which they were constructed, and the way in which they were put together, made them immensely strong. A number of men abreast might have ascended them easily. There are many forms of makeshift ladders, amongst which, perhaps, the following are the most noteworthy. The ordinary rope ladder is too well known to need more than a passing comment. The rope and batten ladder is perhaps not quite so well known, but is far more easy to mount and dismount; its form is shown at A in the accompanying illustration. Two strong chains, and a set of suitable sized bars, form a very useful kind of ladder, much in use among miners; its mode of arrangement is shown at B in the annexed illustration. In South America and some other countries, the notched log ladder is much used both in mining and surface operations. It is, as its name implies, a log notched deeply to receive the feet and hands of the climbers. Another form of log ladder is made by boring a row of auger holes at equal distances, say 2ft. apart, and then driving long stout treenails through them, so that each end of the treenail may project beyond the side of the log, for a hand and foot hold. Long forked branches may have their lateral shoots cut off at convenient distances apart, so as to form a footway of short prongs. A row of spikes or treenails may be driven into the side of a cliff, a wall, or the trunk of a tree to climb up by. The natives of many wild countries adopt this method, about which we shall have more to say when the subject of tree-climbing is under consideration.

{Landing derrick.}

In some parts of the world, the operation of landing from a boat, or embarking from the quays or jetties built out into the sea, is rendered both difficult and dangerous by the great range imparted to the boat by the roll of the swell, which in the Eastern seas is at times very great. In such situations, it is a good plan to have a stout post set in the masonry, or in a hole made in the rock, and to the top of this post a swivel crutch, which holds the trunnions of a long projecting arm, like that of an Egyptian well lever, to the small end of which a rope and cross-bar are securely fastened. To the short, heavy end, several more ropes are attached, by which when the person to be landed has either grasped the cross-bar, or seated himself on it, the contrivance is at once raised aloft, and turned steadily but rapidly inward, when by easing off, the man is allowed to drop easily to his feet on solid ground. There used to be such a contrivance as this at St. Helena, by the aid of which we have often landed. The illustration on p. 349 will serve to show how the apparatus is managed and constructed.

A barrel, stoutly lashed with rope, fitted with a seat, and cut away at the side, so as to admit of the traveller sitting in it, as in a chair, is used for ladies or invalids, who are slung in it at the end of the arm, and hauled in as above described.

{Bridges of boats.}

Sometimes it is necessary to construct bridges of boats; and these are often works of great magnitude, requiring a considerable amount of material, especially when an army with artillery and baggage waggons has to cross. Whether large or small, the method of proceeding must be nearly the same. First, a number of stout beams must be collected, sufficient to make a double line across the river, with their ends overlapping each other by more than the breadth of the boats that are to support them. The boats should be brought to the shore and moored a little above the site of the intended bridge. If anchors are procurable, they should be laid at regular intervals across the river; a buoy should be attached to the end of each cable, and a small line should lead from the farthest to each nearer one in succession, till they are all connected with the shore. A substantial frame of beams should be constructed at the edge of the bank, and a boat brought alongside it riding by the first cable, and secured by a temporary mooring to the shore. Two beams must be launched across her near the head and stern, and firmly lashed to the thwarts and stringers.

The boat must now be swung out to the full extent of the beams; the second cable must be laid hold of, and the first cast off and hauled to shore for the next boat, which is dropped down stream under the shore end of the beams, which are laid upon her gunwales and made fast there; while two others are pushed from the shore and fastened to her as the first pair were to the first boat. Intermediate beams, if requisite, can be laid, and planking lashed or pinned upon them so as to complete that part of the platform. Then other beams and planking, sufficient for a similar platform, should be brought on board, for the purpose of finishing the bridge when this pair of boats reaches the other shore. The outermost boat should now pick up the third cable, and pass the second to the inner one; while the first cable should be taken by a third boat, which will drop down between the others and the shore, to receive her portion of the platform; and so on in succession until the bridge, completed as it goes on, extends so nearly to the other shore that the loose material carried by the first pair of boats serves to complete the connection.

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.

{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.}

There are times when the principle of the common step-ladder might be advantageously remembered; and a traveller who expected to have much climbing might have one of those in which a groove is run in the inside of each standard, and the rungs, working on pivots, are shut up into it, the whole forming a light and compact pole, which a man might easily carry on his shoulder. It would, however, be cheaper and better to purchase this at home than to make it abroad. A rope and batten ladder is more easily made. The rope is doubled, an eye is turned in to the bight, holes are bored in the ends of the steps or rungs, the ends of the rope are passed through, and double knots turned on to keep each step in place. A light ladder, either of this kind or that previously described, with a coil of rope to fling over the lower branches, would enable a botanist or collector of birds or insects to climb many trees otherwise inaccessible.

{Fire-escapes.}

In case of fire in a town, if anything--say the end of a sofa or part of a bed frame--could be projected only 1ft. or 2ft. from a window, and weighted by a chest of drawers on its inner end, it would form what persons unskilled in climbing so much require--a clear point of departure; and the blankets, sheets, and coverlets torn into strips of not less than 4in. or 6in. wide, and twisted into a two-stranded rope, could be fastened to this and used--first, to lower the more helpless persons into the street, and, finally, for the active to glide down by. It would be too much to expect, as has been proposed, that every house should have a coil of rope, but it is well to remember that if there be only a ball of string it may serve to haul up stronger lines, brought by volunteers from without. If infants are to be lowered, it is better to put them in a bag than to tie a rope round their bodies; a couple of pillow cases would be strong enough, and there would be no fear of suffocation during the minute or two of their descent. A man may tie a child on his back or descend with it in his arms, but it is much safer to lower it separately. If flames are bursting from the windows beneath, perhaps the rope may be taken to the next lower story of the opposite house so as to avoid the danger of burning the rope or scorching those who descend. Of regular fire-escapes we need say nothing, as where they are provided competent persons, very frequently seamen, are appointed to work them; but it is well to bear in mind that, as the property of flame and heated air is to ascend, a man creeping close to the floor may often traverse in safety a chamber the upper part of which is impracticable. A towel or piece of sheeting dipped in water and tied round the mouth and nose will prevent heated smoke and particles of burning matter from entering the air passages, and thus enable a person to struggle for life in situations where suffocation would be inevitable without some such expedient for its preservation.