CHAPTER III.
THE WINDOW.—GIRDERS, TIES, AND BUTTRESSES.—THE TUNNEL.—THE SUSPENSION-BRIDGE
The Window, and its Modifications according to Climate.—Bars and Tracery.—The Wheel-window and the Caddis.—Curious Structure of the Caddis-tube.—Object of its Window.—The Girder as applied to Architecture.—The Radius and Ulna.—The Tie as applied to Architecture, and its Value.—Combination of the Tie and Girder.—Structure of the Crystal Palace.—Leaf of the Victoria Regia.—A Gardener turned Architect.—The Buttress in Art and Nature.—The Tunnel used as a Passage of Communication.—Natural Tunnel of the Ship-worm.—The Thames Tunnel.—The Piddock, or Pholas.—The Driver-ant.—The Suspension-bridge.—The Palm-wine Maker and his Bridge.—Suspension-bridges of Borneo and South America.—The Creepers and the Monkey Tribes.—The Spider and Little Ermine Caterpillar.
The Window
HAVING traced, though but superficially, the chief parts of a building, such as the walls, the door which is opened through the walls, and the roof which shelters them, we naturally come to the Windows by which light is admitted to them, and enemies excluded.
There are, perhaps, few points in Architecture in which such changes have been made as in the Window, which, instead of being a difficulty in the way of the architect, is now valued as a means of increasing the beauty of the building. Taking for example even such advanced specimens of Architecture as those furnished by Egypt, Greece, and Rome, we find that the Window is either absent altogether, its place being supplied by a hole in the roof, or that, when it is present, it was made quite subordinate to the pillars and similar ornaments of the building.
This fact is, perhaps, greatly owing to the influence of climate. In the parts of the world which have been mentioned in connection with this subject, light and heat appear to be rather enemies than friends, and the object of the architect was to enable the inhabitants of his houses to avoid rather than to welcome both. Consequently, the Windows were comparatively insignificant. They were not needed for the purposes of light or air, those being generally furnished by the aperture in the roof, and consequently were kept out of sight as much as possible.
But when architects had to build for a sterner, a colder, and a darker clime, where the sun never assumed that almost devouring heat and light which in hot countries drive the inhabitants to invent endless devices for obtaining coolness and shade, a different style of Architecture sprang up. In this the Window became nearly the most prominent part of the building: the elements were excluded by glass instead of stone, and the principal modifications of light were obtained by staining the glass in various rich colours. Perhaps the Window has attained its culminating point in the Crystal Palace, which is all window except its foundations.
Partly in order to enable the glass to be inserted, and partly to increase the beauty of the building, and to avoid the mean appearance of Windows filled in with plain iron bars crossing each other at right angles, the interior of the Windows was adorned with stone “tracery,” varying much according to the epoch of the building.
One of the most beautiful forms of the Window is that which is called the Wheel. The window itself is circular, and the tracery is disposed so as to bear an exact resemblance to an ornamental wheel, the lines of the tracery running from the circumference to the centre, just like the spokes of a wheel. One of these Wheel-windows is shown on the right hand of the illustration.
On the other side is an object, which at a hasty glance might be taken for another Window of the same character. It is, however, the work of an insect, and not of man, and is magnified in order to show its structure better.
Any of my readers who may happen to be entomologists or anglers, or both, are familiar with the Caddis-worm of our fresh waters. Most of us know that the Caddis is the grub or larva of the Stone-fly (Phryganea), an insect haunting the waterside, and so moth-like in its general aspect that many persons think that it is really a brown moth. The changes or metamorphoses of these insects are well worthy of notice.
In one respect the Caddis resembles the larva of the Wax-moth, mentioned on page 151, inasmuch as it has a soft, defenceless body, while the first three segments are comparatively hard. Like the Wax-moth also, the Caddis lives in a tube constructed by itself. Instead, however, of having a long and fixed tube, up and down which it can pass at pleasure, the Caddis makes a tube only a little longer than its body, and light enough to be carried about, just as the hermit-crab carries its supplementary shell. There are many species of Caddis-fly.
The Caddis inhabits fresh waters, and cares nothing whether they be ponds or running streams. In order to defend its white, plump, and helpless body from the fishes and other enemies, it constructs a tube around its body, strengthening it by a wonderful variety of material according to the locality.
Mostly the tubes are covered with little pieces of stick or grass, or leaves, while some species use nothing but sand-grains, constructing with them a tube very much resembling in shape an elephant’s tusk, and reminding the conchologist of the dentalium shell. But they seem to use almost anything that comes to hand. Taking only examples found by myself in a single pond, these cases are formed of sand, stones, sticks, grass-stems, leaves, shells of small water-snails, mostly the flat planorbis, the opercula of the water-snail, empty mussel-shells, a chrysalis of some moth which had evidently been blown into the water from an overhanging tree, and acorn-cups. The larva, however, does not seem to be able to fasten together any objects with smooth surfaces, and though it has been known, when in captivity, to make its cases out of gold-dust or broken glass, it could not use either material when in the form of beads.
When it is full-fed, and about to enter the pupal state, it proceeds to prepare its habitation. As a larva, when it desired to feed, it protruded its head and the front of its body from the mouth of the tube, and then crawled about in search of nourishment, dragging the tube with it, and holding it firmly by means of the claspers with which the end of the body is furnished. But when it becomes a pupa it is no longer able to defend itself, and is instinctively compelled to secure its safety in some peculiar manner.
It cannot fasten up the entrance entirely, because it would not be able to breathe unless water could pass over its body. Accordingly, it constructs a grated window precisely like those of the old castles, so that water can pass freely, while no enemy can gain admittance. Unlike, however, the grated windows of the castle, which had no pretence to beauty, the Caddis always constructs its barriers in some definite pattern. Each species appears to have its own peculiar pattern, but all agree in making their window, if we may so call it, exactly like a wheel-window before the glass is inserted.
When the pupa is about to make its final change into the perfect form, it cuts away the tracery with a pair of sharp jaws, with which it is furnished for this sole purpose, emerges from the water, throws off the pupa-skin, and issues forth as a Stone-fly.
Girders, Ties, and Buttresses
Next in order come the means by which walls are supported internally by Girders and Ties, and externally by Buttresses.
Of late years the Girder, in its many varieties, has come into general use, especially in the construction of railway bridges and similar edifices.
On the right of the accompanying illustration is shown the Girder in its simplest form. The figure was taken from a Girder which is used in supporting the walls of a large building in Bermondsey. Sometimes a transverse stay connects the centres of the two curved beams; but it is seldom needed.
The reader will see that if the interval between the curved beams were to be filled up, we should obtain a form very like that of the engine beam described in page 25; while, if we could imagine two such girders intersecting each other at right angles throughout their length, a section of the two would exactly resemble the section of the engine beam as given in the uppermost figure in page 25.
In the human body there are four admirable examples of the natural Girder, namely, in the bones of the arms and legs.
On the left hand of the illustration are shown the two bones of the fore-arm, technically named the “radius” and “ulna.” It will be seen that these bones are arranged on the principle of the girder. In men who are especially powerful of grasp, it has been noticed that the curve of the radius and ulna has been exceptionally bold, while we have it developed to the greatest extent in the fore-arm of the Gorilla, an animal whose arms are simply gigantic.
The two bones of the legs, from the knee to the ankle, are arranged in a similar manner, and are called the “tibia” and “fibula.” The last named signifies a brooch, and is given to the bone because it is very slender, nearly straight, and when in its place bears no small resemblance to the pin of the fibula, or ancient Roman brooch.
Nature, however, has exceeded Art in her girder. Those of man’s manufacture can only exert their strength in one direction, and would be of little use if force were to be applied to them in any other direction. Those of the human body, however, have the capability of partial revolution on each other at their points of junction, thus enabling the Girder to apportion its strength according to the direction of the resistance which it has to overcome.
We now come to the Ties, i.e. those internal beams, whether of metal, wood, stone, or brick, which prevent walls from falling outwards. There is no danger of the walls falling inward, but there is very great danger of their falling outward, especially when the weight or “thrust” of the roof tends to force them apart.
In some buildings, such as an old country church which I attended for many years, the architect had openly acknowledged the tendency of the walls to fall outward, and had counteracted it by a series of great beams extending completely across the nave and aisle. As he had not even troubled himself to hide their office, so he did not trouble himself to conceal the fact that they were tree-trunks, but left them roughly squared with the axe, lest, if he had squared them throughout their length, he should have diminished their strength.
The effect of the partially squared beam is, of course, far more picturesque than that of a completely squared one. The architect, however, need not have been so careful about strength, for if the beams had been only half their diameter they would have been just as effective. The strain on them is by pulling, and not by pushing. Now, as any one can see by trying the experiment with a splinter of wood—say a lucifer-match—an enormous power is required to break it by tearing the ends asunder, while it can be easily broken by pushing them towards each other.
But for this power of resistance, we should never have had our Crystal Palace. That apparently intricate, but really simple (and the more beautiful for its simplicity), intersection of beams and lines diminishing in the distance to the thickness of spiders’ webs, is nothing more than a combination of the Girder and Tie, the two together combining lightness and strength in a marvellous manner.
The story of the Crystal Palace is now so well known that it need not be repeated in detail. A vast building was required for the Exhibition of 1851, and not an architect was able to supply a plan which did not exhibit some defect which would make the building almost useless.
Suddenly a Mr. Paxton, who was a gardener, and not an architect, produced (on a sheet of blotting-paper) a rough plan of a building on a totally new principle, and not only fulfilling all the requisite conditions, but being capable of extension in any direction and to any amount. There have been very few bolder conceptions than that of making iron and glass take the place of brick, stone, and timber, and the result fully justified the expectations even of the inventor.
How a gardener suddenly developed into an architect remains to be seen; and, indeed, in this case the architecture was the result of the gardening, or rather, of practical botany applied to art. Some years before the invention of the Crystal Palace, that magnificent plant, the Victoria Regia, had been introduced into England. Its enormous leaves, with their wonderful power of flotation, caused a great stir at the time, and some of my readers may remember a sketch which was engraved in the Illustrated London News, and which represented a little girl standing on one of these leaves as it floated on the water.
Mr. Paxton saw how this power was obtained, and the result was that he copied in iron the lines of the vegetable cellular structure which gave such strength to the Victoria Regia leaf, and became more eminent as an architect than he had been as a gardener. The capabilities of the Crystal Palace had lain latent for centuries, but the generalising eye of genius was needed to detect it. A thousand men might have seen the Victoria Regia leaf, and not thought very much of it; but the right man came at the right time, the most wonderful building in the world sprang up like the creation of a fairy dream, and the obscure gardener became Sir Joseph Paxton.
I have no doubt that thousands of similar revelations are at present hidden in Nature, awaiting the eye of their revealer.
Now we come to the principle of the Buttress, i.e. giving support to the exterior, instead of the interior, and strengthening the walls by pushing them together, instead of pulling them together.
Putting aside the “flying” buttress, which is simply one buttress mounted on another to support the clerestory walls, the structure of the ordinary buttress is simple enough.
The most primitive form of the buttress is often found in country farms, where the farmer sees the walls of his barns and outhouses leaning suspiciously on one side, and, instead of going to the root of things, props them up by a stout pole or beam.
This, however, can be nothing but a temporary arrangement, especially as beams have a tendency to rot, and their ends to sink into the earth by the gradual pressure of the wall. The genuine buttress was therefore evolved, the basal part being very thick and heavy, and the upper part comparatively thin and slight. Simple as a buttress looks, much skill is needed in making it, and if it be not rightly built, it does infinitely more harm than good.
A case in point occurs within a short distance of my house. The walls of an ancient edifice having shown symptoms of yielding, and some ominous cracks made their appearance, a couple of very sturdy buttresses had been erected, in order to stop further damage. Unfortunately, the builder was ignorant of the principles of architecture, and though he made the buttresses very strong and massive, he omitted to make a solid foundation on which their bases should rest. Consequently he only hung the buttresses, so to speak, on the wall, and helped to tear it asunder by the additional weight.
Nature, as well as Art, supplies her buttresses. In our own country we find the natural buttress more or less developed in our trees, as it is wanted.
Take, for example, any plantation, and examine the trees. It will be found that those in the centre, which are sheltered on all sides from the force of the wind, shoot up straight towards the light, have comparatively slight and slender stems, and occasionally display such energy in forcing themselves upwards, that when two branches find that there is not room for both, they form a sort of alliance, fuse themselves together, and force their united way towards the sky.
Take, however, the trees in the outside rows of the plantation, and see how they throw out their straight roots and branches towards the outside, and how, on the inside, their trunks are as smooth and their roots as little visible as those of the trees that grow in the centre of the plantation.
Almost any tree will develop itself in this fashion, showing that instinct can rule the vegetable as well as the animal world.
There is, however, a South American tree which far surpasses any of our trees in its power of throwing out spurs or buttresses, principally, I presume, because it may have to endure the fiercest storms from any quarter and at any time. So bold are these projections that several men would be hidden if standing between two of them, and so numerous are they that if a section of the tree were taken at the base of the ground, it would resemble a conventional star or asterisk, *, rather than an ordinary tree-trunk, O.
The scientific name of this curious tree is Aspidomorpha excelsum.
The natural buttresses are so thin and so wide that they look like large planks set on end, with one edge against the tree. Indeed, they are used as planks, nothing more being required than to cut them from the tree.
This is very easy, as, while the wood is green, it is so soft that a blow from a “machete,” or native cutlass, is sufficient to separate it. With the same instrument the native makes these flat planks into paddles for his canoe, the soft wood yielding readily even to the imperfect edge of the rude tool. When the wood dries, it becomes very hard, light, and singularly elastic, all these properties qualifying it for its object. I have several of these paddles in my collection. They are much prized by the natives, and are always stained in various patterns with red and black dyes.
In consequence of the use which is made of this tree, it goes by the popular name of “paddle-wood.”
The Tunnel used as a Passage
As to this division of the subject, I have not been quite sure where it should be placed, but think the present position a tolerably appropriate one.
We have already, in the igloo of the Esquimaux and the winter dwelling of the seal, found examples of the Tunnel when used as an appendage to the houses and a means of security. We now come to the Tunnel as affording the means of locomotion.
Take, for example, our own railway system. Had it not been for the power of tunnelling, the railway would have lost nearly its whole value, for it would have been restricted to local districts, and could not have penetrated, as it now does, to all parts of the country, without reference to hill, dale, or level ground. Our present system of engineering has wonderfully developed the capability of tunnelling. In former times it was thought a most wonderful feat to drive a tunnel under the Thames, while in these days the tunnel through Mont Cenis has been completed, and we are hoping to make a submarine tunnel from England to France.
In Nature we can find many examples of Tunnels used for similar purposes. The silken tunnel of the Wax-moth larva has already been mentioned, and we now come to Tunnels where earth in some form, and not silk, is the material of which they are constructed.
The lowermost figure on the left-hand side of the illustration represents that well-known and most destructive burrower, the Ship-worm (Teredo), which, by the way, in spite of its popular name, is not a worm, but a mollusc. This creature has a peculiar interest for engineering, inasmuch as its mode of working gave Brunel the first idea of subaquatic tunnelling in loose, sandy soil, just as the Victoria Regia leaf gave to Paxton the idea which afterwards developed into the Crystal Palace.
The plan adopted by the Ship-worm is at the same time simple and effective. It feeds upon wood, and gradually eats its way through almost any timber that may be submerged. It does not, however, merely bore its way through the timber, but lines its burrow with a coating of hard, shelly material. Taking this hint, Brunel proceeded in the same fashion to drive his tunnel through the very ungrateful soils which form the bed of the Thames.
He built a “shield,” as he called it, of iron, exactly fitting the tunnel, and divided into a number of compartments, each of which could be pushed forwards independently of the others. In each compartment was a single workman, and, as he excavated the earth in front of him, he pushed forward his portion of the shield, while the interior was cased with brickwork, just as a Teredo tunnel is cased with shell.
Above the Teredo is represented another marine tunnel-maker, as it appears in its burrow.
This is the mollusc popularly known as the Piddock, and scientifically as Pholas dactylus. It may be found abundantly in all our chalk cliffs, boring its tunnels deeply into the stone, and aiding the sea in its slow, but never-ending task of breaking down the cliffs on one side, while it gradually rears them up on another. As the material into which the Piddock burrows is so hard, there is no need for lining the tunnel, as is done by the Teredo. In this point, too, our engineers follow its example. When their tunnels pass through comparatively soft ground, they line it with masonry, proportioning the thickness of the lining to the looseness of the soil. But, when they come to solid rock, they are content with its strength, and do not trouble themselves about the lining.
The mode of action adopted by the Pholas has long been a disputed point, and even now appears to be not quite settled. I think, however, that William Robertson has proved by his experiments that the shell and the siphon are both brought into requisition. The shell perpetually rotates in one direction, and then back again, just like the action of a bradawl, and, by the file-like projections on its surface, rasps away the chalk, converting it into a fine powder. This powder, being of course mixed with water, passes into the interior of the animal, and is ejected through the siphon.
There are many species of Pholas which burrow into various substances, even in floating cakes of wax and resin. The same species, too, will burrow into different substances, and it is worthy of notice that those specimens which burrow into soft ground attain a much larger size, and their shells are in better preservation, than those which force their way through hard rock.
The uppermost figure represents a very remarkable tunnel, having the peculiarity of being built instead of sunk. It is the work of an African Ant belonging to the genus Anomma, and popularly known as the Driver-ant, because it drives away every living creature which comes across its course of march.
There are many Ants which seem to rejoice in the full blaze of the tropical sun, running about with ease on rocks which would scorch and raise blisters on the hand if laid on it, and finding no difficulty in obtaining the moisture needful for the mud walls of their habitations. But the Driver-ants cannot endure the sun, and, unless compelled by necessity, will not march except at night, or at all events during cloudy days. Should, however, they be absolutely forced to march in the sunshine, they construct as they go on a slight gallery, which looks very much like the lining of a tunnel stripped of the surrounding earth. If their path should lead them to thick herbage, sticks, &c., which form a protection from the sun, the Driver-ants do not trouble themselves to make a tunnel, but take advantage of the shade, and only resume the tunnel when they reach the open ground.
Sometimes, when they are on a marauding expedition, they construct a tunnel in a very curious manner, their own bodies supplying the materials. The reader must know that there are several classes of these insects, varying in size from that of a huge earwig to that of the little red ant of our gardens. The largest class seem to care little about the sunshine, the protection being mostly needed by the workers. The following is Dr. Savage’s account of their proceedings:—
“In cloudy days, when on their predatory excursions, or migrating, an arch for the protection of the workers is constructed of the bodies of their largest class. Their widely extended jaws, long, slender limbs, and projecting antennæ, intertwining, form a sort of network that seems to answer well their object.”
“Whenever an alarm is given, the arch is instantly broken, and the Ants, joining others of the same class on the outside of the line, who seem to be acting as commanders, guides, and scouts, run about in a furious manner in pursuit of the enemy. If the alarm should prove to be without foundation, the victory won, or danger passed, the arch is quickly renewed, and the main column marches forward as before, in all the order of an intellectual military discipline.”
How they should be able to direct their course, and to chase an enemy, is not easy to understand; for, as far as is known, they are absolutely blind, not even an indication of an eye being seen.
The Suspension-bridge
The mention of these Ants brings us to another point in architecture. We have already seen that they can not only build arched tunnels, but also can form their own bodies into arches, and we shall presently see how they can form themselves into Suspension-bridges. We will, however, first take the Suspension-bridge, and its vegetable origin, before passing to the animal.
I have little if any doubt that the modern Suspension-bridge, with all its complicated mathematical proportions, was originally suggested by the creepers of tropical climates. There are few points in a tropical forest, no matter in what part of the world, more striking than the wonderful development of the creeping plants. The trees are very much like those of our own forests, and are in no way remarkable, but the creeping plants form the chief feature of the woods.
They extend themselves to unknown lengths, crawling up to the very summit of a lofty tree, hanging down to the very ground, if not caught by a midway branch, running along the earth, making their way up another tree, and so on ad infinitum. They interlace with each other, forming almost impenetrable thickets, as has already been mentioned while treating of Nets, and there is scarcely a tree that is not connected with its neighbour by means of these wonderful creeping plants.
Of course the monkey tribes make great use of them in passing from one tree to another, thus being able to avoid the ground, which is never to a monkey’s liking. Man, therefore, copies the example of the monkey, and makes use, either of the creepers themselves, or of ropes stretched from tree to tree in imitation of them.
In some parts of the world, where palm wine, or “toddy,” is manufactured, the native has recourse to an ingenious device which saves a vast amount of exertion. As the calabash which receives the juice of the palm-tree is always fixed at a considerable height, and as each tree only yields a limited supply, the toddy-maker would be obliged to ascend and descend a great number of trees before he could collect his supply of palm-juice.
In order to save himself trouble, he has the ingenuity to connect the trees with each other by two ropes, the one about six feet above the other. He then has only to ascend once, and descend once, for he ascends one tree, and by means of the ropes passes from tree to tree without needing to descend.
The mode of traversing these ropes is simple enough, the lower rope serving as a bridge, along which the man walks, and the upper rope being held by the hands. Those who see these palm-wine makers for the first time are always greatly struck. At some little distance the ropes are quite invisible, and the man appears to be walking through the air without any support whatever.
In Borneo the Rattan is continually put in requisition as a bridge. It runs to almost any length, a hundred feet more or less being of little consequence; it is lithe and pliant, and so strong that it can hardly be broken. The “canes” formerly so much in vogue among schoolmasters, and now so generally repudiated, are all cut from the Rattan. Chiefly by means of this natural rope, the Dyak of Borneo flings his rude suspension-bridges across chasms or rivers, and really displays a wonderful amount of ingenuity in doing so.
The one fault of these bridges is their tendency to decay, or perhaps to be eaten by the multitudinous wood-eating insects which swarm in that country. However, the materials cost nothing at all, and time scarcely more, so that when a bridge breaks down, any man can fit up another at the expense of a few hours’ work. As, moreover, the Dyaks have a curious way of building their houses on one side of a ravine, they find that a bridge of this kind saves them the trouble of descending and ascending the ravine whenever they wish to visit their house.
In many parts of America the Suspension-bridge is almost a necessity. The country is broken up by vast clefts, technically called “cañons.” These cañons are ravines in the rocky ground, with sides almost perpendicular. For the greater part of the year they are dry, but sometimes, and without the least warning, they become the beds of roaring torrents, rising to some thirty or forty feet in height, and carrying away everything before them.
Over these ravines are thrown suspension-bridges made almost entirely of creepers, and loosely floored with rough planks. Although they are very strong, they appear to be very fragile, and even under the tread of a human being swing and sway about in a manner that always shakes the nerves of one who is unaccustomed to them. Yet, even the mules of the country can cross them, the animals picking their way with the wonderful sure-footedness of their kind, and not in the least affected by the swaying of the bridge.
Passing from the vegetable to the animal world, we revert to the Driver-ants, which have already been mentioned. It has been seen that their soldier-ants can, with their own bodies, form a tunnel, under the shade of which the workers can pass, and we have now to see how they can, with the same materials, form a suspension-bridge.