It often happens that on their march they come to water, and, as they always advance with total disregard of difficulties, they must needs invent some very ingenious way of overcoming the difficulty. One of them climbs a branch which overhangs the water, clasps the undermost twig very tightly, and allows itself to hang from it. Another at once follows, and suspends itself from its comrade in like manner, the powerful and sicklelike jaws doing their duty as well as the legs. A chain of Ants is thus speedily formed. When the lowermost Ant touches the water, it merely spreads all its legs, and awaits the development of events. Another runs over it, holds to the first Ant by its hind-legs, and stands in the water, spreading its limbs as much as possible over the surface. Ant after Ant descends, until quite a long chain of the insects is formed, and is swept downwards with the stream. By slow degrees the chain is lengthened, until the Ants at its head are able to seize the bank on-the opposite side of the water. When they have succeeded in doing so, the bridge is complete, and over that living bridge will pour a whole army of Driver-ants.
Even in those cases where this mode of travelling would be too perilous on account of the rapid torrent, the Ants contrive to suspend themselves in long strings until they effect a communication with the trees of the opposite bank.
It is, perhaps, needless to give more than a passing reference to the Suspension-bridges made by Spiders, by means of which they can traverse considerable distances. The similar bridge of the Little Ermine Caterpillar has already been mentioned, when treating of the subject of Double Walls.
CHAPTER IV.
LIGHTHOUSES.—THE DOVETAIL.—THE DAM.—SUBTERRANEAN DWELLINGS.—THE PYRAMID.—MORTAR, PAINT, AND VARNISH
The Eddystone Lighthouse: its Position, and the Difficulties of building it.—Destruction of successive Lighthouses.—Smeaton’s Idea of Form borrowed from the Tree-trunk.—Mode of building.—Rooting it into the Rock.—Principle of the Dovetail.—Bones of the Human Skull, and their Articulation.—The Dam, and its Uses to Man.—The Lock and the Water-mill.—Dam of the Beaver: its Objects and Mode of Construction.—Popular Errors with regard to the Dam.—Subterranean Dwellings.—The Indian Palace, and its Use in Summer.—Subterranean Dwellings in Kamschatka, and their Use in Winter.—The Wood or Horse Ant, and its double Dwelling.—The upper and lower Nests used according to the Amount of Warmth required.—Section of the Nest, and a Glimpse into its Interior.—The Pyramid.—Derivation of its Name.—Natural Objects from which the Form was derived.—Subaquatic Mortar or Cement, and its Use to Man.—Subaquatic Cement used by the Caddis, the Stickleback, the Terebella, the Sabella, the Serpula, and others.—Paint and Varnish, and their Utility to Man.—Propolis as used by the Hive Bee, and the Source whence it is obtained.
WE now come to some points in Architecture which cannot well be grouped together, and must therefore be treated as Miscellanea.
Our first example is one which was avowedly based upon an imitation of Nature, namely, the celebrated Eddystone Lighthouse, and we shall see that in two points—first its form, and next the mode in which the stones were fixed together—Nature had been closely followed by the architect.
Unlike ordinary lighthouses, this edifice had to be constructed so as to endure the full force of waves as well as wind. A few miles from the southern coasts of Devon and Cornwall there is a rock which in former times greatly endangered the ships which passed along the Channel. Several attempts were made to build a lighthouse on this dangerous spot. Winstanley’s lighthouse, which was finished in 1700, was wholly swept away three years later, together with the architect himself, and some workmen who were engaged in repairs. So terrific is the force of the elements on this spot, that the lighthouse was entirely destroyed, and the only vestiges of it that were ever discovered were some iron bars and a piece of chain.
Another lighthouse was built a few years afterwards, but was burned down, it being of wood instead of stone. At last the work was put into the hands of Smeaton, who saw that he must build on a totally new plan. He took for his model the trunk of a tree, and determined to build his lighthouse of the same form as the tree-trunk, and to fasten it into the rock just as a tree is fastened by its roots. Accordingly, he struck out a new principle in the construction of such edifices, and his model has been followed ever since. The reader will see, by a glance at the illustration, how close is the resemblance in external form. I may mention that the tree in question was sketched from one in a paddock opposite my house.
Having settled the form of the lighthouse, and made it like a tree-trunk, the next business was to fix it firmly in the rock, and, in fact, to give it roots of stone. For this purpose, he made the base of the edifice as wide as the rock would allow, so as to correspond with the wide base of a tree-trunk, and traced a circle of about ninety feet in circumference. Instead, however, of merely laying the stones as is usually done, or even letting them into holes cut in the rock, he hit upon a singularly ingenious device, whereby the building was practically a single stone.
Instead of cutting the stones square or oblong, as is usually done, he had them made so as to “dovetail” into each other, much after the fashion of a child’s puzzle toy, or the junctions at the edge of a box. Thus, each stone fitted into those around it, while the lowest tier was dovetailed in similar fashion into the rock.
The stone employed was that which is called Moorstone, a very hard variety of granite. Each course of stones was carefully fitted together on shore, and their accuracy tested, and they were then taken to the Eddystone rock, and fixed in their places. Beside using these precautions, Smeaton fixed the stones in their place with the strongest cement, and furthermore fastened the stones together and united the several courses by strong oak treenails and iron clamps. As none of the stones weighed less than a ton, and some of them were double that weight, the strength of such an edifice may be imagined.
The accompanying illustration shows the arrangement of these dovetailed stones in one of the courses. It will be seen that the central stone must be laid first, and then the others arranged round it. The whole edifice is rather more than eighty-five feet in height, so that the elements have every chance of demolishing it, as they did that of Winstanley. More than a hundred years have now passed since it was built, and, although the fury of the tempest has been such that the waves have washed completely over its summit, it stands as firmly as it did when it was finished in 1760.
Whether the original inventor of the “dovetail” took his idea from Nature I cannot say, but he certainly might have done so. On the left of the illustration is part of a human skull.
The skull is not, as many persons seem to think, made of a single bone, but it is composed of many bones, united by “sutures,” which are, in fact, natural dovetails. Although in early life these sutures are comparatively loose, they hold the various parts together so firmly, that if the head be violently struck, the bones may break, but the sutures do not give way.
Perhaps some of my readers may ask how it is possible to take a skull to pieces without cutting it or fracturing the sutures. It is done in a way equally simple and ingenious. The skull is filled through the opening with dried peas, and then sunk under water. The peas expand with the moisture, and, as they exert an equable force in all directions, they slowly and quietly pull the sutures asunder, without injuring the bones.
The Dam
In many human operations, where a certain depth of water is required in a running stream, the reasoning powers of man have enabled him to attain his object by building a dam, or obstacle across the stream, which forces the water to rise to its level before it can find a passage. Such, for example, are the Locks which render rivers navigable, and allow even the heavily laden barges to traverse miles of water which would otherwise have been closed to them.
Those mills, again, which are worked by water need that a sufficient amount of water should be ready in order that it may by its weight force the wheel round. Such a Dam is shown on the right hand of the illustration, the height to which it raises the water being shown by the level of the stream below the Dam, and that of the water as it tumbles over in a miniature cascade.
Putting aside the natural dams made by accumulations of the various debris that are washed down by a swollen stream, and which sometimes raise the water to a very great height, we have an example of a natural dam in the curious structure made by the Beaver, for the same purpose as that of the lock in the mill-stream, namely, to insure a depth of water sufficient for the needs of the beings that make them.
Every one has heard of the Beaver’s dam, but there is so much misconception on the subject, that a few words will not be out of place.
Ingenious as is the animal in the construction of its dam, it is not nearly so accomplished an architect as was once supposed. We were told in the earlier books of Natural History that the Beaver felled trees, cut off their branches into convenient lengths, and sharpened one end, like an ordinary stake. Then they were said to drive the sharp end of the stakes into the bed of the river, to set them side by side, to interweave smaller branches among them, and lastly, to fill up the interstices with mud, leaves, and similar materials. In fact, they were supposed to build a “wattle-and-daub” wall, like that which is in use at the present day in Southern Africa.
The Beaver does nothing of the kind. It needs a dam, and it makes one which is far stronger than the wattle-and-daub could be. It begins by felling a tree, and letting it lie across the stream, in some place where the banks are high and tolerably steep. A bend of the river is usually chosen for the new dam. Should not the tree be long enough for the Beaver’s purpose, two trees are felled, one on either side, so that their branches meet in the middle.
These branches, and not any supposed stakes, are really the upright supports of the dam. The trees being thus laid, the Beaver cuts down branches from four to six feet in length, and lays them horizontally among the boughs of the fallen trees. Having thus made the foundations, so to speak, of its dam, the Beaver then proceeds to fill in the spaces with roots, grass-tufts, leaves, mud, and, indeed, almost anything on which it can lay its paws.
After this, the Beaver has to take but little trouble, for the stream itself becomes a silent, slow, but constant labourer, lodging floating debris against the dam, and making a sloping bank which much adds to its strength. By degrees, seeds that lodge on the dam spring into life, and their roots act like chains, binding the materials more closely together. Willow twigs too, if they lodge on the dam and be left undisturbed, are sure to “strike,” as the gardeners say, and further to bind the structure together.
It is evident, from this short description, that the lower part of the dam is more solid than the upper. In fact, the floods are tolerably sure to wash away some eight or ten inches of the upper part every year, and the Beavers have to make it afresh. The height of these dams is not nearly so great as is generally supposed. Mr. Green, a practical trapper, states that the highest which he ever saw was only four feet six inches in height, and that the average is under three feet.
The house of the Beaver is made on the same principle as the dams. Every one knows that when sticks have been in the water for any length of time, they become saturated and sink. These sticks are chosen by the Beaver as the material for its house, and are laid horizontally in the water, the heaviest being reserved for the roof, so as to make it strong enough to ward off the attacks of predacious animals. As with the dam, mud, leaves, &c., are used to consolidate the edifice, but no mud can be seen from the outside, the animal always finishing off with a number of heavy logs laid on the roof.
Subterranean Dwellings
I do not intend in this place to take up the whole subject of Subterranean Dwellings, but only to point out cases where the use of the Subterranean Dwelling depends on the climate of the locality and the time of year, it being sometimes used and sometimes neglected, sometimes inhabited for the sake of warmth, and sometimes for that of coolness.
In various parts of India there are some most remarkable Subterranean Dwellings. They are more than mere dwellings, and are, in fact, magnificent palaces, sunk so deeply in the earth that very little more than their roofs appear aboveground. When, however, a visitor descends the stairs that lead to the interior of the palace, he finds it spacious, and with tiers of chambers one below the other, very much like the wasp-nest which has already been described. Nussur-ed-deen, the second King of Oude, had several of these palaces, but very seldom visited them, he having endeavoured to Europeanise himself as much as possible, and to cast off his native customs. He used occasionally to visit them, but it was only out of etiquette, and he never really lived in them.
However much he might have rejected the ancient customs, it is evident that in this case, at least, he was punishing himself in rejecting these summer dwellings, which are always cool, and where, if one set of apartments is too warm, nothing is easier than to descend to the next.
This dwelling is made for the sake of coolness in summer. Another subterranean dwelling is made for warmth in winter, the non-conducting properties of the earth being in both cases brought into play. This is the winter dwelling of the inhabitants of Kamschatka.
During the summer-time the Kamschatdales live in comparatively slight huts mounted on poles, and having the floor some ten feet from the ground.
During the winter, however, they live in habitations of a very different character.
In order to make these houses, they begin by digging a large hole in the ground, about nine or ten feet in depth. This they line with poles and sticks, making, in fact, a wall as of a house. A stout conical roof is then raised over the hole, and upon the roof earth is thickly strewn and beaten down, just as has been mentioned when treating of the ice-house. The only access to this strange house is by a circular aperture in the centre of the conical roof, serving at once the purpose of a door, a chimney, and a window. A notched pole answers as a ladder, a low wooden dais placed against the wall serves as a bed or a chair, for there is no other, and a few stones placed together act as a fireplace.
In looking at both these subterranean dwellings, I could not but be reminded of a very common insect which has a double dwelling, one moiety being aboveground, and the other moiety below it. This is the common Wood-ant (Formica rufa), whose large, leafy hills are so plentiful in some of our woods. On account of its size, this species is sometimes called the Horse-ant.
At first sight the nest looks something like a small haycock, made entirely of chopped grass. When examined more nearly, it will be found to consist mostly of grass-stems, little bits of stick, and leaves. Those of the fir are in great request, for when they are dry they are very light, and their form enables the Ant to interweave them with each other, so as to form the necessary tunnels and galleries which line the interior of the nest. The materials seem most unpromising, but they are used with wonderful skill, such as no human fingers could equal.
After a little while a number of entrances into the nest are visible. They are almost invariably sheltered by projecting leaves, which act as porches, so that when the nest is viewed from above, they are almost entirely hidden. Each of these openings runs into one of the main galleries of the nest, and from thence issues a perfect labyrinth of passages.
This, however, is only half the nest, for the galleries and tunnels extend far beneath the surface of the earth, and have sundry enlarged portions or chambers wherein the immature pupæ may lie during their period of helplessness.
Owing to the very loose structure of the upper nest, and the tendency of the earth to fall into the galleries of the lower nest, it is very difficult to obtain a trustworthy view of the interior. Perhaps I may here be allowed to extract a passage from my “Insects at Home,” the description of the nest and its interior having been written almost on the spot:—
“I have, however, succeeded in obtaining an excellent view into the interior of a Wood-ants’ nest, though it was but a short one. Accompanied by my friend Mr. H. J. B. Hancock,2 I was visiting some remarkably fine Wood-ants’ nests near Bagshot. We took with us a large piece of plate glass, placed it edgewise on the top of an Ant-hill, and, standing one at each side, cut the nest completely in two, leaving the glass almost wholly buried in it.
“After the expiration of a few weeks, during which time the ants could repair damages, we returned to the spot, and, with a spade, removed one side of the nest as far as the glass, which then served as a window through which we could look into the nest. It was really a wonderful sight.
“The Ant-hill was honeycombed into passages and cells, in all of which the inhabitants were hurriedly running about, being alarmed at the unwonted admission of light into their dwellings. In some of the chambers the pupæ were treasured, and these chambers were continually entered by Ants, which picked up the helpless pupæ, and carried them to other parts of the nest where the unwelcome light had not shown itself.
“Unfortunately this view lasted only a short time. Owing to the partial decomposition of the vegetable substances of which the Ants’ nest is made, the interior is always hot and always moist. Now, the day on which we visited the nest happened to be a cold one, and, in consequence, the moisture of the nest was rapidly condensed on the inner surface of the glass, and in a few minutes completely hid the nest from view, leaving me only time to make a rapid sketch. Unfortunately some one discovered the plate of glass and stole it.
“Next time that I examine a Wood-ants’ nest, I shall take care to insert the glass exactly east and west, and shall open its southern side towards noon on a hot sunshiny day, so that the rays of the sun may warm the glass and prevent evaporation.”
Many other creatures make subterranean dwellings, but the Wood-ant is remarkable for possessing a double dwelling, the two portions communicating with each other, and capable of being used according to the degree of heat required.
The Pyramid
We have already seen how the Eddystone lighthouse was the precursor of many similar buildings all, like their predecessor, having their form copied, with more or less strictness, from the outlines of a tree-stem.
Another form of building which was intended for endurance, and, indeed, is the most enduring of all shapes, is the Pyramid.
We are all familiar with the simple, yet grand outlines of the Pyramids of Egypt, whose vast antiquity takes us back to the times of Isaac and Joseph, and which seem capable of resisting the effects of Time, the universal destroyer, for thousands of years yet to come.
We may ask ourselves what was the natural object from which the Pyramid was copied. The name itself, which is formed from a Greek word signifying fire, shows that a flame was thought to have furnished the idea of this form of building. I cannot, however, but think that the flame had little, if anything, to do with it, and that the real model may be found in the hills which have been formed by Nature.
Examples of the Pyramids and the Hills are given in the accompanying illustration.
Subaquatic Mortar.—Paint and Varnish
Having now disposed of the chief points in Architecture, we take some of the subsidiary details.
Of late years, when the traffic between different continents has so largely extended itself, and when shipping has increased both in the numbers and dimensions of the vessels, it is absolutely necessary that we should have harbours and docks enlarged and multiplied sufficiently to meet the calls upon them.
Now, it is comparatively easy to construct a building on shore, for all the mortars and cements which are used for the purpose of fastening the stones together are applied when wet, and incorporate themselves with the stones as they dry. But to make a mortar which could be applied while the stones were under water, and would “set” while beneath the surface, was a task not easily to be overcome. Yet it has been done so effectively that at the present day we can build beneath the surface of the water as securely, though not as rapidly, as if the stones had been laid on dry ground.
Several such mortars are now known, and, as is so often the case with human inventions, have been anticipated in Nature.
We have already seen how the Caddis-worm of the fresh waters can cement together, while under water, the various materials of which its tubular house is formed. The different Sticklebacks perform similar feats, no matter whether they inhabit fresh or salt water.
All those who take an interest in the productions of the seashore will have noticed upon our coasts the flexible tube of the Terebella, with its curiously fringed ends. This tube, as any one may see at a glance, is composed of grains of sand and similar materials, fastened strongly together by a kind of cement exuded from the worm, and possessing the property of hardening under water. As on some of our coasts fragments of shell are used for the tube, the worm goes by the popular name of Shell-binder.
If one of these worms be taken out of its tube, placed in a vessel with sea-water and a quantity of sand, broken shells, and little pebbles, the mode of building will soon be seen. At the extremity of the head are a number of extremely mobile tentacles, and these are stretched about in all directions, seizing upon the particles of sand and shell, seeming to balance them as if to decide whether they are suitable for the tube, and then fixing them one by one with the cement which has already been mentioned.
Generally speaking, the Terebella works only in the evening, but, if it be hastily deprived of its tube, it cannot help itself, and is perforce obliged to work while it can. It is worthy of remark that the Terebella, although, as a rule, it lives in a tube all its life, is capable of swimming with the usual serpentine motion of marine worms, and, when taken out of its tube, rushes about violently, and soon exhausts itself by its efforts.
Along most of our rocky seashores may be seen vast quantities of a sort of hardened sand, penetrated with small tubes. On a closer examination this sand-mass is resolved into a congeries of tubes, matted and twisted together, and each being the habitation of a marine worm called the Sabella. This name is derived from a Latin word signifying sand, and is given to the worm in allusion to the material of which it makes its habitation.
Like the Terebella, the Sabella uses its tentacles for the purpose of building the tubes, which are much stiffer than those of the Terebella. They are strong enough, indeed, to give the feet a firm hold while traversing the rocks, and this, is a matter of no small moment when the tide is coming in, and the shore has to be regained without loss of time.
Then we have other marine worms, known as Triquetra and Serpula, which make tubes in a somewhat similar manner, but of very fine materials and very strong cement, so that the tube is nearly as hard as stone.
Space would fail me if I were to enumerate these creatures at greater length, but enough has been said to show that man’s invention of subaquatic cement has been anticipated in Nature by the inhabitants both of salt and fresh water.
We now come to the subject of Paint and Varnish. Putting aside their use as a means to increase the beauty of the object to which they are applied, we will view them in the light of preservatives, and acknowledge the truth of the old Dutch proverb, that “Paint costs nothing.” Certainly, when the wood to which it is applied is thoroughly dry from within, it not only costs nothing, but repays itself over and over again as a preservative of the wood, and a defence against moisture from without.
The instances in which Paint is applied to wood are too numerous to be mentioned. Perhaps some of my readers may remember the case of the naval captain who, on taking command of his ship, was supplied, according to custom, with exactly half the amount of paint required for her. The invariable etiquette had been that the captain supplied the remaining half at his own cost. But the officer in question was not at all disposed to be “put upon,” and was a thorn in the sides of the “Naval Lords.”
Finding, by actual measurement, that the paint supplied to him was only half the amount which was really needed for the ship, he sent his respectful compliments to the Admiralty, asking whether they wished the port or the starboard side of the ship to be painted, for that there was only enough paint for one half of the ship, and he awaited instructions as to which side of the vessel it was to be applied. He was impervious to “minutes,” “directions,” &c., and, as far as I remember, this very impracticable man got his way, and was supplied with the requisite amount of paint.
Long before man ever invented paint or varnish the Hive Bee had made use of it.
Every one who has kept bees knows how they always fasten the edge of the hive to the board, and stop up any crevices that may be left open. The material which they use for this purpose is not wax, but a substance called “propolis.” This term is composed of two Greek words, signifying a suburb, or the outskirts of a town, and is given to this stationary substance in consequence of the use which is made of it.
Not only do the bees use it for fastening the hives, but also for strengthening their combs. Wax is a very precious material, and the beautiful hexagonal structure of the bee-comb is intended for the purpose of combining the greatest amount of storing space with the least expenditure of material. The plates of wax of which the cells are composed are so thin that their edges would break down even under the feet of the bees as they passed over it, and accordingly the bees strengthen the edges of the cells with propolis, as any one may see by examining a piece of bee-comb. The propolis is of a darker colour than the wax, and has a peculiar varnish-like appearance.
The propolis, as distinguished from wax, is mentioned by Virgil in his Georgics:—
“Collectumque hæc ipsa ad munera gluten
Et visco et Phrygiæ servant pice lentius Idæ.”—Georg. iv. 40.
It is evident that the propolis cannot be obtained from the same source as the wax. The latter is secreted by the bees under little plates or flaps upon the abdomen, while the propolis is purely a vegetable exudation. It is obtained from many trees, the principal being the horse chestnut. All who have handled the buds of this tree are aware that they are covered with a viscous and very adhesive matter, which serves as a varnish or protection to the bud before the leaves are strong enough to break out. This is the material which the bees gather for their propolis, and at certain times of the year the chestnuts may be seen swarming with bees, all busily engaged in scraping off the varnish.