Читать книгу Nature's Teachings - John George Wood - Страница 6

The Boat-hook and its varied Uses.—The Earth-worm and the Serpula.—Microscopic Boat-hooks.—The Life-belt.—Life-boats and their Structure.—Uses of Cork.—Wine Corks made serviceable.—The Life-collar.—Portuguese Man-of-war.—Captain Boyton’s Life-dress.—The Life-raft.—Victualling a Yacht and Boat.—The Janthina and its Air-vessels.—Cask-pontoon—Pottery-raft and its Uses.

AS all rowing men know, an indispensable appliance to the boat is the Boat-hook, which can be used either as a pole, wherewith to push the boat along, or as a grapnel, by which it can be drawn towards the shore or a ship. As the latter portion has been discussed at the close of the preceding chapter, we may proceed to the former.

Every one knows how a boat may be propelled by a pole pressed against the bank or the bottom of the water, and that there are certain boats, called punts, which are propelled in no other way.

Now, the punt-poles and boat-hooks, of which some examples are given in the accompanying illustration, have long been anticipated in Nature, there being many creatures which have no other mode of progression; such, for example, as the common Earth-worm, which pushes itself along by certain bristles which project from the rings of which the body is composed, and which have the power of extension and contraction to a wonderful extent. As, however, I shall advert to these in another part of the work, I will content myself at present with a single example, namely, the beautiful marine worm known as the Serpula.

This worm lives in a shelly tube, which is lined with a delicate membrane, up and down which it passes with ease, ascending slowly, but generally descending with such wonderful rapidity that the eye cannot follow its movements. The latter movement will be explained in a subsequent part of the book, and we will at present only treat of the former.

If the creature be removed from the tube, and carefully examined, a number of projections will be seen, in each of which is a perforation. If the animal be pressed, a slight glass-like bristle passes through the perforation, and can easily be removed. If properly treated, and placed under a high power of the microscope, the tiny bristle resolves itself into the remarkable object which is shown on the left hand of the illustration.

It consists of a number of spear-like rods, each having a straight shaft, and a curved and pointed tip, deeply barbed on the inner portion of the curve. These curious bundles of spicules can be protruded or retracted at pleasure, and, as they are all directed backwards, it is evident that when they are pushed against the sides of the tube, either the points or the barbs must catch against the membrane which lines the tube, and so propel the animal upwards. When it wishes to descend, it uses another set of implements, and withdraws the first within their sheaths.

This is exactly analogous to the mode of progression employed by punters, who, after they have placed the pole against the bed of the stream, and run along the punt so as to push it as fast as possible, immediately withdraw the pole, and take it to the head of the punt, ready for another push. This, as the reader will see, is exactly the plan pursued by the Serpula in lengthening itself when it wishes to advance, and so to press its spicules against the sides of its tube, and in shortening itself and withdrawing the spicules ready for another push.

Another needful accessory of vessels now comes before us, namely, the capability of forming rafts or life-belts, which will float under any circumstances. Here, again, every human invention of which I know has been anticipated by Nature. Take, for example, the familiar instance of the cork life-belt and the cork edgings of the life-boat. Both are constructed on the same principle, i.e. the maintenance of cells which are filled by air instead of water, and are impervious to the latter.

The material most used for this purpose is cork, and life-belts constructed of it have long been in well-deserved use, the cork-bark having the property of holding much air and excluding water. Many of our life-boats are furnished with a broad and thick streak of cork, so that even if the boat be filled with water and upset, she will right herself and swim. I regret to say that many of the so-called “life-belts” which are offered for sale ought rather to be called “death-belts,” they having been found to be filled with hay and straw, with only a few shavings of cork just under the covering of the belt.

Indeed, so buoyant is this substance that a very efficient belt can be made by stringing together three or four rows of ordinary wine corks, and tying them round the neck like a collar. Under these circumstances it is simply impossible to sink, and though any one may collapse from exhaustion, drowning is almost out of the question. The now well-known cork mattress, which is used in many ships, is another example of the same principle.

Lately there has been invented a “life-collar,” which possesses similar advantages, but occupies less space when not wanted. It is nothing more than a tube of caoutchouc, which can be inflated at pleasure, and tied round the neck. The ordinary life-belt goes round the waist, and needs much more material without obtaining a better result, which is simply the keeping of the mouth and nostrils out of the water.

Perhaps the most buoyant of living beings is the Portuguese Man-of-war (Physalis pelagicus), which floats on the surface of the ocean like a bubble. It can at pleasure distend itself with air and float, or discharge the air and sink.

Now, there is a very remarkable swimming dress, which, though not entirely invented, was at least perfected by Captain Boyton, and which, as it enabled the wearer to cross from France to England under rather unfavourable circumstances, is clearly a most valuable invention.

Whether the inventor knew it or not I cannot say, but the Boyton life-dress is simply a modification of the Physalis, being capable of dilatation with air at will.

So much for the individual life-belt, and we will now pass to those which are intended to sustain more than one individual. It has almost invariably been found that when a ship has been wrecked on a rock, or stove in by the sea, that, although there may be plenty of boats, there is great difficulty in getting them into the water rightly.

Now, if parts of the ship itself could be made of materials which could not be sunk except by enormous pressure, and which might be released by a touch if the vessel were sinking, it is evident that many lives would be saved which have now been lost.

And if such movable parts of the vessel were supplied with water and provisions in air-tight cases, there is no doubt that the number of “missing” ships would be very greatly diminished. I remember an instance where a yacht was “hung up” on a mud-bank, whence there was no escape, for twenty-four hours, and there was one sandwich on board to be divided among the owner, two men, and a boy. Of course the boy had the sandwich, and the men sustained themselves as well as they could with tea, of which there was, fortunately, a canister on board. As it was, they were some thirty-six hours without food.

After such an experience the owner had special lockers made in the yacht and her boat, containing biscuit, potted meats, water, wine, spirits, tobacco, tea, an “etna” for heating the water, and matches. Of course these were on a smaller scale in the boat; but several thick rugs were also stowed away, in case of being separated from the yacht at night. It so happened that they were never needed; but the sense of security which they imparted was worth ten times the expense and trouble, which included a careful inspection of all the stores before each voyage.

In Nature there is just such a raft as is needed, capable of carrying a heavy freight, and which cannot be upset. And it is rather remarkable that it has been unconsciously imitated in various parts of the world.

This is the singular apparatus attached to the Violet Snail (Janthina communis), which is common enough in the Atlantic, and derives its name of Violet-shell from its beautiful colour. The chief interest, however, centres in the apparatus which is popularly called the “raft,” and which sustains the shell and eggs. It is made of a great number of air-vessels, affixed closely to each other, and by the curious property of bearing its cargo slung beneath it instead of being laid upon it.

Beneath the raft are the eggs, or rather, the capsules which contain the eggs, and at one end is the beautiful violet shell itself. The floating power of the raft is really astonishing, and even in severe tempests, when it is broken away from the animal, the raft continues to float on the surface of the waves, bearing its cargo with it.

On the opposite side of the illustration are two examples of rafts constructed so exactly on the same principle as that of the Violet Snail, that they both might have been borrowed from it.

The upper is the kind of raft which has often been constructed by sailors when trying to escape from a sinking ship, or by soldiers when wishing to convey troops across a river, and having no regular “pontoons” at hand. It is made simply by lashing a number of empty casks to a flooring of beams and planks.

The amount of weight which such a structure will support is really astonishing, as long as the casks remain whole, and to upset it is almost impossible. Even cannon can be taken across wide expanses of water in perfect safety, and there is hardly anything more awkward of conveyance than a cannon, with its own enormous and concentrated weight, and all the needful paraphernalia of limber, ammunition (which may not be wetted, and of immense weight), horses, and men.

Yet even this heterogeneous mass of living and lifeless weight can be carried on the cask-raft, which is an exact imitation of the living raft of the Violet Snail.

Beneath the cask-pontoon is to be seen a sketch of a very curious vessel which is in use on the Nile, and I rather think on the Ganges also, though I am not quite sure. It is formed in the following manner:—

In both countries there are whole families who from generation to generation have lived in little villages up the river, and gained their living by making pottery, mostly of a simple though artistic form, the vessel having a rather long and slender neck, and a more or less globular body.

When a man has made a sufficient number of these vessels, he lashes them together with their mouths uppermost, and then fixes upon them a simple platform of reeds. The papyrus was once largely used for this purpose, but it seems to be gradually abandoned.

He thus forms a pontoon exactly similar in principle with the cask-pontoon which has just been described. Then, taking his place on his buoyant raft, he floats down the river until he comes to some populous town, takes his raft to pieces, sells the pots and reeds, and makes his way home again by land.