Nature's Teachings. John George Wood
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Название: Nature's Teachings
Автор: John George Wood
Издательство: Public Domain
Жанр: Природа и животные
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I can only now give a short description of the woodcut which illustrates these points.
On the right hand Art is shown by the screw-blades of the modern steamer. In the middle is the ordinary mode of sculling a boat by an oar in the stern, and below it is the rudder, which, like the sculling oar, may be used either for propulsion or direction.
On the left hand we have three examples of the same mechanical powers as shown in Nature. The uppermost figure represents a fish as in the act of swimming, the dotted lines showing the movement of its tail, and the principle of the wedge. In the middle is an otter, just preparing to enter the water, and below is a seal, both of them showing the identity of mechanism between themselves and the art of man. I need not say that the mechanism of art is only a feeble copy of that of nature, but nothing more could be expected.
While we are on this subject I may as well mention two more applications of the screw principle. The first is the windmill, the sails of which are constructed on exactly the same principle as the blades of the nautical screw. Only, as they are pressed by the wind, and the mill cannot move, they are forced to revolve by the pressure of the wind, just as the screw of a steamer revolves when the vessel is being towed, and the screw left at liberty.
Moreover, just as the modern screws have only two blades, so, many modern windmills have only two sails, the expense and friction being lessened, and the power not injured.
Again: some years ago there was a very fashionable toy called the aërial top. It was practically nothing but a windmill in miniature, rapidly turned by a string, after the manner of a humming-top. The edges of the sails being turned downwards, the instrument naturally screwed itself into the air to a height equivalent to the velocity of the motion.
A similar idea has been mooted with regard to the guidance of balloons, or even to aërial voyaging without the assistance of gas, but at present the weight of the needful machinery has proved to be in excess of the required lifting power.
In fine, the application of the inclined plane, wedge, or screw as a motive power, is so wide a subject that I must, with much reluctance, close it with these few and obvious examples.
It is worth while, by the way, to remark how curiously similar are such parallels. I have already mentioned the very evident resemblance between the water-boatman, the water-beetles, and the human rower, the body of the insect being shaped very much like the form of the modern boat. I must now draw the attention of the reader to the similitude between the very primitive boat known by the name of Coracle, and the common Whirlwig-beetle (Gyrinus natator), which may be found in nearly every puddle. The shape of the insect is almost identical with that of the boat, and the paddle of the coracle is an almost exact imitation of the swimming legs of the whirlwig. And, as if to make the resemblance closer, many coraclers, instead of using a single paddle with two broad ends, employ two short paddles, shaped very much like battledores.
CHAPTER III.
SUBSIDIARY APPLIANCES.—Part I
General Sketch of the Subject.—The Mast of Wood and Iron.—Analogy between the Iron Mast and the Porcupine Quill.—The Iron Yard and its Shape prefigured by the same Quill.—Beams of the Steam-engine.—Principle of the Hollow Tube in place of the Solid Bar.—Quills and Bones of Birds.—Wheat Straws and Bamboos.—Structure of the Boat.—The Coracle, the Esquimaux Boat, and the Bark Canoe.—Framework of the Ship and Skeleton of the Fish.—Compartments of Iron Ship and Skull of Elephant.—The Rush, the Cane, and the Sugar-cane.—“Stellate” Tissue and its Varieties.
HAVING now treated of the raft, the boat, the ship, and their various modes of propulsion and guidance, we come to the subsidiary appliances to navigation, if they may be so called in lack of a better name.
First in importance is necessarily the mast; and the yards, which support the sails, are naturally the next in order. Then there come the various improvements in the building of vessels; namely, the substitution of planks fastened on a skeleton of beams for a mere hollowed log, and the subsequent invention of iron vessels with their numerous compartments, giving enormous strength and size, with very great comparative lightness.
Then we come to the various developments of the ropes or cables, by which a vessel is kept in its place when within reach of ground, whether on shore or at the water-bed. Next come the different forms of anchors which fasten a vessel to the bed of the ocean, of grapnels by which she can be made fast to the shore, or of “drags,” which at a pinch can perform either office, and can besides be utilised in searching for and hauling up objects that are lying at the bottom of the sea.
Next we come to the boat-hook, which is so useful either as a temporary anchor, or as a pole by which a boat can be propelled by pushing it against the shore or the bed of the water; and then to the “punt-pole,” which is only used for the latter purpose.
Lastly, we come to the life-belt and life-raft, which are now occupying, and rightly, so much of the public attention. These subjects will be treated in their order in the present chapter, and I hope to be able to show the reader that in all these points nature has anticipated art.
I presume that most, if not all, of my readers are aware of the rapidly extending use of iron in ship-building, not only in the standing rigging, but in the material of the vessel. First there came iron “knees,” i.e. the angular pieces of wood which strengthen the junctions of the timbers. Formerly these were made of oak-branches, and, as it was not easy to find a bough which was naturally bent at such an angle as was required for a “knee,” such branches were exceedingly valuable. Iron, however, was then employed, and with the best results. It was lighter than the wooden knee, was stronger, could be bent at any angle, and took up much less space.
By degrees iron was used more and more, until vessels were wholly made of that material. Then the masts, and even the yards, were made of iron, and, strange as it may appear, were found to be lighter as well as stronger than those made of wood. Of course, the masts and yards were hollow, and it was found by the engineers that in order to combine lightness with great strength, the best plan was to run longitudinal ridges along the inside of the tube.
A section of one of these masts is given at Fig. B, and taken from the drawings of one of our largest engineering firms. The reader will see that the mast is composed of rather slight material, and that it is strengthened by four deep though thin ribs, which run throughout its length.
When I first saw this mast I was at once struck with the remarkable resemblance between it and the quill of the Porcupine. These quills, as all anglers know, are very light, and of extraordinary strength when compared with their weight. Indeed, they are so light that they are invaluable as penholders to those who are obliged to make much use of their pen. I have used nothing else for a very long time, and the drawing of the Porcupine quill which is here given at Fig. A was made from a small piece cut from the top of the penholder which I have used for some fifteen years, and with which all my largest and most important works were written, including the large “Natural History,” “Homes without Hands,” “Man and Beast,” &c., &c. A portion of the same quill is also shown of its real size.
If the reader will cut a Porcupine quill at right angles, make a thin section of it, and place it under the microscope, or even under an ordinary pocket lens, he will see that the exterior is composed of a very thin layer of horny matter, and the interior filled with a vast number of tiny cells, which are formed much on the same plan as the pith of elder and other plants. The analogies of the pith will be treated in another page.