Nature's Teachings: Human Invention Anticipated by Nature

by J. G. Wood

Then, there is the foot of the duck, goose, swan, and various other aquatic birds, in which the foot presents a broad blade as it strikes against the water, and a narrow edge as it recovers from the stroke. Some years ago, a steam yacht was built and propelled by feet made on the model of those of the swan. She was a very pretty vessel, but art could not equal nature, and at present the swan-foot propeller, however perfect in theory, has not succeeded in action. Perhaps, if some nautical engineer were to take it in hand, he would procure the desired result.

Almost exactly similar is the mode of propulsion employed by the lobster, the prawns and shrimps, their tails expanding widely into a fan-like shape as they strike against the water, and then collapsing when the stroke is withdrawn, so as to allow them to pass through the water with the least possible resistance.

The same principle is to be seen in the lively little Acaleph, for which there is unfortunately no popular name, and which we must therefore call by its scientific title of Cydippe, or Beroë, these names being almost indifferently used. When full grown, it is about as large as an acorn, and very much of the same shape. It is as transparent as if made of glass, and, when in the water, is only visible to practised eyes.

En passant, I may remark that the familiar term of “water,” when applied to diamonds, is owing to their appearance when placed in distilled water. Those which can be at once seen are called stones of the second water. Those which cannot be seen, because their refractive powers are equal to those of the water, are called “diamonds of the first water,” and are very much more valuable than the others.

As the Cydippe is, in fact, little more than sea-water, entangled in the slightest imaginable and most transparent tissue of animal fibre, it is evident that the water and the Cydippe must be of almost equal refracting power, and that therefore the acaleph must be as invisible as diamonds of the “first water.” Indeed, I have often had specimens in a glass jar which were absolutely invisible to persons to whom I wished to show them.

But an experienced eye detects the creature at once. Along its body, at equal distances, are eight narrow bands, over which the colours of the rainbow are, though very faint, perpetually rippling. This appearance is caused by the machinery which impels the body, and which seems never to cease. Each of these bands is composed of a vast number of tiny flaps, which move up and down in regular succession, so as to cause the light to play on their surfaces. And, as they move as if set on hinges, they of course offer no resistance to the water after their stroke is made.

Now let us compare these works of nature with those of art. We have already seen the parallels of the oar, and we now come to those of the paddle-wheel. When paddle-steamers were first invented, the blades were fixed and projected from the wheel, as if they had been continuations of its spokes. It was found, however, that a great waste of power, together with much inconvenience, was caused by this arrangement. Not only was a considerable weight of water raised by each blade after it passed the middle of its stroke, but the steam power was given nearly as much to lifting and shaking the vessel as to propulsion.

A new kind of paddle-wheel was then invented, in which the blades were ingeniously jointed to the wheel, so that they presented their flat surfaces to the water while propelling, and their edges when the stroke was over. This, which is known by the name of the “Self-feathering Paddle-wheel,” was thought to be a very clever invention, and so it was; but not even the inventors were likely to have known that if they had only looked into the book of Nature, they might have found plenty of self-feathering paddle-wheels, beside the few which my limited space enables me to give.

If the reader will look at the illustration, he will see that on one side is represented the self-feathering paddle-wheel of Art, with its ingenious arrangement of rods and hinges. On the other side there comes, first, the common Prawn, shown with its tail expanded in the middle of its stroke.