Pagina-afbeeldingen
PDF
ePub

steady and genial beam, for the purpose which is here stated, and which I believe to be the true one.

VI. Nor is the last the only instance that entomology affords, in which our discoveries, or rather our projects, turn out to be imitations of nature. Some years ago, a plan was suggested, of producing propulsion by re-action in this way: By the force of a steam-engine, a stream of water was to be shot out of the stern of a boat; the impulse of which stream upon the water in the river, was to push the boat itself forward; it is, in truth, the principle by which sky-rockets ascend in the air. Of the use or practicability of the plan, I am not speaking ; nor is it my concern to praise its ingenuity : but it is certainly a contrivance. Now, if naturalists are to be believed, it is exactly the device which nature has made use of, for the motion of some species of aquatic insects. The larva of the dragon-fly, according to Adams, swims by ejecting water from its tail; is driven forward by the re-action of water in the pool upon the current issuing in a direction backward from its body.

VII. Again: Europe has lately been surprised by the elevation of bodies in the air by means of a balloon. The discovery consisted in finding out a mam nageable substance, which was, bulk for bulk, lighter than air: and the application of the discovery was, to make a body composed of this substance bear up along with its own weight, some heavier body which was attached to it. This expedient, so new to us, proves to be no other than what the Author of nature has employed in the gossamer spider. We frequently see this spider's thread floating in the air, and extended from hedge to hedge, across a road or brook of four or five yards width. The animal which forms the thread, has no wings wherewith to fly from one extremity to the

other of this line; nor muscles to enable it to spring or dart to so great a distance; yet its Creator hath laid for it a path in the atmosphere; and after this manner. Though the animal itself be heavier than air, the thread which it spins from its bowels is specifically lighter. This is its balloon. The spider, left to itself, would drop to the ground; but being tied to its thread, both are supported. We have here a very peculiar provi. sion: and to a contemplative eye it is a gratifying spectacle, to see this insect wafted on her thread, sustained by a levity not her own, and traversing regions, which, if we examined only the body of the animal, might seem to have been forbidden to its nature.

I must now crave the reader's permission to introduce into this place, for want of a better, an observation or two upon the tribe of animals, whether belonging to land or water, which are covered by shells.

I. The shells of snails are a wonderful, a mechanical, and, if one might so speak concerning the works of nature, an original contrivance. Other animals have their proper retreats, their hybernacula also, or winter. quarters, but the snail carries these about with him. He travels with his tent; and this tent, though, as was necessary, both light and thin, is completely impervious either to moisture or air. The young snail comes out of its egg with the shell upon its back; and the gradual enlargement which the shell receives, is derived from the slime excreted by the animal's skin. Now the aptness of this excretion to the purpose, its property of hardening into a shell, and the action, whatever it be, of the animal, whereby it avails itself of its gift, and of the constitution of its glands (to say nothing of

the work being commenced before the animal is born), are things which can, with no probability, be referred to any other cause than to express design ; and that not on the part of the animal alone, in which design, though it might build the house, could not have supplied the material. The will of the animal could not determine the quality of the excretion. Add to which, that the shell of the snail, with its pillar and convolution, is a very artificial fabric; whilst a snail, as it should seem, is the most numb and unprovided of all artificers. In the midst of variety, there is likewise a regularity, which could hardly be expected. In the same species of snail, the number of turns is usually, if not always, the same. The sealing up of the mouth of the shell by the snail, is also well calculated for its warmth and security ; but the cerate is not of the same substance with the shell.

II. Much of what has been observed of snails, belongs to shell-fish, and their shells, particularly to those of the univalve kind; with the addition of two remarks: one of which is upon the great strength and hardness of most of these shells. I do not know whether, the weight being given, art can produce so strong a case as are some of these shells. Which defensive strength suits well with the life of an animal, that has often to sustain the dangers of a stormy element, and a rocky bottom, as well as the attacks of voracious fish. The other remark is, upon the property, in the animal excretion, not only of congealing, but of congealing, or, as a builder would call it, setting, in water, and into a cretaceous substance, firm and hard. This property is much more extraordinary, and, chymically speaking, more specific, than that of hardening in the air; which may be reckoned a kind of exsiccation, like the drying of clay into bricks.

III. In the bivalve order of shell-fish, cockles, mus. cles, oysters, &c. what contrivance can be so simple or so clear, as the insertion, at the back, of a tough tendinous substance, that becomes at once the ligament which binds the two shells together, and the hinge upon which they open and shut?

IV. The shell of a lobster's tail, in its articulations and overlappings, represents the jointed part of a coat of mail ; or rather, which I believe to be the truth, a coat of mail is an imitation of a lobster's shell. The same end is to be answered by both; the same propera ties, therefore, are required in both, namely, hardness and flexibility, a covering which may guard the part without obstructing its motion. For this double pure pose, the art of man, expressly exercised upon the subject, has not been able to devise any thing better than what nature presents to his observation.

Is not this therefore mechanism, which the mechanic, having a similar purpose in view, adopts ? Is the structure of a coat of mail to be referred to art? Is the same structure of the lobster, conducing to the same use, to be referred to any thing less than art?

Some, who may acknowledge the imitation, and assent to the inference which we draw from it, in the instance before us, may be disposed, possibly, to ask, why such imitations are not more frequent than they are, if it be true, as we allege, that the same principle of intelligence, design, and mechanical contrivance, was exerted in the formation of natural bodies, as we employ in the making of the various instruments by which our purposes are served ? The answers to this question are, first, that it seldom happens, that precisely the same purpose, and no other, is pursued in any work which we compare, of nature and of art ; secondly, that it still more seldom happens, that we can

arm

imitate nature, if we would. Our materials and our workmanship are equally deficient. Springs and wires, and cork and leather, produce a poor substitute for an or a hand.

In the example which we have selected, I mean a lobster's shell compared with a coat of mail, these difficulties stand less in the way, than in almost

any

other that can be assigned: and the conse. quence is, as we have seen, that art gladly borrows from nature her contrivance, and imitates it closely.

But to return to insects. I think it is in this class of animals above all others, especially when we take in the multitude of species which the microscope discovers, that we are struck with what Cicero has called " the insatiable variety of nature." There are said to be six thousand species of flies ; seven hundred and sixty butterflies; each different from all the rest. (St. Pierre.) The same writer tells us, from his own observation, that thirty-seven species of winged insects, with distinctions well expressed, visited a single strawberryplant in the course of three weeks*. Ray observed, within the

compass

of a mile or two of his own house, two hundred kinds of butterflies, nocturnal and diurnal. He likewise asserts, but, I think, without any grounds of exact computation, that the number of species of insects, reckoning all sorts of them, may not be short of ten thousandt. And in this vast variety of animal forms (for the observation is not confined to insects, though more applicable perhaps to them than to any other class), we are sometimes led to take notice of the different methods, or rather of the studiously diversified

[merged small][merged small][ocr errors]
« VorigeDoorgaan »