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The Relation of Animated Bodies to Inanimate Nature

We have already considered relation, and under different views; but it was the relation of parts to parts, of the parts of an animal to other parts of the same animal, or of another individual of the same species.

But the bodies of animals hold, in their constitution and properties, a close and important relation to natures altogether external to their own; to inanimate substances, and to the specific qualities of these; e. g. they hold a strict relation to the ELEMENTS by which they are surrounded

I. Can it be doubted, whether the wings of birds bear in relation to air, and the fins of fish to water? They are instruments of motion, severally suited to the properties of the medium in which the motion is to be performed: which properties are different. Was not this difference contemplated, when the instruments were differently constituted?

II. The structure of the animal ear depends for its use, not simply upon being surrounded by a fluid, but upon the specific nature of that fluid. Every fluid would not serve: its particles must repel one another, it must form an elastic medium: for it is by the successive pulses of such a medium, that the undulations excited by the surrounding body are carried to the organ; that a communication is formed between the object and the sense; which must be done before the internal machinery of the ear, subtile as it is, can act at all.

III. The organs of voice and respiration are, no less than the ear, indebted for the success of their operation to the peculiar qualities of the fluid in which the animal is immersed. They, therefore, as well as the ear are constituted upon the supposition of such a fluid, i.e. of a fluid with such particular properties, being always present. Change the properties of the fluid, and the organ cannot act; change the organ, and the properties of the fluid would be lost. The structure therefore, of our organs, and the properties of our atmosphere, are made for one another. Nor does it alter the relation, whether you allege the organ to be made for the element, (which seems the most natural way of considering it,) or the element as prepared for the organ.

IV. But there is another fluid with which we have to do; with properties of its own; with laws of acting, and of being acted upon, totally different from those of air and water: and that is light. To this new, this singular element; to qualities perfectly peculiar, perfectly distinct and remote from the qualities of any other substance with which we are acquainted, an organ is adapted, an instrument is correctly adjusted, not less peculiar amongst the parts of the body, not less singular in its form, and in the substance of which it is composed, not less remote from the materials, the model, and the analogy of any other part of the animal frame, than the element to which it relates is specific amidst the substances with which we converse. If this does not prove appropriation, I desire to know what would prove it.

Yet the element of light and the organ of vision, however related in their office and use, have no connexion whatever in their original. The action of rays of light upon the surfaces of animals, has no tendency to breed eyes in their heads. The sun might shine forever upon living bodies, without the smallest approach towards producing the sense of sight. On the other hand also, the animal eye does not generate or emit light.

V. Throughout the universe there is a wonderful proportioning of one thing to another. The size of animals of the human animal especially, when considered with respect to other animals, or to the plants which grow around him, is such, as a regard to his conveniency would have pointed out. A giant or a pigmy could not have milked goats, reaped corn, or mowed grass; we may add, could not have rode a horse, trained a vine, shorn a sheep, with the same bodily ease as we do, if at all. A pigmy would have been lost amongst rushes, or carried off by birds of prey.

It may be mentioned likewise, that the model and the materials of the human body being what they are, a much greater bulk would have broken down by its own weight. The persons of men who much exceed the ordinary stature, betray this tendency.

VI. Again (and which includes a vast variety of particulars, and those of the greatest importance;) how close is the suitablenessof the earth and sea to their several inhabitants; and of these inhabitants, to the places of their appointed residence!

Take the earth as it is; and consider the correspondency of the powers of its inhabitants with the properties and condition of the soil which they tread. Take the inhabitants as they are; and consider the substances which the earth yields for their use. They can scratch its surface, and its surface supplies all which they want. This is the length of their faculties! and such is the constitution of the globe, and their own, that this is sufficient for all their occasions.

When we pass from the earth to the sea, from land to water, we pass through a great change; but an adequate change accompanies us of animal forms and functions, of animals capacities and wants; so that correspondency remains. The earth in its nature is very different from the sea, and the sea from the earth; but one accords with its inhabitants as exactly as the other.

VII. The last relation of this kind which I shall mention is that of sleep to night;and it appears to me to be a relation which was expressly intended. Two points are manifest: first, that the animal frame requires sleep; secondly, that night brings with it a silence, and a cessation of activity, which allows of sleep being taken without interruption, and without loss. Animal existence is made up of action and slumber; nature has provided a season for each. An animal which stood not in need of rest, would always live in daylight. An animal which, though made for action, and delighting in action, must have its strength repaired by sleep, meets by its constitution the returns of day and night. In the human species, for instance, were the bustle, the labor, the motion of life, upheld by the constant presence of light, sleep could not be enjoyed without being disturbed by noise, and without expense of that time which the eagerness of private interest would not contentedly resign. It is happy therefore for this part of the creation, I mean that it is conformable to the frame and wants of their constitution, that nature, by the very disposition of her elements, has commanded, as it were, and imposed upon them, at moderate intervals, a general intermission of their toils, their occupations, and pursuits.

But it is not for man, either solely or principally, that night is made. Inferior, but less perverted natures, taste its solace, and expect its return with greater exactness and advantage than he does. I have often observed, and never observed but to admire, the satisfaction no less than the regularity, with which the greatest part of the irrational world yield to this soft necessity, this grateful vicissitude: how comfortably the birds of the air, for example, address themselves to the repose of the evening; with what alertness they resume the activity of the day!

Nor does it disturb our argument to confess, that certain species of animals are in motion during the night, and at rest in the day. With respect even to them, it is still true, that there is a change of condition in the animal, and an external change corresponding with it. There is still the relation, though inverted. The fact is, that the repose of other animals sets these at liberty, and invites them to their food or their sport.

If the relation of sleep to night, and, in some instances, its converse, be real, we cannot reflect without amazement upon the extent to which it carries us. Day and night are things close to us; the change applies immediately to our sensations; of all the phenomena of nature, it is the most obvious and the most familiar to our experience; but in its cause, it belongs to the great motions which are passing in the heavens. Whilst the earth glides round her axle, she ministers to the alternate necessities of the animals dwelling upon her surface, at the same time that she obeys the influence of those attractions which regulate the order of many thousand worlds. The relation therefore of sleep to night, is the relation of the inhabitants of the earth to the rotation of their globe; probably it is more; it is a relation to the system, of which that globe is a part; and still farther, to the congregation of systems, of which theirs is only one. If this account be true, it connects the meanest individual with the universe itself: a chicken roosting upon its perch, with the spheres revolving in the firmament.

But if any one object to our representation, that the succession of day and night, or the rotation of the earth upon which it depends, is not resolvable into central attraction, we will refer him to that which certainly is,—to the change of seasons. Now the constitution of animals susceptible of torpor, bears a relation to winter, similar to that which sleep bears to night. Against not only the cold, but the want of food which the approach of winter induces, the Preserver of the world has provided in many animals by migration, in many others by torpor. As one example out of a thousand; the bat, if it did not sleep through the winter, must have starved, as the moths and flying insects, upon which it feeds, disappear. But the transition from summer to winter carries us into the very midst of physical astronomy; that is to say, into the midst of those laws which govern the solar system at least, and probably all the heavenly bodies.