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 car, 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 car, 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 for ever 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 suitableness of 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 animal 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 day-light. 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 labour, 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