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,

*

* "The animal frame requires sleep." For after the time of being awake has continued for sixteen or eighteen hours, we have a general feeling of fatigue and weakness; our motions become more difficult, our senses lose their activity, the mind becomes confused, receives sensations indistinctly, and governs muscular action with difficulty. We recognize by these signs the necessity of sleep; we choose a position which can be preserved without effort. The relation of the stillness and obscurity of night to our repose is striking, and calls for our adoration of an indulgent Creator.

The functions periodically rest, by the circulation, respiration, as well as

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 different secretions, and consequently digestion, becoming modified, or less rapid. By peaceful sleep, restrained within proper limits, the powers of our constitution are restored, and the organs recover their facility of action; but if sleep is troubled with unpleasant dreams, or painful impressions, or even prolonged beyond measure, very far from repairing, it exhausts the strength, and may become the occasion of disease.

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.

VIII. 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 the 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.

CHAPTER XVIII.

INSTINCTS.

THE order may not be very obvious, by which I place instincts next to relations. But I consider them as a species of relation. They contribute, along with the

* In this country there are a few animals which, besides daily repose, require annually some months of sleep. This is termed hybernation. The bat, hedge-hog, dormouse, etc. retire from active life, when there is a reduced temperature of the atmosphere, and when food is difficult to be obtained. These again revive when insects are sporting in the air, and the powers of vegetable life are exerted in the various processes of vegetation. Previous to their torpidity they have their bodies charged with fat, which is a sufficient store of nourishment during their profound slumbers, and is sufficient for their sustenance during the period of three or four months. For their temperature and respiration is greatly diminished, and their circulation, digestion, and every function of life proportionably languid. See Fleming's Philosophy of Zoology, article Torpidity.

animal organization, to a joint effect, in which view they are related to that organization. In many cases, they refer from one animal to another animal; and, when this is the case, become strictly relations in a second point of view.

An INSTINCT is a propensity prior to experience, and independent of instruction.* We contend, that it is by instinct that the sexes of animals seek each other; that animals cherish their offspring; that the young quadruped is directed to the teat of its dam; that birds build their nests, and brood with so much patience upon their eggs; that insects, which do not sit upon their eggs, deposit them in those particular situations in which the young, when hatched, find their appropriate food; that it is instinct which carries the salmon, and some other fish, out of the sea into rivers, for the purpose of shedding their spawn in fresh water.†

We may select out of this catalogue the incubation of eggs. I entertain no doubt, but that a couple of sparrows hatched in an oven, and kept separate from the rest of their species, would proceed as other sparrows do, in

* In this chapter it is admirably proved, that animals are not abandoned by nature to chance or to themselves, they are all employed in a series of actions; hence result those marvellous propensities "independent of instruction." To incline animals to a punctual execution of those actions which are necessary for them, nature has provided them with instinct; that is, propensities, inclinations, and wants, by which they are excited to fulfil the intentions of nature. For this purpose we recognize in every animal a double design: first, self preservation; second, the continuation of its own species; and every animal accomplishes this his own way, according to its organization.

The salmon, the shad, the smelt, and the flounder, annually quit the ocean, and come up our rivers to deposit their spawn. On these occasions, the salmon ascends rivers, sometimes a hundred miles from the sea, and surmounts the obstruction of high cataracts by leaping. It has been observed, that there is no danger which they will not encounter, to find a proper place for the deposition of their future offspring.