frequently than any other; nor is the intention of nature less evident, because, either from avarice or the dissipation of luxury, some individuals protract the labours or the pleasures of the day beyond the natural period assigned for those purposes, since these are unnatural exceptions to the observance of the general law.

Although it would be difficult to prove directly that there is any necessary connexion between darkness and sleep, yet this connexion is rendered at least highly probable by the effect usually produced on the approach of darkness upon animals in general, but more remarkably on birds, for, with the exception of those whose habits are nocturnal, all birds betake themselves to sleep as soon as night approaches: and if darkness should anticipate night by many hours, as happens when any considerable eclipse of the sun takes place in the middle of the day, we still find the birds of the field as well as our domesticated fowls give the same indications of composing themselves to sleep, as at the regular period of sunset. If it should be said that this does not more serve to prove a connexion between darkness and sleep with reference to these animals, than to prove the effect of a long continued association resulting from their habit of going to roost at sunset; it may be asked, why should darkness, unless from some inherent cause, lead them to compose themselves to sleep at the hour of noon, instead of the usual hour of evening; since, on the one hand, periodical states of the animal system do not usually recur before the termination of the habitual period; and, on the other hand, the individuals cannot at so early an hour have experienced such a degree of exhaustion as would of itself invite to sleep?

In stating that the voluntary action of the muscles ceases during sound sleep, we ought not to omit the remarkable fact that those muscles which are not under the empire of the will continue their action uninterruptedly through the deepest sleep. Of all

the muscles of involuntary motion, this observation holds most remarkably with respect to the heart; the continued action of which organ during sleep is a phenomenon worthy of the deepest attention of the philosophical mind. All other organs of the body, have their periods either of absolute or comparative rest; the senses are in a measure periodically locked up by sleep during one quarter at least, if not one third of our whole existence; the limbs of the most athletic individual lose their power of motion after a few hours of unremitted exertion; even the brain, which during the hours of sleep and the interruption of all the common functions of the body frequently represents to the internal senses the most busy scenes of active life-even the brain may be exhausted by unusual fatigue, or other causes, and may thus involve the general system in the stupor of apparent death-but the heart, unless on such occasions as the momentary interruption of a swoon, never rests: so that, whether we look back to that period of our existence, when, in our yet imperfect state, there could scarcely be discovered the faint outline of those members, which in after life constitute man's strength and beauty, the presence of the heart may be recognised by the impulse of its vibratory motion, though its form is yet undefined, or at least indistinguishable; or whether, on the other hand, we look forward to the latest moments of protracted disease, or expiring old age, the same organ is the last part of our frame which continues to give immediate proof of vital motion.

The privation of light is rarely, if ever, total; for though the empire of time is divided in nearly equal proportion between day and night, there are comparatively few nights in which there is not diffused through the air a sufficient quantity of light for many of the purposes of life. Nor, with respect to those persons who either were born blind, or became blind in early infancy, is the absence of light felt with any degree of severity; for, in such instances, although

the individual may be made to understand that he wants some faculty which those around him possess, there cannot be however any consciousness of privation where there never had been actually any enjoyment; or where there was no recollection of it, if it had for a time existed. And even in the case of individuals who have been deprived of sight long subsequently to birth, although the recollection of the former enjoyment must more or less imbitter their present state; yet so long as the offices of surroundings friends are the means of administering to their comfort, more especially if those offices are fulfilled with kindness, the mind soon becomes reconciled to the privation for it is a fact, repeatedly observed, that blind persons under such circumstances are usually cheerful. Nor ought we to forget the compensation which nature affords to those who are deprived of sight, in the consequently quickened activity of some of the other senses.

Let us however suppose for a moment that, all the faculties and recollections of man remaining unaltered, and the general processes of nature continuing, if possible, the same as they are now, the existence of light were withdrawn from this earth: what would then be the condition of mankind? How could those occupations of life be pursued which are necessary for the supply of our simplest wants? Who in that case should yoke the ox to the plough, or sow the seed, or reap the harvest? but indeed under such a supposition there would soon be neither seed for the ground, nor grain for food: for, if deprived of light, the character of vegitation is completely altered; and its results, as far as general utility is concerned, destroyed. Or suppose, further, that these necessary supplies of life were no longer required, on account of some consequent alteration in our physical constitution; or that they were procured for us by any unknown means; yet, in all the higher enjoyments of our nature, how cheerless, how utterly miserable

would be our situation. Under such circumstances, wisdom would not only be

"at one entrance quite shut out,"

but no other entrance could then be found for it; for of the other senses, the only remaining inlets of knowledge with reference to an external world, there is not one, which, if unaided by sight, could be of any practical value. With respect indeed to our inward feelings, though we should, on the one hand, be spared, by the privation of light, the worse than corporeal pain of the averted eye of those who ought to meet us with gratitude and affection; we should, on the other hand, lose the beams of filial or parental love; of which even a momentary smile outweighs an age of pain.

As in mathematical reasoning the truth of a proposition is sometimes indirectly proved by showing that every process of proof but the one proposed would lead to an absurd conclusion: so, though the supposition of a general and total privation of light is on all probable grounds of reasoning inadmissible, it may yet serve to show us indirectly the value of the good we enjoy. But it is sufficient to have given a few instances of the necessary effects of such a privation: and it will be a more grateful task to enumerate the actual benefits which we derive from the agency of light.

Ex

In the vegetable world, upon the products of which animal existence ultimately depends, light is the prime mover of every change that takes place, from the moment the germ emerges from the soil. clude the agency of light, and in a short time the most experienced botanists might possibly be at a loss to know the plant with which he is otherwise most familiar; so completely obliterated are all its natural characters, whether of colour, form, taste, or odour. Thus the faded colour, of the interior leaves of the lettuce and other culinary vegetables is the result of such a degree of compression of the body of the

plant as excludes the admission of light beyond the exterior leaves. And, again, if a branch of ivy or of any spreading plant happen to penetrate during the progress of its vegetation into a dark cellar, or any similar subterraneous situation, it is observable, that, with the total loss of colour, its growth advances with great rapidity, but its proportions alter to such a degree as often to mask its original form. And, lastly, which in a practical point of view is of the greatest importance, if a plant which has grown without the influence of light be chemically examined, its juices, it might almost be said its whole. substance, would be found to consist of little else than mere water; and, whatever odour it may have, is characteristic, not of its original nature, but of its unnatural mode of growth; becoming, in short, very like that of a common fungus. The total result is, that all the native beauties and uses of a vegetable growing under these circumstances are lost: the eye is neither delighted by any variety or brightness of colour; nor is the sense of smell gratified by any fragrance: the degeneracy of its fibre into a mere pulp renders it unfit for any mechanical purpose; and the resinous and other principles on which its nutritive and medicinal virtues depend, cease to be developed. In some instances, however, the bleaching or etiolation of plants is useful in correcting the acrid taste which belongs to them in their natural state; as in the case of endive and of celery.

Its

The effect of light upon vegetation has been selected in the preceding paragraph as affording the most powerful instance of the adaptation of this natural agent to the physical condition of man. effects upon individuals of the mineral and animal kingdom are neither so easily to be traced, nor are nearly so important in their consequences, at least in a practical point of view; and therefore it is not proposed to bring them forward in a more particular

manner.

The observation of those modifications which light