Among the innumerable mortifications that waylay human arrogance on every side, may well be reckoned our ignorance of the most common objects and effects, a defect of which we become more sensible, by every attempt to supply it. Vulgar and inactive minds confound familiarity with knowledge, and conceive themselves informed of the whole nature of things when they are shown their form or told their use; but the speculatist, who is not content with superficial views, harasses himself with fruitless curiosity, and still as he inquires more, perceives only that he knows less. Sleep is a state in which a great part of every life is passed. No animal has been yet discovered, whose existence is not varied with intervals of insensibility; and some late philosophers have extended the empire of sleep over the vegetable world. Yet of this change, so frequent, so great, so general, and so necessary, no searcher has yet found either the efficient or final cause; or can tell by what power the mind and body are thus chained down in irresistible stupefaction; or what benefits the animal receives from this alternate suspension of its active powers. Whatever may be the multiplicity or contrariety of opinions upon this subject, nature has taken sufficient care that theory shall have little influence on practice. The most diligent inquirer is not able long to keep his eyes open; the most eager disputant will begin about midnight to desert his argument; and, once in four-and-twenty hours, the gay and the gloomy, the witty and the dull, the clamorous and the silent, the busy and the idle, are all overpowered by the gentle tyrant, and all lie down in the equality of sleep. Philosophy has often attempted to repress insolence, by asserting, that all conditions are levelled by death; a position which, however it may deject the happy, will seldom afford much comfort to the wretched. It is far more pleasing to consider, that, sleep is equally a leveller with death; that the time is never at a great distance, when the balm of rest shall be diffused alike upon every head, when the diversities of life shall stop their operation, and the high and the low shall lie down together[1]. It is somewhere recorded of Alexander, that in the pride of conquests, and intoxication of flattery, he declared that he only perceived himself to be a man by the necessity of sleep. Whether he considered sleep as necessary to his mind or body, it was indeed a sufficient evidence of human infirmity; the body which required such frequency of renovation, gave but faint promises of immortality; and the mind which, from time to time, sunk gladly into insensibility, had made no very near approaches to the felicity of the supreme and self-sufficient nature.