The observations of medical men, whose inquiries have been directed to this point, have decided, that from six to eight hours, is the amount of sleep demanded by persons in health. Some constitutions require as much as eight, and others no more than six, hours of repose. But eight hours is the maximum for all persons in ordinary health, with ordinary occupations. In cases of extra physical exertions, or the debility of disease, or a decayed constitution, more than this is required. Let eight hours, then, be regarded as the ordinary period required for sleep, by an industrious people, like the Americans. According to this, the practice of rising between four and five, and retiring between nine and ten, in Summer, would secure most of the sunlight, and expose us the least to that period of the atmosphere, when it is most noxious. In Winter, the night air is less deleterious, because the frost binds noxious exhalations, and vegetation ceases its inspiring and expiring process; and, moreover, as the constitution is more tried, in cold, than in warm, weather, and as in cold weather the body exhales less during the hours of sleep, it is not so injurious to protract our slumbers beyond the proper period, as it is in the warm months. But in Winter, it is best for grown persons, in health, to rise as soon as they can see to dress, and retire so as not to allow more than eight hours for sleep. It thus appears, that the laws of our political condition, the laws of the natural world, and the constitution of our bodies, alike demand that we rise with the light of day to prosecute our employments, and that we retire within doors, when this light is withdrawn. In regard to the effects of protracting the time spent in repose, many extensive and satisfactory investigations have been made. It has been shown, that, during sleep, the body perspires most freely, while yet neither food nor exercise are ministering to its wants. Of course, if we continue our slumbers, beyond the time required to restore the body to its usual vigor, there is an unperceived undermining of the constitution, by this protracted and debilitating exhalation. This process, in a course of years, renders the body delicate, and less able to withstand disease; and in the result shortens life. Sir John Sinclair, who has written a large work on the Causes of Longevity, states, as one result of his extensive investigations, that he has never yet heard or read of a single case of great longevity, where the individual was not an early riser. He says, that he has found cases, in which the individual has violated some one of all the other laws of health, and yet lived to great age; but never a single instance, in which any constitution has withstood that undermining, consequent on protracting the hours of repose beyond the demands of the system.