In grown persons seven hours of sleep, or at the most eight, are sufficient for any one: there is even a danger in sleeping longer, and in remaining longer a bed, which throws one into the same disorders as an excess of rest. If any could wish to indulge it longer, it might be those who give themselves a great deal of motion, and of violent motion, during the day time; but it is not those who practise such indulgence; on the contrary, it is those who lead the most sedentary life. Thus that term ought never to be exceeded, unless one should be fallen into such a degree of weakness as not to have the strength necessary left for the being long up; in which case, however, one should try to keep so as long as possible. “The more moderate the quantity of his sleep (says Mr. LEWIS) the sweeter and more invigorating will it be.” It stands demonstrated, that the air of the night is less healthy than that of the day, and that the weakly sick are more susceptible of its influences in the evening than the morning; as then, during our sleep, we are confined to a small part of the atmosphere, which our bodies also would not fail of corrupting; it is to sleep that that time should be appropriated, in which the air is the least healthy, and in which the being up in it would be the most pernicious; so that it is best to go to bed early, and rise early. This is a precept so commonly known, that it may appear trivial to recall it to mind; but it is actually so much neglected, the consequence of it seems to be so little felt, though infinitely greater than it is believed to be, that it is very allowable to suppose it unknown, and to re-inculcate it by an insistence on its importance, especially to valetudinarians. Mr. LEWIS gives it for his opinion, “That if a patient lies down at ten o’ clock, which hour he should never exceed, he ought to rise in the summer-time at four or five, in the winter at six or seven, under an absolute prohibition of an indulgence in bed in the morning.” He recommends even the forming a habit of getting up after one’s first sleep, and avers, that uneasy as this custom might be at the first, it would soon become easy and agreeable[112]. A number of examples attest the salutariness of this advice: there are many valetudinarians who feel themselves light and well on waking out of their first sleep, and who experience a laborious restlessness on yielding to the temptation of going to sleep again: they are as sure of passing a good day of it, if, at whatever the hour be of their waking out of their first sleep they immediately get up, as of passing it disagreeably, if they give way to the second. Sleep is not tranquil but where there are no causes of irritation: which ought therefore to be carefully prevented. Three of the most important attentions are; _First_, Not to be in a hot air, and to be neither too much nor too little covered.