During ordinary health, the hours spent in actual sleep should not exceed eight out of the twenty-four; and if the sleep is sound, continuous and refreshing, six will be sufficient for some persons. (See Rest and Change.)

It is of great importance, especially with the young and the weak, to maintain the due proportion between the number of waking and sleeping hours. If, therefore, it is necessary, as in going to places of amusement, to sit up unusually late, the waking hours, thus spent, should be compensated by a similar number of sleeping hours, taken in the preceding day; so that over-fatigue may be prevented. For example, if the usual hour for rising is 8 and for bed 11, and it is proposed to stay up to 3, the hour for rising should be changed to 12; or 4 hours' rest should be taken at some other time during the day.

During sleep, it is equally important to keep the body pleasantly warm, and to avoid keeping it over heated; and, as serious changes in the weather may happen in the night, and the lowest temperature in the twenty-four hours naturally occurs between 2 o'clock and 6 o'clock a.m., the ventilation and clothing must be prepared for these contingencies. Some extra article of clothing should be at hand to be put on the bed if necessary. (See Ventilation and Clothing.)

Every precaution should be taken to secure dark and quiet sleeping-rooms. (See Appendix, "London Noise and London Sleep.")

Those who wish to work at night after a long, busy day, should take a short sleep, followed by a cup of tea, before beginning the night's work; where this is impossible after dinner, it should be taken before dinner.

If sleep is taken after meals, it should be immediately after, and ought not to exceed an hour in duration; it should be taken sitting back in an easy chair - not lying down - with the head supported behind; not sitting with the chin resting on the breast; the feet should be kept warm, and the dress loose round the neck and waist.