The soundness, as well as other qualities, of sleep, differs greatly in different individuals; and even in the same night, with the same individual in different circumstances. The first four or five hours of sleep are usually more sound than the remainder. Hardly anything will interrupt the repose of some persons during the early part of the night, while they awake afterwards at the slightest noise or movement—the chirping of a cricket, or the playing of a kitten.

In profound sleep, we probably dream very little, if at all; but in other circumstances, we are constantly disturbed by dreaming, and sometimes start and wake in the greatest anxiety or horror.

Nightmare is generally accompanied by dreams of the most distressing kind. We imagine a wild beast, or a serpent in pursuit of us; or a rock is detached from some neighboring cliff, and is about to roll upon and crush us; and yet all our efforts to fly are unavailing. We seem chained to the spot; but while in the very jaws of destruction, perhaps we awake, trembling, and palpitating, and weary, as if something of a serious nature had really happened.

In the case of nightmare, it is more than probable that we fall asleep with our stomachs too heavily loaded with food, or with a smaller quantity of that which is highly indigestible. Or it may sometimes arise from an improper position of the body, such as disturbs the action of the stomach or lungs, or of both these organs. Lying on the back, when we first go to sleep, is very apt to produce nightmare.

But distressing dreams often follow an evening of anxious cares, especially if those cares preyed upon us for the last half hour; and also after late suppers, even if they are light—and late reading. Hence the injunctions of the last section. Hence, too, the importance of taking our last meal two or three hours before sleep, and of engaging, during these hours, in cheerful conversation, and in the social and private duties of religion. Family and private worship, in the evening, are enjoined no less by philosophy than they are by christianity; and every young mother will do well to understand this matter, and train her offspring accordingly.

"That sleep from which we are easily roused, is the healthiest," says Macnish. "Very profound slumber partakes of the nature of apoplexy." I should say, rather, that a medium between the two extremes is healthiest. Profound apoplectic sleep, I am sure, is injurious; but that from which we are too easily roused cannot, it seems to me, be less so. Thus, I have often gone to sleep with a resolution to wake at a certain hour, or at the striking of the clock; and have found myself able to wake at the proposed time, almost without one failure in twenty instances where I have made the trial. But my sleep was obviously unsound, and certainly unsatisfying. The desire to awake at a certain moment or period, seemed to buoy me above the usual state of healthy sleep, and render me liable to awake at the slightest disturbance. Were it not for sacrificing the ease of others, it would be far better, in such cases, to rely upon some person to wake us, instead of charging our own minds with it.

The quality of our sleep will be greatly affected by the quantity. But this thought, if extended, would anticipate the subject of our next section; so easily does one thing, especially in physical education, run into or involve another. I will therefore, for the present, only say that if we confine ourselves to a smaller number of hours than is really required, our sleep becomes too sound to be quite healthy, as if nature endeavored to make up in quality, for want of due quantity. On the contrary, if we attempt to sleep longer than is really necessary to restore us, the quality of our sleep is not what it ought to be; for we do not sleep soundly enough.

The silence and darkness of the night tend to induce sleep of a better quality than the noise and activity of day. It is unquestionably desirable that children should be able to sleep, at least occasionally, without absolute quiet. And yet such sleep cannot be sufficiently sound to answer the purposes of health, if frequently repeated.

Hence it is, perhaps—at least in part—that the maxim has obtained currency, that one hour of sleep before midnight is worth two afterward. The comparison has probably been made between the quiet and darksome hours of evening and those which followed daybreak, when light, and music, and bustle conspire, as they should, to make us wakeful. No person can sleep as soundly and as effectually, when light reaches his closed eyes, and sounds strike his ears, as in darkness and silence. He may sleep, indeed, under almost any circumstances, when fatigue and exhaustion demand it; but never so profoundly as when in absolute abstraction of light, and complete quiet.