Sleep.
Children need a great deal of sleep because they take a great deal of exercise. The one acts as corrective to the other, so that both are necessary. As nature teaches us, night is the time for rest. Constant observation shows that sleep is softer and more profound while the sun is below the horizon. The heated air does not so perfectly tranquillize our tired senses. For this reason the most salutary habit is to rise and to go to rest with the sun. In our climate man, and animals generally, require more sleep in winter than in summer. But our mode of life is not so simple, natural, and uniform that we can make this regular habit a necessity. We must without doubt submit to regulations; but it is most important that we should be able to break them without risk when occasion requires. Do not then imprudently soften your pupil by letting him lie peacefully asleep without ever being disturbed. At first let him yield without restraint to the law of nature, but do not forget that in our day we must be superior to this law; we must be able to go late to rest and rise early, to be awakened suddenly, to be up all night, without discomfort. By beginning early, and by always proceeding slowly, we form the constitution by the very practices which would ruin it if it were already established.
It is important that your pupil should from the first be accustomed to a hard bed, so that he may find none uncomfortable.
Generally, a life of hardship, when we are used to it, gives us a far greater number of agreeable sensations than does a life of ease, which creates an infinite number of unpleasant ones. One too delicately reared can find sleep only upon a bed of down; one accustomed to bare boards can find it anywhere. No bed is hard to him who falls asleep as soon as his head touches the pillow. The best bed is the one which brings the best sleep. Throughout the day no slaves from Persia, but Émile and I, will prepare our beds. When we are tilling the ground we shall be making them soft for our slumber.