I have noticed that children are rarely afraid of thunder, unless, indeed, the thunder-claps are so frightful as actually to wound the organ of hearing. Otherwise, they fear it only when they have been taught that thunder sometimes wounds or kills. When reason begins to affright them, let habit reassure them. By a slow and well conducted process the man or the child is rendered fearless of everything. In this outset of life, while memory and imagination are still inactive, the child pays attention only to what actually affects his senses. The first materials of his knowledge are his sensations. If, therefore, these are presented to him in suitable order, his memory can hereafter present them to his understanding in the same order. But as he attends to his sensations only, it will at first suffice to show him very clearly the connection between these sensations, and the objects which give rise to them. He is eager to touch everything, to handle everything. Do not thwart this restless desire; it suggests to him a very necessary apprenticeship. It is thus he learns to feel the heat and coldness, hardness and softness, heaviness and lightness of bodies; to judge of their size, their shape, and all their sensible qualities, by looking, by touching, by listening; above all, by comparing the results of sight with those of touch, estimating with the eye the sensation a thing produces upon the fingers. By movement alone we learn the existence of things which are not ourselves; and it is by our own movements alone that we gain the idea of extension. Because the child has not this idea, he stretches out his hand indifferently to seize an object which touches him, or one which is a hundred paces distant from him. The effort he makes in doing this appears to you a sign of domination, an order he gives the object to come nearer, or to you to bring it to him. It is nothing of the kind. It means only that the object seen first within the brain, then upon the eye, is now seen at arm's length, and that he does not conceive of any distance beyond his reach. Be careful, then, to walk often with him, to transport him from one place to another, to let him feel the change of position, and, in this way to teach him how to judge of distances. When he begins to know them, change the plan; carry him only where it is convenient for you to do so, and not wherever it pleases him. For as soon as he is no longer deceived by the senses, his attempts arise from another cause. This change is remarkable and demands explanation.