Parents are seldom aware how fast their children are growing and increasing in strength, both of body and mind. The evidences of this growth, in respect to the limbs and muscles of the body, are, indeed, obvious to the eye; and as the growth advances, we have continual proof of the pleasure which the exercise of these new powers gives to the possessor of them. The active and boisterous plays of boys derive their chief charm from the pleasure they feel in testing and exercising their muscular powers in every way. They are always running, and leaping, and wrestling, and pursuing each other, and pushing each other, and climbing up to high places, and standing on their heads, and walking on the tops of fences, and performing all other possible or conceivable feats, which may give them the pleasure of working, in new and untried ways, their muscular machinery, and feeling its increasing power, and in producing new effects by means of it. They get themselves into continual difficulties and dangers by these things, and cause themselves a great deal of suffering. Still they go on, for the intoxicating delight of using their powers, or, rather, the irresistible instinct which impels them to use them, has greater force with them than all other considerations. We see all this very plainly in respect to the action of the limbs and organs of the body; for it is palpably evident to our senses, and we feel the necessity of providing safe and proper modes of expending these energies. Since we find, for example, that boys must kick something, we give them a football to kick; which, being a mere ball of wind, may be kicked without doing any harm. And so with almost all the other playthings and sports which are devised for boys, or which they devise for themselves. They are the means, simply, of enabling them to employ their growing powers and expand their energies, without doing any body any harm. We know very well that it is not safe to leave these powers and energies unemployed.