The force which the elements display in these reunions is always—­and this is one aspect of the great discovery of modern times in respect to the persistence or constancy of force which has already been referred to—­precisely the same in amount as that which was required for dissevering them from their original combinations with such substances at some previous time.  The processes of vegetation are the chief means employed for effecting the original separations, by the power of the sun, and for forming the unstable compounds by which this power is held in reserve.  The animal system, on the other hand, takes in these compounds, remodels them so far as is required to adapt them to its structure, assimilates them, and then, as occasion requires quires, it releases the concealed force, which then manifests itself in the forms of animal heat, of muscular motion, and of cerebral and nervous power.

In what way, and to what extent, the knowledge of these truths should influence us in the management and training of children in respect to their extraordinary activity, is the question we have next to consider.

Practical Applications of these Principles.

If we watch a bird for a little while hopping along upon the ground, and up and down between the ground and the branches of a tree, we shall at first be surprised at his incessant activity, and next, if we reflect a little, at the utter aimlessness and uselessness of it.  He runs a little way along the path; then he hops up upon a twig, then down again upon the ground; then “makes believe” peck at something which he imagines or pretends that he sees in the grass; then, canting his head to one side and upward, the branch of a tree there happens to strike his eye, upon which he at once flies up to it.  Perching himself upon it for the moment, he utters a burst of joyous song, and then, instantly afterwards, down he comes upon the ground again, runs along, stops, runs along a little farther, stops again, looks around him a moment, as if wondering what to do next, and then flies off out of our field of view.  If we could follow, and had patience to watch him so long, we should find him continuing this incessantly changing but never-ceasing activity all the day long.

We sometimes imagine that the bird’s movements are to be explained by supposing that he is engaged in the search for food in these evolutions.  But when we reflect how small a quantity of food his little crop will contain, we shall be at once convinced that a large proportion of his apparent pecking for food is only make-believe, and that he moves thus incessantly not so much on account of the end he seeks to attain by it, as on account of the very pleasure of the motion.  He hops about and pecks, not for the love of any thing he expects to find, but just for the love of hopping and pecking.