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.

The real explanation is that the food which he has taken is delivering up,
within his system, the force stored in it that was received originally from
the beams of the sun, while the plant which produced it was growing. This
force must have an outlet, and it finds this outlet in the incessant
activity of the bird's muscles and brain. The various objects which attract
his attention without, _invite_ the force to expend itself in _certain
special d