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 directions; but the impelling cause is within, and not without; and were there nothing without to serve as objects for its action, the necessity of its action would be none the less imperious.  The lion, when imprisoned in his cage, walks to and fro continuously, if there is room for him to take two steps and turn; and if there is not room for this, he moves his head incessantly from side to side.  The force within him, which his vital organs are setting at liberty from its imprisonment in his food, must in some way find issue.

Mothers do not often stop to speculate upon, and may even, perhaps, seldom observe the restless and incessant activity of birds, but that of their children forces itself upon their attention by its effects in disturbing their own quiet avocations and pleasures; and they often wonder what can be the inducement which leads to such a perpetual succession of movements made apparently without motive or end.  And, not perceiving any possible inducement to account for it, they are apt to consider this restless activity so causeless and unreasonable as to make it a fault for which the child is to be censured or punished, or which they are to attempt to cure by means of artificial restraints.  They would not attempt such repressions as this if they were aware that all this muscular and mental energy of action in the child is only the outward manifestation of an inward force developed in a manner wholly independent of its will—­a force, too, which must spend itself in some way or other, and that, if not allowed to do this in its own way, by impelling the limbs and members to outward action, it will do so by destroying the delicate mechanism within.  We see this in the case of men who are doomed for long periods to solitary confinement.  The force derived from their food, and released within their systems by the vital processes, being cut off by the silence and solitude of the dungeon from all usual and natural outlets, begins to work mischief within, by disorganizing the cerebral and other vital organs, and producing insanity and death.

Common Mistake.

We make a great mistake when we imagine that children are influenced in their activity mainly by a desire for the objects which they attain by it.  It is not the ends attained, but the pleasurable feeling which the action of the internal force, issuing by its natural channels, affords them, and the sense of power which accompanies the action.  An end which presents itself to be attained invites this force to act in one direction rather than another, but it is the action, and not the end, in which the charm resides.