which some exaggerate and others deny, is simply the force of ideas and feelings. We can not bring too much scientific exactness to the determination of the extent and limitations of this force. We start from the principle that every idea tends to realize itself; and it does so in fact, if it is not counterbalanced by a superior force. The principle of the struggle for existence and of selection is applicable, therefore, to ideas not less than to living individuals and species. A selection is produced in the brain in favor of the strongest and most exclusive idea, which carries the whole organism. The child's brain is a battlefield of ideas and the impulses they generate; every new idea is an additional force encountering ideas already installed and impulses already developed. Education is, then, a work of intellectual selection. Let us suppose a mind still void, into which is abruptly introduced the representation of movement, the idea of some action, as of raising the arm. The idea being solitary and without any counterpoise, the disturbance begun in the brain takes the direction of the arm, because the nerves abutting in the arm have been disturbed by the representation of it; consequently the arm rises. To think of a movement is to begin it. A movement once existing can not be lost, but is communicated as of necessity from the brain to the organs—unless it is arrested by some other representation or impulsion. This propagation of motion is assured physiologically by the symmetry of the limbs, which tend to execute the same movement in succession. The brain provides the theme and the limbs reproduce it, and we have sympathy and synergy of the organs. The contagion of the idea to the limbs is infallible if the idea is solitary or predominant. We call this the law of idea-forces.
Chevreul's well-known experiments with the exploratory pendulum and the divining rod show that, if we represent to ourselves a motion in any direction, the hand will unconsciously realize it and communicate it to the pendulum. The tipping table realizes a movement we are anticipating, through the intervention of a real movement of the hands, of which we are not conscious. Mind-reading, by those who divine by taking your hand where you have hidden anything, is a reading of imperceptible motions by which your thought is translated without your being conscious of them. In cases of fascination and vertigo, which are more visible among children than among adults, a movement is begun the suspension of which is prevented by a paralysis of the will, and it carries us on to suffering and death. When a child, I was navigating a plank on the river without a thought that I might fall. All at once the idea came like a diverging force, projecting itself across the rectilinear thought which had alone previously directed my action. It was as if an invisible arm