External stimuli may be determined in quality and quantity.—Nothing can be more interesting than such experiments. By their means external stimuli may be determined with the greatest precision, both as regards quality and quantity. For instance, very small objects of various geometric forms will only attract the fugitive attention of a child of three years old; but by increasing the dimensions gradually, we arrive at the limit of size when these objects will fix the attention; then such objects excite an activity which becomes permanent, and the resulting exercise becomes a factor of development. The experiment is repeated with a number of children, and thus the dimensions of a series of objects are established.
It is the same with colors and with every kind of quality. In order that a quality should be felt to such a degree as to fix the attention, a certain extension and a certain intensity of the stimulus are necessary, which may be determined by the degree of psychical reaction shown by the child; as, for instance, the minimum chromatic extension sufficient to attract the attention to the colored tablets, etc. Quality, therefore, is determined by a psychical experiment demonstrating the activity it produces in a child, who will continue the exercise with the same object for a long time, thus elaborating a phenomenon of internal development, of self-formation.
Among the characteristics of the objects, one must be pointed out, which demands the highest degree of activity in the intelligence: they contain in themselves control of error.
To make the process one of self-education, it is not enough that the stimulus should call forth activity, it must also direct it. The child should not only persist for a long time in an exercise; he must persist without making mistakes. All the physical or intrinsic qualities of the objects should be determined, not only by the immediate reaction of attention they provoke in the child, but also by their possession of this fundamental characteristic, the control of error, that is to say the power of evoking the effective collaboration of the highest activities (comparison, judgment). For instance, one of the first objects which attract the attention of the child of three years old, the solid insets (a series of cylinders of various dimensions to be placed in or taken out of a block with corresponding holes) contains the most mechanical control, because if a single mistake be made in placing the cylinders, one of these must be left out at the end of the exercise. Hence a mistake is an obstacle only to be overcome by correction, for without it the exercise cannot be completed. On the other hand, the correction is so easy that the child makes it himself. The little problem suddenly presenting itself to the child, almost like the unexpected object of a jack-in-the-box, has "interested" him.
It is, however, noteworthy that the "problem" thus presented is not in itself the stimulus to interest; it is not that which incites to the repetition of the act—to the progress of the child. What interests the child is the sensation, not only of placing the objects but of acquiring a new power of perception, enabling him to recognize the difference of dimension in the cylinders, a difference which he did not at first notice. The problem presents itself solely in connection with the error, it does not accompany the normal process of development. An interest stimulated merely by curiosity, by a "problem," would not be that formative interest which wells up from the needs of life itself, and therefore directs the building up of the spiritual personality. If it were only the problem which should lead the soul to find itself, order might be dissipated by it, as by any other external cause which tends to seduce life into false paths. I lay, perhaps, excessive stress upon this point, in answer to very important objections and observations that have been made to me.
Indeed in the second series of objects designed to educate the eye to appreciate dimensions, the control of error is not mechanical, but psychological; the child himself, whose eye has been educated to recognize differences of dimension, will see the error, provided the objects be of a certain size and attractively colored. It is for this reason that the next objects contain, so to say, the control of error in their own size and in their bright colors. A control of error of a totally different kind, and of a much higher order, is that offered by the material of the arithmetical frame, in which the control will consist in the comparison of the child's own work with that of a model, a comparison which denotes a remarkably intelligent effort of will on the part of the child, and places him thenceforth in the true conditions of conscious auto-education. But, however slight the control of error may be, and in spite of the fact that this diverges more and more from an external mechanism, to rely upon the internal activities which are gradually developing, it always depends, like all the qualities of the objects, upon the fundamental reaction of the child, who accords it prolonged attention, and repeats the exercises.
On the other hand, the experimental criterion is different, in determining the quantity of the objects. When the instruments have been constructed with great precision, they provoke a spontaneous exercise so coordinated and so harmonious with the facts of internal development, that at a certain point a new psychical picture, a species of higher plane in the complex development, is revealed.
The child turns away spontaneously from the material, not with any signs of fatigue, but rather as if impelled by fresh energies, and his mind is capable of abstractions. At this stage of development, the child turns his attention to the external world, and observes it with an order which is the order formed in his mind during the period of the preceding development; he begins spontaneously to make a series of careful and logical comparisons which represent a veritable spontaneous acquisition of "knowledge." This is the period henceforth to be known as the period of "discoveries," discoveries which evoke enthusiasm and joy in the child.
This more elevated level of development is extremely fruitful in its last ascent It is essential that the child's attention should not be directed to the objects when the delicate phenomenon of abstraction begins. For instance, the teacher who invites the child to continue his operations with the material at such a moment, will retard his spontaneous development and place an obstacle in his way. If the enthusiasm which leads the child to rise to greater heights and experience so many intellectual emotions be extinguished, a path of progress has been closed. Now the same error may be committed by an excessive quantity of the educative material; this may dissipate the attention, render the exercises with the objects mechanical, and cause the child to pass by his psychological moment of ascent without perceiving it and seizing it. Moreover, such objects are then futile, and, by their futility, "the child may lose his soul."
The thing to be exactly determined is: what is necessary and sufficient as a response to the internal needs of a life in process of development, that is, of upward progression, of ascent? Now in determining the "quantity" we must be guided by the expression and at the same time by the active manifestations of the child. Those children who have long been occupied with these determined objects, showing every sign of absorbed attention, will, all of a sudden, begin to rise gradually and insensibly, like an aeroplane when it completes its short journey upon the ground. Their apparent indifference to the objects is revealed in its true essence by the intense and radiant expression of the face, which is animated by the liveliest joy. The child may seem to be doing nothing, but this will only be for a moment; very soon he will speak, and so will reveal what is happening within him, and then his ebullient activity will carry him along in a series of explorations and discoveries. He is saved.