EDUCATION OF THE SENSES 171
an opening that is a little too large for it, and then collects all the successive cylinders in openings just a little too large, he will find himself at the last with the big cylinder in his hand while only the smallest opening is empty. The didactic material controls every error. The child proceeds to correct himself, doing this in various ways. Most often he feels the cylinders or shakes them, in order to recognise which are the largest. Sometimes, he sees at a glance where his error lies, pulls the cylinders from the places where they should not be, and puts those left out where they belong, then replaces all the others. The normal child always repeats the exercise with growing interest."
Indeed, it is precisely in these errors that the educational importance of the didactic material lies, and when the child with evident security places each piece in its proper place, he has outgrown the exercise, and this piece of material becomes useless to him.
This self-correction leads the child to concentrate his attention upon the differences of dimensions, and to compare the various pieces. It is in just this comparison that the 'psycho-sensory exercise lies.
There is, therefore, no question here of teaching the child the knowledge of the dimensions, through the medium of these pieces. Neither is it our aim that the child shall know how to use, without an error, the material presented to him thus performing the exercises well.
That would place our material on the same basis as many others, for example that of Froebel, and would require again the active work of the teacher, who busies herself furnishing knowledge, and making haste to correct every error in order that the child may learn the use of the objects.