In the didactic material there are also geometrical solids––pale blue in color––a sphere, a prism, a pyramid, a cone, a cylinder. The most attractive way of teaching a child to recognize these forms is for him to touch them with closed eyes and guess their names, the latter learned in a way which I will describe later. After an exercise of this kind the child when his eyes are open observes the forms with a much more lively interest. Another way of interesting him in the solid geometrical forms is to make them move. The sphere rolls in every direction; the cylinder rolls in one direction only; the cone rolls round itself; the prism and the pyramid, however, stand still, but the prism falls over more easily than the pyramid.
Fig. 26.––Sound Boxes.
Little more remains of the didactic material for the education of the senses. There is, however, a series of six cardboard cylinders, either closed entirely or with wooden covers. (Fig. 26.)
When these cases are shaken they produce sounds varying in intensity from loud to almost 59 imperceptible sounds, according to the nature of the objects inside the cylinder.
There is a double act of these, and the exercise consists, first, in the recognition of sounds of equal intensity, arranging the cylinders in pairs. The next exercise consists in the comparison of one sound with another; that is, the child arranges the six cylinders in a series according to the loudness of sound which they produce. The exercise is analogous to that with the color spools, which also are paired and then arranged in gradation. In this case also the child performs the exercise seated comfortably at a table. After a preliminary explanation from the teacher he repeats the exercise by himself, his eyes being blindfolded that he may better concentrate his attention.
We may conclude with a general rule for the direction of the education of the senses. The order of procedure should be:
(1) Recognition of identities (the pairing of similar objects and the insertion of solid forms into places which fit them).