206 THE DISCOVERY OF THE CHILD ILLUSTRATIVE APPLICATIONS: GUIDE TO THE MATERIAL SOLID INSETS Dimensions. The teacher, after the child has had long practice in handling the three solid insets and has acquired confidence in the exercise, takes all the cylinders of equal height and spreads them out on the table close together. Then she chooses the two extremes saying: "This is the thickest," and " This the thinnest". She places them side by side to make the comparison more telling, and then, taking each one of them by the knob, she places them tase to base in order to mark the extreme difference. Then she places them close together again and upright, in order to show that they are of equal height. Meanwhile she may be repeating many times: "Thick, thin". She must every time follow the other stages of verification in which she asks: " Give me the thickest, the thinnest," and finally the language test: " What is it like?" In later lessons the teacher removes the two extremes and repeats the lesson with the two remaining at the extremities. Finally, she uses all the pieces, chooses one of them by chance, and asks: "Give me one thicker than this, or thinner than this." The teacher proceeds in the same way with the second set of solid insets. In this case she places the pieces upright, all of them having a base wide enough to maintain them in this position. She says: "It is the tallest, it is the shortest." Then she places the extreme pieces in juxta-position, having removed them from the row; she places their bases, end to end, showing that they are equal. From the extremes she passes to the middle pieces, as in the first exercise. With the third set of solid insets, the teacher, after having placed all the pieces ia a graduated row, points to the first, saying: **It is the largest," .and to the last saying: "It is the smallest," Then she places them close together and points out how they differ in height as well as in the size of the base. The proceeding is similar to that in the two preceding exercises.