[Illustration: SOLID GEOMETRICAL INSETS. Copyright 1912, by Carl R. Byoir]
One of the exercises which it is usual to offer him next is the construction of the Tower. This game could be played (and often is) with the nest of hollow blocks which nearly every child owns, and it consists of building a pyramid with them, the biggest at the bottom, the next smaller on this, and so on to the apex made by the tiniest one. This is to learn the difference between big and small; and as the child progresses in exactitude of vision, the game can be varied by piling the blocks in confusion at one side of the room and constructing the pyramid, a piece at a time, at some distance away. This means that when the child leaves his pyramid to go and get the block needed next, he must “carry the size in his eye” as the phrase runs, and pick out the block next smaller by an effort of his visual memory.
The difference between long and short is taught by means of ten squared rods of equal thickness, but regularly varying length, the shortest one being just one-tenth as long as the longest. The so-called Long Stair (illustration facing page 74) is constructed by the child with these. This is perhaps the most difficult game among those by which dimensions are taught, and a good many mistakes are to be anticipated. The material is again quite self-corrective, however, and little by little, with occasional silent or brief reminders from the adult onlooker, the child learns first to correct his own mistakes, and then not to make them. Thickness and thinness are studied with ten solids, brick-like in shape, all of the same length, but of regularly varying thickness, the thinnest one being one-tenth as thick as the biggest one. With these the child constructs the Big Stair (illustration facing page 74). Later on (considerably later), when the child begins to learn his numbers, these “stairs” are used to help him. The large numbers cut out of sandpaper and pasted on smooth cardboard, are placed by the child beside the right number of red and blue sections on each rod of the Long Stair.
After the construction of the Long and Big Stair the child is usually ready for the exercises with different fabrics to develop his sense of touch, and for the first beginning of the exercises leading to writing; especially the strips of sandpaper pasted upon smooth wood used to teach the difference between rough and smooth. At the same time with these exercises, begin the first ones with color which consist of simply matching spools of identical color, two by two.