EDUCATION OF THE SENSES 193
cise is not certain, as it was in the solid cylindrical insets. There, the large cylinders could not enter the small opening, the taller ones would project beyond the top of the block, etc. In this game of the Big Stair, the eye of the child can easily recognise an error, since if he mistakes, the stair is irregular, that is, there will be a high step, behind which the step which should have ascended, decreases.
(b) Length: Long and Short Objects: — This set consists of ten rods. These are four-sided, each face being 3 centimetres. The first rod is a metre long, and the last a decimetre. The intervening rods decrease, from first to last, 1 decimetre each. Each space of 1 decimetre is painted alternately red or blue. The rods, when placed close to each other, must be so arranged that the colours correspond, forming so many transverse stripes — the whole set when arranged has the appearance of a rectangular triangle made up of organ pipes, which decrease on the side of the hypothenuse.
The child arranges the rods which have first been scattered and mixed. He puts them together according to the graduation of length, and observes the correspondence of colours. This exercise also offers a very evident control of error, for the regularity of the decreasing length of the stairs along the hypothenuse will be altered if the rods are not properly placed.
This most important set of blocks will have its principal application in arithmetic, as we shall see. With it, one may count from one to ten and may construct the addition and other tables, and it may constitute the first steps in the study of the decimal and metric system.
(c) Size: Objects, Larger and Smaller: — This set is made up of ten wooden cubes painted in rose-coloured