The fourth dimension

APPENDIX I THE MODELS

Ix Chapter XI. a description has been given which will enable any one to make a set of models illustrative of the tesseract and its properties. The set here supposed to be employed consists of :—

1. Three sets of twenty-seven cubes each.

2. Twenty-seven slabs.

3. Twelve cubes with points, lines, faces, distinguished by colours, which will be called the catalogue cubes.

The preparation of the twelve catalogue cubes involves the expenditure of a considerable amount of time. It is advantageous to use them, but they can be replaced by the drawing of the views of the tesseract or by a reference to figs. 103, 104, 105, 106 of the text,

The slabs are coloured like the twenty-seven cubes of the first cubic block in fig. 101, the one with red, white, yellow axes.

The colours of the three sets of twenty-seven cubes are those of the cubes shown in fig. 101.

The slabs are used'to form the representation of a cube in a plane, and can well be dispensed with by any one who is accustomed to deal with solid figures. But the whole theory depends on a careful observation of how the cube would be represented by these slabs.

In the first step, that of forming a clear idea how a

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