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THE SIMPLEST FOUR-DIMENSIONAL SOLID 163<br />
us as a representation of one of the sixteen tesseracts<br />
which form one single block in four-dimensional space.<br />
Each cube, as we have it, is a tray, as it were, against<br />
which the real four-dimensional figure rests—just as each<br />
of the squares which the plane being has is a tray, so to<br />
speak, against which the cube it represents could rest.<br />
If we suppose the cubes to be one inch each way, then<br />
the original eight cubes will give eight tesseracts of the<br />
same colours, or the cubes, extending each one inch in<br />
the fourth dimension.<br />
But after these there come, going on in the fourth dimension,<br />
eight other bodies, eight other tesseracts. <strong>The</strong>y<br />
must be there, if we suppose the four-dimensional body<br />
we make up to have two divisions, one inch each in each<br />
of four directions.<br />
<strong>The</strong> colour we choose to designate the transference to<br />
this second region in the fourth dimension is blue. Thus,<br />
starting from the null cube and going in the fourth<br />
dimension, we first go through one inch of the null<br />
tesseract, then we come to a blue cube, which is the<br />
beginning of a blue tesseract. This blue tesseract stretches<br />
one inch further on in the fourth dimension.<br />
Thus, beyond each of the eight tesseracts, which are of<br />
the same colour as the cubes which are their bases, lie<br />
eight tesseracts whose colours are derived from the colours<br />
of the first eight by adding blue. Thus—<br />
Null gives blue<br />
Yellow ,, green<br />
Red ,, purple<br />
Orange ,, brown<br />
White ,, light blue<br />
Pink ,, light purple<br />
Light yellow ,, light green<br />
Ochre ,, light brown<br />
<strong>The</strong> addition to blue of yellow gives green—this is a