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REMARKS ON THE FIGURES 179<br />
ochre cube, and the last bounding cube, the other ochre<br />
cube. Practically three intermediate sectional cubes will<br />
be found sufficient for most purposes. We will take then<br />
a series of five figures—two terminal cubes and three<br />
intermediate sections—and show how the different regions<br />
appear in space when we take each set of three out<br />
of the four axes of the tesseract as lying in our space.<br />
In fig. 107 initial letters are used for the colours.<br />
A reference to fig. 103 will show the complete nomenclature,<br />
which is merely indicated here.<br />
b0 b1 b2 b3 b4<br />
x<br />
interior<br />
Ochre<br />
interior<br />
L. Brown<br />
interior<br />
L. Brown<br />
Fig. 107.<br />
interior<br />
L. Brown<br />
interior<br />
Ochre<br />
In this figure the tesseract is shown in fig stages<br />
distant from our face: first, zero; second 1⁄4 in.; third,<br />
1⁄2 in.; fourth, 3⁄4 in.; fifth, 1 in.; which are called 0, b b1,<br />
b2, b3, b4, because they are sections taken at distances<br />
0, 1, 2, 3, 4 quarter inches along the blue line. All the<br />
regions can be named from the first cube, the b0 cube,<br />
as before, simply by remembering that transference along<br />
the b axis gives the addition of blue to the colour of<br />
the region in the ochre, the b0 cube. In the final cube<br />
b4, the colouring of the original b0 cube is repeated.<br />
Thus the red line moved along the blue axis gives a red<br />
and blue or purple square. This purple square appears<br />
as the three purple lines in the sections b1, b2, b3, taken<br />
at 1⁄4, 1⁄2, 3⁄4 of an inch in the fourth dimension. If the<br />
tesseract moves transverse to our space we have them in<br />
this particular region, first of all a red line which lasts<br />
for a moment, secondly a purple line which takes its