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236<br />
THE FOURTH DIMENSION<br />
familiarity with out cube. Turn the catalogue cube (or<br />
imagine the coloured figure turned) so that the red line<br />
runs up, the yellow line out to the right, and the white<br />
line towards you. <strong>The</strong>n turn the block of cubes to<br />
occupy a similar position.<br />
<strong>The</strong> block has now a different wall in contact with<br />
the plane. Its appearance to a plane being will not be<br />
the same as before. He has, however, enough slabs to<br />
represent this new set of appearances. But he must<br />
remodel his former arrangement of them.<br />
He must take a null, a red, and a null slab from the<br />
first of his sets of slabs, then a white, a pink, and a white<br />
from the second, and then a null, a red, and a null from<br />
the third set of slabs.<br />
He takes the first column from the first set, the first<br />
column from the second set, and the first column from<br />
the third set.<br />
To represent the half-way-through appearance, which<br />
is as if a very thin slice were cut out half way through the<br />
block, he must take the second column of each of his<br />
sets of slabs, and to represent the final appearance, the<br />
third column of each set.<br />
Now turn the catalogue cube back to the normal<br />
position, and also the block of cubes.<br />
<strong>The</strong>re is another turning—a turning about the yellow<br />
line, in which the white axis comes below the support.<br />
You cannot break through the surface of the table, so<br />
you must imagine the old support to be raised. <strong>The</strong>n<br />
the top of the block of cubes in its new position is at the<br />
level at which the base of it was before.<br />
Now representing the appearance on the plane, we must<br />
draw a horizontal line to represent the old base. <strong>The</strong><br />
line should be drawn three inches high on the cardboard.<br />
Below this the representative slabs can be arranged.<br />
It is easy to see what they are. <strong>The</strong> old arrangements