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Hinton - The Fourth Dimension.pdf

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RECAPITULATION AND EXTENSION 213<br />

Thus, if the cube be turned by an x to w turning, both<br />

the edge AB and the edge AC remain<br />

w stationary; hence the whole face<br />

ABEF in the yz plane remains fixed.<br />

y<br />

G <strong>The</strong> turning has taken place about<br />

E<br />

C the face ABEF.<br />

Suppose this turning to continue<br />

A<br />

x<br />

till AC runs to the left from A.<br />

Fig. 7 (135).<br />

<strong>The</strong> cube will occupy the position<br />

shown in fig. 8. This is the looking-glass image of the<br />

cube in fig. 3. By no rotation in three-dimensional space<br />

H F z can the cube be brought from<br />

the position in fig. 3 to that<br />

D<br />

shown in fig. 8.<br />

y<br />

B<br />

We can think of this turning<br />

G<br />

E<br />

as a turning of the face ABCD<br />

about AB, and a turning of each<br />

C A x x<br />

section parallel to ABCD round<br />

2<br />

the vertical line in which it<br />

intersects the face ABEF, the<br />

space in which the turning takes place being a different<br />

one from that in which the cube lies.<br />

One of the conditions, then, of our inquiry in the<br />

direction of the infinitely small is that we form the conception<br />

of a rotation about a plane. <strong>The</strong> production of a<br />

body in a state in which it presents the appearance of a<br />

looking-glass image of its former state is the criterion<br />

for a four-dimensional rotation.<br />

<strong>The</strong>re is some evidence for the occurrence of such transformations<br />

of bodies in the change of bodies from those<br />

which produce a right-handed polarisation of light to<br />

those which produce a left-handed polarisation; but this<br />

is not a point to which any very great importance can<br />

be attached.<br />

Still, in this connection, let me quote a remark from<br />

nd position 1st position<br />

Fig. 8 (136).

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