The
stereoscope is the instrument which effects this result by
bringing the two pictures together in the senses. The stereograph
produces this result in another way than by prisms as in the
stereoscope. In the first place there is
[Illustration: Looking Through the Colored Gelatine]
only one picture, not two mounted side by side. The stereograph
consists of a piece of card, having therein two circular openings
about 1-1/4 in. diameter, at a distance apart corresponding to the
distance between the centers of the pupils. The openings are
covered with transparent gelatine, the one for the left eye being
blue, that for the right, orange. The picture is viewed at a
distance of about 7 in. from the stereograph. As a result of
looking at it through the stereograph, one sees a colorless black
and white picture which stands out from the background. Try
looking at the front cover of Popular Mechanics through these
colored gelatine openings and the effect will be produced.
If one looks at the picture first with the right eye alone through
the orange glass, and then with the left eye through the blue
glass, one will understand the principle on which the little
instrument works.
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