But if, at this moment, the spectator places a green glass before his
right eye and a red one before his left, he will find himself in the
condition desired for realizing the effect sought.
Each eye will then see only the image responding to the coloration
chosen, and, as it is precisely the one which has the perspective
proper to it, the relief appears immediately. The effect is striking.
We perceive a diffused image upon the screen with the naked eye, but
as soon as we use one special eye-glass the relief appears with as
much distinctness as in the best stereoscope. One must not, for
example, reverse his eye-glass, for if (things being arranged as we
have said) he looks through a red glass before his right eye, and
through a green one before his left, it is the image carrying the
perspective designed for the right eye that will be seen by the left
eye, and reciprocally. There is then produced, especially with certain
images, a very curious effect of reversed perspective, the background
coming to the front.
Now that photography is within every one's reach, and that many
amateurs are making stereopticon views and own projection lanterns,
we are persuaded that the experiment will be much more successful than
it formerly was. An assemblage of persons all provided with colored
eye-glasses is quite curious to contemplate. Our engraving represents
a stereopticon seance, and the draughtsman has well rendered the
effect of the two luminous and differently colored fascicles
superposed upon the screen.
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