POLARIZED LIGHT APPLIED TO STEREOSCOPY 215portance when polarization is used for anaglyphic stereo pro-
j ection.
Many years ago, indeed about a half century ago, when stereo
was highly popular and when polarized light was a prime favorite
among both amateur and professional scientists, a patent was
granted upon polarized anaglyphic stereoscopic projection.
According to the specification, this patent called for a double
projector which projected two superimposed images upon the
screen. Each projection lens was fitted with a polarizer. Those
who were to see the projected image in stereo relief were pro-
vided with a pair of polarizers to be supported before the eyes.
The axes of the viewing polarizers were to be crossed as were those
of the projector so that each eye saw nothing but its appropriate
image. That is exactly the nature of the polarization projection
which we have today to the last detail. And the patent is dated
before igoo!
However, the drawings and specification both were made
around the use of Nicol prisms as the polarizers, which made the
system both bulky and costly. These prisms were not specified
because polarizing films were unknown at that date, but simply
because the Nicol was the acknowledged supreme polarizing agent
of its day.
POLARIZING FILMs.-The general use of polarizing agents today
is largely due to the development of a system by which polarizing
films may be made to a given standard, and in quantity. The idea
that the polarizing film itself is new is erroneous. In the Quar-
terly Journal of Microscopical Science for January, 1854, Dr.
Herapath gives directions for making the films of iodosulfate of
quinine, markedly similar to the commercial films which we have
today. Many attempts have been made to produce these films,
often successful ones, but because of the quality and uniformity
of their product the Polaroid Corporation produces most of the
polarizing films used in this country today.
The fact that a single film mounted between two relatively thin
glasses will perform in all major respects similarly to the very
bulky and costly Nicol and similar prisms, has placed in our hands
the availability of unlimited variations of polarization of light.
THE POLARIZATION ANAGLYPH.-The use of the polarized an-
aglyph has become commonplace, and practically every stereo