292 THREE-DIMENSIONAL PHOTOGRAPHY
and always in the presence of witnesses who can swear that the
picture is truly representative of the original.
Since the stereo revival, stereograms have been received favor-
ably by many courts, and the effect upon a jury is great because
there is no room for interpretation. The original is seen as though
it were present. Although, as far as we can learn, stereo started in
the legal field with the presentation of evidence in a civil case,
police photographers are now taking it up and using it to supple-
ment or replace planar photography in the routine of criminal
investigations.
A widely read book devoted to a popular explanation of physics
is illustrated with just this kind of free vision stereograms. The
readers do not seem to have had any difficulty in seeing them in
three dimensions.
Restricted Subjects.-Much of the subject matter of forensic,
biological and medical work is such that it would not ordinarily
be returned from the laboratory; but when it is fully understood
that such films are of serious, professional nature this will not be
the case.
On the contrary there is one class of subject matter which is in-
herently restricted-records of experiments and progress of secret
developments. Ordinarily these would be safe enough, but there
is always the slight chance that someone who is not authorized
might see the pictures. At the same time, ordinary home process-
ing involves the loss of color which is often of the first importance.
Then there is only one course open. That is the use of home
processed color such as Ansco color or Ektachrome. Both of these
are widely used in stereo and have given highly satisfactory re-
sults. Of course, it is necessary to learn the routine, but that is
true of any kind of photographic processing when it is first
undertaken.
Stereo Radiography.-One of the first types of technical stereo
was the stereo X-ray, first made before igoo and used to some
extent ever since that time. The manufacturers of X-ray equip-
ment have produced special tube mounts and calibrated tables
to facilitate the use of stereo in X-ray, but the technique has
not been widely used for one reason. The radiographers do not
take sufficient time to master the fundamental principles of stereo.
In fact, from time to time articles have appeared in professional