294 THREE-DIMENSIONAL PHOTOGRAPHY
proximately three feet. It is understood, of course, that the axis
of rotation is perpendicular to the central ray of the tube.
By the use of a single fundamental technique, all object sizes
and distances normal for any part of the human body can be used.
Vectogruph.-The clinical X-ray is greatly increased in value
through the use of the Vectograph. The Wheatstone stereoscope
has never been really satisfactory as a stereo viewer. It is used
simply because, until the advent of the Vectograph, it was the only
form of stereoscope suitable for use with the large image sizes
incident to X-ray work.
When Vectographic prints are made, it is possible to hang the
X-ray film over the illuminator in the operating theatre. Then, by
using Polaroid 3D viewers with the bottom sectors cut away to
provide unobstructed direct vision, a surgeon has the full three
dimensional guide before him at all times, and it can be seen at
any distance which would be practical with the conventional
X-ray, It is a single film, as easily handled as the conventional
type, and it may be used with the same illuminators and is in
every physical way comparable to the single, conventional X-ray
film.
One of the greatest of the advantages of the Vectograph is the
fact that the three dimensional aspect is clearly seen at any dis-
tance at which the image itself may be seen; and it may be viewed
at any angle without disturbing the full stereo relief.
As has been described elsewhere in this volume, the Vectograph
process is easy, and does not require too much time. In emergen-
cies, of course, the time factor might be important, but ordinarily
the Vectograph should be available within one hour after the
original film is dry.
Another value of the Vectograph is that by using a ruler of
transparent material with one edge covered with Polaroid along
one axis and the other covered with the opposed axis, the two
component views are revealed. This makes it possible to make
direct measurements between the two positions of any embedded
object. This is very important in locating foreign bodies or even
tumors. This simple device makes it possible to locate such inclu-
sions in the most direct (and accurate) manner and with no loss
of time or involved computations.