APPENDIX C 38interpupillary. The individual with widely spaced eyes can view
the narrow stereogram comfortably; but the one with closely set
eyes cannot see the wide stereogram except by painful divergence.
The worst obstacle is the seeming impossibility of the thing at
first. Try as one will, the fused image is out-of-focus, or the sharp
image is seen double. It is best to let the focus (accommodation)
go and learn to hold fusion. With fusion locked, accommodation
is tried. The images fly apart, and one starts over again. Repeti-
tion and more repetition slowly brings results. When the 20mm
picture can be held and focused the battle is over. Spreading the
ability to wider and wider separations is a matter of a little prac-
tise. The big difficulty comes in holding the first nomm picture.
Just how practical is it?
My wife was mildly irritated because I would glance at stereo-
grams without a viewer and comment upon them. She wanted to
see “if it were possible.” You will find this skepticism quite com-
mon. Although at that time she was not particularly interested in
stereography, I undertook to teach her. It required five periods
of five minutes each, with five minute rest periods between. At the
end of that time she was fusing and focusing a normal 6x13 stereo-
gram. (No graded series was available at the time.) Since that
time there are intervals of six or eight weeks during which she
has no occasion to use the ability, but when it arises she views the
stereogram as easily as a page is read. Not only that, but she fuses
a standard 3x6 paper print with homologous separation up to
8omm! The latter I find difficult, but she does it easily. And her
vision is excellent.
Similar results have occurred in teaching a number of students
the same skill. The time varies, but once the first free fusion has
been accomplished the rest follows easily; the acquired skill is
permanent and general visual comfort is usually increased in that
headaches from visual fatigue and the like are less common,
“tired eyes” almost unknown and the ability to consciously relax
convergence gives the physical comfort incident to relaxation of
any muscles.
Problem.-The single problem is to persuade any publisher that
the thing is feasible. He is sold on the stereo idea, he can learn
it himself but he cannot be persuaded that his readers share his
own ability to acquire the skill.