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Appendix
The stereoscope, as I stated last August in my address at Plymouth, affords a very easy
method of optically superimposing two portraits, and I have much pleasure in quoting the
following letter, pointing out this fact as well as some other conclusions to which I also
had arrived. The letter was kindly forwarded to me by Mr. Darwin; it is dated last
November, and was written to him by Mr. A. L. Austin, from New Zealand, thus affording
another of the many curious instances of two persons being independently engaged in the
same novel inquiry at nearly the same time, and coming to similar results
“INVERCARGILL, NEW ZEALAND,
“November 6th, 1877.
“To CHARLES DARWIN, Esq.
“SIR,—Although a perfect stranger to you, and living on the reverse side of the globe, I have
taken the liberty of writing to you on a small discovery I have made in binocular vision in the
stereoscope. I find by taking two ordinary carte-de-visite photos of two different persons’ faces, the
portraits being about the same sizes, and looking about the same direction, and placing them in a
stereoscope, the faces blend into one in a most remarkable manner, producing in the case of some
ladies’ portraits, in every instance, a decided improvement in beauty. The pictures were not taken in
a binocular camera, and therefore do not stand out well, but by moving one or both until the eyes
coincide in the stereoscope the pictures blend perfectly. If taken in a binocular camera for the
purpose, each person being taken on one half of the negative, I am sure the results would be still
more striking. Perhaps something might be made of this in regard to the expression of emotions in
man and the lower animals, &c. I have not time or opportunities to make experiments, but it seems
to me something might be made of this by photographing the faces of different animals, different
races of mankind, &c. I think a stereoscopic view of one of the ape tribe and some low-caste human
face would make a very curious mixture; also in the matter of crossing of animals and the resulting
offspring. It seems to me something also might result in photos of husband and wife and children,
&c. In any case, the results are curious, if it leads to nothing else. Should this come to anything you
will no doubt acknowledge myself as suggesting the experiment, and perhaps send me some of the
results. If not likely to come to anything, a reply would much oblige me.
“Yours very truly,
“A. L. AUSTIN, C.E., F.R.A.S.”
Dr. Carpenter informs me that the late Mr. Appold, the mechanician, used to combine
two portraits of himself under the stereoscope. The one had been taken with an assumed
stern expression, the other with a smile, and this combination produced a curious and
effective blending of the two.
Convenient as the stereoscope is, owing to its accessibility, for determining whether
any two portraits are suitable in size and attitude to form a good composite, it is
nevertheless a makeshift
