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 at which I also had arrived. The
Fig. 3.
The accompanying woodcut is as fair a representation of one of the composites as is practicable in ordinary printing. It was photographically transferred to the wood, and the engraver has used his best endeavor to translate the shades into line engraving. This composite is made out of only three components, and its threefold origin is to be traced in the ears, and in the buttons to the vest. To the best of my judgment the original photograph is a very exact average of its components; not one feature in it appears identical with that of any one of them, but it contains a resemblance to all, and is not more like to one of them than to another. However, the judgment of the wood-engraver is different. His rendering of the composite has made it exactly like one of its components, which, it must be borne in mind, he had never seen. It is just as though an artist drawing a child had produced a portrait closely resembling its deceased father, having overlooked an equally strong likeness to its deceased mother, which was apparent to its relatives. This is to me a most striking proof that the composite is a true combination. (I trust that the beauty of the woodcut will not be much diminished by the necessarily coarse process of newspaper-printing.
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 6, 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 stereo-scope, 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
