464 THE POPULAR SCIENCE MONTHLY. 



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 cf 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 No- 

 vember, 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 



