It will, I am sure, surprise most persons to see how well defined these composites are.  When we deal with faces of the same type, the points of similarity far outnumber those of dissimilarity, and there is a much greater resemblance between faces generally than we who turn our attention to individual differences are apt to appreciate.  A traveller on his first arrival among people of a race very different to his own thinks them closely alike, and a Hindu has much difficulty in distinguishing one Englishman from another.

The fairness with which photographic composites represent their components is shown by six of the specimens.  I wished to learn whether the order in which the components were photographed made any material difference in the result, so I had three of the portraits arranged successively in each of their six possible combinations.  It will be observed that four at least of the six composites are closely alike.  I should say that in each of this set (which was made by the wet process) the last of the three components was always allowed a longer exposure than the second, and the second than the first, but it is found better to allow an equal time to all of them.

[Illustration:  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 endeavour 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.]

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:—­