I have shown that, if we have the portraits of two or more different persons, taken in the same aspect and under the same conditions of light and shade, and that if we put them into different optical lanterns converging on the same screen and carefully adjust them—­first, so as to bring them to the same scale, and, secondly, so as to superpose them as accurately as the conditions admit—­then the different faces will blend surprisingly well into a single countenance.  If they are not very dissimilar, the blended result will always have a curious air of individuality, and will be unexpectedly well defined; it will exactly resemble none of its components, but it will have a sort of family likeness to all of them, and it will be an ideal and an averaged portrait.  I have also shown that the image on the screen might be photographed then and there, or that the same result may be much more easily obtained by a method of successive photography, and I have exhibited many specimens made on this principle.  Photo-lithographs of some of these will be found in the Proceedings of the Royal Institution, as illustrations of a lecture I gave there “On Generic Images” in 1879.

The method I now use is much better than those previously described; it leads to more accurate results, and is easier to manage.  I will exhibit and explain the apparatus as it stands, and will indicate some improvements as I go on.  The apparatus is here.  I use it by gaslight, and employ rapid dry plates, which, however, under the conditions of a particularly small aperture and the character of the light, require sixty seconds of total exposure.  The apparatus is 4 feet long and 6-1/2 inches broad; it lies with its side along the edge of the table at which I sit, and it is sloped towards me, so that, by bending my neck slightly, I can bring my eye to an eye-hole, where I watch the effect of the adjustments which my hands are free to make.  The entire management of the whole of these is within an easy arm’s length, and I complete the process without shifting my seat.

The apparatus consists of three parts, A, B, and C. A is rigidly fixed; it contains the dark slide and the contrivances by which the position of the image can be viewed; the eye-hole, e, already mentioned, being part of A. B is a travelling carriage that holds the lens, and is connected by bellows-work with A. In my apparatus it is pushed out and in, and clamped where desired, but it ought to be moved altogether by pinion and rack-work.[24] The lens I use is a I B Dallmeyer.  Its focal length is appropriate to the size of the instrument, and I find great convenience in a lens of wide aperture when making the adjustments, as I then require plenty of light; but, as to the photography, the smaller the aperture the better.  The hole in my stop is only two-tenths of an inch in diameter, and I believe one-tenth would be more suitable.

[Footnote 24:  I have since had a more substantial instrument made with these and similar improvements.]