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222 galton.org
222
Appendix
process of which I there spoke enables us to obtain with mechanical precision a
generalised picture; one that represents no man in particular, but portrays an imaginary
figure possessing the average features of any given group of men. These ideal faces have a
surprising air of reality. Nobody who glanced at one of them for the first time would doubt
its being the likeness of a living person, yet, as I have said, it is no such thing; it is the
portrait of a type and not of an individual.
I begin by collecting photographs of the persons with whom I propose to deal. They
must be similar in attitude and size, but no exactness is necessary in either of these
respects. Then, by a simple contrivance, I make two pinholes in each of them, to enable
me to hang them up one in front of the other; like a
pack of cards, upon the same pair of pins, in such a way that the eyes of all the portraits
shall be as nearly as possible superimposed; in which case the remainder of the features
will also be superimposed nearly enough. These pinholes correspond to what are
technically known to printers as “register marks.” They are easily made: A slip of brass or
card has an aperture cut out of its middle, and threads are stretched from opposite sides,
making a cross
.[1]
Two small holes are drilled in the plate, one on either side of the
aperture. The slip of brass is laid on the portrait with the aperture over its face. It is turned
about until one of the cross threads cuts the pupils of both the eyes, and it is further
adjusted until the other thread divides the interval between the pupils in two equal parts.
Then it is held firmly, and a prick is made through each of the holes.
The portraits being thus arranged, a photographic camera is directed upon them.
Suppose there are eight portraits in the pack, and that under existing circumstances it
would require an
[1]
I am indebted for the woodcuts to the Editor of Nature, in which journal this memoir first
appeared.
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