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286   Life and Letters of Francis Galton

apparatus for photographing the composite image either from below the screen or from the eye-piece side.

The paper of 1878 to which reference has more than once been made' describes for the first time the very simple arrangement-a window with two cross-hairs or wires and two pinholes in the,frame-by which Galton at first registered the series of photographs to be compounded. For full face one hair was taken horizontally bisecting the pupils and the other, the vertical, bisecting the distance between the pupils. A prick made in each pinhole then registered the photograph. It is requisite that the whole series of photographs should be practically of the same size, or if not, reduced to the same size. All that is needful is, if n seconds be the correct exposure and there be m photographs, to give n/m seconds to each. If we suppose n = 50 and m = 8, we combine eight portraits. If we wish to combine more, it is better to combine composites of 8 to 10 each to obtain the full composite. Of this Galton writes

"Those of its outlines are sharpest and darkest that are common to the largest number of the components ; the purely individual peculiarities leave little or no visible trace. The latter being necessarily disposed on both sides of the average, the outline of the composite is the average of all the components'. It is a band and- not a fine line, because the outlines of the components are seldom exactly superimposed. The band will be darkest in its middle whenever the component portraits have the same general type of features, and its breadth, or amount of the blur, will measure the tendency of the components to deviate from the common type. This is so, for the very same reason that the shot-marks on a target are more thickly disposed near the bull's-eye than away from it, and in a greater degree as the marksmen are more skilful. All that has been said of the outlines is equally true as regards the shadows; the result being that the composite represents an averaged figure, whose lineaments have been softly drawn. The eyes come out with appropriate distinctness, owing to the mechanical conditions under which the components were hung.

A composite portrait represents the picture that would rise before the mind's eye of a man who had the gift of pictorial imagination in an exalted degree. But the imaginative power even of the highest artists is far from precise, and is so apt to be biased by special cases that may have struck their fancies, that no two artists agree in any of their typical forms. The merit of the photographic composite is its mechanical precision, being subject to no errors beyond those incidental to all photographic productions." (p. 134.)

Galton exhibited at the meeting composites of criminals, and notes of them that the special villainous irregularities have disappeared and the common humanity that underlies them has prevailed'. This I think should have been used as an argument that the criminal is not a distinct physical type, criminality is a mentality and the physical and the mental are not closely correlated. On the other hand, when composite photography is applied to a physically differentiated race, e.g. the Jews, it does in a marked manner indicate a type`. And therein, I think, its future usefulness lies.

' "Composite Portraits," Journal of the Anthropological Institute, Vol. viii, pp. 132-42, 1878.

2 Galton recognised later that this early composite was an "aggregation" rather than an average.

3 Mr Hyde Clarke in the discussion which followed asserted that the criminal characteristics were eliminated, and they had a natural type of man instead, and attributed the result to the process producing merely an 'average,' instead of arguing that there was not a distinct physical criminal type.   4 See our pp. 293-4 and Plates XX VIII and XXIX.