CHAPTER XVIII
COMPOSITE PORTRAITS AND STEREOSCOPIC MAPS
Sir Edmund Du Cane and criminal characteristics-Principle of composites-Analytical photography-Stereoscopic photographs of models of mountainous districts
M Y first idea of composite portraiture arose through a request by Sir Edmund Du Cane, R. E., then H. M. Inspector of Prisons, to examine the photographs of criminals, in order to discover and to define the types of features, if there be any, that are associated with different kinds of criminality. The popular ideas were known to be very inaccurate, and he thought the subject worthy of scientific study. I gladly offered to do what I could, and he gave me full opportunities of seeing prisons and of studying a large number of photographs of criminals, which were of course to be used confidentially.
At first, for obtaining pictorial averages I combined pairs of portraits with a stereoscope, with more or less success. Then I recollected an often observed effect with magic lanthorns, when two lanthorns converge on the same screen, and while the one is throwing its image, the operator slowly withdraws the light from it and throws it on to the next one. The first image yields slowly to the second, with little sense of discordance in the parts that at all resemble one another. It was
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