538 THE POPULAR SCIENCE MONTHLY. 



whenever I put any three of the five together, I arrive at very nearly 

 the same typical face.* 



The process is one of pictorial statistics, suitable to give us generic 

 pictures of man, such as Quetelet obtained in outline by the ordinary 

 numerical methods of statistics, as described in his work on " Anthro- 

 pometric." He procured the measurements of the limbs of a large 

 number of person of both sexes and of various ages, and of the dis- 

 tances between such points on the surface of the body as are sufficient- 

 ly defined to measure from. From these numerical data he calculated 

 and laid down upon paper the average positions of those points, and 

 therefrom constructed sketches of the typical man at various periods 

 of his growth, like Flaxman's drawings or Retsch's outlines. By the 

 process of composites we obtain a picture and not a mere outline. It 

 is blurred, something like a damp sketch, and the breadth of the blur 

 measures the variability of individuals from the central typical form. 



It may be objected that the contribution from each portrait, when 

 there is a multitude of them, is so small that, in the great majority of 

 cases, it might perhaps leave no trace at all in the generic portrait, or, 

 at all events, on the photograph ; consequently, that the result may 

 not be what it professes, but is, perhaps, due to a comparatively small 

 portion of the components, in which the lights and shades happen to 

 be sufficiently marked to create a decided impression. I therefore 

 tried a simple experiment, which leaves no doubt that this objection is 

 unfounded under even very exceptional circumstances, so far as the 

 photographs are concerned, and, therefore, a fortiori, as regards com- 

 posite results by purely optical means. I contrived a small apparatus 

 to be held in one hand. It had a receptacle behind for sensitized 

 paper, in front of which was a hole closed by a shutter, that sprang 

 back when I pressed my finger on a catch, and closed at the moment 

 that I released the pressure. In the other hand I held a chronograph, 

 in which the hand that marked quarter-seconds began to travel the 

 instant I pressed a catch, and stopped when I released it. I worked 

 these two instruments simultaneously, holding one in each hand. The 

 chronograph readings gave me the sum of the successive short periods 

 of exposure of the sensitized paper, and I could watch the length of 

 each of them. Thus provided, I made several experiments, and can 

 testify to the identity of the tint made by one thousand short expos- 

 ures with that made by a single exposure of the same length of time 

 as all the thousand put together. "What differences there were, lay 

 well within the limits of error in experimenting. 



Composite portraits are, therefore, much more than averages, be- 

 cause they include the features of every individual of whom they are 

 composed. They are the pictorial equivalents of those elaborate sta- 



* I exhibited many photographic composites at the Royal Institution on the 25th of 

 April. Some were transparencies thrown upon a screen, others were made before the 

 audience by converging magic lanterns. 



