164 Mr. Francis Gallon [April 25, 



a fourth magic lantern with a brighter light behind it, and its image 

 is thrown on the screen by the side of the composite produced by 

 direct optical superposition. It will be observed that the two pro- 

 cesses lead to almost exactly the same result, and therefore the fair- 

 ness of the photographic process may be taken for granted. How- 

 ever, two other comparisons will be made for the sake of verification, 

 namely, between the optical and photogra23hic composites of two 

 children, and again between those of two Roman contadini. 



The composite portraits that will next be exhibited are made by 

 the photographic process, and it will now be understood that they 

 are truly composite, notwithstanding their definition and apparent 

 individuality. Attention is, however, first directed to a convenient 

 instrument not more than 18 inches in length, which is, in fact, a 

 photographic camera with six converging lenses and an attached 

 screen, on which six pictures can be adjusted and brilliantly illumi- 

 nated by artificial light. The effect of their optical combination can 

 thus be easily studied ; any errors of adjustment can be rectified and 

 the composite may be photographed at once. 



It must not be supposed that any one of the components fails to 

 leave its due trace in the photographic composite, much less in the 

 optical one. In order to allay misgivings on the subject, a small 

 apparatus is laid on the table together with some of the results 

 obtained by it. It is a cardboard frame, with a spring shutter closing 

 an aperture of the size of a wafer, that springs open on the pressure 

 of a finger, and shuts again as suddenly when the pressure is with- 

 drawn. A chronograph is held in the other hand, whose index begins 

 to travel the moment the finger presses a spring, and stops instantly 

 on lifting the finger. The two instruments are worked simulta- 

 neously ; the chronograph checking the time allowed for each expo- 

 sure and summing all the times. It apj)ears from several trials that 

 the effect of 1000 brief exposures is practically identical with that of 

 a single exi)osure of 1000 times the duration of any one of them. 

 Therefore each of a thousand components leaves its due photo- 

 graphic trace on the composite, though it is far too faint to be visible 

 unless reinforced by many similar traces. 



The composites now to be exhibited are made from coins or 

 medals, and in most instances the aim has been to obtain the best 

 likeness attainable of historical personages, by combining various 

 portraits of them taken at different periods of their lives and so to 

 elicit the traits that are common to each series. A few of the 

 individual portraits are placed in the same slide with each composite 

 to give a better idea of the character of these blended representatives. 

 Those that are shown are (1) Alexander the Great, from six com- 

 ponents ; (2) Antiochus, King of Syria, from six ; (3) Demetrius 

 Poliorcetes, from six ; (4) Cleopatra, from five. Here the composite is 

 as usual better looking than any of the components, none of which 

 however give any indication of her reputed beauty ; in fact, her 

 features are not only plain but to an ordinary English taste are simply 



