COMPOSITE PORTRAITS. ^6 7 



to give four images of equal brightness, occupying the four corners of 

 a rhombus whose acute angles are 45. Three prisms will give eight 

 images ; but this is practically not a good combination, the images fail 

 in distinctness, and are too near together for use. Again, each lens 

 of a stereoscope of long focus can have one or a pair of these prisms 

 attached to it, and four or eight images may be thus combined. 



Another instrument I have made consists of a piece of glass in- 

 clined at a very acute angle to the line of sight, and of a mirror beyond 

 it, also inclined, but in the opposite direction to the line of sight. Two 

 rays of light will therefore reach the eye from each point of the glass ; 

 the one has been reflected from its surface, and the other has been first 

 reflected from the mirror, and then transmitted through the glass. 

 The glass used should be extremely thin, to avoid the blur due to 

 double reflections ; it may be a selected piece from those made to 

 cover microscopic specimens. The principle of the instrument may 

 be further developed by interposing additional pieces of glass suc- 

 cessively less inclined to the line of sight, and each reflecting a differ- 

 ent portrait. 



I have tried many other plans ; indeed, the possible methods of opti- 

 cally superimposing two or more images are very numerous. Thus I 

 have used a sextant (with its telescope attached) ; also strips of mir- 

 rors placed at different angles and their several reflections simultane- 

 ously viewed through a telescope. I have also used a divided lens, 

 like two stereoscopic lenses brought close together, in front of the 

 object-glass of a telescope. 



I have not yet had an opportunity of superimposing images by 

 placing glass negatives in separate magic - lanterns, all converging 

 upon the same screen ; but this or even a simple dioramic apparatus 

 would be very suitable for exhibiting composite effects to an audience, 

 and if the electric light were used for illumination, the effect on the 

 screen could be photographed at once. It would also be possible to 

 construct a camera with a long focus, and many slightly-divergent ob- 

 ject-glasses, each throwing an image of a separate glass negative upon 

 the same sensitized plate. 



The uses of composite portraits are many. They give us typical 

 pictures of different races of men, if derived from a large number of 

 individuals of those races taken at random. An assurance of the truth 

 of any of our pictorial deductions is to be looked for^in their substan- 

 tial agreement when different batches of components have been dealt 

 with, this being a perfect test of truth in all statistical conclusions. 

 Again, we may select prevalent or strongly-marked types from among 

 the men of the same race, just as I have done with two of the types 

 of criminals by which this memoir is illustrated. 



Another use of this process is to obtain by photography a really 

 good likeness of a living person. The inferiority of photographs to 

 the best works of artists, so far as resemblance is concerned, lies in 



