370 Mr. R. W. Wood on an Application of 



tration of the different portions of the picture could not be 

 obtained. 



One of the great advantages of this method is the facility 

 with which duplicates can be made. If we place the finished 

 picture in a printing-frame over a glass plate coated with 

 bichromated gelatine, and expose it to sunlight, on washing 

 the plate in warm water we obtain, by a single printing 

 process, a second colour-photograph, equal to the first in every 

 respect, and also positive. From this second copy we can 

 print others, all being positive. 



The apparatus for viewing the pictures consists of a cheap 

 double-convex lens mounted on a little frame, as shown in 

 fig. 1, with a perforated screen for bringing the eye into the 



right position. I find that, by using a lens of proper focus, 

 it is possible to so adjust the apparatus that the picture can be 

 seen in its natural colours with both eyes simultaneously, 

 since corresponding overlapping spectra are formed on each 

 side of the central direct image. A gas- flame turned edge- 

 wise, or the filament of an incandescent light, makes a con- 

 venient source of light. The colours are of great brilliancy 

 and purity, almost too brilliant in fact, though dark reds and 

 ochres are reproduced with considerable fidelity. The pictures 

 can be projected by employing a powerful arc-light, placing 

 a rather wide slit in the overlapping spectra, and mounting 

 the projecting lens beyond this. The pictures that I have 

 obtained thus far measure 2'5 in. by 2*5 in., and have been 

 thrown up about 3 feet square. The fact that only a small 

 percentage of the light is utilized makes great amplification 

 difficult. Certain experiments that I have made lead me to 

 believe that the process can be greatly simplified. 



I have exposed an ordinary photographic plate in a camera 



