Sachse.] ^'^^ [May 15, 



sensations, red, green, blue, the colors orange, yellow-green and blue- 

 violet. Experience lias taught him that not onlywere the former colors 

 unsuitable for the purpose, but that to reproduce the effect of natural 

 colors, a somewhat different screen must be used over the resultant 

 positive image. For this purpose Prof. Joly rules a screen in pure red, 

 green and blue-violet. This he calls his viewing screen. 



[For the red-selecting lines of the "taking" screen. Prof. Joly uses 

 a spectrum color, such as that to be found at one-sixth of the distance 

 from the line D to the line C ; for the green-selecting lines he uses a 

 color coi'responding to that of the spectrum at about one-third of the 

 distance from the E line to the D line ; and for the blue-violet-selecting 

 lines he uses a color corresponding to the spectrum color near the F line, 

 but toward the G line. On comparison of the "taking" screen with 

 the spectrum, these colors can be called a red-orange, yellow-green, and 

 a violet-blue. For the colors of the "viewing" screen he uses a pure 

 red not far from the C line ; a green near the E line ; and for the blue- 

 violet lines he takes a spectrum color between Gr and H, the object 

 being in the "viewing" screen to transmit fundamental color sensa- 

 tions only, and to let the eye do its own mixing ; the eye is assisted by 

 the depth of light and shade in the linear areas of the positive ; for 

 instance, if the full amount of light of two adjacent red and green 

 lines be transmitted, the eye sees a yellow ; if now some of the green 

 be obstructed or shut out by the positive over it, then the eye will see 

 an orange ; and if, on the other hand, some red be shut out by the posi- 

 tive, then the eye sees a yellow-green, and it is easy to see that one can 

 run all the colors from pure red to pure green by the varying amounts 

 of the red or green lines shut out by the positive.] 



The first specimen we have here is a negative of a china plate and 

 jug, photographed through the "taking" sci-een. 



The next one is a glass positive printed in contact from the above 

 negative. It will be noticed that neither of these specimens differ from 

 ordinary photographic results except that lines due to the use of the 

 screen are somewhat prominent. 



The third specimen is a positive similar to the one just shown, phiced 

 in register with a "viewing " screen ; and by holding it up to the light, 

 and viewing it through the ruled grating, we see the china plate and 

 jug in the bright colors of the original objects. 



The next subject is a male portrait from life ; this illustrates the pos- 

 sibility of the process in its application to professional portraiture. 



We now have a portrait of an "Irish peasant girl," not from life, it 

 is true, but from a water color, which is here before us. The specimen 

 labeled No 7 is placed in contact with a "viewing "screen. The original 

 is here offered for comparison, so that you may judge of the fidelity of 

 the reproduction to the colors of the original. To prove the correctness 

 of his theory, Prof. Joly here presents another specimen of the same 

 subject. No. 13. This is taken and placed in contact with the same 



