EDWARD ELS WORTH. 179 



Spectrum rays which most powerfully excite a primary 

 color sensation are not the ones which represent the 

 character of that sensation. The primary sensations are 

 red, green and blue (violet), but it is not the red, green 

 and violet spectrum rays which most powerfully excite 

 these sensations. The orange spectrum rays excite the 

 red sensation more strongly than the brightest red rays, 

 but also excite the green sensation. The greenish yellow 

 rays excite the green sensation more strongly than the 

 purest green rays, but also excite the red sensation. 



The yellow rays excite the red sensation as intensely 

 as the brightest red rays, and the green sensation as in- 

 tensely as the purest green rays. 



Acting upon these principles Ives produced one nega- 

 tive by the joint action of the orange, red, yellow, and 

 yellow green rays in definite proportions to represent 

 the red sensation. One by the joint action of the 

 orange, yellow, green and green blue rays in definite 

 proportions to represent the green sensation, and one by 

 the joint action of the blue green, blue and violet rays 

 in definite proportions to represent the blue sensation. 



Lantern slide positives are made from these negatives 

 and by exactly reversing their light and shade the 

 plates must also represent the effect of the photographic 

 object upon the respective color sensations. 



One lantern positive when seen by transparency in red 

 light produces the effect of the object upon the primary 

 red sensation. 



Another view in the same manner by green light re- 

 produces the effect of the object upon the green sen- 

 sation. 



The third viewed by blue violet light reproduces the 

 effect upon the blue sensation. 



The combination of these three images into one must 

 form a reproduction of the object as seen by the eye, 

 correct in form, color, light and shade. 



135 



