60 Application of Maxwell's Curves to Three-colour Work, &c. 



These ratios (omitting the ones in brackets where the lack of light 

 made the readings too uncertain) do not differ from the mean by one 

 in eight, and omitting the ones marked *, the difference is not more 

 than one in fourteen. 



20. Experiment to see whether the Colour produced by Blue and Yellow side 

 by side .matched that when they were printed on one another. 



Mr. Gamble prepared for me a card printed with blue and one 

 printed with yellow. Then also a third printed with both the blue and 

 the yellow; this, of course, made green. I cat the blue and yellow 

 into discs about 8 inches in diameter, and the green into one about 



4 inches in diameter. Also I cut a white the white on which they 

 had all been printed into a disc 4 inches in diameter. Then I set 

 them on a motor, as in Maxwell's discs, with equal areas of blue and 

 yellow, and of green and white. These ought when rotated to match 

 if the inks are to be used for process work. I found there was a very 

 great difference in both hue and luminosity. To make a match it was 

 necessary to reduce the yellow to only 125 and increase the blue to 

 235, and by making the white 125 and the green 235 the match was 

 correct in luminosity as well as hue. 



Thus, as would be expected since the inks had not abrupt absorp- 

 tions, it made a very great difference if the colours were superposed or 

 were side by side. 



