Page:Proceedings of the Royal Society of London Vol 69.djvu/68

60 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.