Page:Proceedings of the Royal Society of London Vol 69.djvu/43

Rh receives of this colour (B), and the pink absorbs half of what is left, so that finally a quarter of the light falling on that half of the paper or one-eighth of the total light of this colour is reflected. Adding this to the white reflected from the white half, we see that five-eighths of the total light of this colour is now reflected, instead of the one-half which is reflected when they are adjacent.

The colour at C is entirely absorbed by one ink and is unaffected by the other. The pink ink absorbs the light which falls on its half, and as the blue ink does not affect this colour it will riot matter whether it is on the pink or adjacent to it.

Also at D, where one ink is partly transparent and the other completely so, it cannot matter whether the perfectly transparent one is above or adjacent to the other.

If one or other of the inks is perfectly transparent at every point, the extent to which the dots overlap in immaterial. If the absorptions of the inks

Blue

Pink

overlap one another, as in Diagram 2 at E, the results are much worse. This colour is entirely absorbed by each ink. If then the dots are adjacent, the colour is absorbed everywhere and none reflected. But Avhen they coincide half the paper is white, and therefore half the total light of that colour is reflected. Thus the reflected light of that part of the spectrum where the absorptions overlap will vary from nothing up to half the total light.

In the case of the pink and blue inks this overlapping would occur at the yellow, where their absorption terminates, the very brightest part of the spectrum. According to Abney's curves, the luminosity of the yellow from A 56 to X 60 is about 50 per cent, of the whole white light.

Thus the addition of one-half of this band of light would be sufficient