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



35 



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 



D 2 



