38 Dr. 11. S. Clay. On the Application of 



Thus the blue ink should not be the complementary of the red sensa- 

 tion. And in fact the ink will be far from complementary to the red. 

 I find by taking the areas of Abney's curves up to B' with a 

 planimeter, that it should very nearly match the green at about 

 A 50-3. 



The yellow ink would be made complementary to the violet sensa- 

 tion by ending the absorption at A, but it would be very pale, for it 

 would transmit a large amount of white, as there is a large proportion 

 of the violet beyond A. The result will be an unnecessary amount of 

 white in the final picture. The result will be better if the absorption 

 reaches to A'. Thus this ink also should not le complementary to the 

 violet sensation. The pink ink at the red end of the spectrum 

 transmits red and green, and at the other end chiefly violet and green. 

 If the violet is equal to the red it will be complementary to the green 

 sensation. This can be achieved by moving A towards the violet end, 

 but only at the expense of the yellow, which would be rendered very 

 pale. So this ink also should not le complementary. 



I have gone into this rather fully as it has so frequently been stated 

 that the inks ought to be complementary to the colour sensations. In 

 a very rough and general way this is true, but there is no advantage 

 in such inks; on the contrary, they would, even if obtainable with 

 abrupt absorptions, not be so good as others that are not comple- 

 mentary. The only possible advantage in using complementary inks 

 would arise in the case in which the absorptions were abrupt, for then 

 the filters would be complementary to Maxwell's curves. But the 

 advantage here is only one of theory, the printed result being, as we 

 have seen on the preceding page, a picture with a very large excess of 

 white. As in practice the filters would be adjusted by trial, even this 

 advantage is illusory. 



To summarise. The inks could only be complementary 



1. If they had abrupt absorptions with limits near the ends of the 



spectrum, when the colours would be in some cases mere 

 tints ; or 



2. If they have overlapping absorptions, or if some colours are 



absorbed by more than one ink, both of which are bad, since 

 the resultant absorption will follow a geometrical and not an 

 arithmetical law. 



The exact positions of the limits will, no doubt, finally depend on 

 the fact that there will be very few pigments which sufficiently fulfil 

 the conditions, and the blue and pink ones with abrupt absorptions 

 near the yellow will not be numerous. Still it is theoretically 

 interesting to determine the best positions, apart from the difficulty of 

 finding inks to suit. This will be best done by calculating the curves 

 for different absorption limits and estimating the amount and distribu- 



