Page:Proceedings of the Royal Society of London Vol 69.djvu/53

Rh I selected the above positions partly because they divide the spec- trum about evenly, but also because most of the pink inks have their absorptions at about X 59, and the yellows at about A 49. As the blue inks are all bad, it is no use considering where their absorp- tions are.

Another interesting place for the absorptions to end is at the points of intersection of the ray composition curves, namely, at A 50'5, where the green and violet curves cross, and at A 57 '5, where the green and red cross. It is useful to compare the excess of white and its distribution in the two cases.

The results of these calculations are given in the following tables:

Absorptions at A 49 and A 59.

Wave-length.

Luminosity.

Percentage area not covered by inks.

Excess of white.

Yellow.

Pink.

Blue.

38

0-25

10-4

___

0-8

0-63

40

075

25-5

2-0

1-5

42

1-3

43-4

3-18

2-6

44

2-1 66-0

5-0

3-8

46

3-5

64-0

1-4

0-9

48

7-5

56-0

10-0

6-7

50

18-0

42-4

31-4

19-2

52

56-0

28-0

83'2

23-4

54

80-0

14-3

94-4

35-5

56

95-0

76-0

19 '7 16 -7

58

99-0

50-0

66 '5 12 -2

60

85-0

16-0

94-5 4-1

62

59-0

6-2

95 -5 -2

64

26-Q

5-3

48-4

0-2

66

10-0

2-35

19-3

0-07

68

3-2

0-92

6-4 -03 70 0-9 0-3 1-8 o-oi 125 -74

The sum of the ray compositions for the same wave-lengths is 1120. Thus the excess of white is about 9 per cent.

It will be seen that the excess is chiefly in the brighter part of the spectrum, though it seems rather in the green than the yellow.

These calculations entirely agree with the arguments advanced in the earlier part of this paper to show that the light filters for three- colour printing should be entirely different from those used for three- colour projection.