Page:Proceedings of the Royal Society of London Vol 69.djvu/64

56 Per cent.

Average

Per cent.

Product

for red

Scale.

aperture for yellow

White.

Per cent.

for pink ink.

of per- centages.

ink from experi-

ink.

ment.

10

78-5

82-0

95-7

76-7

73-3

75-7

15

79-0

85-0

93-0

21-9

20-4

20-3

20

79-5

86-5

92-5

6-37

5-9

4-5

25

77-0

86-2

88-5

4-4

3-9

5-7

30

67-7

83-5

80-0

4-7

3-76

5-8

35

34-0

76-5

44-5

9-0

4-0

6-3

40

15-0

69-5

21 -fi

16-2

3-5

7-4

45

7-7

fi4-4

11 -94

23-0

2-75

7-1

50

6-0

57 '3 10 -46

33-4

3-5

6-2

55

4-5

50-5 8'9

46-6

4-16

6-1

In the above table the column headed " Average aperture for yellow ink " gives, for each spectrum colour, the aperture of the sector which made the light reflected from the white patch equally bright with that reflected from the patch printed with the yellow ink. The next column, headed " White," gives the aperture of the sector which made the two patches equal when both were white. This column would have been constant but for the polarisation by reflection at the surface of the refracting prism already referred to. From these two columns the proportion of the light reflected by the ink as compared with that reflected by white paper can be calculated. The result appears in the column headed " Per cent."

In the same way the percentage light reflected by the pink and the red patches were found, and are entered in the fifth and seventh columns. In the sixth column I have calculated the light which should be reflected from a paper printed with both the yellow and the pink inks. The agreement is very fair. The actual red reflects more in all the darker parts than calculated. This may be due to the yellow not being quite so heavily printed, but it is more probably because the pink ink, which was uppermost, was not quite transparent, and some light was reflected directly from it instead of from the white paper beneath. Such light would not suffer by the absorption of the yellow ink.

The " red " resulting from these printings has a very orange hue, as was to be expected.

A yellow ink by Mander, No. 226 (Curve No. 25), was less heavily printed than those previously examimed, and therefore seems better in the green and blue green, but the absorption in the violet suffers in consequence.

A pink ink by Mander, No. 0227 (Curve No. 26), comes up fairly in the violet, but is not opaque enough in the green.