Composition of Tones.                     2.i

table showing percentage of white and black,

respectively,  in   each  tone  of  the

tone or luminosity scales.

All of the vertical scales in the original Plates of
this work (the scale of carbon grays alone excepted)
contain the following percentages by color-wheel meas¬
urement :
 

(White)

(g)
f

(e)

d
(c)

b

(a)

(Full Color;

(h)

i

(J)
k

(1)

m

(n)

(Black)
 

Percentages.
 

White.

100

70
45
32

22.5
15
9.5
5
 

Color.     I     Black.
 

30
55
68
77.
85
90.
95
100
64
55
41
29.
20
12.
6
 

26
45
59
70. i

80
87.^
94
100
 

One of the most serious diflSculties encountered in the
preparation of the Plates of this work was the apparent
impracticability of reproducing satisfactory shades of
pure colors. This originated in the fact that there seems
to be no substance (pigment, dye, or fabric) which repre¬
sents a true black, all reflecting more or less of white
light, and consequently producing shades which are dull