Explanation of Plates. 
5 
by the middle horizontal line of color-squares on Plates 
I-XII (together with an equal number of intermediates 
represented by blank spaces), requiring a separate curve 
and consequently different relative proportions of the 
two component colors for each series of hues—that is, 
the series from red to orange, orange to yellow, yellow 
to green, green to blue, blue to violet, and violet to red, 
respectively; but the progressive increments of white in 
the scales of tints, black in those of shades, and neutral 
gray in the several series of broken colors are exactly 
the same in every case. The first series of Plates (I-XII) 
shows the pure, full spectrum colors and intermediate 
hues (middle horizontal line, nos. 1-72),* each with its 
vertical scale of tints (upward, a-g) and shades (down¬ 
ward, .k-n), the increments of white for the tints being 
9.5, 22.5, and 45 per cent., respectively, those of black 
in the shades being 45, 70.5, and 87.5 percent. The 
remaining Plates show these same thirty-six colors or 
hues in exactly the same order and similarly modified 
(vertically) by precisely the same progressive incre¬ 
ments of white (upward) and black (downward), but 
all the colors are dulled by admixture of neutral gray; 
the first series (l'-72\ Plates XIII-XXVI) containing 32 
per cent, of neutral gray, the second (l"-72", Plates 
XXVII-XXXVIII) 58 per cent., the third (l"'-72'", 
Plates XXXIX-XLIV) 77 percent., and the fourth (l""- 
72"", Plates XLV-L) 90 per cent. The last three 
Plates (LI-EM) show the six spectrum colorst (also 
purple, the intermediate between violet and red) still 
further dulled by admixture of 95.5 per cent, of neutral 
*The number is doubled so that every other one represents an intermediate hue 
not shown in color. 
fOwing to the circumstance that spectrum orange does not, at least when mixed 
with gray, fairly represent a medium hue between red and orange, being much 
nearer the former, a hue much near to yellow (yellow-orange, No. 15) has been 
selected. 
