Krieger: Ridgway’s New Color-Book 
31 
PI .II ii k = V\.IIgj 
PI. II ii m = PI. II 9 m 
PI. Ill 15 m = PI. Ill I3.m (almost) 
PI. IV 23 /=P 1 . IV 21 f 
PI. IV 23 k = V\. IV 20 k 
PI. XXXIX 5'" rf = Pl. XXXIX T" c 
PI. XL 21"' / = P 1 . XXXIX 14'" e 
If one desired, tests might be carried on with sheets represent- 
ing all of the colors of the spectrum, but in each test it would 
be found that the color tested had undergone a change of aspect, 
the degree and direction depending upon the color in juxta- 
position. Indeed, by the use of a set of differently colored ex- 
cluders a large number of new tones, each one a standard, might 
be obtained ; but unfortunately, it would not be possible to turn 
these new tones to account, as the excluder, applied to the color 
to be compared, would itself have to be excluded, and without 
this important factor, comparison would be reduced to the hit-or- 
miss method we are endeavoring to eliminate. 
In view of the discomforting deductions which cannot but be 
drawn from these tests, one is bound to accept the conclusion, 
long ago arrived at by artists, physicists, and others, that colors, 
as perceived by the human eye, are of an illusive nature and not 
fixed in the way generally supposed. This conclusion accepted, 
it behooves the devotees of the descriptive sciences to agree upon 
some means by the aid of which this source of error may be 
controlled. 
The writer would suggest the issuing of two excluders (in 
supplementary form), each measuring 15.5 cm. by 29 cm., and 
colored to match the mounts in Color Standards. In the center 
of each, there should be an aperture of the size of the color 
squares. In addition, a note might be included enjoining the 
use of the excluders when accurate records are to be made. The 
note ought to state further, that users of the book, when referring 
to a tone, should indicate whether the excluders were employed. 
The abbreviation “ -(- std. excl.” (plus standard excluders), added 
to a symbol, would suffice to show whether the observer had 
availed himself of this necessary adjunct in the work of color dis- 
crimination. 
U. S. Department of Agriculture. 
