Bauhaus-Universität Weimar

Titel:
Chapter XIX. Holmgren's Method of Testing.- Examination and Diagnosis
Person:
Jeffries, Benjamin Joy
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit38628/14/
ITS DANGERS AND ITS DETECTION. 209 
color-blind avoids detection with more difficulty, and the 
diagnosis hence is more readily made, the greater the num¬ 
ber of the various colors. The normal-eyed readily selects 
the right ones from the mass; whilst the color-blind, al¬ 
though the right ones are directly before him, picks out the 
wrong ones, thereby disclosing the character of his defect. 
Therefore the greater the number of colors the better, of 
course, within certain limits. 
“ What color shall we take for our sample ? This is of 
importance; for we must of course decide on some one 
color. Experience, as well as the Young-Helmholtz theory, 
teaches us that more than one color may serve as the sample 
in searching for a sure and definite characteristic of defec¬ 
tive chromatic sensation. All colors do not, however, meet 
this equally well : hence it is worth while to establish cer¬ 
tain rules as to a correct choice. 
“ The faculty possessed by the eye of distinguishing colors, 
and that of defining the degrees of light and color (of 
“saturation”) are relatively very different ; but these spe¬ 
cial faculties have this in common, that they have their 
maximum activity in a certain intermediary region of abso¬ 
lute intensity of light, and their minimum at the two limits 
of this region. Just as we experience the most difficulty in 
distinguishing between the shades of intensity of light by 
a very feeble or very strong illumination, so it is difficult for 
us to distinguish colors slightly or strongly luminous, or the 
deepest and the lightest. It is therefore necessary to select 
as a suitable color for discovering a feeble chromatic sense 
either the lightest or darkest shades. The well-defined 
kinds and degrees of a defective chromatic sense confound 
only colors of mean intensity. But in this case, also, it is a 
question what tones of color to choose. For my choice I 
have been guided by the Young-Helmholtz theory, and for 
the reason that I have proposed my method in support and 
proof of that theory. As a fact the examination of thou¬ 
sands of persons has convinced me of the excellence of my 
choice. I have selected, to determine whether the chromat¬ 
ic sense is or is not defective, a light green (dark green may 
be also used), because green, according to the theory, is the 
whitest of the colors of the spectrum, and consequently is 
most easily confused with gray. For the diagnosis of the
        

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