# Bauhaus-Universität Weimar

### Volltext Chapter XXII. Method of deciding the Precise Amount of Color-Blindness by Professor Holmgren´s Chromatoskiameter, or Color-Sense Tester. - Professor Donder´s Method of determining Quantitative Color-Perception

Titel:
Chapter XXII. Method of deciding the Precise Amount of Color-Blindness by Professor Holmgren´s Chromatoskiameter, or Color-Sense Tester. - Professor Donder´s Method of determining Quantitative Color-Perception
Person:
Jeffries, Benjamin Joy
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit38626/5/
```ITS DANGERS AND ITS DETECTION. 245
a disturbance of the color-sense in the individual case,
whereby the sensibility for one of the primary colors, inde¬
pendently of its real value, is reduced in comparison with
sensibility of the other two. This explains a large number
of the cases tested with this instrument. Hence it is of
value to test each case with two complementary colored
glasses. The difference between the distances of the mirror
for each expresses the value of the defect to be ascertained.
“ The absolute distance of the mirror has of course only
a relative value, does not immediately represent the intensity
of the illumination of the shadow ; that is, the sensitiveness
of the eye examined. This, however, we can deduce from
a formula I will here give. Taking the abovp figures as
representing the average distance of the mirror, the sensi¬
tiveness of the normal eye (the intensity of the lamp being
unity)
For the red light = 0.115.
For the green light = 0.137.
The average sensitiveness of the red-blind
For red light = 0.048.
The average sensitiveness of the green-blind
For green light = 0.088.
Or, if we regard the normal color-sense as a measure for
the sensitiveness,
Normal color-sense = 1.00.
Red-blindness = 0.42 (R.).
Green-blindness = 0.64 (Gr.).
By the value gained from the distance of the mirror, applied
to normal color-sense, we may calculate the absorptive power
of the glass. The absorption by the glass, expressed as loss
of light, is thus : —
For the red glass = 42.5 centimetres.
For the green glass = 43.1 centimetres.
“Thus, by using a larger number of suitable colored
glasses, we can study not only the normal chromatic sense,
but also the various forms of color-blindness. The princi¬
ple of the method does not, however, restrict us in practice
to colored shadows ; but it may be extended to any colored
```

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