Bauhaus-Universität Weimar

Titel:
Helmholtz's treatise on physiological optics. Volume 2. Edited by James P. C. Southall. Translated from the 3rd German edition
Person:
Helmholtz, Hermann von
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39650/431/
418 
The Sensations of Vision 
[350, 351. K. 
One of the methods used by Brücke1 consisted in mixing small 
amounts of different greys with the colour to be tested. If a small 
piece of grey paper is placed on a coloured disc so as to make a ring of 
the right width when the disc is set in rotation, it can be decided with 
a comparative degree of certainty whether the ring is brighter or darker 
than the rest of the disc ; that is, whether the grey is brighter or darker 
than the coloured paper. Fundamentally, this procedure is also a 
direct comparison of the luminosity of unlike colours (which differ also 
in saturation). There is the advantage, however, of being able to com¬ 
pare two colours of the same hue that do not differ much in saturation. 
Lastly it will be recalled that Fraunhofer tried to compare the 
luminosity of light of different colours directly by their subjective 
impression, the colours being visible. This method was subsequently 
undertaken again by König2 on a rather bigger scale. His results on 
five normal subjects are given in the following table. 
Wave-length 
Luminosity for Observer 
w 
I 
II 
III 
IV 
V 
670 
0.855 
1.120 
— 
— 
— 
650 
2.381 
2.137 
1.15 
— 
0.64 
625 
3.460 
3.413 
2.06 
1.10 
1.24 
605 
3.650 
3.247 
2.56 
1.66 
1.56 
590 
3.030 
2.645 
2.38 
2.05 
1.58 
575 
2.358 
1.923 
2.00 
2.08 
1.56 
555 
1.695 
1.389 
1.50 
1.65 
1.36 
535 
1 
1 
1 
1 
1 
520 
0.554 
0.553 
•—- 
— 
— 
505 
0.224 
0.250 
— 
— 
— 
490 
0.0994 
0.092 
— 
— 
_ 
Accordingly, in approximate agreement with the peripheral values 
and flicker values and also with the minimum-field luminosities, the 
maximum luminosity, on the average anyhow, is on the red side of the 
sodium line. The results for the different subjects, it is true, vary a 
good deal, especially too in the position of this maximum. Incidentally, 
these tests have been shown to be quite uncertain. The setting of two 
unlike colours at equal luminosity is very variable and often also seems 
to be somewhat arbitrary. And hence it is difficult too to decide 
whether the individual differences exceed the degrees of uncertainties 
and fluctuations of this nature. 
Some of the investigations referred to above have been extended to 
a larger number of persons, normal and anomalous. These results 
must now be briefly considered, as they are of some theoretical interest. 
1 Pflügers Archiv XCVIII S. 90. 
2 Helmholtz Festschrift. 1891. S. 350.
        

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