178 PROFESSOR WARTMANN ON DALTONISM, 
sults that the appreciation of the equality of intensity of two com- 
plementary colours is not the same with him as with us,—a con- 
sequence which I had previously deduced from the experiments 
made with the coloured glasses numbered 6, 7, 14 and 18 (‘Ta- 
ble I.). The very great number of trials by which D*** was 
examined show, moreover, with extreme probability, that he does 
not perceive differences between colours which appear to us 
identical. M. Seebeck has come to the same conclusion*. 
D *** assured us moreover that he found a total and abrupt 
difference between the colours of the twenty-fifth and twenty- 
sixth observations, circle right,—colours which pass at once 
from the finest red to very rich deep blue. To our eye the 
distinction was far from being so marked, which shows that his 
visual organ was unable to perceive the different mixtures of 
the red which accompany the blue to make it pass into purplish 
violet,—a red which becomes so evident when two or several 
plates of cobalt blue glass are superposed and are placed between 
the eye and an object in a good light. This precise circum- 
scription of the constitutive domain of a colour is a fact which 
seems to me new and worthy of being remarked. 
I shall notice, lastly, another striking observation. On the 
10th of December, 1839, near 2 o’clock P.M., we were engaged 
in repeating the preceding experiments with the same apparatus 
similarly arranged. The sky was slightly overcast, and the in- 
dications of the daltonian corresponded exactly to those of which 
I have above given the abstract. Suddenly the sun shone out, 
and cast much more light upon the apparatus and the observer. 
The latter immediately told me that the colours assumed a dif- 
ferent tint to his sight, and all reddened in a sensible manner. 
He called red that which he before named green and ill-defined 
blue. For myself, I could see no other change in the colours 
than an increase of their brilliancy and strength. I also con- 
sider it very probable that his impossibility of determining the 
shades of the plates marked 27, 1, 20, 35, 34, 3 and 4, proceeded 
from the obscurity of their tint. Perhaps he would have assigned 
to them a particular one if a brighter light than that of the sun 
had illuminated them, or if their thickness had given passage to 
a greater proportion of the rays of that luminaryt. 
* Mem. cited, p. 219. 
+ M. Seebeck thinks that when two colours are different, the eye of the dal- 
tonian may make him perceive that difference, but never greater than it ap- 
pears to a normal eye.—(Mem. cit. p. 179, note.) 
