AMERICAN JOURNAL OF SCIENCE. 
[THIRD SERIES.] 
© & Oo --- 
Art. 1X.—On the effects produced by mixing White with Colored 
Lnght ; by Prof. O. N. Roop, of Columbia College. 
IT was noticed several years ago that when white light was 
mixed by the method of rotating discs with light of an ultra- 
marine (artificial) hue, the result was not what one would 
naturally have expected, viz: instead of obtaining a lighter or 
paler tint of violet-blue the color inclined decidedly toward 
violet, passing, when much white was added, into a pale violet 
hue. ‘Two attempts have been made to account for this curi- 
ous fact: Briicke supposes that the light which we call white 
is really to a considerable extent red, and that the mixture of 
this reddish white light with the blue causes it to change to 
violet. Aubert, on the other hand, following a suggestion of 
Helmholtz, reaches the conclusion that violet is really only a 
lighter shade of ultramarine-blue. He starts with the assump- 
tion that we obtain our idea of blue mixed with white from 
the sky, which, according to him, is of a greenish-blue color. We 
then apply, as he thinks, this idea to the case of a blue which 
1s not greenish, namely, to ultramarine-blue, and are surprised 
to find that the result is different. 
Am. Jour. eon SEeRIzs, Vou. XX, No. 116.—Ave., 1880, 
