THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Aet. I. — Studies of the phenomena of Simultaneous Con- 

 trast-Color ; and on a Photometer for measuring the inten- 

 sities of Lights of different Colors / by Alfred M. Mayer. 



It is often desirable in the study of simultaneous contrast- 

 colors to have large surfaces colored by contrast, so that we 

 can the better match the colors of these surfaces with rotating 

 colored disks and thus arrive at quantitative statements of 

 their hues. This is especially desirable in ascertaining the 

 hues of the light of flames, of the Welsbach incandescent lamp 

 and of the arc electric light when compared with daylight, or, 

 when compared one with another. The result of many experi- 

 ments is the apparatus described in the following section and 

 which is useful for this purpose. 



Screen for ascertaining the hues of lights and the contrast- 

 colors of these lights. — A ring is formed of white card-board by 

 cutting out a central opening of 12 cms in diameter in a disk of 

 22 cm3 in diameter. This ring has a breadth of 5 cms . Another 

 ring is made similar to this one, except that it has four narrow 

 radial arms to support a disk of thin translucent white paper, * 

 35 cms in diameter. This paper disk is placed between the 

 rings, which are then fastened together and screwed to a thin 

 rod, on a stand, as shown in fig. 1. 



* Trials with rnany kinds of paper showed that a white linen tracing-paper was 

 the best. It is not possible to describe this so that one may be sure of selecting 

 a similar paper. It was obtained of Keuffel and Esser, Fulton St., N\ Y., and 

 sold as "No. 202 Alba tracing paper." 



Am. Jour. Sci.— Third Series, Yol. XLYI, No. 271.— July, 1893. 



1 



