THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



AUGUST 1893. 



XV. Studies of the Phenomena of Simultaneous Contrast- 

 Colour ; and on a Photometer for Measuring the Intensities 

 of Lights of different Colours. By Alfred M. Mayer*. 



IT is often desirable in the study of simultaneous contrast- 

 colours to have large surfaces coloured by contrast, so 

 that we can the better match the colours of these surfaces 

 with rotating coloured 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 com- 

 pared with daylight, or when compared one with another. 

 The result of many experiments 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- 

 Colours of these Lights.— A ring is formed of white card- 

 board by cutting out a central opening of 12 centim. in dia- 

 meter in a disk of 22 centim. in diameter. This ring has a 

 breadth of 5 centim. 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 f 35 centim. 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. 



* Communicated by the Author. 



t Trials with many 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." 



Phil. Mag. S. 5. Vol. 36. No. 219. Aug. 1893. M 



