and the Intensities of Lights of different Colors. 



The petroleum flame used in these experiments was that of 

 a Belgian burner, giving about 35 candles. The 



daylight was obtained from a window 85 cms - o i 



square ; the lower half of which when viewed M 

 from the screen, was occupied by the snow-clad 

 surface of an opposite hill. The day was very 

 clear, and the sky very slightly tinted with 

 blue. 



The colors of the sides of the ring of the 

 screen are complementary. — I combined the 

 Prussian blue, emerald green, chrome yellow 

 and orange red on a disk on the rotator and 

 found that when the disk was formed of sectors 

 having 60 parts of Prussian blue, 11 of emerald 

 green, 19 of chrome yellow, and 10 of red lead, 

 I obtained a gray which was exactly matched by 

 a central disk formed of 71 parts of dead ivory- ~~^ R ' 

 black and 29 of white cardboard. See fig. 2. % 3. 

 These measures gave the following equation : 



60 Prussian blue \ 

 11 Emerald green \ 



- + 



j 19 Chrome yellow 

 ( 10 Red lead 



Gray 



71 Black 

 29 White 



It is rather difficult to get the exact match on the rotating 

 disk of the hues on the front and back of the card-board ring 

 of the screen on account of the 

 illumination of these surfaces. 

 The rotator must be placed 

 nearer the window than the 

 screen so that it is well illumi- 

 nated. 



The equation shows that the 

 cyan-blue of 60 parts of Prussian 

 blue +11 of emerald green is 

 complementary to an orange yel- 

 1 o w of 19 of chrome yellow 

 + 10 of red lead. The hue of 

 this orange of the lamp side of 

 the ring, as given by the rotator 

 was 50 chrome yellow + 30 red 

 lead + 20 white, which mixture 

 is approximately in the proportion of 19 to 1 0. The corre- 

 spondence of the two experiments is, I suppose, about as near 

 as could be expected from the difficulty of matching the 

 illuminated hues of the ring of the screen. 



The small central disk on the rotator gave a gray of 71 parts 

 of ivory-black + 29 of white cardboard, which matched the 

 gray given by 71 parts of cyan-blue + 29 parts of orange. 



Rg: 2 



