of Simultaneous Contrast- Colour. 



155 



O L 



of a petroleum-flame when compared, in this 

 manner, with the light of the sun. 



The petroleum-flame used in these experi- 

 ments was that of a Belgian burner, giving 

 about 35 candles. The daylight was obtained 

 from a window 85 centiin. square, the lower 

 half of which, when viewed 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 Colours 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 grey which was exactly 

 matched by a central disk formed of 71 parts of dead ivory- 

 black and 29 of white cardboard (see fig. 2). These measures 

 gave the following equation : — 



Fig. 3, 



I 69 Prussian-blue ) , 1 19 Chrome-yellow [ _ ^ 

 (Emerald-green f ~*~ (Bed-lead | 



. , 71 Black I 

 e ^ 1 29 White f • 



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

 disk of the hues on the front and back of the cardboard ring 

 of the screen on account of 

 the illumination of these sur- 

 faces. The rotator must be 

 placed nearer the window 

 than the screen so that it is 

 well illuminated. 



The equation shows that 

 the cyan-blue of 60 parts of 

 Prussian blue + 11 of emerald- 

 green is complementary to an 

 orange-yellow of 19 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 approxi- 

 mately in the proportion of 19 to 10. The correspondence 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 grey of 7 1 parts 



M2 



fig. 2 



