154 Mr. A. M. Mayer on the Phenomena 



Place the screen, thus formed, in front of a petroleum-lamp 

 and exclude the daylight from the side thus illuminated. 

 The other side of the screen is 

 illuminated by the light of the 

 sky admitted through a distant 

 window. The cardboard ring is 

 thus illuminated on one side only 

 by the lamp, on the other side 

 only by the daylight. The trans- 

 lucent paper transmits the lamp- 

 light to the side facing the window, 

 while it transmits the daylight to 

 the side facing the lamp. On the 

 side of the screen facing the window 

 the cardboard ring appears cyan- 

 blue, while on the side facing the 

 lamp the ring appears orange- 

 yellow. 



Hues of the Sides of the Ring. — 

 An idea of the hues and intensities 

 of these colours, which cause as- 

 tonishment even in those who are 

 experimenters in chromatics, will 

 be given by the description of the 

 following experiments. 



By means of a Bunsen-photoineter disk I adjusted the dis- 

 tance of the lamp from the screen so that I obtained, as nearly 

 as I could judge, equal illumination of the sides of the screen. 

 I then found that the blue was matched in a rotator by a disk 

 having a sector of 60 parts of the circumference of Prussian 

 blue, with a sector of 10 parts of emerald-green and a sector 

 of 30 parts of white cardboard. The blue was that of one of 

 the many coloured disks given me by Professor 0. N. Rood, 

 and was marked " Blue between cyan-blue and the ultra- 

 marine of the physicist, but nearer the latter. Near F and 

 on its more refrangible side. Made with Prussian blue." The 

 blue on this disk appeared as saturated in hue as could be 

 made by the pigment. 



The match of the colour of the side of the ring facing the 

 lamp, L, in fig. 3, was obtained by placing a silvered mirror, 

 M, so that the reflexion of this side of the ring, S, was seen 

 close to the rotator, It. 



The colour of the cardboard ring facing the lamp was 

 matched by the rotation of a disk formed of 50 parts of 

 chrome-yellow, 30 parts of red-lead (red-orange), and 20 parts 

 of white cardboard. Such appears to be the hue of the light 



Fig.l 



