156 Mr. A. M. Mayer on the Phenomena 



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

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

 Calling the intensity of the orange 100, we have 100 x 29 = 71 1, 

 which gives for I (the intensity of the cyan-blue) only 40'8 

 per cent, of that of the orange. 



The orange-yellow of the side of the ring ^^^P^- 



facing the lamp and of the side of the trans- M 

 lucent paper facing the daylight is comple- 

 mentary to the cyan-blue of the side of the 

 ring facing the daylight and of the side of — — ^s 



the translucent paper facing the lamp. 



In fig. 4, L is the lamp ; S the screen, 

 which in this experiment is deprived of the 

 border of translucent paper ; W , the window ; 

 M, a silvered mirror which reflects the back ^„c.s. 



of the screen to the eye which looks through 

 an achromatized double refracting calc-spar 

 prism at C.S., and sees two images of the 

 side of the screen reflected from the mirror w 



and two images of the side of the screen . 



facing the window. By suitably inclining x £" * 



and rotating the calc-spar prism, these images 

 may be brought into the positions shown in fig. 5, in which 

 A represents one of the images of the side of the screen 

 facing the window ; B, the other image of the same ; is one 

 of the images of the side of the screen facing the lamp and 

 seen by reflexion from the mirror. 



The overlapping of these images, when the illumination is 

 properly adjusted, gives the following results, as shown by 

 the letters in fig. 5, where B stands for cyan-blue, Y for 



Fig, 5. 



orange-yellow, and W for white. The translucent paper Y 

 of B overlaps the ring of A and gives white, and the blue of 

 the ring of B overlaps Y of the translucent paper of A and 

 gives white. In the same manner the orange-yellow of the 

 cardboard ring of C overlaps the blue of the ring of A and 

 gives white, Where the ring of C overlaps the translucent 



