210 



TRANSACTIONS OF THE 



[mar. 1, 



to the large green disk and the measured difference in luminosity 

 was 4.4 per cent. This combination was rotated on the machine 

 and the flickering inside was found to be more violent than the 



Fig. IV. 



flickering on the outside. We may, therefore, conclude that 

 if the difference in color on the outside causes any flickering 

 such flickering cannot amount to as much as the flickering due 

 to a difference in luminosity of 4.4 per cent. — 1.2 per cent. = 3.2 

 per cent. 



To find out if a more precise conclusion could not be drawn, 

 the following experiment was tried. From m^' set of colored 

 disks I selected a large yellow disk, Yellow 1 (See Fig. V.), and 



Fig. V. 



a large blue disk, Blue 2, such that their measured difference in 

 luminosity was 2.1 per cent. A small yellow disk, Yellow 2, 

 was found such that the difference between the luminosity of it 

 and that of Yellow 1. was 2.2 per cent. These three disks were 

 combined as shown in Fig. Y, rotated on the axis of the machine 

 and the inside and outside flickers compared. We would ex- 

 pect the inside flicker to be slightly more violent than the out- 

 side flicker. It was found, however, that the outside flicker was 



