16 Mayer — Phenomena of Simultaneous Contrast-Color, 



first step and the last, Hering's theory is distinctly a physio- 

 logical theory, and at least holds out for us the promise of be- 

 ing able to push the physiological explanation nearer and 

 nearer home before we are obliged to take refuge in the 

 methods of psychology." 



A Photometer for measuring the intensities of differently 

 colored lights. — It has already been shown that, in certain con- 

 ditions of illumination and in certain directions of sight, a 

 screen formed of perforated cardboard covered with translu- 

 cent paper appears with complementary colors, and that if the 

 screen be in the form of a disk with alternate sectors cut out 

 of it, and is illuminated on one side by daylight and on the 

 other side by lamplight, that the blue of one side of the disk 

 and the orange of the other appear intensified on slowly rotat- 

 ing the disk. On increasing the velocity of rotation the com- 

 plementary colors gradually blend and when the velocity of 

 rotation has banished all flickering light from the disk it 

 appears nearly white. The side facing the daylight has a 

 slight yellowish tint ; the side facing the lamp appears whiter, 

 but is tinted with a feeble bluish hue. 



To study more minutely these phenomena I made a disk 



which could be readily taken 

 apart and mounted with different 

 translucent papers and have at- 

 tached to it disks and rings of 

 various colors. I shall call this 

 disk, the photometer disk. It is 

 made as follows : 



Two disks, 13 cms in diameter, 

 and having eight sectors cut out, 

 as shown in fig. 13, w r as made of 

 thin Bristol board. A circle of 

 2 cms in diameter was left in the 

 center of the disk, from which 

 the cardboard sectors radiate. 

 The border of the disk is a ring 

 of -J cm wide, which was painted 

 olack. Clamps, made of thin hammered brass, held these 

 disks together. 



Between these disks was placed a circle of the same white 

 translucent paper used in the construction of the large con- 

 trast-color screen, fig. 1, and the disks were clamped together 

 with the open sectors of the two disks coinciding in position. 

 A black disk of 8'2 cms in diameter was placed on each side of 

 the photometer disk, thus leaving between it and the black 

 peripheral ring an annular space of 1 9 cm wide, formed of alter- 

 nate spaces of cardboard and of translucent paper. The disk 



Fi*.13. 



