and the Intensities of Lights of different Cohort 



heighten the contrast-color in such a remarkable manner that 

 the blue sectors by their more intense color appear separated 

 from the rim and central circle appear in a plane farther from 

 the eye than the plane of the center and rim. On the side of 

 the disk illuminated by the lamp the same effects are produced, 

 only they appear more marked. A change will also be observed 

 in the hue of the advancing and following edges of the sectors, 

 on both sides of the disk ; the advancing edges appearing 

 more saturated in hue than the following edges. 



A mode of observation by which contrast-colors are intensi- 

 fied. — Simultaneous contrast-colors are generally viewed by 

 placing gray or tinted surfaces on colored grounds, or by the 

 juxtaposition of colored surfaces. The effects thus produced 

 are of such constant occurrence in the paintings of artists, and 

 in colored fabrics, that their study is of great interest. The 

 contrast-colors thus produced have generally been studied by 

 simply placing on a colored ground smaller gray or tinted sur- 

 faces and observing these with the unaided eye. This method 

 has been improved by H. Meyer* who viewed the gray on the 

 colored ground when both were covered with white transparent 

 paper. 



The mode of observation I have devised for the study of 

 contrast-colors is as follows. A glass tube of 2-7 cms in interior 

 diameter and 10 cms long is coated on the outside with black 

 Japan varnish, so as to have reflection only from the interior 

 surface of the tube. A ring of 3 cms in diameter with a cen- 



The gray of this 



tral opeuing of 2 cms is cut out of gray paper 

 ring was matched on the rotator 

 by a disk having 57 parts of 

 ivory-black and 43 parts of white 

 Bristol board. This ring, placed 

 on a surface of emerald green 

 appears of a rose color. If at 

 the distance of distinct vision 

 we look at the ring through the 

 tube we shall see the ring by 

 direct vision inclosing a circle of 

 green and surrounded by a ring 

 of emerald green, and this in- 

 closed by a rose colored ring, 

 produced by reflection from the 

 interior of the tube, and sur- 

 rounding this ring is another of emerald green, as shown in 

 fig. 9 ; in which fi and R are the red rings and G, G, and G, 

 the circle and the two rings of emerald green. 



* Pogg. Ann., xcv, 170. 



