of Simultaneous Contrast- Colour. 



159 



while it is viewed on the side 

 facing the window. The blue 

 sectors thus take successively 

 the places just before occupied 

 by the sectors of orange-yellow, 

 and the effect is to heighten the 

 contrast-colour in such a re- 

 markable manner that the blue 

 sectors by their more intense 

 colour appear separated from 

 the central circle and rim and 

 appear in a plane farther from 

 the eye than the plane of the 

 centre and rim. On the side 

 of the disk illuminated by the 

 lamp the same effects are produced, only they app ear 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- Colours are Inten- 

 sified. — Simultaneous contrast-colours are generally viewed 

 by placing grey or tinted surfaces on coloured grounds, or by 

 the juxtaposition of coloured surfaces. The effects thus pro- 

 duced are of such constant occurrence in the paintings of 

 artists, and in coloured fabrics, that their study is of great 

 interest. The contrast-colours thus produced have generally 

 been studied by simply placing on a coloured ground smaller 

 grey or tinted surfaces and observing these with the unaided 

 eye. This method has been improved by H. Meyer*, who 

 viewed the grey on the coloured ground when both were 

 covered with white transparent paper. 



The mode of observation I have devised for the study of 

 contrast-colours is as follows : — A glass tube of 2*7 centim. in 

 interior diameter and 10 centim. long is coated on the outside 

 with black Japan varnish, so as to have reflexion only from the 

 interior surface of the tube. A ring of 3 centim. in diameter 

 with a central opening of 2 centim. is cut out of grey paper. 

 The grey of this 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 colour. If at the distance of distinct vision 

 we look at the ring through the tube, we shall see the ring- 

 by direct vision enclosing a circle of green and surrounded by 



Pogg. Ann. xcv. p. 170. 



