io6 LANDSCAPE DESIGN 



to escape. In these ways different objects have different colors,* that 

 is, they send to the eye light of certain wave lengths only, which pro- 

 duce the sensations of certain colors. By what physical machinery the 

 eye perceives these colors we do not yet know with certainty. It 

 seems to be determined, however, that our primary color sensations 

 are red, green, violet-blue. At least it is the fact that the effect of any 

 other colors of the spectrum may be produced upon the eye by an 

 appropriate mixture of beams of light of these colors thrown upon a 

 white surface. Red and green so mixed make yellow ; yellow and 

 violet-blue make white. 



The effects of pigment colors are quite different. With them, the 

 accepted primaries are red, yellow, and blue. Appropriate mixtures of 

 pigments of these colors will produce any other color. Red and yellow 

 make orange ; orange and blue make black. The reason for this dif- 

 ference between pigment and spectral color lies in the physical fact 

 which we have already pointed out, that the color of a pigment is 

 due to its having absorbed all the light which falls upon it except that 

 to which it owes its color. The light sent back from a surface on 

 which there are two pigments, therefore, is only such light as is absorbed 

 by neither. The greater the number of different translucent pigments 

 which are applied to a surface, therefore, the darker that surface be- 

 comes. On the other hand, the greater the number of different colored 

 lights which shine upon a surface, the brighter it becomes. One is a 

 subtraction, the other an addition of light. 



Hue, Intensity, In considering color composition, we are concerned not much with 



and Value in co lored lights as such, but rather with colored surfaces seen close to- 



sition gether or in immediate succession. Each surface will have its own effect 



in the composition according as the light which is sent out from it is in 



any way different from that sent out from the adjoining surfaces. 



These differences may be of three kinds : differences of hue, differences 



in intensity, or richness of the hue, and differences of value, that is, 



differences in the strength of light-effect upon the eye. This value is 



relatively high in the case of white surfaces, because they send back 



nearly all the light that they receive. It is high in the case of surfaces 



* The term color or local color of an object is commonly taken to mean the 

 color that an object shows when illumined by white light. 



