LANDSCAPE COMPOSITION 105 



of light and color, especially out of doors, might help him to think 

 more clearly on the subject. 



We give the name of light to those vibrations of the ether which are Color and 

 within the range of frequency capable of being perceived by the human -^^S^^ 

 eye. There are also ether vibrations faster and slower, but they do not 

 affect our sense of sight. The different frequencies of vibration which 

 we can see produce upon the eye the effect of different hues, ranging 

 from the sensation of violet produced by the fastest visible vibrations 

 to that of deep red produced by the slowest visible vibrations. The 

 greater the wave height of a light of a definite wave length, and so of a 

 definite hue, the greater will be the intensity of the hue. Light all of 

 which has the same wave length will produce upon the eye the effect 

 of "pure color," that is, it will be all of the same hue. The light of 

 the sun is a mixed light, containing practically an infinite gradation of 

 wave lengths corresponding to the gradations of frequency of vibration 

 within the limits which we have already mentioned. Red light is the 

 least refrangible by a prism ; violet light is the most so. Placing a 

 prism in the path of a beam of sunlight will therefore separate this 

 mixed light into its component hues. These are practically infinite in 

 number. For purposes of convenience, however, men have been ac- 

 customed to name only certain of these hues and to consider the others 

 as intermediates between them. The "colors of the rainbow" are 

 commonly spoken of as red, orange, yellow, green, blue, and violet. 



When sunlight falls upon an object, it may be sent back again un- 

 changed except in direction, as when it is reflected from the surface of 

 a perfect mirror; or it may be dispersed in many directions from a 

 surface like frosted silver or white paper ; or it may be broken up into 

 its constituent colors, as by a prism ; or some of its constituent colors 

 may be absorbed and the others only allowed to go on, as by a sheet of 

 colored glass. The color of ordinary surfaces, a wash of water-color, 

 for Instance, Is due to this last effect. If a surface Is absolutely Imper- 

 vious to light. It reflects the light unchanged In color. If It is at all 

 pervious, like paper or cloth or paint, the light penetrates and then Is 

 reflected, at different depths below the surface. And In going through 

 the substance near the surface of any "colored" material, certain defi- 

 nite wave lengths of light are absorbed, and only the others allowed 



