NATURE'S COLOR. 225 



JSTow, if we turn down the red light the green 

 shadow disappears, or if we turn down the green 

 light the red shadow disappears. So we discover the 

 fact that while the two lights are turned up each 

 throws its color in the shadow produced by the other. 

 Again, if we light a white-shaded lamp in the day- 

 time (it should be a cloudless day), and place it on 

 a table covered with a white cloth in a room where 

 the light is admitted through but one window, the 

 shadow of a napkin ring on the cloth cast by the 

 lamplight will appear quite blue. In this instance 

 we have discovered that the daylight, more or less 

 influenced by the reflected blue of the sky, casts a 

 blue light in the shadow thrown by the lamplight. 



Now our blue shadows out of doors are thorough- 

 ly accounted for ; the intense blue sky throws a blue 

 light in every shadow cast by the sun. It is also the 

 fact that the purple of distant mountains is partially 

 due to the blue of the sky above. The poet Whit- 

 tier more than once has alluded to " the purple of 

 mountain sunsets." The word purple, however, but 

 vaguely describes the roseate hues cast upon the 

 blue mountain by the setting sun. If we will turn 

 our head upside down again and study the sunset 

 glow on the far-away hills, we will see there nearly 

 every color related to purple, but hardly purple it- 

 self ; the summits of the rocky hills are bathed in a 

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