16 



NATURE FOR ITS OWN SAKE 



Spectrum 

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twilight hardly admit of description. All hues, 

 all tints are possible, and nothing is of long 

 duration. The appearance is almost as tran- 

 sient as the aurora, for it is shifting in position, 

 shifting in light and color continually. When 

 there are no clouds, the normal evening sky 

 shows a continuous spectrum, and the order of 

 colors begins with red at the horizon and ex- 

 tends in successive bands through orange, yel- 

 low, green, and finally shades into the blue of 

 the upper sky. These colors are intensified 

 or depressed by atmospheric conditions, and 

 they are complicated by the appearance of 

 clouds, though the order of their appearance 

 even with clouds is usually maintained, the 

 reds being the lowest down and the succession 

 rising through the intermediate colors to blue. 

 The most splendid evening effects are, gen- 

 erally speaking, in the autumn, when with 

 Indian summer there is much heat and dust in 

 the air. Scarlets, carmines, rubies, and burn- 

 ing golds are then apparent. After several 

 days of rain have left a damp, thick atmos- 

 phere, a clearing western sky with fleecy clouds 

 will often show very brilliant yellows in bands, 

 and in between these bands small spaces of 

 malachite green. The winter and the early 



