THE SKY OF THE ALPS 137 



able. Toward evening the sky above the mountains op- 

 posite to my place of observation yielded a series of the 

 most splendidly-colored iris-rings ; but on lowering the sel- 

 enite until it had the darkness of the pines at the oppo- 

 site side of the Rhone valley, instead of the darkness of 

 space, as a background, the colors were not much dimin- 

 ished in brilliancy. I should estimate the distance across 

 the valley, as the crow flies, to the opposite mountain, 

 at nine miles; so that a body of air of this thickness can, 

 under favorable circumstances, produce chromatic effects 

 of polarization almost as vivid as those produced by the 

 sky itself. 



Again: the light of a landscape, as of most other things, 

 consists of two parts; the one, coming purely from super- 

 ficial reflection, is always of the same color as the light 

 which falls upon the landscape; the other part reaches us 

 from a certain depth within the objects which compose the 

 landscape, and it is this portion of the total light which 

 gives these objects their distinctive colors. The white 

 light of the sun enters all substances to a certain depth, 

 and is partly ejected by internal reflection; each distinct 

 substance absorbing and reflecting the light, in accordance 

 with the laws of its own molecular constitution. Thus the 

 solar light is sifted by the landscape, which appears in 

 such colors and variations of color as, after the sifting 

 process, reach the observer's eye. Thus the bright green 

 of grass, or the darker color of the pine, never comes to 

 us alone, but is always mingled with an amount of light 

 derived from superficial reflection. A certain hard bril- 

 liancy is conferred upon the woods and meadows by this 

 superficially-reflected light. Under certain circumstances, 

 it may be quenched by a Nicol's prism, and we then ob- 



