THE SKY OF THE ALPS. 271 



These points were further elucidated by the deportment 

 of the selenite plate, with which the readers of the fore- 

 going discourse are already acquainted. On some of the 

 sunny days of August the haze in the valley of the Rhone, 

 as looked at from the Bel Alp, was very remarkable. Tow- 

 ward evening the sky above the mountains opposite to my 

 place of observation yielded a series of the most splendidly- 

 colored iris-rings ; but on lowering the selenite until it had 

 the darkness of the pines at the opposite side of the Rhone 

 valley, instead of the darkness of space as a background, 

 the colors were not much diminished in brilliancy. I should 

 estimate the distance across the valley, as the crow flies, to 

 the opposite mountains, at nine miles ; so that a body of 

 air nine miles thick 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 part comes purely from 

 superficial reflection, and this light is always of the same 

 color as that which falls upon the landscape ; the other 

 part comes to 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 partially ejected by internal reflec- 

 tion ; each distinct substance absorbing and reflecting the 

 light in accordance with the laws of its own molecular con- 

 stitution. 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 proper to the 

 pine, never comes to us alone, but is always mingled with 

 an amount of really foreign light derived from superficial 

 reflection. A certain hard brilliancy is conferred upon the 

 woods and meadows by this superficially-reflected light. 



