NEW CHEMICAL REACTIONS. 97 



ored 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 mountain, at nine miles; so that a 

 body of air of this thickness can, under favorable circum- 

 stances, 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 superfi- 

 cial 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 land- 

 scape, 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 briliancy is 

 conferred upon the woods and meadows by this superfi- 

 cially reflected light. Under certain circumstances, it may 

 be quenched by^a NicoFs prism, and we then obtain the true 

 color of the gra'ss and foliage. Trees and meadows, thus 

 regarded, exhibit a richness and softness of tint which they 

 never show as long as the superficial light is permitted to 

 mingle with the true interior emission. The needles of 

 the pines show this effect very well, large-leaved trees still 

 better; while a glimmering field of maize exhibits the most 

 extraordinary variations when looked at through the rotat- 

 ing Nicol. 



Thoughts and questions like those here referred to took 

 me, in August, 1869, to the top of the Aletschhorn. The 

 effects described in the foregoing paragraphs were for the 

 most part reproduced on the summit of the mountain. J 

 scanned the whole of the sky wich my Nicol. Both alone, 

 and in conjunction with the selenite, it pronounced the 



