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 grass 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. I 
scanned the whole of the sky with rny Nicol. Both alone, 
and in conjunction with the selenite, it pronounced the 
