NEW CHEMICAL REACTIONS. 95 
of its protuberance was strong or weak according to the 
position of the prism. The summit also underwent 
striking changes. In one position of the prism it exhibited 
a pale white against a dark background; in the rectangular 
position it was a dark mauve against a light background. 
The red of the Matterhorn changed iu a similar manner; 
but the whole mountain also passed through wonderful 
changes of definition. The air at the time was filled with 
a silvery haze, in which the Matterhorn almost disappeared. 
This could be wholly quenched by the Nicol, and then the 
mountain sprang forth with astonishing solidity and 
detachment from the surrounding air. The changes of 
the Dom were still more wonderful. A vast amount of 
light could be removed from the sky behind it, for it 
occupied the position of maximum polarization. By a 
little practice with the Nicol it was easy to render the ex- 
tinction of the light, or its restoration, almost instan- 
taneous. When the sky was quenched, the four minor 
peaks and buttresses, and the summit of the Dom, to- 
gether with the shoulder of the Alphubel, glowed as if set 
suddenly on fire. This was immediately dimmed by turn- 
ing the Nicol through an angle of 90 degrees. It was not 
the stoppage of the light of the sky behind the mountains 
alone which produced this startling effect; the air between 
them and me was highly opalescent, and the quenching of 
this intermediate glare augmented remarkably the dis- 
tinctness of the mountains. 
On the morning of August 24 similar effects were finely 
shown. At 10 A.M. all three mountains, the Dom, the 
Matterhorn, and the Weisshorn,were powerfully affected 
by the Nicol. But in this instance also, the line drawn to 
the Dorn being very nearly perpendicular to the solar beams, 
the effects on this mountain were most striking. The 
gray summit of the Matterhorn, at the same time, could 
scarcely be distinguished from the opalescent haze around 
it; but when the Nicol Quenched the haze, the summit 
became instantly isolated, and stood out in bold definition. 
It is to be remembered that in the production of these 
effects the only things changed are the sky behind, and the 
luminous haze in front of the mountains; that these are 
changed because the light emitted from the sky and from 
the haze is plane polarized light, and that the light from 
the snows and from the mountains, being sensibly unpolar- 
