126 FRAGMENTS OF SCIENCE. 



Looking at the Weisshorn through the Nicol, the 

 glow of its protuberance was strong or weak according 

 to the position of the prism. The summit also under- 

 went 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 

 in 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 polarisation. By a little practice 

 with the Nicol it was easy to render the extinction of 

 the light, or its restoration, almost instantaneous. 

 When the sky was quenched, the four minor peaks and 

 buttresses, and the summit of the Dom, together with 

 the shoulder of the Alphubel, glowed as if set suddenly 

 on fire. This was immediately dimmed by turning the 

 Nicol through an angle of 90. 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 quench- 

 ing of this intermediate glare augmented remarkably the 

 distinctness of the mountains. 



On the morning of August 24 similar effects were 

 finely shown. At 10 A.M. all three mo an tains, the Dom, 

 the Matterhorn, and the Weisshorn, were powerfully 

 affected by the Nicol. But in this instance also, the 

 line drawn to the Dom being very nearly perpendicular 

 to ths solar beams, the effects on this mountain were 



