270 FRAGMENTS OF SCIENCE. 



Nicol. It will also be understood that it is not the interposi- 

 tion of the haze as an opaque body that renders the moun- 

 tains indistinct, but that it is the light of the haze which 

 dims and bewilders the eye, and thus weakens the defini- 

 tion of objects seen through it. 



The results have a direct bearing upon what artists call 

 " aerial perspective." As we look from the summit of the 

 Aletschhorn, or from a lower elevation, at the serried crowd 

 of peaks, especially if the mountains be darkly colored — 

 covered with pines, for example — every peak and ridge is 

 separated from the mountains behind it by a thin blue haze 

 which renders the relations of the mountains as to distance 

 unmistakable. When this haze is regarded through the 

 Nicol perpendicular to the sun's rays, it is in many cases 

 wholly quenched, because the light which it emits in this 

 direction is wholly polarized. When this happens, aerial 

 perspective is abolished, and mountains very differently dis- 

 tant appear to rise in the same vertical plane. Close to the 

 Bel Alp, for instance, is the gorge of the Massa, and beyond 

 the gorge is a high ridge darkened by pines. This ridge 

 may be projected upon the dark slopes at the opposite side 

 of the Rhone valley, and between both we have the blue 

 haze referred to, throwing the distant mountains far away. 

 But at certain hours of the day this haze may be quenched, 

 and then the Massa ridge and the mountains beyond the 

 Rhone seem almost equally distant from the eye. The one 

 appears, as it were, a vertical continuation of the other. 

 The haze varies with the temperature and humidity of the 

 atmosphere. At certain times and places it is almost as 

 blue as the sky itself; but to see its color, the attention 

 must be withdrawn from the mountains and from the trees 

 which cover them. In point of fact, the haze is a piece of 

 more or less perfect sky ; it is produced in the same man- 

 ner, and is subject to the same laws, as the firmament it- 

 self. We live in the sky, not under it. 



