96 FRAGMENTS OF SCIENCE. 



ized, is not directly affected by the Nicol. It will also be 

 understood that it is not the interposition of the hazes?i 

 opaque body that renders the mountains indistinct, but 

 that it is the light of the haze which dims and bewilders 

 the eye, and thus weakens the definition of objects seen 

 through it. 



The results have a direct bearing upon what artists call 

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

 Blanc, or from the lower elevation, at the serried crowd of 

 peaks, especially if the mountains be darkly colored cov- 

 ered 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 

 distant 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 oppo- 

 site 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 the haze may be 

 quenched, and then the Massa ridge arid the mountains be- 

 yond 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 must be withdrawn from the mountains and from the trees 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 

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



These points were further elucidated by the deportment 

 of the selenite plate, with which the readers of the forego- 

 ing pages are so well acquainted. On some of the sunny 

 days of August the haze in the valley of the Rhone, as 

 looked at from the Bel Alp, was very remarkable. Toward 

 evening the sky above the mountains opposite to my place 

 of observation yielded a series of the most splendidly col- 



