128 FKAGMENTS OF SCIENCE. 



we have the blue haze referred to, throwing the dis- 

 tant mountains far away. But at certain hours of the 

 day the haze may be quenched, and then the Massa 

 ridge and the mountains beyond the Ehone 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 atmo- 

 sphere. At certain times and places it is almost as 

 blue as the sky itself; but to see its colour, the atten- 

 tion must be withdrawn from the mountains and from 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 manner, 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 deport- 

 ment of the selenite plate, with which the readers of 

 the foregoing 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 re- 

 markable. Towards evening the sky above the moun- 

 tains opposite to my place of observation yielded a 

 series of the most splendidly-coloured 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 colours 

 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 favourable cir- 

 cumstances, produce chromatic effects of polarisation 

 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 superficial reflection, is always of the same colour 



