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.

These results have a direct bearing upon what artists call 'aerial
perspective.' As we look from the summit of Mont Blanc, or from a
lower elevation, at the serried crowd of peaks, especially if the
mountains be darkly coloured--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
polarised. 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 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 the 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to see its colour, the attention must be withdrawn from the mountains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 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 deportment 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 remarkable. Towards evening the sky above the mountains
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 w