with perfectly neutral chloride of gold, acquires a brownish-yellow hue.
The first impression of light seems rather to whiten than darken the paper,
by discharging the original color, and substituting for it a pale
greyish tint, which by slow degrees increases to a dark slate color;
but if arrested, while yet, not more than a moderate ash grey, and held
in a current of steam, the color of the parts acted upon by light--
and of that only--darkens immediately to a deep purple.

Here I must leave the subject of the action of light upon metalic compounds--
referring to Mr. Hunts work for any further information the student may
desire on the other metals--as I find myself going beyond my limits.
I cannot, however, entirely dismiss the subject without giving a few examples
of the action of light on the juices of plants, some of which produce
very good photographic effect.

CORCHORUS JAPONICA--The juice of the flowers of this plant
impart a fine yellow color to paper, and, so far as ascertained,
is the most sensitive of any vegetable preparation;
but owing to its continuing to change color even in the dark,
photographic images taken on paper prepared with it soon fade out.

WALL FLOWER.--This flower yields a juice, when expressed
with alcohol, from which subsides, on standing, a bright
yellow finely divided faecula, leaving a greenish-yellow
transparent liquid, only slightly colored supernatant.
The faecula spreads well on paper, and is very sensitive to light,
but appears at the same time to undergo a sort of chromatic analysis,
and to comport itself as if composed of two very distinct
coloring principles, very differently affected. The one on
which the intensity and sub-orange tint of the color depends,