mixture be then made, in the dark, the precipitation takes place instantly.
Here is again, evidence of either an absorption of some material agent from
the sunbeam, or an alteration in the chemical constitution of the body.
It was from understanding these principles and applying them that philosophers
were enabled to produce the Calotype, Daguerreotype, &c. For the effects
and action of light on the camera, see Chapter V.

Some advances have been made towards producing Photographic
impressions in color--the impossibility of which some of our
best and oldest artists have most pertinaciously maintained.
The colored image of the spectrum has been most faithfully copied,
ray for ray, on paper spread with the juice of the Cochorus Japonica,
(a species of plant) and the fluoride of silver;
and on silver plate covered with a thin film of chloride.
The day may be still remote when this much to be desired
decideratum shall be accomplished in portrait taking;
but I am led to hope that future experiments may master
the secret which now causes it to be looked upon, by many,
as an impossibility.

That great advantages have resulted, and that greater still will
result from the discovery of the Photographic art, few will deny.
The faithful manner in which it copies nature, even to the most
minute details, renders it of much value to the painter; but a few minutes
sufficing to take a view that formerly would have occupied several days.
Its superiority in portraits, over miniature or oil painting has been
tacitly acknowledged by the thousands who employ it to secure their own,
or a friends likeness, and by the steady increase in the number of
artists who are weekly, aye daily springing up in every town and village
in the land.