Hitherto we have presented to the reader the representations of distant
objects, obtained by the use of a Camera Obscura. But the present plate
represents an object of its natural size. And this is effected by quite a
different and much simpler process, as follows.
A leaf of a plant, or any similar object which is thin and delicate, is
laid flat upon a sheet of prepared paper which is moderately sensitive.
It is then covered with a glass, which is pressed down tight upon it by
means of screws.
This done, it is placed in the sunshine for a few minutes, until the
exposed parts of the paper have turned dark brown or nearly black. It is
then removed into a shady place, and when the leaf is taken up, it is
found to have left its impression or picture on the paper. This image is
of a pale brown tint if the leaf is semi-transparent, or it is quite white
if the leaf is opaque.
The leaves of plants thus represented in white upon a dark background,
make very pleasing pictures, and I shall probably introduce a few
specimens of them in the sequel of this work: but the present plate shews
one pictured in the contrary manner, viz. dark upon a white ground: or,
speaking in the language of photography, it is a _positive_ and not a
_negative_ image of it. The change is accomplished by simply repeating
the first process. For, that process, as above described, gives a white
image on a darkened sheet of paper: this sheet is then taken and washed
with a fixing liquid to destroy the sensibility of the paper and fix the
image on it.
This done, the paper is dried, and then it is laid upon a second sheet of
sensitive paper, being pressed into close contact with it, and placed in
the sunshine: this second process is evidently only a repetition of the
first. When, finished, the second paper is found to have received an
image of a contrary kind to the first; the ground being white, and the
image upon it dark.
[PLATE VIII. A SCENE IN A LIBRARY.]