Do not stop down the lens, as this makes long exposure necessary,
and the subject may move. Correct exposure depends, of course, on
the lens, light and the plate. But remember that a black and white
negative is wanted with as little detail in the features as
possible. The best plate to use is a very slow one, or what is
called a process plate.
[Illustration: Sample Silhouette]
In developing get all possible density in the high lights, without
detail in the face, and without fog. Printing is best done on
contrasty development paper with developer not too strong.
The ideal silhouette print is a perfectly black profile on a white
ground. With a piece of black paper, any shape in stopping off
print may be made as shown at C in the sketch.
** How to Make a Galvanoscope [68]
A galvanoscope for detecting small currents of electricity can be
made from a coil of wire, A; a glass tube, B, full of water; a
core, C; and a base, D, with binding posts as shown. The core C,
which is made of iron and cork, is a trifle lighter than the water
it displaces and will therefore normally remain in the top of the
tube; but as soon as a current of electricity passes through the
coil, the core is drawn down out of sight.
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