in, in a person of middle
stature, in the middle of the length, and higher according to the
proportional height of the person."

In regard to the proper elevation of the camera, it may be here stated
that I have found it best in taking portraits where the hands are
introduced, to place the camera at about equal height with the eyes of
the sitter, in order to bring the face and hands equi-distant from the
tube. It will be found, if the above be followed, that by attaching a
string to the camera tube, and making a semi-circle, that the face and
hands of the sitter will occupy a corresponding distance, and the
consequence is that the impression will appear without the hands being
magnified. It has been found that a person with a freckly face can
have as fine, fair, and clear an impression as the most perfect
complexion; this may be done by the subject rubbing the face until it
is very red. The effect is to lessen the contrast, by giving the
freckles and skin the same color and the photogenic intensity of the
red and yellow being nearly the same, an impression can be produced
perfectly clear.

When a child is to be taken, and there are doubts of its keeping still,
the operation may be accelerated by placing it nearer the window
bringing the screen nearer, and placing a white muslin cloth over the
head; this will enable you to work in one third of the usual time.
Should the person move, or the plate become exposed to the light, it
may be restored to its original sensitiveness by placing it over the
quick, one or two seconds.

Developing the Daguerreotype.--After the plate has been submitted to
the operation of the light, the image is still invisible. It requires
to be exposed to the vapors of heated mercury. It is not absolutely
necessary to apply artificial heat to the mercury to develop the image,
for fair proofs have been produced by placing a plate over the bath at
the ordinary temperature of the atmosphere. This plan, however,
requires a long time and cannot be adopted in practice, even if it were
advisable. The time more usually required in developing the image over
the mercurial vapors, is about two minutes, and the temperature is
raised to a point necessary to produce the desired effect in that time.
This point varies as indicated by different scales, but for the
ordinary scales it is not far from 90 deg. cen.

The mercury bath is accompanied with a centigrade thermometer, by which
the heat is regulated.