The box is
perforated at one side by a circular opening, 13/4 inches in diameter,
from the margin of which projects at a right angle a long brass tube
(Fig. 1), which carries the lens. In Fig. 2 the lid of the box has
been removed, and the bottom of the box, with the wheels, springs, and
partially closed shutter, is presented. The lid is double--that is, it
is a flat box in itself. It contains nothing but the dry plate,
supported at its center upon a small brass disk, against which disk it
is firmly pressed by a pivot attached to a spring fastened in the lid.
The aperture in one side of this double lid, which corresponds with
that seen in the floor of the box, may be closed by a slide, so that
the lid containing the plate can be removed like an ordinary plate
holder and carried to a dark room, where it is opened and the plate is
changed. When the lid is replaced this slide is removed, and as the
shutter is made to revolve, the light falls upon whatever portion of
the dry plate happens to be opposite the opening.
By reference to Fig. 2, it will be seen that when the large wheel
which projects outside of the box is revolved by a crank, it turns the
small ratchet wheel, which bears an eccentric pawl. (The crank has
been removed in Fig. 2; it is seen in Fig. 1.) The central wheel has
only six cogs.
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