A brass plate, A, whereon the rays of light impinge inside a camera, in
their various forms and colors, from the external objects placed before the
lens, the said plate being coated with selenium on the side intended to
face the dark portion of the camera This brass plate has its entire surface
perforated with small holes as near to one another as practicable. These
holes are filled with selenium, heated, and then cooled very slowly, so as
to obtain the maximum sensitiveness. A small brass wire passes through the
selenium in each hole, without, however, touching the plate, on to the
rectangular and vertical ebonite plate, B, Fig. 1, from under this plate
at point, C. Thus, every wire passing through plate, A, has its point
of contact above the plate, B, lengthwise. With this view the wires are
clustered together when leaving the camera, and thence stretch to their
corresponding points of contact on plate, B, along line, C C. The surface
of brass, A, is in permanent contact with the positive pole of the battery
(selenium). On each side of plate, B, are let in two brass rails, D and E,
whereon the slide hereinafter described works.
[Illustration: Fig. 1]
Rail, E, communicates with the line wire intended to conduct the various
light and shade vibrations. Rail, D, is connected with the battery wire.
Along F are a number of points of contact corresponding with those along
C C. These contacts help to work the apparatus, and to insure the perfect
isochronism of the transmitter and receiver. These points of contact,
though insulated one from the other on the surface of the plate, are all
connected underneath with a wire coming from the positive pole of a special
battery. This apparatus requires two batteries, as, in fact, do all
autographic telegraphs--one for sending the current through the selenium,
and one for working the receiver, etc. The different features of this
important plate may, therefore, be summed up thus: