The Osceola times., 1881-05-28
TELEGRAPH PHOTOGRAPHY.
The Transmission of Pictures by Telegraph
illustrated Before "a London Society.
London Times

Illustrated Before "a London society.
London Times.
A great deal of interest has been ex-
cited lately by the proposals which have
been made for the Transmission of pic
lures by telegraph. At a recent meeting
of the Physical society, two pieces Of APP
paratus were shown by which pictures
of a rudimentary sort were actually sent
along a short length Of wire and repro
duced at its opposite end. These two
are quite distinct in idea and construc-
ton; one was by Mr.. Shelford Bidwell,
and the other was the joint invention of
Messrs. Ayrton and Perry. Mr.. Bidwell's
machine was again exhibited at the
Royal Institution last week, and an i'm
proved form of Messrs. Ayrton and Per-
ry's apparatus has also been shown re-
Gently elsewhere in London.
The power which an electric current
possesses of decomposing certain chemi-
cal solutions has been turned to account
in various telegrapkic instruments, no.
tably in Bain's chemical telegraph and
in Bakewell's copying telegraph. A pa
per moistened with this solution is laid
on metal plate, to which the wire from
one pole of the battery is joined. The
other pole of the battery is connected to
a metal style. As soon as the style
touches the paper the current passes, the
solution is decomposed, and the paper is
marked. If the style moved over the
paper line is drawn, and if the paper il
drawn along under the style the same
result is obtained. But the marks are
only made while the current is passing,
and as often as the current is interrupted
the line is interrupted too. Thus there
may be produced broken line of dots
and dashes corresponding with any series
of breaks in the electric current. If the
style be moved across and across the pa
per in parallel straight lines the breaks
may be arranged to form any desired
pattern. Evidently the same effect may
be produced if the style traces a course
round and round a cylinder, instead of
across Il flat plate; and this is actually
the method usually employed. In pre-
vious telegraphic instruments various
devices were employed for controlling
the electric current at the sending sta
ton, but it occurred to Mr.. Bidwell that
this might be done by the action of light
itself on selenium, the curious metal.
The properties of which have been made
familiar to the public by Prof. Bells
photophone. Selenium, it will be re-
membered, under certain conditions, al
lows electricity to pass through it more
freely in the light than in the dark. A
properly constructed "cell" of selenum,
forming part of an electric circuit. will
vary the strength of the current precise
ly in accordance with the amount of
light falling on it. IT, now, we imagine
Photographic image focused on selen-
ium cell, and such an arrangement made
that the selenium can "see' only mi
mute portion of the picture at time,
then if it is moved over the picture in
straight lines, so rs to receive the lights
and shadows Of it in succession, it might
conceivably regulate an electro.chemical
drawing arrangement such as that above
described, provided, of course, that the
style of the drawing apparatus and the
selenium receiver moved in absolute
correspondence. On this principle Mr..
Bidwell has actually made piece of ap-
paratus by which ne can transmit rough
outlines of very simple figlTes-squ
or diamond-shaped holes, for instance,
cut in pieces of zine. In this experiment.
al apparatus, the great difficulty of insur-
ing absolute synchronsm between the
two parts of the apparatus is evaded by
the simple plan of driving both by one
handle, but this device is hardly applica-
BILE when the sending and receiving
stations are more than few inches
apart
The apparatus for the same purpose by
Messrs. Ayrton and Perry consists of
mosaic of selenium cells, each cell in
telegraphic communication with one of
a corresponding number of devices, by
which a small mirror is adjusted to throw
more or less light on screen. They
thus hope to produce a pattern in light
and shade corresponding with the amount
of light and shade thrown on the selen-
ium cells by a picture thrown on them
| from magic lantern or otherwise, Just
as photograph represents in light and
shade the object from which it is taken.
This is, indeed, very bald outline of
their proposal, but it may suffice to give
notion of its principle. In practice
they hope TO use a few cells only, NOV
ing rapidly over the field of view, and
also 10 limit the number Of wires which
would be required if each cell had a sep
arate circuit. Further, they are irving TO
avail themselves Of the properties Of the
japanese "magic mirror by using met
al plate and a system of magnets behind
it. They think it might be possible thus
| TO act upon surface sufficiently to affect
| the shadows thrown upon it, and even
to make them represent the figures
| thrown ON the selenium cells, us the
shadows from the "magic mirror repre-.
sent the invisible figures impressed upon
IT,