14 
SCIENCE. 
VISUAL TELEGRAPHY. 
For many years past scientific men have been 
familiar with the fact, that the reflected images of 
objects could be reproduced at a distance by the aid 
of electricity, but recently the matter has been again 
taken up, and is now being prominently brought before 
the public under headings of “seeing by telegraph.” — 
The general principle involved may be gathered 
from the description of the “ Diaphote” an instrument 
introduced by Dr. H. E. Licks of Bethlehem, Penn., 
“ for seeing by telegraph.” He calls it by this name 
“ from two Greek words, dia, through, and phos, light.” 
He lately read a paper in Reading, and ex- 
hibited his instrument. This consists of a receiving 
mirror, the wires, a battery, and a reproducing speculum. 
The receiving mirror is an amalgam of selenium and 
iodide of silver ; the reproducing speculum is a com- 
pound of selenium and chromium. The wires are 
numerous, as it is necessary for distinctness that a 
wire should be required to affect but a very small 
space. The instrument exhibited had a mirror six 
inches by four, composed of seventy-two small plates 
to each of which a wire was attached, the whole being 
wrapped by a fine insulated covering. These wires 
run to a common galvanic battery and thus connect 
with the reproducing plate. When the circuit is 
closed, the rays of light are conducted through an 
ordinary camera, and the accompanying heat produces 
chemical changes in the the amalgam of the mirror, 
which, modifying the electric current, cause similar 
changes in the reproducing speculum. In the ex- 
periments at the close of the explanatory lecture, an 
instrument was taken to a lower room of the building 
and operated from there to the stage in the presence 
of the audience. Before the mirror in the lower room 
the committee held in succession an apple, a pen knife, 
and a trade dollar, which were distinct on the platform 
above. The date on the trade dollar, thrown on an 
enlarged screen, was plainly visible, as well as the 
goddess of liberty. A watch was next used, and the 
audience could see the movement of the hands. An 
ink bottle, a flower, parts of a theatre hand-bill, were 
also shown, and when the head of a live kitten was 
exhibited, there was great applause, and the inventor 
warmly congratulated on his success. The opinions 
entertained of its practical value are very high — it be- 
ing possible for a signal officer on a railroad to see 
hundreds of miles of track at the same instant.” 
We are informed by a gentlemen residing near New 
York, that during a visit to France a few years ago, 
his attention was called to the successful attempt of 
the police authorities aided by a Scientest, to repro- 
duce at a distant city by telegraph the features of a 
criminal who was fleeing from justice. In this case 
the means employed were perfectly successful, and 
the results obtained identical to those claimed in the 
“ Diaphote." 
There are other methods by which “ seeing by tele- 
graph” can be accomplished. Professor Graham 
Bell has deposited with the Smithsonian Institute a 
sealed description of an instrument he has invented, 
which has caused Messrs. Ayrton & Perry of England, 
who have been working on the same problem, to offer 
the following statement, which indicates the means 
they employ: 
“ While we are still quite in ignorance of the nature 
of this invention, it may be well to intimate that com • 
plete means for seeing by telegraphy have been known 
for some time by scientific men. The following plan 
has often been discussed by us with our friends, and 
no doubt has suggested itself to others acquainted 
with the physicial discoveries of the last four years. 
It has not been carried out because of its elaborate 
nature and on account of its expensive character. 
Nor should we recommend its being carried out. 
Our transmitter at A — that is, the apparatus for re- 
ceiving the light impressions and transmitting them 
electrically — consisted of a large surface made up of 
very small separate squares of selenium. One end of 
each piece was connected by an insulated wire to the 
distant place, and the other end of each piece with the 
ground, in accordance with the plan commonly em- 
ployed with telegraph instruments. The object whose 
image was to be sent by telegraph was illuminated 
very strongly, and by means of a lens a very large 
image was thrown on the surface of the above trans- 
mitter. Now, it is well known if each little piece of 
selenium forms part of a circuit in which there is a 
constant electromotive force, say of a voltaic battery, 
the current passing through each piece will depend on 
its illumination. Hence, the strength of the electric 
current in each telegraph line will depend on the 
illumination of its extremity. Our receiver at the 
other end, B, was, in our original plan, a collection of 
magnetic needles, the movements of each of which 
(as in the ordinary needle telegraph) were controlled 
by the electric current passing through the particular 
telegraph wire with which it was in connection. Each 
magnet by its movement closed or opened an aper- 
ture through which light passed to illuminate the back 
of a sheet of frosted glass. There were, of course, 
as many of the illuminated squares at B as of selenium 
squares at A, and it is quite evident that since the 
illumination of each receiving square depends on the 
strength of the current in its circuit, and this current 
again depends on the illumination of the selenium at 
the other end of the wire, the image of a distant ob- 
ject might in this way be transmitted as a mosaic by 
electricity. 
A more promising arrangement, suggested by Pro- 
fessor Kerr’s experiments, consisted in having each 
square at B made of silvered soft iron, and forming the 
end of the core of a little electro-magnet, round which 
passed the current, coming from the corresponding 
selenium square at the other end. We proposed that 
the surface formed by these squares at B should be 
illuminated by a great beam of light, polarized by re- 
flection from glass, and received again by an analyzer. 
It is then evident that since the intensity of the 
analyzed light depends on the rotation of the plane of 
polarization, by each little square of iron, and this de- 
pends on the strength of the current, and that again 
on the illumination of the selenium, we have another 
