IMPROVE- MENTS IN TELEGRAPHY BY MEANS OF A SYSTEM, OF PHOTO-TELEGRAPHY
Year: 1885

page_text: I, WILLIAM GEMMILL, M.B., C.M., F.S.A. Scot., F.R.P.S.E. general medical and
surgical practitioner, residing at Drummore in the Parish of Kirkmaiden and
County of Wigton do hereby declare the nature of my invention for IMPROVE-
MENTS IN TELEGRAPHY BY MEANS OF A SYSTEM, OF PHOTO-TELEGRAPHY to be as
follows:-
The object of the system is to connect a selenium-celled circuit with a separately
supplied one, lighting an electric lamp so that when light or shadow falls on the
selenium cell the light of the lamp flashes out or becomes more or less extinguished
as the case may be, and further to vary the illumination of the lamp with the
degree of light falling on the selenium, so as to make the lamp available for
photo-telegraphy or the transmission of photo-telegrams or photautographs by the
ordinary postal wires.
It mediates the two circuits so that any degree of illumination of a point at the
despatching end may produce a corresponding illumination on a corresponding
point at the receiving one, so that if the two points-the despatching, illuminated
(in picture thrown on selenium by a lens)-and the receiving, illuminating (being
the light of the lamp condensed to a point and thrown on the new picture-taking
surface) be made to travel over similar areas consentaneously an image is
transmitted.
-
The whole apparatus consists essentially of three parts, viz. despatching, com-
mutating, and receiving.
These may be provisionally described as follows.
I. DESPATCHING.
A plate bearing the despatch message is made to traverse in front of an aperture
fitted with a powerfully condensing lens arrangement by which the light behind is
thrown through the message in the form of a sharp point or pointed shadow as the
case may be and falling on the selenium cell admits or stops the electric current in
mit in fitted with a powerful electromagnet which becomes
the init
L

page_text: II. THE COMMUTATING ARRANGEMENT.
The magnet in the despatching circuit is brought close to a break in the lamp-
lighting or receiving circuit, the break being, during the activity of the magnet,
more or less closed by a series of springs of various resistance attached to an
upright at one wire-end, and, when attracted, coming in contact with the other
wire-end or ends, so that as fewer or more of the springs are attracted, that is, as
less or more light falls on the selenium, a smaller or greater quantity of electricity
may be thrown into the lamp; or it instantaneously extinguished or lit.
III. THE RECORDING OR RECEIVING APparatus.
The light of the lamp is powerfully condensed to a point and made to traverse
the photographic recording plate consentaneously with the movement of the
despatch in the other circuit. Let us say the plate is six inches long and three
deep and that it traversed right to left before a weak lamp in five seconds; and
back, after having descended the one one-hundredth of an inch, in the same time;
and so on until the whole record is completed like the despatch. Or, as with the
despatch, the recording plate may be made to traverse behind a point-aperture
from or through which the light would fall.
I
The traversers for reception and despatch can by simple machinery be made to
make so many traverses per hour, a line of light, say at the side of the upper right
hand corner of the latter being used to indicate the correct position of the former.
When the adaptation is correct the escape-pallets starting the movements of both
traversing pieces of machinery are simultaneously set free by electro-magnets on
the same wire-circuit and under the influence of the same current.
Dated at Stranraer this eighteenth day of April eighteen hundred and eighty-

page_text: I, WILLIAM GEMMILL, M.B., C.M., F.S.A. Scot., F.R.P.S.E., general medical and
surgical practitioner, residing at Drummore in the parish of Kirkmaiden and
the County of Wigton do hereby declare the nature of my invention for THE
IMPROVEMENT OF TELEGRAPHY BY A SYSTEM OF PHOTO-TELEGRAPHY and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
The object of the system is to enable a picture or writing to be photographed at
a distance through the medium of telegraphic wires and that with delicate details of
light and shade and sharp outlines. The arrangement acts by conveying an electric
current, that has passed through a selenium cell (there varying in electro-motive
force as more or less light falls on the cell), to the receiving station, where it excites
an electro-magnet that by its attraction on a series of switches, having graded
spring recoils, does by them switch on or off a greater or less number of subsidiary
currents to an incandescent (or other) electric lamp, previously so supplied as to be
in a state of slight glow. With each successive switch lifted, as the magnet becomes
stronger through more light falling on the selenium, the lamp flashes out the
brighter. Every apparent point of light of a particular intensity in the image to
be sent would, on being projected on the selenium cell, cause the lamp to give
a corresponding light, which, focussed to a point on the receiving plate or sheet,
would represent that in the despatch, but far out-rivalling it in brilliancy. If
a line of the image be travelled over through its lights and shades, and mean while
thrown on the cell, while any ordinary rapidly sensitive photographic plate is
similarly and simultaneously moved over the focus of the distant lamp, the same
succession of lights and shadows that are in the despatch will be recorded. Line
may follow line, at distances scarely appreciable to the naked eye, till the whole
image is secured. Drums revolving by clockwork on a fine threaded axial screw
have already, for many purposes, been employed to effect a close succession of lines
traced over by a style stationary at its side. The spiral at each complete revolution
would be, as it were, one line crossing the sheet (surrounding the drum and on
which the tracing was being taken) somewhat obliquely instead of horizontally;
the next revolution bringing the neighbouring line in at the distance of the thread
of the screw, and so on till the whole was covered. For photo-telegraphy, instead
of a style being used as a tracer, the focus of a source of light must be substituted.
The track over the despatch must be illuminated and the light from it thrown on
the selenium cell; the condensed light of the distant lamp, responding thereto,
forms the illuminating tracer for the new picture-taking surface. This is accom-
plished as follows. The cylinders at both stations are of glass, and each enclosed
in an outer dark shield; the latter having a perforation through which the focussed
light may be thrown on the cylinder as it turns round and round in ascent or

page_text: descent.. Both the message to be despatched and the sensitive receiving sheet are
wound round the cylinders and clipped in situ. The former is of some transparent
flexible material, such as waxed paper, and the message is written or drawn in as
dense an ink as possible. The latter has its sensitised surface turned outward. At
the despatching station the light of a strong lamp is then sharply focussed on the
message sheet through the aperture in the shield, and the cylinder set so that,
whether ascending or descending, its revolution for a certain period would allow
the whole message to be traversed. If the focus be an acute one no further optical
apparatus, such as an erecting lens, will be needed, the illuminated spot being so
small that it alone is sufficient for accurate delineation. The cone of light is then
allowed to pass through the message and expand more or less beyond it before
falling on the selenium cell. At the receiving station the lamp, responding to the
light and shadow on the selenium, has its light focussed through the aperture in
the shield so as to fall on the sensitised surface. The two cylinders being similarly
set and revolving simultaneously with the same number of revolutions per minute,
the lights and shadows traced over at the near station are delineated photo-
graphically at the distant one:
But, as the commutator, chiefly, is sought to be protected,-viz., the use of
changes of current (induced by varying lights falling on the selenium cell) for the
purpose of causing corresponding lights, that could be photographed in their
disposition and degree, to flash out from an electric, or other, lamp at a distance-
the above description may be held to be sufficient to shew how the commutator
can be applied for the purposes of telegraphic photography; and its detailed
description may be proceeded with.
The arrangement in part of the system has been named a commutator, thoughi
the same name has been given to other well known pieces of electrical apparatus
used for totally different purposes, and it has been so-because it commutes or
changes an influence of the degree of the light-energy on a spot into a modification
of an electric current that causes an electric or gas or other lamp at a distant
station to produce a relatively similar illumination of a corresponding spot. It may
be called the photo-telegraphic commutator because by the aid of proper traversing
apparatus &c. it enables images to be photographed through the medium of
telegraph wires, and lays' the foundation for the transmission of photographs
electrically to any required distance, which might be effected by the intermediation
of relays and the use of sufficiently powerful apparatus.
Besides the sources of electric supply and the conductors, the chief elements of
the commutator requiring particular description are the selenium cell, the electro-
magnet, the switches, and the modified lamp; but one and all of these may be of
various forms though their purport and arrangement be the same, viz a selenium
cell modifying an electric current, which, conveyed to a distance, there electro-
magnetically brings an electric lamp into a state of illumination corresponding with
the light falling on the selenium; or turns the stop-cock of a gas-jet, though the
lamp is far better.
The currents in both the selenized and lamp-lighting circuits may either be
dynamo-electric or Galvanic or one may have the one and the other the other.
A magneto-electric machine, owing to its power of overcoming resistances, might
be better for the selenized circuit, and a distributing dynamo'inachine such as are
supplied by Gramme, Brush, or Siemens, but giving much lesser subdivisions, would
be by far the preferable source of supply for the lamp. The division of the power
of a battery into the subsidiary currents is however a simple matter, while in the
other case there would be difficulty in obtaining the small currents required as
they would have to be kept separate throughout, except in the incandescent part
of the lamp, say, the loop of platinum wire, or of carbonized material, or what-
ever other arrangement is adopted. The wires for each lamp, after insulation,
might be made up in a small cable. The glow-wire, that which kept the lamp in
a state of faint glow, would have to offer considerably less resistance than the

page_text: others, and, of course, would be of larger diameter. That the current through the
smaller wires might be shut on and off when requisite, these wires must be
interrupted in such a manner that their continuity would be resumed when their
particular switches were brought into play by the magnet; at least this would be
the case where very strong light was not required, and the greatest possible
simplicity was desirable-Where very powerful currents are brought into operation,
closing and opening the circuits thus would be inadmisable, as no contact points
could stand the spark. In this case arrangements must be made for only partially
or gradually reducing or increasing the currents, for instance by interposing in
the subsidiary circuits electro-magnets to which a greater or less amount of work
could be given and the lamp-light thus reduced or raised in accordance with the
degree of illumination of the selenium, or the currents could be shunted off into
manageable quantities could be dealt with on the shunts. If from the nature of
the electric supply to the lamp earthplates are substituted for the return wires,
the currents may emerge from the lamp by a single wire if it be of low resistance
and earths near.
Perhaps one of the most convenient forms of selenium cell for use in the
commutator is a short cylinder (solid) of vitreous selenium th or in. or more in
diam. into opposite sides (not the ends) of which the pole-pieces, viz. two platinum
arcs, one for each side and having a wire rising from its outer surface, are inserted
warm, and the cell then slowly annealed. One of the flat ends should be the part
exposed to the light at some distance from where it focusses on or through the
transparent despatch-sheet with its densely opaque message, so that the cone of
light or shadow, dispersing beyond the focus, may spread out over the face of the
cell. The cell may have a glass envelope through which the platinum wires are
fused. The size of the cell must vary with the amount of the current required to.
pass through it to overcome the external resistances, namely, those due to the
conducting wires, electro-magnet, movement of switches &c. Its own resistance
in the dark must always be in a very appreciable ratio to all these, and yet not be
so great but that variations in the lighting up of it would give a sufficiently delicate
record at the switches.
The current varying with the amount of light falling on the selenium is carried
on by an insulated wire to the coil surrounding the core of the electro-magnet, and
thence by a return wire or else to an earthplate. It has no direct connexion
whatever with that supplying the lamp; but, if in exceptional circumstances, it
have the same source the two must be distributed in different circuits or must be-
quite separately shunted.
The core of the magnet is better built up of thin pieces of iron than consisting
of a single large one. It may be of different forms, e.g. a bar, or a horse-shoe
magnet, it may have a flat face or one spread out, like the fingers from the hand,
in order to oppose only the armatures by which the switches are swung back against
their springs, and so on; but, the magnetic field at its face must be extensive
enough to have free play over all the armatures by the attraction of which the
switches are brought into action. The current passed through the selenium cell
must be strong enough to enable the magnet to lift the switches easily against their
recoil springs, which in turn should draw them all back freely one by one as
the light from the despatch to the selenium changed from its brightest to total
obscurity.
The switches may be of many and varied forms. Every automatic relay at once
suggests means of accomplishing their object, which is either step by step, i.e. one
after another, to bridge over breaks in the wires conveying the subsidiary currents.
to the lamp, to add more and more current as more and more light has to be
recorded; or they may act inversely. by introducing new labour into the circuits
and letting the lamp down in response to a failure of light on the selenium. The
switch, bridging over the interrupted wire, is the simplest of all. Each would
consist of four parts and act pretty much like a lever of the first order. Firstly,

page_text: there would be the insulated middle part turning on a pivot or axis. Secondly
from this, below, there would hang a bar of steel, the armature, which would be
attracted as the electromagnet was made or became high enough in power. Thirdly,
above; the middle part would support the bridge which would be of platinum or
some other refractory metal when strong currents were used. When the armature
was attracted below, the bridge above would be swung back on the wire terminals,
whether these were small roughened plates, or metallic brushes, or other, and would
thus close the break in the circuit and raise the light of the lamp. Fourthly, there
would be the recoil spring to withdraw the armature from the magnet and unbridge
the break when the light required reduction. If the spring were a tension one it
would be attached to the armature itself, if a torsion one to the axial part. Equal
movements of the spring would require equal expenditures or loss of power, whereas
the activity of the magnet decreases inversely as the square of the distance. So
in rapid work with strong lights a compound system of leverage must be employed
to move the bridge, in order that the closing and opening of the circuit may require
as small a movement of the armature as possible. The recoil springs must be
graduated in power so that the weakest would be overcome by the magnetization
induced by a light a little above shadow falling on the selenium and the strongest
resist all but the fullest light used in the despatch. The range of resistance
between these would be divided into equal increments according to the number of
switches employed. In a switch, like the above, the residual magnetism of the
armature might be so far obviated by having the armature made of two plates one
of which is pivoted on and turns on the other. It is claimed for "Siemens' polarised
relay" that it is entirely clear of residual magnetism and a modification of it might
be used to work a series of switches, namely, to have a vertical succession of
tongues, and of the moveable arms over the electromagnet resting on the north
pole of the permanent magnet. If such were used it would be this electro-magnet
only that would receive the current passing through the selenium cell.
The dropping out of any of the subsidiary. current-supplies to the lamp does not
produce any reciprocal rise of power of the others, nor the switching in of any
produce a lowering of the rest-if the generating electrical machine be self-
regulating, or if the lamp-supply be only a small portion of its work; for the
currents are distinct from the sub-dividing or distributing machine on to the lamp
itself.
The focal points of strong lights either on the despatching or receiving-photo-
graphic plate must as much as possible be deprived of heat-rays. This may best
be effected by the interposition (between the lamps & their foci) of cells containing
a stronger or weaker solution of sulphate of copper.
It will be seen that the system of photo-telegraphy opens up an entirely new
field in telegraphy, namely, the actual reproduction of photographs through the
mediuin of electrically conducting wires. For the transmission of writing or of
monotint drawings it may be divested of much of its complexity, as the lamp
would then only require to be switched on up to its full or down to its lowest ;
or a gas-jet do.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that what
I claim is
The arrangement by which a selenium-celled electrical circuit is connected with
a separately supplied one, or series of separately supplied ones, lighting an electric
lamp in such a manner that, when light or shadow falls on the selenium cell, the
light of the lamp flashes out or becomes more or less extinguished, as the case may
be; and further, the varying of the illumination by the lamp with the degree of
light falling on the selenium so as to make the lamp available alike for the
transmission of writings, drawings, paintings and other gradually shaded pictures
-through the medium of telegraphic wires, and for their reproduction. faithfully.

page_text: photographed. It employs the varying current, passing through the varyingly
lighted selenium cell, to excite the distant electromagnet, which for the trans-
Inission of simple outlines throws on and off the current to an electric lamp-or,
it may be so, turns the stopcock of a gas-jet-and for shaded pictures switches on
a greater or less number of subsidiary currents to the lamp according as more or
less light falls on the selenium.
Dated this eleventh day of December eighteen hundred and eighty five years
WILLIAM GEMMILL