Improved Method of and Means for Telegraphing by Means of Light.
Year: 1888

page_text: Date of Application, 18th May, 1888
Complete Specification Left, 18th Feb., 1889
Complete Specification Accepted, 23rd Mar., 1889
[Communicated from abroad by PAUL LA COUR, of Askoohus, in the Kingdom of
Denmark, Electrical Engineer.]
Improved Method of and Means for Telegraphing by Means of Light.
I, HENRY HARINGTON LEIGH, Fel. Inst. P.A., Assoc. M. Inst. C.E., practising.
as Phillips & Leigh at No. 22, Southampton Buildings, Chancery Lane, in the
County of Middlesex, Engineer and Patent Agent, do hereby declare the nature of
this invention to be as follows:-
The systems of optical telegraphy in vogue at the present day are based upon the
use of rays of light differentiated in respect of their terms of exhibition, or of their
colour; or upon the use of luminous points placed at certain respective distances, and
in certain relative positions, according to a code of signals familiar to both sender and
receiver. The first mentioned system suffers from the drawback that the changes of
rays follow each other so rapidly that perception of them becomes painful, and even
impossible, when the rate at which they are exhibited is increased. The latter system,
that of luminous points or objects, such as flags, in common use in marine signalling,
is open to the objection that the apparent size of the signals diminishes according to
the distance separating them from the observer.
Now my invention produces signals which reach the receiver's eye of a size quite
unaffected by the distance between their source and him. Moreover, the nature of my
invention permits of the use of alphabets such as that known to telegraphists as the
Morse alphabet.
According to my invention, the transmitter does not send all sorts of luminous
colours, nor an accidental mass of different colours; but, by means of refraction be
transmits a definite combination.
In carrying this invention into effect, 1 support a concave mirror opposite any con-
venient source of light in a position adapted for reflecting the light-rays upon a
screen. There are formed in this screen a series of orifices of different sizes and
separated by unequal distances. They constitute the particular signal-alphabet which
it is intended to employ.

page_text: The which
rays pass through the orifices next pass through a lens held at its focal
distance from the screen, and then enter a prism.
The luminous rays which issue from, say, orifice No. 1 in the screen are after their
passage through the lens moving in their original direction. They are then refracted
and dispersed by the prism through a certain angle forming a fan of rays. In the
same way the rays issuing from orifice No. 2 are dispersed through an angle forming
a second fan, and if No. 2 orifice be wider than No. 1, more rays will appear in the
latter refraction. The rays issuing from other orifices are dispersed in the same way,
the several fans overlapping each other.
The observer or signal receiver occupies a position somewhere along a central line.
He will receive of the fan No. 1 only a small portion (blue) of the spectrum, and at
the same time, a green band, but of an increased width, of the fan, No. 2; from No. 3
fan a yellow band; from No. 4 an orange band; and from fan No. 5 a red band.
If the receiver examines the signal with the naked eye, or through an ordinary
glass, he will only see one luminous point, white or with more or less colour according
to the number or name of the rays concerned. But if he make use of a prism, or
what is better, a spectro-telegraphic glass, he will effect the decomposition of the rays.
The spectro-telegraphic glass may be constructed by applying a prism with direct
vision to an ordinary telescope. The latter should have a field large enough to easily
receive all the rays to be noted. The direct-vision prism is preferably applied in front
of the objective. It should be sufficiently large to prevent any reduction of the field
being caused, and its dispersive power should be proportional to the magnifying power
of the lens, so that the entire spectrum can be viewed at a glance. Any one looking
through such a glass at the light coming to him along the central line on which he
stands will see an image in which bands of colour appear grouped according to the
orifices on the screen in point of relative position and width, and differentiated in
respect of colour; and which image, although of various colours, represents the signs
of an alphabet, such as for instance as the Morse alphabet.
Now this image, no matter what may be the distance of the receiver from the source
of light, will appear to him full size, but more or less brilliant according to the distance.
This invention may be pratically applied in several different ways, but the following
is a convenient one, and places the nature of the invention and the means of carrying
it into effect clearly before the reader.
According to an international code, marine signals are transmitted, by day, by
means of flags. Four of these standing for as many words are hoisted and the receiver
looks out in his code-book the signalled combination, and so, word-by-word, reads the
signal, question or answer, or whatever it may be. Up to the present time, such a
system of signalling could not be used by night; but by means of the following
method, the light can easily be utilised for signalling purposes.
The ship is provided with a lantern containing the above described optical apparatus.
A number of plates in which are formed slits, some narrow and some wide according to
the signs of the Morse alphabet, and each one corresponding with a signal flag, are also
provided.
Two grooves are fixed upon the screen in which the selected plates are arranged.
The sender slides his arrangement of plates backwards and forwards so that the receiver
may have time to note the signals. The series of equal and equidistant slits prevents
the receiver losing the rays constituting the signals. As the signalman is moving the
screen to and fro, the observer will perceive the signals moving from one side to the
other of the illuminated field of his glass.
I wish it to be distinctly understood that the above described method of applying
my invention is only given as an illustrated one.
If it is desired to make use of my spectro-telegraphic system for more general
purposes, as for instance for sending military signals or messages, either a perforated
paper or one or more screens previously slotted to convey alphabetical signs may be
caused to move in the plane of the perforated screen first mentioned.
In addition to transmitting signals, my invention can be used for the purpose of
issuing directions as to change of course.

page_text: The apparatus, or a modification of it, may be fixed at the entrance to a port and
shewing a signal intended for a ship making that port. Such a signal would be easily
distinguishable from the harbour lights, inasmuch as it would be the only one shewing
a broken spectrum.
A lantern embodying the apparatus may be fixed to a ship's mast, so that the look-
out on another vessel will see in his spectro-telegraphic glass one signal if he is on the
right of the signalling vessel, and a different signal if he is on the left. Then if the
vessel carrying the lantern shall change her course, the look-out will see the spectrum
in his glass move accordingly. So that the relative positions of the two vessels, and
the fact of one changing her course will be seen at a glance.
The above described transmitting device may be also used as a spectro-telegraphic
glass.

page_text: COMPLETE SPECIFICATION.
Improved Method of and Means for Telegraphing by Means of Light.
I, HENRY HARINGTON LEIGH Fel. Inst. P.A., Assoc. M. Inst. C.E., practising
as Phillips & Leigh of No. 22 Southampton Buildings Chancery Lane in the County
of Middlesex Engineer and Patent Agent, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The mode of optical telegraphing as hitherto practised, for the purpose of trans-
mitting communications in the night is based upon the use of rays of light, which
alternate in longer or shorter durations, or upon the use of variously colored rays of
light through the means of colored glasses, or upon the combination of colored
lights which are placed at certain distances apart and in a certain order in which
everything is varied in accordance with arrangements previously made and is
selected according to the information which is desired to be given to the observer.
All these processes and methods have the great disadvantage that the visible size
of the signal decreases with the distance at which the observer is placed.
The process hereinafter described, which forms the subject of the present invention,
gives optical signals, the size of which is, as will be hereafter explained, indepen-
dent of the distance which separates the observer from the source of the light, and
which moreover permits of the use of alphabets, especially the Morse alphabet. The
theoretical basis, on which this new process is founded, may be looked upon as entirely
new, and will be explained in the following specification.
In the accompanying drawings;
Fig. 1 is a horizontal section through the emitting apparatus. Here F is the source
of light, in the present case a lamp--A is a screen or slide provided with perforations.
LL are two lenses possessing the same axis (and therefore conjugate). PP are
two refraction prisms. R is a reflector. N N are two doors made in the frame, so as
to be able to get inside it. b is a peep hole, for observing the flame. X is a pair of
mitre wheels which are set in motion from the rod T and thus rotate the cylinders Y,
which carry with them the slide A. A is a fixed metal plate provided with a
sufficiently large open space, which serves to give a firm hold to the slide A.
Fig. 2 is a front view of the slide A.
Fig. 3 shows a signal received in the scope of view of the telescope.
Fig. 4 is a mathematical drawing which will serve to explain the theoretical
development on the image produced. In this, F is again the source of light, A the
screen provided with the holes a¹ a a³, La lens, P a prism.
Fig. 5 shows the receiving apparatus as described hereunder.
The white rays of light which penetrate through the small cleft a¹ are carried on
through the lens parallel to the line a¹ o. The axial ray a² o is scattered by the
prism into a bunch of light, the red rays of which go in the direction, while the
violet rays go towards ¹. As regards the other rays which pass through the lens,

page_text: before being. scattered by the prism they are parallel to the ray al o, and are scattered
by the prism in such a way that all rays of the same spectral colour are, after the
dispersion, parallel to each other. The observer at a great distance will therefore
receive from all parts of the surface (or the refraction edge) of the prism m n, light-
rays of exactly the same colour,-let us say for instance orange, when he is, for
example, in the direction 9,-while the rays of other colour are dispersed in the
directions to v¹ according to the different colouring; so that, therefore, when the
observer is so far from the surface of the prism, he will only see the surface as a
colored point in this instance orange,--when the rays come through the cleft a¹ from
the source of light.
If the cleft is moved from a¹ to the point a² then the white rays which go through
the lens L, are moved through the angle a', o, a³ in the plane of dispersion; the rays
dispersed by the prism then move through the same angle to ². The observer at
the same spot as before will now catch sight of those rays of light, which are removed
by the angle a¹ o a², from the orange rays, and will therefore get, through the cleft a',
rays of, let us say, green colour. The cleft a will then show the observer violet rays.
Through the points on the slide between a' and a², you can show the observer, in the
direction of g, the colours which lie between orange and, green, and when the light
comes between the points a² and a³, the colours which lie between green and violet
will be visible. Thus any desired combinations can be made by using different slides,
which fulfil the corresponding conditions.
With the naked eye, the observer sees the light, coming from the emitting apparatus
as a colour which is combined of all the elementary colours which correspond to the
respective cleft. In order to observe the corresponding image on the slide it is
necessary to observe it with the receiving apparatus, ciz: the spectro-telegraphic
telescope.
This latter consists of a telescope either a Galileo telescope, a land telescope, an
astronomical or other telescope which is provided with a prisin for a direct and little
dispersed diffraction.
Fig. 5 shows a Galileo telescope B, the magnifying power of which is three or four-
fold. The prismp which is composed of two prisms is fitted in the diaphragm d, near
the eye glass e, in such a way that the light dispersing edge or surface of the prism
stands vertical; it may however also be fitted in various places in the telescope, as for
instanco outside or inside the object glass, according to the magnifying power of the
telescope, the dispersing capacity of the prism, and the size at which it is desired to
receive the siguals. The prism can also be suitably composed of three, four or five
prisms.
If, through this telescope, you look at a white lantern at some distance, you see, in
the telescope, instead of a bright point, a small spectrum changing about from red to
violet. The light received through the new apparatus, which which does not contain
all the colours of the spectrum, will not give a continuous spectrum, but only a dis-
continuous interrupted spectrum, according to the apertures applied to the slide, and
will only show those colours which correspond to the respective slits as is hereinbefore
explained. If the slits in the slide are of different widths and so selected that they
correspond to the ordinary Morse characters, as shown in Fig. 2, the observer sees in
the telescope an image such as is shown in Fig. 3.
In order that the observer, even when he is above or below the horizontal plane,
may see the light, a certain vertical length is given to the slits-The rays which
proceed from a point of the slit over the horizontal plane, are deflected through the
lens L and the prisms, and are accordingly visible under the horizontal plane, and
vice versa.
If the slide A is moved to and fro in front of the light, the observer through his
telescope will see the signal moving with the same rapidity. In this way a continuous
signalling can be organised, by suitably moving the slide, duly prepared in advance, as
may be seen in Fig. 1, to and fro in front of the source of light by means of the
cylinders Y, or by bringing the corresponding letters in one way or the other in front
of the source of light.

page_text: As the image which gives the signal is only dependent upon the retraction
Spectro-Telegraphic Telescope and the magnifying power of the latter, it will, as
regards its size, be independent of the distance of the observer from the signalling
apparatus, and only the brightness and intensity will diminish as the distance increases.
The image which the observer receives will be formed by the dispersion of the light in 5
At those distances, at which the source of light is seen,
the telescope of such observer.
the latter appears to the naked eye of the observer as an illuminating point without
extension, but if it is looked at through a spectro-telegraphic telescope, the source of
light will appear like a narrow line shaped spectrum, the length of which corresponds
to the dispersing capacity of the said telescope. This length is the same for all dis- 1
tances; the breadth certainly decreases theoretically with the distances, but from a
practical standpoint the image is an illuminating line, both for short and long
distances.
The process of Spectro-Telegraphy above described has several advantages:
(1.) It is possible to establish a complete optical telegraphy, which is surer, easier
and more rapid than that of the usual methods, which consist in the use of rays of
light of a longer or shorted duration of illumination, because the human eye can inore
easily receive and distinguish light-impressions of longer duration and coming upon
several different points of the retina, and a greater impression can therefore be made
upon the eye by sending the light to it in this way, than by subjecting the same
point of the retina to repeated and short impressions of light. The image in the
receiving apparatus can be read with same rapidity as the Morse characters on a
strip of paper, and the signaller can send off this writing as quickly as the observer
and signal receiver can read it.
(2.) The new process can be used on ships as it supplements the use of flag signals.
It is only necessary to replace the flags, in the present international signal system,
by Morse characters, and signals can then be given in the night under observance
of the international signal marks.
(3.) The new process gives a simple means of providing light houses and harbour
lights with distance siguals, by using in them definitely settled spectro-telegraph
signals.
(4.) The new process also affords a means of fixedly pointing out an important
direction, for instance in harbours and principally at sea, by the use of a lantern
which always gives a definite signal in this direction.
once,
the
(5.) If a ship carries an emitting apparatus, the slide of which is made in a specific
way, an observer can see, at a single glance through his telescope at
direction in which the ship is turning, as the image in the observer's telescope wil
turn in one direction or the other.
According to its various kinds of applications, the form of the apparatus may var
greatly. The number and size of the lenses and prisms, the form and manner
the lamp and its glass, the form of the slide and the mode in which it is moved
can always be suitably selected. The construction of the emitting apparatus is how
ever sufficiently particularized above.
As regards the spectro telegraphic telescope (i.e., the receiving apparatus) it
distinguished from all the telescopes hitherto used and from the spectroscop
telescopes, which are intended to examine the Franenhofer lines of the spectru
merely by the fact that the dispersing or light-scattering power of the telescope,
be used as receiving apparatus for the new process, is extraordinarily small and t
angle of sight of the spectrum, which this telescope forms from the white rays, do
not exceed a length of 15°.
Having now particularly described and ascertained the nature of my s
Invention and in what manner the same is to be performed I declare that w
I claim is:
(1.) A process for optical telegraphy, called spectro telegraphy, distinguished by
so altered by means of a slide w
fact that the light of any desired source of light
narrow and wide slits and by means of lenses and prisms, that light radiating out

page_text: every direction is only composed of certain kinds of spectral colour rays, which com-
position corresponds to the order of succession of the apertures of the slide; and this
light, consisting of single kinds of colour rays, if observed through a telescope
provided with a direct sight prism, shows an uninterrupted spectrum, consisting of
points and streaks, which form telegraph signs corresponding to the succession of the
apertures of the slide, the size of this image, which is dependent only on the dispersion
in the telescope, being the same for all distances.
(2.) For the process particularized in claim 1, an emitting or sending apparatus,
which is formed of a perforated slide A which divides the light into narrow and wide
bunches of light LL, which break the light issuing through each single point of tho
slide into parallel rays, and prisms PP, in such a way that from each cone of parallel
rays only a single kind of colour ray is sent in each direction, and thus the apparatus
renders possible a composition of the light rays going in each direction, which is
determined only by order of succession of the apertures of the slide used, but may in
other respects be any desired composition.
(3.) For the process particularized in claim 1, a spectro-telegraphic telescope, called
the receiving apparatus, formed of an ordinary telescope, which is provided with a
direct sight prism of small dispersing power, and which shows, in the light coming
from the emitting or sending apparatus, a spectrum, which is interrupted according to
the position of the rays, i.e., to the succession of the apertures of the slide, and forms
telegraph signs.
Data: 101. 1
TA
1000