IMPROVEMENTS IN ELECTRIC TELEGRAPHY AND IN APPARATUS FOR THE
Year: 1874

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane,
in the County of Middlesex, Patent Agent, for the Invention of
"IMPROVEMENTS IN ELECTRIC TELEGRAPHY AND IN APPARATUS FOR THE
."-A communication from abroad by Georges d'Infreville
and William Nevins Armstrong, both of the City, County, and State
SAME.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his
Petition, on the 17th March 1874.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County
of Middlesex, Patent Agent, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN ELECTRIC TELEGRAPHY, AND IN Apparatus -
FOR THE SAME," to be as follows:
-
The object of this Invention is to obtain a simple method of sending
messages simultaneously over the same wire in opposite directions,

page_text: use, and for this purpose and for illustration the Morse system is adopted
for example.
The Invention requires the following arrangements :-
⋅
First. Opposing to cach other through a telegraphic line at its
extremities the similar poles of the terminal batteries so that they have
a common circuit and neutralize each other.
Second. In using a single contact key at each station in working the 1
linc for duplex transmission. The anvil of this koy connects with the
ground, while a wire from its lever is in junction with a proper point
in the wire of the helices of the main electro-magnet, the purpose of
which will be described hercafter.
Third. The exposing of one or more layers or parts of the helices of 1
one spool of the main electro-magnet so that direct contact can be made
at any desirable point in the helices with the wire from the lever of the
key.
Fourth. A shunt circuit of variable and proper resistance, one
extremity of which is attached to the wire connecting the key with the 2
helices above described, the other extremity being connected when
required with one or the other end of the wire going out of the electro-
magnet, as explained hereafter.
By way of explanation it may be stated that in a. common circuit
when the poles of the two batteries are opposed there is no current, but 2
if a wire connects the common circuit with the ground two distinct
circuits are at once made. Also if one spool of a. common electro-magnet
be traversed by an electric current, and the other spool be traversed by.
a current in an opposite direction, they tend to neutralize each other's
effect, while either current acting alone would produce magnetization.
3
The Invention consists in the combination and use of the above
mentioned opposing batteries, electro-magnet, single contact keys with
shunt circuit, if necessary, so that the depressing of the key at the
sending station divides the common circuit of the batteries herein-before
described into two independent circuits, one of the distant and receiving 3
station through the line and sending station, and the other a short circuit
i

page_text: of the battery at the sending station, the former recording signals at
receiving station, and both circuits neutralizing each other's effect in tho
sending station, so that its armature is not affected'; and also by
depressing simultaneously these keys at terminal stations two distant
local and independent circuits are made at each station, and each station
records only the signal of the other. The circuit reversers are here used
in order to show how this system can be used with the common Morse
plan and the single transmitting and ordinary method used by simply
moving the circuit reverser and connecting the line and batteries in
the usual way.
This new system when used alone would connect through wire e the
electro-magnet and battery pole B, dispensing with X; a', ',.d', and
negative pole A would go directly to ground, see Figure 1 of the accom-
panying Drawings, which represents a plan view of the system, showing
the arrangement for a line of three stations, two terminal and one way,
all in the same circuit; the disposition is the same if more stations aro
used; Figure 2 is a sectional view of one of the stations; Figure 3, à
detail end view of one coil of the main electro-magnet. Similar letters
of reference indicate corresponding parts.
The letter A represents the negative and B the positive poles of the
- main battery at terminal station C, the other terminal station D has -
the poles of its main battery represented by E for the negative and F
for the positive pole; G is a way station without any main battery, the
poles of the batteries are connected with the arms of the circuit reversers
X and X' repectively.
The Drawing shows the line ready for duplex transmission. The circuit
of the battery at the station C is as follows:-From the positive pole B
through arm a of circuit reverser X, conductor 6', anvil of common
key R (used in single transmission), circuit closer d¹ of the key R,
conductor e, helices of electro-magnet H through line wire I, and if the
cut out is open, as shown, at way station G through the clectro-
magnet J and circuit closer j (of the common key for single trans-
mission), conductor 1, again line I, helices of electro-magnet L at
terminal station D, conductor e, circuit closer d², conductor 6ª, and
conductor a of circuit closer X³, which is attached to the screw.
post of the positive pole F through battery at D, ground wire N, ground
conductor N, and other arm of circuit reverser a to negative pole A,
.

page_text: Also circuit froni battery at station D is from positive pole F, through
a², b², d², c², magnet L, line I (and way station G), nagnet H, wire
e, d', b¹, arm a¹ of circuit reverser X to positive pole B, through battery
at C, other arm of circuit reverser ✗, conductor N2, to ground and N
to negative pole E, all as indicated by arrows in Figure 1.
It will be noticed in the Drawing that the Morse key with circuit
closer is shown in direct circuit in all the stations, so that by merely
changing the position of the circuit reverser of either terminal station
the line can be worked on the closed circuit system for simple trans-
mission, the relay armatures being attracted when line is not worked.
Fig. 1 shews at station C a small rheostat o in the shunt circuit, one
extremity of which is connected with conductor h², while the other part
of shunt may be brought in contact with e when necessary through aṛm m.
Similar dispositions are made at the other stations, at the way stations
the movable arm of the reostal can be brought in contact with one or the
other extremity of the electro-magnet, as may be required, through a
commutator or switch attached to the arm.
In the position as shown in the Drawing, with the batteries opposed
and the key at rest, no current flows in the line sufficient to overcome
the springs of the armatures, because the circuit of both batteries being
always closed and the batteries being connected to the line so as to
oppose each other, the currents become opposed to cach other and
neutralize the effect in the electro-magnets.
One condition of duplex telegraphy is that a station shall send signals
without affecting its own magnet and armature, although they are in
the direct circuit.
The operation is as follows:-Let key M³ (used for duplex transmission)
be depressed at station C, at once the current from positive pole B at
station C passes through conductor a¹, b', circuit closer of single
transmission key d', conductor e, entering the spool H at the right side
in drawing off the clectro-magnet H, running over a part of its helices
but leaving it where wire ² is attached to it through h², key M³, part
of conductor N2, and returning through branch of circuit reverser X to
the negative pole of battery. The other current from positive pole F
at station D being no longer opposed by current from B at station C
passes through conductors a, b, circuit closer d', conductor e², helices
of electro-maget L, magnetizing its cores, attracting its armature,
recording signal of M₁ through line I, the magnets at way stations

page_text: recording the same signal by attracting their armatures, then to and
through a part of electro-magnet at station C to the junction of wire
with helices, then through wire h³, through key M³, conductor N³, to
the ground, back to negative pole E of battery at D, through part of N
and circuit reverser X³, back to negative pole E of battery at D. It
will be noticed that the current from B, working in local circuit, and
the current from F both use the wire ², key M², and part of conductor N³,
in common from the junction of ³, with the helices II, and as far as
the circuit reverser X. The key M³, serves to conduct two currents.
While all the electro-magnets of the line have their armatures
attracted by the current from D the electro-magnet H at C', the sending
station, does not attract its armature, for it has been divided by wire h
into two parts, which are now travelled by opposite currents of different
intensities. Each current tends to produce a magnetic polarity different
from that of the other. If the two parts of the helices are so divided.
that the polarity which the strongest current coming from the now
local battery tends to produce in going through the shortest part nearly
counterbalances or neutralizes the polarity which the weaker current
coming from the distant battery tends to produce in going through the
longer part and in opposite direction, no appreciable magnetization will.
take place in the cores of the electro-magnet, and the armature of H.
will not be attracted.. Thus one important condition of duplex
telegraphy is secured..
The dividing of the helices into two parts, so that the current in one
part shall neutralize properly the opposing current in the other part, is
made by connecting the wire 72 to the exposed layers of the electro-.
magnet at a point which the working of the line will determine.
any
The proper connection is made when on depressing the key at
station its own armature is not affected, the other keys being at rest.
If the key M at station D is also depressed alone the results are the
same. Its armature is not affected, but the armature of receiving
station is at work. It thus appears that by this disposition of the line
and instruments, one key alone being depressed, that the sending station.
records its signal at the receiving station by receiving instead of sending
a current, and allowing the current of the receiving station its full force
in recording. Thus far the working of the current when one key only,
for instance M², is depressed has been explained. The duplex trans-

page_text: '
mission will now be shown. If while the key M2 is depressed, as above
described, working the distant stations with its own at rest the key M at
station D is also depressed the current from positive pole F at D ceases
to pass through the line to C, because a short circuit is instantly
established. The current runs from positive pole F through a², d, e,.
through part of a magnet L, back through wire hand N to negativo
pole E. As this current, moving on a short circuit, no longer runs
along wire I to magnet H the neutralization existing at H when M² was
alone depressed is destroyed, and and its armature is at once attracted
through the magnetization of local current at C made by depressed key M³.
The currents of both batteries move in local circuit, because they meet the
least resistance in that way. The circuit is not broken through the.
line; the very slight escape of electricity in H and L to the line from
the local circuits still oppose each other. The armature at D, which was
attracted by the depressed key M², still remains depressed, because the
ourrents from F still run through a part of magnet L, and with
increased power, because it is on a short circuit. Stations C and D are
now in the same conditions. If now key M be raised the condition_of_
the current and working is again the same as when M² alone worked.
The current from pole F again runs over line to H, neutralizes
current from B, and armature of H goes back, while armature at L
remains attracted as before by the working of key M². Thus the
working of the armature at each terminal station is dependant upon and
controlled by the working of the key at opposite terminal station.
Although the way station G has no main battery it sends and receives
messages in the same way. If the key P is depressed the two currents
from C and D cease to oppose each other, and go to the ground in
common through key P and conductor Q back to their respective
negative poles. For it is well known that if two batteries are opposed
to each other in a line a ground wire at any part of the line will divide
this line in two distinct circuits, each of which will operate without
interfering with the other. The armature of H and of other way
stations, if any, one attracted by current from positive pole B, going
to G and armatures at D, and at other way stations, if any, are
attracted by current from positive pole F going to G. The opposite
currents meeting in the electro-magnet at G neutralize each other, so
its own message is not recorded.
·
•
The way station does not require a main battery; station G does not
require a main battery to transmit to or receive from C; it uses the mai

page_text: battery at D for its local neutralization exactly as D uses it; only it is at
a distance. Also G will use main battery of C for its local neutralization
when it is signalling with D and G in duplex transmission with D'will
operate exactly as if it was station C. This is an important part of the
Invention. Thus any two stations, either terminal or way, or terminal
and way, can perform duplex transmission. As above described the
wire h² is connected with a point in the helices of electro-magnet H, so
as to effect neutralization of current. The desired point may not always
be available, as it may be in the interior of the magnet.
The shunt circuit will secure a finer adjustment if needed, as described,
and adjusted it draws off a part of one of the currents which produces
too much polarity. If M³ is depressed and the current of pole B is
creating too much polarity in magnet H, because h³ is not at the proper
point, the shunt circuit draws off a part of current from B at e until the
neutralization is as complete as possible. The small rheostat in this
shunt serves to regulate its resistance according to the changes which may
occur in different parts of the circuit. This shunt is not new in itself,
but it is new when used in the condition shewn; that is for securing a
neutralization of currents' effects in the electro-magnet by drawing off
an excess of electricity. This system has been shewn in combination
with the Morse system of working in a closed circuit. It can readily
and as easily be combined with such system working in an open circuit,
simply by using a triple-pointed key, and a suitable commutator. In this
case the key and the receiving instrument change places with reference
to the line and the battery.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Alexander Melville Clark in the Great Seal Patent
Office on the 17th September 1874.
:
- TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
› MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her. Letters
Patent, bearing date the Seveteenth day of March, in the year of our
Lord One thousand eight hundred and seventy-four, in the thirty-seventh

page_text: "
year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto I, the said Alexander Melville Clark, Her special
licence that I, the said Alexander Melville Clark, my executors, admini-
strators, and assigns, or such others as I, the said Alexander Melville
Clark, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make;
use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN ELECTRIC TELEGRAPHY, AND IN APPARATUS FOR THE SAME," a
communication to me from abroad by Georges d'Infreville and William
Nevins Armstrong, both of the City, County, and State of New York,
United States of America, upon the condition (amongst others) that
I, the said Alexander Melville Clark, my executors or administrators,
by an instrument in writing under my, or their, or one of their hands
and seals, should particularly describe and ascertain the nature of the
said Invention, and in what manner the same was to be performed,
and cause the same to be filed in the Great Seal Patent Office within
six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Alexander Melville Clark, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the accompanying
Sheet of Drawings, and to the letters and figures marked thereon (that
is to say):-
The object of this Invention is to obtain a simple method of sending
messages simultaneously over the same wire, in opposite directions,
cither between terminal, or terminal and way, or way and way stations..
It has for a further object the sending of messages as above set forth
with the least possible change of instruments and dispositions already in
use, and for this purpose and for illustration the Morse system is
exhibited in the Drawing.
The Invention requires the following arrangements :--
First. Opposing to each other through a telegraphic line at its
extremities the similar poles of the terminal batteries, so that they have
a common circuit and neutralize each other...

page_text: Second. In using a single contact key at each station in working the
line for duplex transmission; the anvil of this key connects with the
ground, while a wire from its lever is in junction with a proper point in
the wire of the helices of the main clectro-magnet, the purpose of which
will be described hereafter.
Third.. The exposing of one or more layers or parts of the helices of
one spool of the main electro-magnet, so that direct contact. can be made
at any desirable point in the helices with the wire from lever of the
key.
Fourth. A shunt circuit of variable and proper resistance, one extremity
of which is attached to the wire connecting the key with the helices
above described, the other extremity being connected when required
with one or the other end of the wire going out of the electro-magnet, as
explained hereafter..
By way of explanation it may be stated that in a common circuit
when the poles of the two batteries are opposed there is no current, but
if a wire connects the common circuit with tlie ground two distinct
circuits are at once made; also if one spool of a common electro-magnet
be traversed by an electric current, and the other spool be traversed by a
current in an opposite direction, they tend to neutralize each other's
effect, while either current acting alone would produce magnetization..
-
The Invention consists in the combination and use of the above-
mentioned opposing batteries, electro-magnets, single contact keys with
shunt circuit, if necessary, so that the depressing of the key at the
sending station divides the common circuit of the batteries herein-before
described into two independent. circuits, one of the distant and receiving
station through the line and sending station, and the other a short
circuit of the battery at the sending station, the former recording signals
at receiving station, and both circuits neutralizing each other's effect in
the sending station, so that its armature is not affected; and also by
depressing simultaneously the keys at terminal stations two distinct local
and independent circuits are made at each station, and each station
records only the signal of the other. The circuit reversers are here used
in order to show how this system can be used with the common Morse
plan, and the single transmitting and ordinary method used. by simply
moving the circuit reverser, and connecting the line and batteries in the..
usual way.

page_text: i
This new system, when used alone, would connect through wire e the
electro-magnet and battery. pole B, dispensing with X, a¹, b¹, d¹, and
-negative pole A would go directly to ground.
:
In the accompanying Drawings Figure 1 represents a plan view of the
system, showing the arrangement of a line of three stations, two terminal
and one way, all in the same circuit.. The diposition is the same if more
stations are used. Figure 2 is a sectional view of one of the stations
Figure 3, a detail end view of one coil of the main electro-magnet.
Similar letters of reference indicate corresponding parts.
i
The letter A represents the negative; and B, the positive pole of the
'main battery at terminal station C. The other terminal station D has
the poles of its main battery represented by E for the negative, and F
for the positive poles. G is a way station without any main battery.
The poles of the batteries are connected with the arms of the circuit
reversers X and X² respectively.
The Drawing shows the line ready for duplex transmission. The circuit of
the battery at station C is as follows: From the positive pole B, through
arm a¹ of circuit reverser X, conductor 6', anvil of common key R (used
in single transmission), circuit closer d¹ of the key R, conductor e,
helices of electro-magnet H, through line wire I, and if the cut out g is
open, as shown at way station G, through: the electro-magnet. J, and
circuit closer j (of the common key for single transmission), conductor 7,
again line I, helices of electro-magnet L at terminal station D, con-
ductor e, circuit closer d³, conductor 62; and conductor a³ of circuit
closer, which is attached to the screw post of the positive pole F,
through battery at D, ground wire N, ground conductor N³, and other
arm of circuit reverser X, to negative pole A; also circuit from battery
at station D is from positive pole F, through a, b, d, e, magnet L,
line I (and way station G), magnet H, wire e¹, d¹, b', arm a¹ of circuit
reverser X to positive pole B, through battery at C, other arm of circuit
reverser X, conductor N³; to ground, and N to negative pole E, all as
indicated by arrows in Figure 1.
It will be noticed in the Drawing that the Morse key with circuit
closer is shown in direct circuit in all the stations, so that by. merely
changing the position of the circuit reverser of either terminal station,
the line can be worked on the closed circuit system for simple trans-
mission, the relay armatures being attracted when line is not worked.

page_text: Figure 1 shows at station C a small rheostat o in the shunt circuit,
one extremity of which is connected with conductor 2, while the other
part of shunt may be brought in contact with e when necessary through
arm m.
Similar dispositions are made at the other stations; at the way
stations the movable arm of the rheostat can be brought in contact with
one or the other extremity of the clectro-magnet as may be required,
through a commutator or switch attached to the arm.
In the position as shown in the Drawing with the batteries opposed
and the key at rest, no current flows in the line sufficient to overcome
the springs of the armatures, because the circuit of both batteries being
always closed and the batteries. being connected to the line so as to
oppose each other, the currents become opposed to each other and
neutralize the effect in the electro-magnets.
One condition of duplex telegraphy is that a station shall send signals
without affecting its own magnet and armature, although they are in the
direct circuit.
The operation is as follows:-Let key M² (used for duplex trans-
mission) be depressed at station C at once, the circuit from positive
pole B at station C passes through conductor a¹, b', circuit closer of single
transmission key d' conductor e, entering the spool H at the right side
in Drawing of the electro-magnet H, running over a part of its helices
but leaving it where wire he is attached to it, through h², key M³, part of
conductor N³, and returning through branch of circuit reverser X to the
negative pole of battery. The other current from positive pole F at
station D being no longer opposed by current from B at station C passes
through conductors a², 62, circuit closer d², conductor e², helices of
electro-magnet L, magnetizing its cores, attracting its armature,
recording signal of M³ through line I, the magnets at way stations
recording the same signals by attracting their armatures, then to and.
through a part of clectro-magnet at station C, to the junction of wire h
with helices, then through wire ³, through key M³, conductor Nº, to the
ground, back to negative pole E of battery at D, through part of N and
circuit reverser X², back to negative pole E of battery at D. It will be
noticed that the current from B working in local circuit and the current
from F, both use the wire h², key M², and part of conductor N³, in
common from the junction of h² with the helix H, and as far as the
circuit reverser X. The key M serves to conduct two currents.

page_text: While all the electro-magnets of the line have their armatures
attracted by the current from D, the electro-magnet H at C the sending
station does not attract its armature, for it has been divided by wire 7³
into two parts which are now travelled by opposite currents of different
intensitics. Each current tends to produce a magnetic polarity different
from that of the other. If the two parts of the helices are so divided
that the polarity which the strongest current coming from the now local
battery tends to produce in going through the shortest part, nearly
counterbalances or neutralizes the polarity which the weaker current.
coming from the distant battery tends to produce in going through the
longer part and in opposite direction no appreciable magnetization will,
take place in the cores of the clectro-magnet, and the armature of H.
will not be attracted. Thus one important condition of duplex.
telegraphy is secured.
The dividing of the helices into two parts so that the current in ono
part shall neutralize properly, the opposing current in the other part is
made by connecting the wire 2 to the exposed layers of the electro-
magnet at a point which the working of the line will determine.
The proper connection is made when on depressing the key at any
station its own armature is not affected the other keys being at rest.. If
the key M. at station D is also depressed alone the results are the same.
Its armature is not affected but the armature of receiving station is at
work. It thus appears that by this disposition of the line and instru..
ments one key alone being depressed, that the sending station records its
signal at the receiving station by receiving instead of sending a current
and allowing the current of the receiving station its full force in
recording. Thus far the working of the current when one key only, for
instance M², is depressed has been explained. The duplex transmission
will now be shown. If while the key M² is depressed as above described
working the distant stations with its own at rest the key M at station D
be also depressed, the current from positive pole Fat D ceases to pass
through the line to C because a short circuit is instantly established.
The current runs from positive pole F through a², d², e², through part of
magnet L, back through wire and N to negative pole E. As this
current moving in a short circuit no longer runs along wire I to magnet
H the neutralization existing at H when M² was alone depressed is
destroyed, and its armature is at once attracted through the magnetization
of local current at C made by depressed key M². The currents of both

page_text: batteries move in local circuits because they meet the least resistance in
that way. Their circuit is not broken through the line, the very slight
escape of electricity in H and L to the line from the local circuits still
oppose each other. The armature at D which was attracted by the
depressed key M² still remains depressed because the currents from F
still run through a part of maguct L, and with increased power because
it is on a short circuit. Stations C and D are now in the same condition.
If now key M be raised the condition of the current and working is.
again the same as when M² alone worked. The current from pole F
again runs over line to H, neutralizes current from B, and armature of H
goes back, while armature at L remains attracted as before by the work-
ing of the key M². Thus the working of the armature at each terminal
station is dependent upon and controlled by the working of the key at
opposite terminal station. Although the way station C has no main
battery it sends and receives messages in the same way. If the. key P is
depressed the two currents from C and D cease to oppose cach other,
and go to the ground in common through key P and conductor Q back
to their respective negative poles. For it is well known that if two
batteries are opposed to each other in a line, a ground wire at any point
of the line will divide this linc in two distinct circuits each of which will
operate without interfering with the other. The armature of H and of
other way stations if any are attracted by current from positive pole B
going to G and armatures at D, and at other way stations if any are
attracted by current from positive polc F going to G. The opposite
currents meeting in the electro-magnet at G neutralize. each other so
that its own message is not recorded.
The way station does not require a main battery. Station G docs
not require a main battery to transmit to or receive from C. It uses
the main battery D for its local neutralization exactly as D uses it, only
it is at a distance. Also G will use main battery of C for its local
neutralization when it is signalling with D and G in duplex transmission
with D will operate exactly as if it was station C. This is an important
part of the Invention. Thus any two stations, either terminal or way,
or terminal and way, can perform duplex transmission. As above
described the wire is connected with a point in the helices of electro-
magnet H so as to effect neutralization of current.. The desired point
may not always be available, as it may be in the interior of the
magnet.

page_text: t
+
,
A's
The shunt circuit will secure a finer adjustment if needed.
described and adjusted it draws off a part of one of the currents which
produces too much polarity. If M² is depressed, and the current of
pole B is creating too much polarity in magnet H. because 2 is not at
the proper point, the shunt circuit draws off a part of current from Bate
until the neutralization is as complete as possible. The small rheostat
in the shunt serves to regulate its resistance according to the changes
which may occur in different parts of the circuit. This shunt itself
is not new in itself, but it is new when used in the condition shown, that
is, for securing a neutralization of currents' effects in the electro-magnet
by drawing off an excess of electricity. This system has been shown in
combination with the Morse system of working on a closed circuit. It
can readily and as casily be combined with such system working in an
open circuit simply by using a triple-pointed key and a suitable com-
mutator. In this case the key and the receiving instrument change
places with reference to the line and the battery.
Having described the nature of the Invention and the manner of
performing the same, I declare that what I claim as the Invention to be
protected by the herein-before in part recited Letters Patent is,—
1stly. The method of duplex telegraphing, essentially as described, by
localizing or short circuiting the main battery at the sending station,
thereby preserving the magnetic equilibrium in the signalling instru-
ments of that station, and allowing the battery at the receiving station
to there exert its full force and record or indicate the signal, substantially
as herein described.
2ndly. In combination with a normally closed telegraph line having
main batteries, one at each terminal connected to the line in opposition
to each other, an open circuit, single contact keys M, M², and branch
circuits h, h², connected to the relay magnets at a suitable point, the
closing of said, keys, short circuiting, or localizing the battery of the
sending station through the proper proportion of the coils of the relay,
substantially as set forth.
3rdly. In combination with a relay magnet having its layers exposed
at intervals for connection to key and for approximate adjustments, as
described, the shunt circuit m and rheostat o, substantially as and for the
purposes set forth,

page_text: 4thly. In combination with the normally closed line having the branch
circuits h, 3, and open circuit, single contact keys, and opposed batteries,
as described, the battery reversers and closed circuit keys, substantially
as set forth.
5thly. The combination with the main line of a duplex telegraph at an
intermediate or way station of the open circuit key|P and branch circuit i
connected to the relay between its terminals, the depression of the key
closing simultaneously independent circuits for both terminal batteries,
giving signals to both sides of the way station in single transmission,
or forming a duplex line with one terminal, substantially as described.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and scal, this Sixteenth day of September,
in the year of our Lord One thousand eight hundred and seventy-
four.
Witness,
HARRY SWALES,
53, Chancery Lane,
London.
A. M. CLARK. (L.S.)