IMPROVEMENTS IN TELEPHONIC AND TELEGRAPHIC SIGNALLING APPARATUS
Year: 1882

page_text: LETTERS PATENT to Alfred Charles Brown and Henry Alfred Charles Saunders
both of 66 Old Broad Street in the City of London for an invention of
"IMPROVEMENTS IN TELEPHONIC AND TELEGRAPHIC SIGNALLING APPARATUS"
PROVISIONAL SPECIFICATION left by the said Alfred Charles Brown &
Henry Alfred Charles Saunders at the Office of the Commissioners of Patonts
on the 20th April 1882.
ALFRED CHARLES BROWN and HENRY ALFRED CHARLES SAUNDERS both of
66 Old Broad Street in the City of London "IMPROVEMENTS IN TELEPHONIC
AND TELEGRAPHIC SIGNALLING APPARATUS,"
This Invention has for its object improvements in telephonic and telegraphic
signalling apparatus.
The purpose of our invention is to enable a number of stations connected by
one line wire to communicate under such conditions that any station can speak to
any other, the remaining stations meanwhile being prevented from overbearing or
interrupting.
A patent having the same object in view was granted to us No. 2995 in the
year 1881. Since the date of this Patent we have made further improvements
which we will now proceed to describe.
We will first explain the mechanical construction of the apparatus and afterwards
we will trace the electrical connections.
The apparatus consists mechanically of an axis which can be rotated step by
step, a ratchet wheel upon it being propelled by a click nechanism upon a lever
which at the proper times receives movement from an electro magnet.
This axis carries an index which points upon a dial to the number of the station
which is called to converse, this index stands at zero when the line is out of use.
The axis also carries two cams, one of these simply exercises a mechanical control
of the key hereinafter described, whilst the other opens and closes electrical
contacts.
The key is specially designed to give firm contacts of sufficient duration under
all circumstances; it consists of a plunger with a collar upon it, this is received

page_text: When
between two projections upon a lever which is capable of turning about a pivot
with sufficient friction to remain wherever it may be placed. The lever is capable
of assuming three positions, in each of which it makes a separate contact.
the plunger is first pushed in it carries the lever from the first contact over the
second or intermediate contact to the third contact; the collar on the plunger 5
pushing the lever before it. On the release of the plunger however the lever does
not immediately return for the plunger has to travel a distance before the collar
comes against the second projection on the lever to push it back. Nor does the
lever on its return come back to the first contact from which it started, for the
control mechanism operates to limit the movement of the plunger and the lever is 1
left upon its second contact.
The control mechanism consists simply of the collar upon the plunger and a
lever lying in the path of the collar but which when the index is at the zero point
is lifted away by the control cam. When the index is at zero point therefore the
plunger can be thrust in, but this movement of the plunger (operating electrically) I
gives a step to the index of the instrument with the result that the control lever is
released, and an adjustable weight provided for the purpose causes it to return.
A like movement takes place in every instrument on the line.
The control lever being now in the way of the collar on the plunger, the plunger
already pushed in can only make a partial return but it is free to be used again 2
and again to move its contact lever to and fro between the second and the third
contacts. The plungers which have not been operated upon are locked by the
control lever so that they cannot be moved at all until the index next comes to tho
zero point.
This steady contact key is applicable to other electrical apparatus. The details 2
of its construction may be varied.
The contact cam upon the axis operates simply to make contact with a spring
and to lift it from a stop against which at other times it rests. The cam does this
at the time when the index points to the number of the station to which the
particular instrument belongs.
3
The electrical connections may be traced as follows:-
1st Those of the line circuit. The terminal stations are provided with equal
batteries, and these are opposed to each other. Hence so long as the line is
isolated throughout, no current passes.
In each instrument there is on one side a
permanent connection from line, through the electro magnet to the contact lever of 3
the key; also on the other side of the instrument from line through the telephonic
instruments, to the contact lover.
The third contact (to which the contact lever is brought when the plunger is
pushed in) is coupled to earth hence this movement of the plunger brings the
batteries into effective action. The electro-magnets then move the propelling 4
levers, and in each instrument on the line the index movos a step.
So long as the contact lever remains upon its first contact a shunt is completed
from one side to the other of the telephonic instruments which are thus put out of
operation and their resistance excluded from the line circuit. The course in the
shunt is then from the contact lever, through the first contact, to the contact 4
spring and thence to the stop against which the spring normally rests. This stop
has a permanent connection with the line on the further side of the telephones.
If the station be the called station this shunt is interrupted, for then the contact
cam holds the spring off the stop, consequently at the called station the telephones
are in effective connection with the line.
2nd The connections of the local circuit. The local current, when the circuit
is complete, passes as usual through the bell, (except when the bell is shunted) and
through the transmitting telephone and the primary coil.-Any form of transinitter
may be used.
5
'One pole of the local battery is connected with an insulated stop against which 5
the propelling lever rests when not attracted by the electro magnet and then a
path for the current is provided to the metal frame of the instrument, but at all

page_text: other times the local circuit is incomplete; hence the bell does not ring whilst the
propelment is in progress and the index is travelling around the dial.
The local circuit however is complete throughout in at most two of the stations
on the line; namely at the calling station and at the called station. At the calling
station it may be traced from the frame to the intermediate contact, through the
contact lever of the key, the transmitting telephone and bell or shunt to the other
battery pole.
At the called station the course of the local current is from the frame of the
instrument, by the contact cam and spring to the first contact and thence by the
contact lever as before traced.
To ensure unison in the instruments throughout the line the following means
are resorted to :—At each terminal station a resistance is provided in the course
of the intermediate earth connection. The batteries and the control levers of
the instruments are so adjusted that the distant battery working through the
resistance cannot throw back the control lever, but without the resistance it is
able to do so.
Hence by operating with the key in the usual way all the instruments whatever
may have been the original position of the index are brought to a position removed
by one step from the zero. Then at the same time as the operator gives a final
thrust to the plunger he also presses another button by which the resistance is
shunted thereby causing all the indices simultaneous to move to the zero point.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alfred Charles Brown & Henry Alfred Charles Saunders in the
Great Seal Patent Office on the 19th October 1882.
ALFRED CHARLES BROWN and HENRY ALFRED CHARLES SAUNDERS both of
66 Old Broad Street in the City of London "IMPROVEMENTS IN TELEPHONIC
AND TELEGRAPHIC SIGNALLING APPARATUS."
This Invention has for its object improvements in telephonic and telegraphic
signalling apparatus.
The purpose of our invention is to enable a number of stations connected by one
line wire to communicate under such conditions that any station can speak to any
other, the remaining stations meanwhile being prevented from overhearing or
interrupting.
A patent having the same object in view was granted to us No. 2995 in the
_year 1881. Since the date of this Patent we have made further improvements
which we will now proceed to describe.
We will first explain the mechanical construction of the apparatus and afterwards.
we will trace the electrical connections.
The apparatus consists mechanically of an axis which can be rotated step by
step; a ratchet wheel upon it being propelled by a click mechanism upon a lever
--which, at the proper times receives movement from an electro-magnet.
-
This axis carries an index which points upon a dial to the number of the station
which is called to converse; this index stands at zero when the line is out of use.
The axis also carries two cams one of these simply exercises a mechanical control
of the key hereinafter described, whilst the other opens and closes electrical
contacts.
The key is specially designed to give firm contacts of sufficient duration under
all circumstances; it consists of a plunger with a collar upon it this is received
between two projections upon a lever which is capable of turning about a pivot
with sufficient friction to remain wherever it may be placed. The lever is capable
of assuming three positions; in each of which it makes a separate contact. When
the plunger is first pushed in it carries the lever from the first contact over the
second or intermediate contact, to the third contact; the collar on the plunger
pushing the lever before it. On the release of the plunger however the lever does
not immediately return for the plunger has to travel a distance before the collar
comes against the second projection on the lever to push it back. Nor does the
lever on its return come back to the first contact from which it started, for the
control mechanism operates to limit the movement of the plunger and the lever is
left upon its second contact.
The control mechanism consists simply of the collar upon the plunger and a
lever lying in the path of the collar but which when the index is at the zero point is
lifted away by the control cam. When the index is at the zero point therefore
the plunger can be thrust in, but this movement of the plunger (operating
electrically) gives a step to the index of the instrument with the result that the
control lever is released, and an adjustable weight provided for the purpose causes
it to return. A like movement takes place in every instrument on the line.
The control lever being now in the way of the collar on the plunger the
plunger already pushed in can only make a partial return but it is free to be used
again and again to move its contact lever to and fro between the second and the
third contacts. The plungers which have not been operated upon are locked by
the control lever so that they cannot be moved at all until the index next comes
to the zero point.

page_text: This steady contact key is applicable to other electrical apparatus. The details
of its construction may be varied.
The contact cam upon the axis operates simply to make contact with a spring
and to lift it from a stop against which at other times it rests. The cam does this
at the time when the index points to the number of the station to which the
particular instrument belongs.
The electrical connections may be traced as follows:-
:-
1st Those of the line circuit. The terminal stations are provided with equal
batteries, and these are opposed to each other. Hence so long as the line is
isolated throughout, no current passes. In cach instrument there is on one side a
permanent connection from line, through the electro-magnet, to the contact lover
of the key; also on the other side of the instrument, from line, through the
telephonic instruments to the contact lever.
The third contact (to which the contact lever is brought when the plunger is
pushed in) is coupled to earth, hence this movement of the plunger brings the
batteries into effective action. The electro magnets then move the propelling
levers and in each instrument on the line the index moves a step. So long as the
.contact lever remains upon its first contact a shunt is completed from one side to
the other of the telephonic instruments which are thus put out of operation
and their resistance excluded from the line circuit. The course in the shunt is
then from the contact lever, through the first contact, to the contact spring, and
thence to the stop against which the spring normally rests. This stop has a
perinanent connection with the line on the further side of the telephones.
If the station be the called station this shunt is interrupted, for then the contact
cam holds the spring off the stop, consequently at the called station the telephones
are in effective connection with the line.
2nd. The connections of the local circuit. The local current, when the circuit
is complete passes as usual through the bell (except when the bell is shunted) and
through the transmitting telephone and the primary coil. Any form of transmitter
may be used.
One pole of the local battery is connected with an insulated stop against which
the propelling lever rests when not attracted by the electro-magnet and then a path
for the current is provided to the metal frame of the instrument, but at all other
times the local circuit is incomplete; hence the bell does not ring whilst the
propelment is in progress and the index is travelling around the dial.
The local circuit however is complete throughout in at most two of the stations
on the line; namely at the calling station, and at the called station. At the
calling station it may be traced from the frame, to the intermediate contact through
the contact lever of the key, the transmitting telephone and bell or shunt to the
other battery pole.
At the called station the course of the local current is from the frame of the
instrument by the contact cam and spring, to the first contact and thence by the
contact lever as before traced.
To ensure unison in the instruments throughout the line the following means
are resorted to:-At each terminal station a resistance is provided in the course of
the intermediate earth connection. The batteries and the control levers of the
instruments are so adjusted that the distant battery working through the
resistance cannot throw back the control lever, but without the resistance it is able
to do so.
Hence by operating with the key in the usual way all the instruments whatever
may have been the original position of the index are brought to a position
removed by one step from the zero.
Then at the same time as the operator gives
a final thrust to the plunger he also presses another button by which the resistance
is shunted, thereby causing all the indices simultaneously to move to the zero
point.
In order that our said invention may be most fully understood and readily
carried into effect we will proceed to describe the Drawings hereunto annexed.

page_text: The plunger has upon it the collar and a coiled-spring presses it outwards.
m is a contact making lever, it has its fulcrum at m¹ and its other end bears upon
the pillar n, which consists of three metal discs n¹ n³ n³ electrically separated the
one from the other. The lever m also is isolated and the end of it which comes
-against-the pillar n is armed with a piece of platinum wire m² to form a sharp
well defined contact edge m³ m³ are two ivory pins inserted into the lever mone
of them is above and the other below the collar of the key or plunger. The
drawing represents the lever m upon the first contact n'. When the plunger lis
pushed in the lever m is moved to its third contact n³, the return of the plunger
does not immediately affect the contact lever for the collar has to traverse the
space between the two pins m³ m³ before it operates to move the lever. By these
means a contact of a certain duration is ensured. This key is useful not only in
the instrument now being described but in other apparatus in which a key giving
well defined prolonged contacts is required.
o is a lever pivotted at its upper end at o' it has an adjustable weight o² upon it
which holds it, when otherwise free, in contact with the stop o³, in this position the
lower end of the lever is in the way of the collar of the plunger and the plunger
if out cannot be pushed in, or if in, cannot spring out to the full distance. There
is however on the main axis d, a cam p and this when the index is at the zero
point has thrust the lever to the left clear of the collar 1. The main axis d also
has upon it another cam 9 which at one point in the rotation of the axis comes into
contact with a light isolated spring r and lifts it off an adjustable isolated stop 8
against which at other times it bears. This takes place when the index is at the
number of the station to which the instrument belongs.
tt are binding screws to receive the circuit wires and the thick dotted lines
passing from these indicate the electrical connections, but these we can better trace
by the aid of the diagram Figure 4. This diagram includes not only the
connections within the instrument represented by the preceding figures but also
the connections with the receiving and transmitting instruments and tho batteries
at the terminal stations. uu are the opposed terminal batteries each with ono
pole to earth and between are the complete connections of one station and every
station is in this respects similar.
The parts of the instrument Figures 1, 2 and 3 which are marked in this
diagram are; the electro-magnet a. the contact lever m, its three contact discs n¹ n²
and ³, the cam g, the spring r, and the stop s. Also the pawl lever c and its back
stopf which is isolated from the frame and connected with the copper pole of v
a local battery. The diagram also indicates w a bell, the transmitting telephone,
y y¹ the primary and secondary of an induction coil and z the receiving telephone.

page_text: The parts cn and q are in permanent condition with the metal frame of the
instrument.
When the station at which the instrument is is neither the calling or the called
station a current entering by the line wire may be traced from left to right of the
diagram as follows:-through the coils of the magnet a, thereby (if the current be
a battery current) moving the index a step, thence to the lever m the contact
disc n¹ the spring and the stop s to the line wire on the right.
If the station be the calling station, when the lover m is upon the disc n³, the
current may be traced from the terminal battery u, on the right hand through all
the instruments on this side of the calling station, through the magnet a to the
lever m and the disc ³ to earth and so back to the battery. At the same time
the current from the other terminal battery passes through all the instruments on
the right side of the calling station, through the secondary coil y' and the telephone
to the lever m and to carth. Hence each time that the lever m is placed upon tho
contact disc n³ the index of every instrument in circuit moves a step. Supposing
the station required to have been called, the state of affairs at the calling station
is then as follows:-the lever m is upon the disc n², the incoming telephonic
currents then pass in part through the telephone z and are translated into audible
speech. And in part (following the diagram in which the secondary and the
receiving telephone are shown as in parallel circuit) they pass through the
secondary coil y' and so on by the line wire. The local battery circuit is also
closed through and c and n² and m and y and x and w. The bell w however does
not ring for it is short circuited by the usual switch hook which cuts out the bell
whenever the receiving telephone is taken down for use. When by speaking
into the transmitting telephone x the local current is caused to be affected with
the voice undulations, similar undulations are induced in the secondary coil y¹
which flow throughout the entire main circuit and are translated into voice sounds
by the receiving telephones in this circuit.
Again if the station be the called station the lever m will be upon the disc n¹
and the cam g will havo lifted the spring + from the stop 8.
The main and the
local circuits can now be traced as in the calling instrument with the exception
that the local circuit is closed through q and r and n' and m. It will be observed
that on hanging up the telephone at the calling or called station the bell will
commence to ring, as then it will no longer be short circuited, and this is a useful
reminder to the operator to clear the line by bringing the index to zero. r in the
diagram marks the position in which, if the instrument belongs to a terminal
station, a resistance coil is inserted. About 80 ohms will be found a suitable
resistance. It comes in as will be seen between the disc n³ and its earth connection.
The effect is to reduce the strength of the current with which the terminal station
normally operates below that which is employed by the other stations; so that the
normal current from the terminal station may be mado insufficient to move the
lever o of any of the instruments in circuit. Consequently when the terminal
station is operating, all the instruments can be brought to stop at the point where
the camp bears against the lever o that is to say, at one step removed from the
zero, and so they are syncronised. This having been done the operator at the
terininal short circuits this resistance by means of a press button provided for the
purpose and by another pressure upon the plunger he brings all the indices
simultaneously to the zero
Having thus described the nature of our said invention and the manner of
performing the same we would have it understood that we claim :-
First. Our prolonged contact key for effecting well defined and prolonged
contacts and consisting of the plunger I, the lever m and the pillar n or their
equivalents arranged and combined substantially as described.
Second. The combination substantially as described with the parts I m and n or
their equivalents of the controlling lever o or its equivalent, controlling the contacts
brought about by the action of the other parts.
Third. The lever m under the control of the key or plunger, and forming at one

page_text: time a portion of the local circuit and at another of the main circuit shunting the
speaking instrument substantially as described.
Fourth. The pawl lever c serving both to propel the main axis d and to complete
the local circuit by resting against the back stop f substantially as described.
Fifth. The method of syncronising the indices k, when working with opposed
batteries, by so arranging that a strong action of the propelment is requisite for
one of the steps of the index, and by providing a resistance in the earth connection
at the terminal station which can be short circuited at the pleasure of the operator
substantially as described.
Sixth. Our improvements in telephonic and telegraphic signalling apparatus
substantially as described.
In witness whereof we the said Alfred Charles Brown and Henry Alfred
Charles Saunders have hereunto set our hands and seals this fourth day of
October in the year of our Lord One thousand eight hundred and eighty