IMPROVEMENTS IN TELEPHONIC AND TELEGRAPHIC SIGNALLING APPARATUS
Year: 1881

page_text: LETTERS PATENT to Alfred Charles Brown and Henry Alfred Charles
Saunders, both of 6G, Old Broad Street, in the City of London, for an
PROVISIONAL SPECIFICATION left by the said Alfred Charles Brown and
Henry Alfred Charles Saunders at the Office of the Commissioners of
Patents on the 24th November 1881.
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.
Our improvements are applicable mainly where a series of stations are connected
by a line wire, and where it is desired that any station may, when the line is
unoccupied, be able to place itself in communication with any other station on tho
line, excluding other stations, so that they can neither hear nor interrupt.
First. We provide at each station an instrument with a graduated series of
resistances which the operator can insert in the line circuit to vary its resistance.
Second. We provide each instrument with an electro-magnet with armatures
held back by springs differently adjusted, or other like contrivance for appreciating
the resistance in the line circuit (the battery remaining constant). This appre-
ciating contrivance controls the connections both of the resistances and of the
receiver and transmitter, preventing their being placed in effective connection with
the line circuit, except the resistance of the line circuit has been set to a pre-
arranged quantity.
Third. We provide each instrument with blocking parts, which render the
variation of the resistance inoperative in the instrument in which it is produced.
This combination works together in the following manner:-An operator wishing
to call another station moves a handle to a corresponding mark, and thereby he
first blocks and renders inoperative the appreciating contrivance of his own
instrument, and then adjusts the resistance of the line circuit. The appreciating
contrivances at all the other stations respond, preventing effected connection being
established with the line at all stations but the one having an instrument adjusted

page_text: to the particular resistance which has been brought about. The bell at this
station being rung, the operator there moves his handle, thereby blocking his
instrument also, and establishing the communication. On the handles being
replaced the line is ready for other stations similarly to converse.
When an induction coil is made use of in connection with telephonic apparatus,
a secondary coil is divided into sections and made use of as resistance to be added
to the line circuit to effect the desired adjustment. The coils of the telephone can
be similarly employed.
One of the stations may if desired be a central office or exchange, and the
apparatus can then be arranged so that any subscriber on this circuit can be plugged
through or connected to any other subscriber on the exchange system, whether or not
he be on a similar or dissimilar system to our own, or brought on to the exchange
by any other system whatsoever.
To do this we make use of an arrangement which permits of our line being
earthed or grounded at each end, while still establishing speaking communication
with any branch line with which the exchange may connect it, and that without
making any electrical contact with the said branch line, or in any way altering
the resistance of our main lines and set of apparatus by the connection.
We accomplish this by simply inserting in our apparatus at the exchange in
place of the telephone and secondary one coil of a special induction coil having two
coils of about equal resistances. The second coil of the induction then communi-
cates the one end with earth and the other end with the branch line, over which
it is desired to establish communication. The resistance of our line is evidently
therefore not affected by the connection since the two coils are insulated from one
another, while the inductive effect of the one on the other establishes effective
speaking communication between them.
All the exchange has to do therefore when a subscriber on our system calls up
is to call the attention of the subscriber on the branch line wanted, and connect the
said branch line to the wire leading from the end of the second coil of our induction
coil, the same as they would connect two branch lines together in the ordinary
manner, or vice versa.
The speaking instruments of the central office itself may be intermediate in this
branch circuit or in the main line circuit itself, as desired.
At telephone stations we sometimes make the following arrangements in order
that the removal of the receiving telephone from its hook may place it and its
secondary coil in the line circuit, and also close the local circuit through the
transmitter and the primary of the induction coil.
We couple the bell, the secondary, and the telephone in series in the line circuit,
and arrange that when the telephone is hanging on its hook and the hook is
depressed, contact is made on a stud so as to establish a short circuit for the
current in which it passes in preference to the secondary coil and telephone. On
removing the telephone from the hook this short circuit is broken. The hook is
connected with one pole of the local battery, and when the telephone is removed
the hook rises and makes contact with another stud, thereby closing the circuit
through the transmitter and primary coils.
When using step by step or clock mechanism to put any one of a number of
instruments on the same circuit into effective connection with the line, as described
in our former Specification, No. 2995, of the present year, in place of embodying
a constant current on the line, which is caused momentarily to cease in order to
give motion to the clocks, we now work the clocks with opposed batteries, so that
normally no current passes in the line, and we give motion to the clocks by
momentarily earthing the line at the calling station, thereby dividing the line into
two sections, in each of which a current passes and causes the clocks to advance a
step.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alfred Charles Brown and Henry Alfred Charles Saunders in the
Great Seal Patent Office on the 23rd May 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.
Our improvements first berein described are applicable mainly where a series of
stations are connected by a line wire, and where it is desired that any station may,
when the line is unoccupied, be able to place itself in communication with any
other station on the line excluding other stations, so that they can neither hear nor
interrupt.
First. We provide at each station an instrument with a graduated series of
resistances which the operator can insert in the line circuit to vary its resistance.
Second. We provide each instrument with an electro-magnet with armatures
held back by springs differently adjusted or other like contrivance, for appreciating
the resistance in the line circuit (the battery remaining constant). This appreciating
contrivance controls the connections both of the resistances and of the receiver and
transmitter, preventing their being placed in effective connection with the line
circuit except the resistance of the line circuit has been set to a pre-arranged
quantity.
Third. We provide each instrument with blocking parts which render the
variation of the resistance inoperative in the instrument in which it is produced.
This combination works together in the following manner:-An operator wishing
to call another station moves a handle to a corresponding mark, and thereby he
first blocks and renders inoperative the appreciating contrivance of his own
instrument, and then adjusts the resistance of the line circuit. The appreciating
contrivances at all the other stations respond, preventing effective connection being
established with the line at all stations but the one having an instrument
adjusted to the particular resistance which has been brought about. The bell at
this station being rung the operator there moves his handle, thereby blocking his
instrument also and establishing the communication. On the handles being replaced
the line is ready for other stations similarly to converse.
When an induction coil is made use of in connection with telephonic apparatus,
a secondary coil is divided into sections and made use of as resistance to be added
to the line circuit to effect the desired adjustment. The coils of the telephone can
be similarly employed.
Our apparatus
shown in Figures 1, 2, in which Figure 1 is a front elevation
of the complete instrument with the door open to show the details, and Figure 2 is
a detail Drawing of the switch nechanism.
Every station is provided with such an instrument, differing only from one
another in their adjustments.
In Figure 1, Q is a back board or case carrying or containing a single or double
electro magnet R, having three armatures numbered respectively 1, 2, and 3.
This electro magnet may be of any shape or may in fact take the form of a
galvanometer coil and needle, the latter having contact arms.
The instrument also contains a switch arm capable of sweeping over and
successively making contact with studs. The secondary coil of the induction
bobbin T is split up into sections of various resistance. There is an ordinary
trembling or vibrating bell mechanism U and a switch hook V making contact
with a stud at the back when the telephone is off the hook, and a lightning
guard W.
The switch arm S has also a projection from its end (as shown more clearly in

page_text: Figure 2), which, when the switch is turned to the right, comes into contact with
and slightly lifts the end of a spring X which carries little blocking pieces a,
which when the spring X is so lifted by the switch S come against the underside
of and jam or hold by friction the ends of the armatures 1 and 3 of electro magnet R
in whatever position they were when the switch was moved over, and the said
pieces will not move the armatures by themsolves but simply fix them in
whatever position they were when the switch,S was moved over.
When the switch arm S is on its normal zero stud, the spring X is not lifted,
and the armatures 1 and 3 of electro magnet R are therefore free to move, but
the action of the lifting spring X fixing the armatures 1 and 3 is completely
accomplished during the passage of switch S from zero on to its stud No. 1.
When the spring X is so lifted it also makes contact at its end with another
spring Y, but does not make contact therewith when it is not so lifted.
The connections of the apparatus are then as follows:-A wire leads from the
terminal marked line 1 or L¹ to one side of the coil of the electro magnet R, calling
on its way at a screw stud, where it joins one of the wires from the lightning
guard W.
This as before may be of any ordinary form, but consists in the instrument
shown of three insulated wires wound together on to a small bobbin, one end of
each wire being cut off short, and the other ends joined respectively to the wires
leading from the terminals marked L', earth or E, and line 2 or L.)
From the other end of the coil or electro magnet R a wire leads to the back
contact studs of armatures 1 and 3 of electro magnet R, and thence on to the stud
on which switch S rests when in its normal zero position.
From this point a wire leads to one of the pair of terminals to which the
telephone cord is attached, and from the second of this pair of terminals a wire
leads to the stud No. 1 of switch S, i.c., the first stud which the switch touches
after leaving its normal zero position. From this point a wire leads on to one end
of the secondary coil of the induction coil T. This secondary coil is split up into
portions of various resistances, as before mentioned, and a wire from the end of
each of these portions goes respectively to the studs numbered 2 to 6 or upwards
of the switch arm S. A wire then connects the pivot or centro of motion of
switch S with armatures 2 and 3 of electro magnet R, and thence leads on to the
terminal marked L, calling on its way at the screw stud, where it meets the second
wire from the lightning guard W. This completes the set of connections for the
line circuit. A wire then lends from the terminal marked local copper, or L.C., to
the back contact stud of armature No. 2 of electro magnet R, and thence on to the
lifting spring X. A wire also connects the small spring Y, with which spring X
nakes contact when lifted with the small brass plate or stud Z, fixed on the side of
the bobbin of electro magnet R in such position that armature No. 3 quakes contact
therewith when it is towards the pole of the magnet. From this point a wire leads
on to the top of switch hook V and to one end or pole of the bell actuating coil.
From the bell post or second electrical pole of the bell actuating mechanism a wire
then leads to stud of switch hook, and also through one of the door hinges to one
side of the transmitter. From the other side of the transmitter a wire then leads
through the second door hinge and primary coil to the terminal marked local zinc,
or L.Z., thus completing the set of connections for the local circuit.
It will be seen from the above that the switch arm S with the other parts form
a rheostat, and by sweeping over the various contact studs the arm can put various
electrical resistances into the line circuit. It can only do this however providing
the resistances between the various studs be not all short circuited by the armatures
of electro magnet R, which it will be seen have the power by making and breaking
their various contacts of short circuiting the rheostat resistances. The short circuit
is established when armature 1 is open or away from the pole of the magnet, and
armatures 2 and 3 closed or. towards the pole of the magnet. When armature
No. 2 opens however as well as No. 1, this short circuit is broken, but is again made
when No. 3 also opeus. There is also no short circuit when all three armatures are

page_text: closed, which is their normal zero or line disengaged position. The action of the
whole is then as follows:-When the line is disengaged a subscriber can call any
other station by altering the resistance of the line circuit by moving the rheostat
switch S, and although by this alteration of resistance one or more of his own
electro magnet armatures would tend to fly open, and so short circuit his added
resistance, yet this is prevented from taking place by the blocking of the armatures
1 and 3 by the lifting of spring X by switch S during its motion from zero on to
stud No. 1, and therefore before it begins to affect the resistance. Armature No. 2
does not short circuit the rheostat in opening.
At all other stations however some or all of the armatures fly open according to
the following conditions:-The hauling off springs of armatures No. 1 are so
adjusted at all stations as to pull them off or open when the resistance of the
circuit reaches or exceeds the amount produced by the insertion of the resistance
between the zero stud and stud No. 1 of the rheostat switch S at the calling
station.
The springs of armatures No. 2 are so adjusted at the several stations that the
armature of any particular station will open when the resistance introduced by the
the caller equals or exceeds that between his zero stud and the stud marked with
the corresponding number or signal of that particular station.
The springs of armatures No. 3 also at the several stations are so adjusted that
the armature at any particular station will open when the resistance introduced
exceeds that for which armature No. 2 is adjusted at that particular station, the
critical point at which it is adjusted to move being somewhat below that at which
armature No. 2 at the next higher station is set to move, so as to ensure that any
one station shall be short circuited when the next or any other station is being
spoken to. In all cases mentioned above when we speak of a point of resistance it
must be understood to mean any point within a certain range of the fixed or
critical point, the magnitude of such range depending on the sensitiveness of the
armatures which must be adjusted to move within this working range of the fixed
critical points. A higher resistance must be placed between the successive studs
from 1 upwards in order to compensate for the bigher total resistance of the circuit
as we successively insert rheostat resistances, it being required that as each stud is
passed, the resistance between it and the next may make by its insertion an
appreciable difference in the total resistance of the line circuit.
When the caller therefore moves his switch over on to a particular stud, the
armature No. 2 as well as No. 1 would have opened at the station marked with
the corresponding number or signal.
Armature No. 3 at this station however would still remain closed. This station
only therefore (with the exception of the calling station) would be un-short
circuited, while at the same time his bell would be sounded in consequence of the
local current being completed through it, together with the transmitter, as will be
seen by tracing the local connections. It is open to him therefore to reply, which
he prepares to do, by moving his switch arın S over to the highest stud (inarkod
"speak" as well as its proper number), and taking his telephone off the hook aud
calling "yes" through the transmitter.
The effect of doing this would bo by the motion of switch S to insert his own
telephone and secondary into the line circuit, the blocking of the armatures by the
blocks on spring X preventing the station from being short circuited by this
additional insertion of resistance, and by the motion of the switch hook V to short
circuit the bell and so stop its sounding, and concentrate the current on to the
transmitter and primary.
The caller, who would be listening at his telephone for receiver to reply by so
calling "yes," would then push his switch S right over on to the stud marked
"speak" and commence conversation, having both thus put their apparatus into
speaking condition.
At all stations however, in consequence of only armature 1 or else both 1, 2,
and 3 being open, the speaking apparatus would be short circuited, and the pushing

page_text: over of switch arm S therefore at one of those stations would only block their
armatures in their short circuited positions, and consequently the rheostat resistances
could not be added, nor any other effect produced on the line circuit by any of
those stations.
When the communicating stations have finished speaking they hang up their
telephones and thus unshort circuit their bells, which consequently, as in the first
method, commence ringing to give them a signal to clear the line should they tend
to omit to do so.
This they do by simply pushing their switch arms S back into their normal zero
studs, and so alter the resistance back to its normal zero point. The armatures at
all stations therefore take their normal zero positions, and the line is open for any
other subscriber who may wish to use it.
We render our apparatus, according to this method, applicable for use with
telegraphs by providing means to balance or eliminate the effects of our line current
on the telegraphic apparatus, such telegraphic apparatus being inserted instead of
the telephone between any pair of the studs of the rheostat switch, and parts of its
resistance may or may not form the working resistance of the rheostat with
which we control the calling and short circuiting or un-short circuiting of the
particular stations.
Our improvements further relate to the arrangements to be made at central
offices or exchanges. Thus one of the stations previously spoken of may, if desired,
be a central office or exchange, and the apparatus can then be arranged so that
any subscriber on this circuit can be plugged through or connected to any other
subscriber on the exchange system, whether or not he be on a similar system to
our own, or brought on to the exchange by any other system whatsoever.
To do this we make use of an arrangement which permits of our line being
earthed or grounded at each end, while still establishing speaking communication
with any branch line with which the exchange may connect it, and that without
making any electrical contact with the said branch line, or in any way altering the
resistance of our main lines and set of apparatus by the connection.
We accomplish this by simply inserting in our apparatus at the exchange, in
place of the telephone and secondary, one coil of a special induction coil having
two coils, as shown in Figure 3. The second coil of the induction coil then
communicates the one end with earth and the other end with the branch line
over which it is desired to establish communication. The resistance of our lino is
evidently therefore not affected by the connection, since the two coils are insulated
from one another, while the inductive effect of the one on the other establishes
effective speaking communication between them.
All the exchange has to do therefore when a subscriber on our system calls up
is to call the attention of the subscriber on the branch line wanted, and connect
the said branch line to the wire leading from the end of the second coil of our
induction coil, the same as they would connect two branch lines together in the
ordinary manner, or vice versa.
The speaking instruments of the central office itself may be intermediate in this
branch circuit, or in the main line circuit itself, as desired.
This method of connecting subscribers by inductive couplings at the exchange is
applicable generally at telephone exchange offices.
At telephone stations we sometimes make the following arrangements in order
that the removal of the receiving telephone from its hook may place it and its
secondary coil in the line circuit, and also close the local circuit through the
transmitter and the primary of the induction coil:-We couple the bell, the
secondary, and the telephone in series in the line circuit; and arrange that when
the telephone is hanging on its hook and the hook is depressed, contact is made on
a stud, so as to establish a short circuit for the current in which it passes in
preference to the secondary coil and telephone. On removing the telephone from
the hook this short circuit is broken. The hook is connected with one pole of the
local battery, and when the telephone is removed the hook rises and makes contact

page_text: with another stud, thereby closing the circuit through the transmitter and primary
coils.
Thus an ordinary two way switch hook is enabled to do the double work of
shunting the line current and of making or breaking the local current for the
transmitter without requiring an extra set of contacts, as in all previous
arrangements.
Figure 4 shows a diagram of connections according to this arrangement.
As previously stated we include the telephone and secondary coil of the induction
coil in one and the same circuit as the bell coils, and we use the motion of the
switch hook to short circuit the telephone and secondary coils when the telephone
is on the hook and the latter in contact with stud or spring No. 1, or to break the
above mentioned short circuit and complete the battery circuit for the transmitter
when the telephone is off the hook and the latter in contact with stud or spring
No. 2.
In the position in which the parts are seen in the Drawing, the line circuit may
be traced from the terminal marked E and LZ. through the switch hook, the stud
No. 1, and the bell. The local circuit is open, the transmitter hook being separated
from the stud 2.
When the receiving telephone is removed from the hook the line circuit may be
traced from E and L.Z. through the receiving telephone, the secondary of the
induction coil, and the coils of the bell magnets.
The local circuit is now closed as follows:-From battery by E and L.Z. to the
telephone hook, the stud 2, the transmitting telephone, the primary of the induction
coil, and so to the battery. The receiving telephone and secondary may be in
parallel circuit instead of in series.
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. The combination, substantially as described, on a telephonic or telegraphic
circuit of a series of transmitting and receiving instruments, all differently
adjusted and dependent for their effective connection with the line upon the
amount of resistance in circuit.
Second. The combination, substantially as described, in a telephonic or tele-
graphic call instrument of (1) resistances which can be inserted in the line circuit,
(2) appliances which admit the receiving and operating parts into effective
connection with the line circuit only when the resistance in the line circuit has a
prearranged value.
Third. Our improved telephonic and telegraphic apparatus, substantially as
described and illustrated by Figures 1 and 2 of the annexed Drawings.
Fourth. The method, substantially as described, of coupling two telephone
circuits by means of an induction bobbin.
Fifth. The switch arrangement, substantially as described, in respect to Figure 4,
by which, in one position, the secondary coils of the induction bobbin and the
receiving telephone are shunted out of the line circuit, and in the other position are
in effective connection with the line circuit, and the local battery circuit is also
closed through the transmitter.
In witness whereof, we, the said Alfred Charles Brown and Henry Alfred
Charles Saunders, have hereunto set our hands and seals, this Seventeenth
day of May in the year of our Lord One thousand eight hundred and
A. C. BROWN.
(L.B.)
H. A. C. SAUNDERS. (L.S.)