Improvements in Telephonio Systems and in Switching Apparatus for Use therein.
Year: 1896

page_text: Date of Application, 6th Feb., 1896-Accepted, 7th Mar., 1896
COMPLETE SPECIFICATION.
Improvements in Telephonio Systems and in Switching Apparatus
for Use therein.
We, ALFRED ROSLING BENNETT, of 22 St. Alban's Road, Harlesden, in the
County of Middlesex, and GEORGE JOHN SOMERVILLE, of 9 Tatton Road
North, Heaton Chapel, in the County of Lancaster, Electrical Engineers, 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:-
Our invention relates to the metallic circuit telephonic exchange system in
which communication is established between the subscriber and the operator by
means of an earth circuit including a battery; and a specially-constructed sub-
scriber's telephone receiver provided with two equally-wound coils from between
which a branch is taken to earth through a contact key by means of which the
subscriber is enabled to connect to earth his end of the metallic circuit which joins
his instrument to the exchange. According to this system at the exchange an
electro-magnet provided with two specially-wound coils is placed and from between
the coils a branch is similarly taken to earth through a battery. The depression
of the subscriber's contact key completes the circuit and a current then flows from
the battery and splits between the coils of the electro-magnet, the two wires of the
metallic loop and between the coils of the subscriber's instrument; then the two
currents re-unite and pass to earth and so back to the battery at the exchange.
The armature of the electro-magnet is thus attracted and is arranged to bring the
operator's telephone into connection with the metallic loop and so into communi-
cation with the telephone of the subscriber who is then enabled to speak to the
operator so long as he keeps his contact key depressed.
Our present invention consists of improvements on and developments of the
aforesaid system.
One part of our present invention renders it unnecessary in the aforesaid system
to provide a specially-wound electro-magnetic switch at the exchange.
A second part of our invention renders it unnecessary to employ a specially
constructed telephone at the subscriber's office.
A third part of our invention enables a subscriber to originate communication
at will with either of two operators at the exchange instead of with one only.
A fourth part of our invention renders it possible for a subscriber to originate
communication at will with any one of four operators at the exchange.
Another part of our invention relates to the electrical contacts and connections
of the electro-magnetic switch employed to join the operator's telephone to the
subscriber's metallic circuit.
A further part of our invention relates to the employment of relays or electro-
magnetic switches provided with two or more interlocking connections.
In order that our invention may be clearly understood we will now proceed to
describe it with reference to the accompanying drawings, in which
Figure 1 is a diagram of the electro-magnetic switch arranged as in the system
herein before alluded to.
Figure 2 is a diagram illustrating the method we adopt to obviate the employ-.
ent at the exchange of a specially wound electro-magnetic switch.
Figure 3 is a diagram of the method we adopt to obviate the employment at the
subscriber's office of a specially constructed telephone.

page_text: .
Figure 4 is a diagram of the system as arranged to enable a subscriber to
originate at will communication with one or other of two operators at the exchange
by the aid of a battery at his own office.
Figures 5 and 6 illustrate in side elevation and plan respectively the details of
one form which the aforesaid electro-maguetic switch may assume in practice.
Figure 7 is a transverse section of the said switch taken on the line,
Figure 5.
Figures 8, 9 and 10 are similar views of another form of the switch.
Figure 11 is a general scheme of the system when employed with a simple form
of multiple switch-board, the connections of the operator's telephone being omitted
for the sake of clearness.
Figure 12 is a view on a larger scale of a double plug and connecting cord for
making the connections at the central station.
Figure 13 is a plan of a double electro-magnetic switch hereinafter described.
. Figure 14 is a plan of a polarised double switch.
Figure 15 is a diagram of the connections at a subscriber's office for commu-
nicating with either of two operators by the aid of a battery at the central
station.
Figure 16 is a diagram shewing another arrangement of the said connections.
Figure 17 is a diagram of the connections at the central station when either of
two operators are to be communicated with by the aid of a battery at the central
station.
Figure 18 is a diagram shewing another arrangement of the said connections.
Figure 19 is a diagram of the connections at a subscriber's office when any one
of four operators at the central station are to be communicated with.
Figure 20 is a diagram shewing another arrangement of the said connections.
Figure 21 is a diagram of the connections at the central station when any one of
four operators is to be communicated with by a subscriber.
Referring to Figure 1, E M, E M are electro-magnets, the coils of which are of
equal resistance or nearly so and are wound differentially, that is to say, the one
left-handed and the other right-handed so as to exert an equal and opposite effect
on the armature A when used in series. The two coils are joined at W from
which point a branch or leg is taken through the voltaic battery or other source
of electricity Z to earth at G. The coils E M, EM are furnished with soft-iron
cores and pole-pieces and a soft-iron armature in the manner of an ordinary
unpolarised electro-magnet. A current entering at W and splitting between the
coils will magnetise both cores in the same sense and will cause the coils to attract
the armature. M', M are the two wires of the metallic loop coming from
subscriber's office; they are connected to the mutually-insulated metallic
strips H', H' attached to the armature A. When the armature becomes attracted
the strip H¹ makes contact with the metal post L', and the strip H makes contact
with the metal post L which posts L', L'are in permanent connection respectively
with the terminals of the operator's telephone OT. The two wires M', M' of the
loop are also respectively in permanent connection with the coils E M, E M of the
electro-magnetic switch.
B
The system described in connection with Figure 1 forms no part of our
present invention and is here inserted in order that our improvements may be
clearly understood.
In Figure 2 M¹, M' are again the two wires of a metallic loop entering the
exchange from a subscriber's office. The said wires are in permanent connection
with metallic strips H', H' attached to, or moved by, the armature A of the
electro-magnetic switch and making contact, when the said armature becomes
attracted, with posts L', L' which, as in the system above described, are per-
manently connected to the terminals of the operator's telephone OT. Across the
metallic loop M, M are joined two equally-wound resistance coils B', B; from
the point W between the coils is taken a wire to earth at G through the coils E MEM
of the electromagnetic switch and the battery or other source of electricity Z. In

page_text: this case the coils of the electro-magnetic switch must not be differentially wound
and no connection is taken off from between them.
In Figure 3, B, B is a balanced resistance composed of two coils of equal
resistance or nearly so from between which a branch or leg is taken through the
lever K to earth at G. ST is the subscriber's telephone with its coil or coils
arranged in the ordinary way without any branch or leg: It is connected across
between the wires M', M of the subscriber's metallic loop in shunt with the
coils B, B. Any ordinary type of telephone can be employed so that existing
instruments are by this method rendered suitable for use with our system without
alteration.
In Figure 4 are shown the arrangements necessary when it is desired to give any
subscriber the power to switch his instrument at will on to that of either of two
operators at the exchange, such as an operator who deals with local com-
munications only or one whose duty it is to establish trunk-line communications;
or when, as is sometimes the case, the lines of the subscribers are divided between
two switch-boards, the subscriber may connect himself at will to an operator
having control of, say, Nos. 1 to 4000 or to one controlling Nos. 4001 to 8000.
M', M are the wires of the metallic loop proceeding from the subscriber's office
to the exchange.; B1, B2 are two equally wound resistance coils arranged according
to the plan shewn in Figure 2. In the circuit of the ground wire G are joined
two polarised electro-magnetic switches PS1, PS constructed substantially
according to the well-known principle of the polarised relay. One of the
switches, say PS1, is arranged to have its armature attracted by the passage
through its coils of a positive current and repelled by a negative current while
the armature of the other switch PS2 is repelled by a positive current and
attracted by a negative current. Both switches possess armatures and contact
arrangements substantially like those hercinbefore described with reference to
Figure 2 or like those hereinafter described with reference to Figures 5, 6 and 7
or to Figures 8, 9, and 10. The switches may be connected in series instead of in
parallel as shown. In practical work these two polarised switches may be combined
with advantage in one instrument having an armature pivoted at its centre,
each end of the armature being operated upon by properly-wound coils
arranged, on the principle of the polarised relay, to cause one end of the
armature to be attracted while the other is repelled by positive current
and the reverse with a negative current. Not only will speed be saved by
this method but both sets of coils will perform useful work at the same time since,
when either end of the armature becomes attracted, its movement will be reinforced
by the repelling force at the other, and the certainty with which the local circuit
to the operator's instrument is closed will be increased, or a deflection of ordinary
force may be produced with less battery power. When two separate switches are
employed as in Figure 4 the repelling force is lost since it simply pushes the
repelled armature against an idle stop. At the subscribers office are two equilly-
wound coils B B similar to those described in connection with Figure 3, an
ordinary subscriber's set of speaking and signalling apparatus S T and two keys or
contact levers K', K' arranged substantially in the same manner as the signalling
keys in submarine telegraphy. When the key K' is depressed the positive pole C
of the battery CZ is joined to the metallic loops M, M and the armature of the
switch PS being attracted, the operator's telephone OT is brought into circuit,
while the armature of the switch PS is repelled against its idle stop and the
operator's telephone OT remains unaffected. When the subscriber presses the
key K the negative pole Z of the battery is joined to line, and the armature
of the switch 'S' is attracted and that of the switch P S repelled thus bringing
the operator's telephone O T' in circuit while allowing the telephone OT to
remain unaffected.
According to this plan the battery is situated at the subscriber's office instead
of at the exchange which for a large number of subscribers would be objectionable
on the score of expense and inconvenience in maintenance, but it is only necessary

page_text: to furnish such home batteries to 'those subscribers who make frequent use of the
trunk lines or have some other occasion to communicate promptly with a second
operator. For all the others the battery or other source of electricity may still
be located at the exchange. But the use of a voltaic battery at the subscribers
office may be dispensed with in any case if magneto-electric or dynamo-electric
machines commutated so as to send continuous currents to line instead of the
ordinary alternating currents are provided. The construction of such machines is
well understood. For use in a subscriber's office they may be driven by hand
but more conveniently by clockwork, or by the descent of a weight, or by any
water, gas, hot-air, electric or other motor capable of being quickly started and
stopped.
Instead of connecting the metallic loop to the terminals of the operators' sets of
instruments one or both of the electromagnetic switches PS PS in Figure 4 may
be arranged by means of local batteries to operate indicators or annunciators on
the switch-board or switch-boards although the switches themselves may be located
elsewhere.
In Figures, 6 and 7 are shown the details of an electro-magnetic switch suitable
for use when the plan set forth in Figure 2 is the one adopted. E M, E M are the
coils; A is the armature supported in pivot bearings A', A' (Figure 6) S is a stop
(preferably tipped with an insulating substance) for limiting the upward movement
of the armature; X is a spiral spring connected at one end to a depending arm A'
of the armature A, and at the other end to an adjusting screw X'; L' L' are two
posts or pillars in permanent connection with the operator's telephone by tho
wires OT indicated in Figure 7. So far as yet described the electro-magnetic
switch closely resembles an ordinary unpolarised relay, but as there are two local
contacts to be made and broken a modification of the ordinary armature and its
connections is necessary. The armature, herein before referred to in connection
with Figures 1 and 2, is built up of two mutually-insulated metallic strips but as
the connections through the pivots must also be kept mutually insulated such a
built-up armature is costly to make and not very satisfactory in practice. For these
reasons we, according to our present invention, prefer to retain the armature in its
simple form and to furnish it with an insulating cross-piece I Figures 5 to 7 which,
when the armature A becomes attracted, depresses the springs H¹, R' against
metallic adjustable stops carried by the insulated metal pillars L, L. In Figure 7
the arrangement of the pillars L, L is clearly shown. The springs H', H' are
mounted on two insulated supports or posts P1, P' which are in permanent
connection with the loop wires M¹ M. The depression of the armature therefore
brings the wires M', M³ into connection with the operator's telephone through the
pillars P1, P with which the wires M1, M2 are connected, the springs H', H', the
pillars L, L' and the wires marked OT, OT.
In Figures 8, 9 and 10 the same reference letters indicate the corresponding
parts of another form which the electro-magnetic switch may take. In this case
the armature A is a bent lever, pivotted at A³, and supporting an insulating cross-
piece I which, when the armature becomes attracted, lifts the springs H', H' and
presses them against the stops carried by the posts L', L'.
In Figure 11 which is a diagram of the system as improved by us combined with
a simple form of multiple switch board, but with the operator's telephone con-
nections (which are shown separately in Figure 2) omitted, ST, ST, ST are
three subscribers' telephones connected by the metallic loops marked M' M,
M M', M' M², to an exchange or central station and by levers or keys K', K³, K'
to earth at G, G, G. B', B' are the balanced resistances at the subscribers'
offices. At the exchange J, J, J; J¹, J³, J³; J¹, J, J; represent jacks or
sockets connected in branches between the wires of each metallic loop; E M',
EM', EM EM, EM, E M³, are the electro-magnetic switches, and B B
BB, B³ B, the equally-wound resistances all arranged as in Figure 2, and Z is
the common battery or other source of electricity joined to earth at G. The
subscribers' loops are connected together as desired by double-conductor plugs

page_text: adapted to fit into the sockets J, J, J. Such a double plug connected by a.
cord is shown on an enlarged scale at P, P, Figure 12.
From a consideration of the foregoing description and of the drawings it will be
understood that when the subscriber's key K Figure 3 is depressed the wires of
the metallic loop M', M' are connected to earth at the subscriber's office through
the balanced coils BB; and as at the exchange the wires M', M' are permanently
grounded through the coils E M, E M of the electromagnetic switch Figure 2, and
through the battery Z, a current will traverse both wires of the loop M', M' and
the earth so long as the key K is kept depressed. When this circuit is established
the armature A is attracted. The springs H' H³ (Figures 5, 6 and 7) are thereby
brought into contact with the stops carried by the pillars L, L' and the terminals.
of the operator's telephone thus become connected to the line. The subscriber
is thus enabled to establish communication with the operator at any moment
for demanding a connection with another subscriber, for notifying the termina-
tion of a conversation, or for other purposes. Keeping his key depressed, the
subscriber speaks his message to the operator and as the electrical disturbance due-
to his speech, starting from the telephone ST for example (Figure 11) travels.
along the metallic circuit his communication to the operator enjoys all the-
advantage of metallic circuit speaking and is not interfered with by induction from.
other lines. The subscriber having received notification of the receipt of bis.
message, allows the key K' to rise whereupon the armature ceases to be attracted
and the connection with the operator's telephone is broken. The communication.
asked for having been established, the subscriber finds himself in metallic circuit.
communication with his correspondent, and the two connected subscribers are free
to ring each other's bells without disturbing the exchange since such ringing currents.
pašs round the metallic circuits without affecting the electro-magnetic switches.
In practice an electro-magnetic switch is required in the exchange for each
ordinary subscriber and an additional switch for each subscriber who desires special.
trunk line facilities or to call up more than one operator. The switches replace-
the annunciators or other indicators of an ordinary telephone exchange and an.
important feature of our invention is that it saves space on the switch-board.
Ordinary annunciators must be in sight of the operator and their presence on tho
switch-board occupies space which could be more usefully devoted to other
purposes. Our electro-magnetic switches, may be arranged at a distance from the-
switch-board and may even be in another room or another building. The switches
should be mounted in cases with close-fitting doors and they should be disposed so.
as to admit of easy access for cleaning purposes and for adjustment.
The battery or other source of electricity Z at the exchange may be common
to several or all of the switches and lines. If separate batteries are employed.
at the exchange they should be of equal strength, otherwise the stronger battery
will send current through the weaker battery when two subscribers' circuits are
connected.
The resistance of the coils employed may vary within wide limits, but for
ordinary purposes the coils E M, EM may be wound to 500 ohms each aud the
coils B, B to 1000 ohms each. The latter coils may be provided with iron cores
or arranged as self-induction bobbins, in which case their resistance may be much
reduced, but this is not necessary.
In case of need, electro-magnetic switches of the construction shown in Figures 5, 6.
and 7 or Figures 8, 9, and 10 may be arranged to close more than two local circuits
by providing additional insulated springs to be depressed (by the insulating cross-
piece attached to the armature) against contacts mounted on additional insulating
pillars or stands.
Should two subscribers whose switches are in the same group, that is to say,
allotted to the same operator, depress their keys K at the same moment both will
find themselves in connection with the operator's telephone and with each other.
This is, however, only what frequently happens with the well-known Law and Mann
-telephone systems without inconvenience. The operator receives the two subscribers'

page_text: instructions consecutively and as soon as the desired connections are established
communication between the two subscribers through the operator's telephone
circuit ceases.
At night, or at other times when the communications are few the operator's
telephone may be replaced by an electro-magnetic or other suitable indicator and a
special battery interposed between the contacts L', L (Figure 2) or we may employ
an indicator alone, joined in the wire between the battery Z and the switch coils
(Figure 2). A call having been notifical to the exchange the operator switches in
the telephone OT and receives the subscriber's instructions.
When, for any reason, the employment of an earth connection is undesirable a
return wire may be substituted in order to complete the circuit of the battery Z
and the key K.
Having thus given a general description of our invention and its simplest
methods of application we will now describe several developments of which it is
capable.
By the use of a double electro-magnetic switch having two armatures so arranged
that when one is attracted to its electro-magnet the other cannot be attracted it
becomes possible for a subscriber to speak at will to either of two operators at the
central station without employing batteries or other sources of electricity at his
end of the line since the connections can then be su arranged as to bring the central
station battery into play for this purpose. Such a double electro-magnetic switch
is shown in plan in Figure 13 in which E M' E M' are ordinarily-wound electro-
magnets with soft-iron cores; A' A' are soft-iron armatures: 111 are insulating
cross-pieces attached to the armatures; X'X' are springs controlled by screws
for adjusting purposes; BS BS are back stops for "controlling the play of
the armatures; H H are contact springs which when the armatures are
attracted are pressed against the contact stops P P and Q is a light bar or rod
sliding freely in guides G1 G2 and of such length that when the armature A¹ is
attracted the said rod Q is pushed against the armature A and vice versa. Two
contact springs and two contact stops or pillars are provided for each armature as
has been described in reference to Figures 5, 6 and 7,hut only one of each is shown
in Figure 13.
In Figure 15 M' M' is the metallic circuit proceeding from the subscriber's
office to the exchange. K K are two contact levers or finger switches each
having three contact springs arranged as shown in circuit with the coils B', B
The said levers have metallic arms QQ which are normally insulated but which
when depressed bring the contact springs 1 and 2 into connection first and an instant
later join contact 3 to the other two, the spring 3 being shorter than the springs 1
and 2. When not touched by the arms the springs or contacts 1, 2, 3 are mutually
insulated. Keferring now to the switch K the effect of pushing down the lever is
in the first place to connect contacts 1 and 2 together and so to ground the wire M
through the resistance coil B and in the second place to bring contact 3 into
connection with the other two and so to ground the wire M' through the coil B
Similarly, the depression of the lever of the switch K first grounds the wire M
through the coils B and then the wire M' through the coil B. The subscriber by
operating the switch K' or K' can therefore ground either of the wires M' or M
first as he pleases. The speaking .and signalling set ST is joined between the
wires M' and M' in parallel with the coils B' B.
This arrangement of the apparatus at the subscriber's end may be varied as is
shown in Figure 16 in which arrangement the two contact levers or finger
switches KK each possess an arm which is divided into two insulated metallic
portions QQ. Normally the part Q of the arm in each switch rests against aud
serves to connect the contacts 1 and 3; when depressed the part Q leaves the
contacts 1, 3 and the latter are then disconnected; then part Q touches and
connects the contacts 5, 6. And finally the part Q1 touches and connects the
contacts 2, 4. M M are the two wires of the metallic loop M' being connected to
the springs 1 and 2 of the contact lever K. From the springs 3 and 4 the wire is

page_text: prolonged to one side of the resistance eoil B' and to one terminal of the speaking
and signalling set S T. From between the two resistance coils 1 13 an attachment
is made by the wire W to the springs 6 and from the springs 5 a wire is taken
to ground G. The switch K is similar to the switch K and its springs are
connected in the same manner in respect to the wire M³, coil B' and instrument S T..
When the switch K' is at rest the springs 1, 3 are in contact with each other.
and the wire M' is continued through the part Q to the coil B1 and instrument S T.
When the lever of the switch K is depressed the part Q first leaves the"
springs 1, 3, and breaks the continuity of the wire M'; then contact is made by
the part Q between the springs 5, 6 thus creating a path for the current of the
exchange battery along the wire M2, through the springs 1, 3 of the switch K,
coil B2, and the centre wire W to the spring 6 of the switch K and thence by the
part Q and spring 5 to ground G. When wholly depressed the part Qalso
makes contact between the springs 2, 4 which are shorter than the springs 5 and 6
and so re-connects the wire M' to the subscriber's instrument ST which then has
the benefit of the metallic circuit for communicating with the central station. It
will be understced that the exchange battery sends first its current along the
wire M and then on the full depression of the lever along the wire M' also. The
subscriber by operating the appropriate switch K or K may thus ground either.
of the wires M or M first at his pleasure.
There are thus two methods (Figures 15 and 16) by which either wire of the
metallic loop may be grounded at the subscriber's end an instant before the other.
There are also two methods of connecting the apparatus at the central station in
order to take advantage of this fact for connecting at will with the apparatus of
either of two operatora. These methods are represented in Figures 17 and 18, and
it must be understood that either of the arrangements at the subscriber's end may
be used with either of the arrangements at the exchange. Referring now to
Figure 17 DS is a double unpolarised electro-magnetic switch substantially of the
same construction as that shown in Figure 13, having two pairs of ordinarily-wound
coils EM EM and two soft-iron armatures A. A between which the sliding
locking rod Q moves. M' M are the two wires of the metallic circuit respectively
joined through the coils EM E M' and the battery Z to ground at G. Now,
suppose that the wire M' is grounded at the subscriber's end by either of the
methods described in reference to Figures 15 and 16 and that the wire M' is
likewise grounded an instant later. On the grounding of the wire M' a current
flows from the battery Z through the coils E M' to the wire M' and so to ground
at the subscriber's end. The armature A' of the switch DS is attracted towards
the cores of the electro-magnet E M' and the sliding rod Q is pushed against the
inside of the armature A. When the wire M also becomes grounded by the
further depression of the subscriber's finger switch the battery Z will also send a
current through the coils EM' to the wire M but this will not attract the
armature A to the electro-magnet E M' since the armature A' is already attracted
to the electro-magnet E M' and is keeping the sliding rod Q pressed against the
inside of the armature A'. As the forces operating are equal and the armature A³
is further from the coils of the electro-magnet E M than is the armature A' from
the electro-maguet E M' the armature A cannot overcome the push exerted ou it
by the armature A through the sliding rod Q and it will therefore remain
stationary. If therefore the electro-magnets E M'E M' are provided with insulating
cross-pieces, contact springs and stops and if they are arranged and connected for
looping in operator's apparatus all as described with reference to Figures 5, 6
and 7 it is obvious that one operator will be joined to the loop when the wire M' is
grounded first and another when the wire M is grounded first.
The second method of arranging the apparatus at the exchange end is shown in
Figure 18. M' M² are the two wires of the metallic loop, B B are two resistance
coils and DS is an unpolarised double electro-magnetic switch, such as that shown
in Figure 13, with ordinarily-wound electro-magnets E M'E M' and two soft-iron
armatures A¹ A' but with the sliding locking rod Q omitted. The armatures are

page_text: each furnished with insulating cross-pieces as described with reference to Figures 5, 6
and 7 which when attracted depress the contact springs H H and H H for the
purpose of connecting the metallic loop with the terminals of the operators'
instruments all as described with reference to the said figures. H H are additional
contact springs which like the springs H H', H H', are worked by the insulating
cross-pieces, but which are arranged to more between two contact stops S S
and SS', making contact with both stops S₁ and S when the armatures remain
unattracted and with either stop S or S according to which armature is attracted
when the electro-magnets become excited by currents from the battery . If,
for example, the arminture A' becomes attracted the spring H will be depressed
against the stop S while the spring H will remain in contact with the upper.
stop S. The spring H of the electro-magnet E M' is joined to the wire 'M
through the resistance coil B³ as shown; its top contact stop S' is connected
through the electro-magnet E M³ and the battery Z to ground at G while its lower.
contact stop S' is likewise joined to the battery Z and ground G through its own
electro-magnet E M¹. Similarly the spring H of the electro-magnet E M is
connected to the wire M2 through the coil B; the stop S is connected to the
electro-magnet E M battery Z and ground G and the stop S to the electro-
magnet E M battery Z and ground G. Supposing the wire M' to have been
grounded at the subscriber's end the current of the battery Z finds a path through
the electro-maguet E M², stop S, spring H, and resistance coil B³ to the wire M'
with the result that the armature A is attracted and the apparatus looped in of
the operator appointed to attend to calls coming on the wire M'. An instant
later when the subscriber's finger switch has become fully depressed the wire M'
will also be grounded and the current of the battery Z will then split equally
between the wire M¹ via coils E M2, stop S', spring H and coil B' and the wire M
via coils E M³, stop S, spring H and coil B. The sequence of operations is
reversed when the wire M is grounded before the wire M' which will be the case
when the subscriber wishes to loop in and speak with the operator whose appa-
ratus is worked by electro-magnet E M' and armature A¹. It will be understood
that although by both the above described methods the current that determines
which operator is to be looped in flows by one wire of the metallic loop only yet
both wires of the loop are re-joined in a metallic circuit by the time the connection
has been made so that the speaking which follows enjoys the advantage of a
metallic circuit. In the method described with reference to Figure 18 a sliding
locking rod between the two armatures is not required since each electro-magnet is
cut out by the attraction of the armature of its neighbour.
Instead of connecting the inetallic loop to the terminals of the operators' sets of
instruments either or both of the armatures A' A' in Figures 17 and 18 may
be arranged by means of local batteries to operate indicators or annunciators on
the switch-board or switch-boards although the switches themselves may be located
elsewhere.
By using a double polarised electro-magnetic switch and by placing the batteries
at the subscribers' offices the plans described with reference to Figures 15 to 18
may be extended so as to permit any one of four operators at the central station
being spoken to at will by the subscriber. Such a polarised double switch is
shown in Figure 14 and consists of the switch described with reference to
Figure 13 with the addition of the permanent magnets P M P M. To one
pole, say the positive pole of these magnets the soft-iron cores of the electro-
magnets E ME M' are bolted or otherwise united and in the other pole the ends
of the soft-iron armatures A¹ A' are pivoted or otherwise supported so that
the armatures acquire by induction the polarity of the magnets. The parts of
the armatures which extend beyond the cores of the electro-magnets should be
of some non-magnetic metal. The coils are wound so that both armatures are
attracted by a current of one sign and repelled by a current of the other sign.
In Figure 19 M' M' are. the two wires of a metallic loop coming into a
subscriber's office and B¹ B' are two equally-wound resistance coils. K₁K'K' K

page_text: are four contact levers or finger switches each having a metallic arm divided into
two insulated portions Q'Q. Normally the arms do not touch any of the springs
or contacts. The connections are made as follows: The spring 1 of each finger
switch is grounded; the coil B¹ is connected to the springs 4 of the switches K'
and K and to the springs 5 of the switches K and K'; the eud C of the
battery CZ to the springs 3 of the switches K and K and to the springs 2 of the
switches K and K'; and the end Z of the battery CZ to the springs 2 of
the switches K and K and to the springs 3 of the levers K² and K. The
.subscriber's set of speaking and signalling apparatus ST is joined between the
wires M¹ and M2 in parallel with the coils B¹ B'.
the switch K' the part Q joins the springs 1 and 2 and the part Q joins the
On depressing the lever of
springs 3 and 4 first and subsequently the spring 5 to the springs 3 and 4. The
effect of this is first to join the positive pole of the battery CZ, vi part Q and
coil B¹ to wire M' and then via Q spring 5 and coil B to wire M² while the
:negative pole is connected via the spring 2, part Q', and spring 1 to ground, thus
sending a positive curreut first along the wire M' and then along wire M2 also to
the exchange. The depression of the contact lever K³ on the other hand will
send a negative current first along the wire M' and then along the wire M². The
depression of the contact lever K2 sends a positive current first along the wire M²
and then along the wire M' while the depression of the contact lever K sends a
negative current first along the wire M2 and then along the wire M. Four
combinations each capable of producing a distinctive effect at the exchange are
thus obtainable at the will of the subscriber.
The arrangement at the subscriber's end may be varied in the manner shewn in
Figure 20 which is an adaptation to the calling of four operators of the plan
disclosed in reference to Figure 16. M' M are the two wires of a metallic loop
coming into a subscriber's office and B' B2 are two equally-wound resistance coils
joined across the loop in parallel with the subscriber's set of instruments ST.
KKKK are four contact levers or finger switches, each being a metallic arm
divided into three mutually insulated portions Q1Q3 Q3. Normally the arm of
each switch rests against the contact springs 1, 3 which are joined by the portion Q.
The connections are made as follows: Spring 5 of each finger, switch is grounded,
coil B is connected to the springs 3 and 4 of the switch K¹; coil B² to springs 3
and 4 of switch K; springs 1 and 2 of switch K¹ to springs 3 and 4 of switch K³;
springs 1 and 2 of switch K2 to springs 3 and 4 of switch K+; wire M³ to springs 1
and 2 of switch K³; wire M2 to springs 1 and 2 of switch K; a point between
the two resistance coils by a wire W to spring 8 of each finger switch; the positive
pole of battery CZ to the spring 6 of switches K and K and to spring 7 of
switches K¹ and K2; and the negative pole of battery CZ to the spring 7 of
switches K and K and to spring 6 of switches K¹ and K. When the lever
of the switch K is depressed the part Q' leaves the springs 1 and 3 insulated thus
breaking the continuity of the wire M and the parts Q and Q immediately
afterwards effect connections respectively between the springs 5 and 6 and 7 and 8
of the same finger switch the result of which is that the negative pole of the
battery CZ is grounded via spring 6, part Q spring 5 and G while its positive
pole is connected to the wire M via spring 7, part Q3, spring 8, wire W, coil B,
spring 3, part Q and spring 1 of switch K and spring 3, part Q', and spring 1 of
the switch K. A positive current is thus sent along the wire M' to the central
station. On the further depression of the lever of the switch K' springs 2 and 4
are connected with the result that the continuity of the wire M¹ is re-established
(but not before the positive current has flowed along the wire M³) so that the
speaking from ST has the advantage of a metallic circuit. It will be noted that
by this plan the current from the battery CZ traverses both wires of the loop
equally when the finger switch lever has been fully depressed. Similarly, the
lepression of the switch lever K2 sends a positive current along the wire M¹ first
and then along the wire. M3; the depression of the switch K³ sends a negative

page_text: current along the wire M' first and then along the wire M', and the depression of
the switch lever K₁ sends a negative current along the wire M' first and then along
the wire M. Four combinations each capable of producing a different effect
at the central station are thus obtained.
At the exchange the apparatus is arranged in the following maner. Two
polarised double electro-magnetic switches similar to that shown in Figure 14 are
used as indicated in Figure 21 in which M M are the wires of the metallic loop
coming from a subscriber's office, E M'E M', E ME M are the electro-magnets
respectively of the double switches DS' DS and A' A', A' A' are the four
armatures each pair having a sliding locking rod Q Q between them. The electro-
magnets are so wound that a positive current from the wire M passing through
the coils E M' of the switch D S and electro-magnet E M³ of the switch D S' will
attract the armature A' and repel the armature A'. On the further depression
of the subscriber's finger switch a positive current will also arrive from the
wire M2 and circulate in the coils E M² of the switch D S¹ and in the coils E M
of the switch D S. The tendency of this current will be to attract the armature A*
and repel the armature A' but the armature A cannot more, being kept away
from its electro-magnet by the sliding rod Q which is pushed by the armature A¹
which has already been attracted. Since the armature A2 cannot move and
the armatures A and A' are repelled, the armature A¹ will be the only one
of the four that will be attracted to its corresponding coils and the operator
connected with it by the arrangement of springs and contacts already described
with reference to Figures 5, 6 and 7 will be the only one whose apparatus is
looped in. A negative current from the wire M' will repel the armature A¹
and attract the armature A³ which will push the sliding rod Q against the
armature A and the latter will therefore be unable to move when, a moment
later, in the further depression of the subscriber's finger switch, a current
circulates in the coils E M' repelling the armature A, and in the coils E M*.
The operator in connection with the electro-magnet EM will consequently be
the only one looped in. Similarly positive currents arriving from the wire M²
will attract the armature A, lock the armature A¹ and repel the armature A
so bringing in the operator connected to electro-magnet E M'; while negative
currents from the wire M will repel the armature A', attract the armature A and
lock the armature A so looping in the operator connected to electro-magnet E M
Instead of being joined in series as shown the electro-magnets may be joined
in parallel E M with E M³ and E M' with E M. Each of the electro-magnets
being arranged to loop in an operator in the manner already described with
reference to Figures 5, 6 and 7 it is obvious that the subscriber who is connected
to the exchange by the metallic circuit M M has by the above described
means the power of connecting himself at will with any one of four central station
operators.
Instead of connecting the metallic loop to the terminals of the operators' sets of
instruments any or all of the armatures A¹ to A may be arranged by means
of local batteries to operate indicators or annunciators on the switch-board or
switch-boards although the switches themselves may be located elsewhere.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. In the telephone system herein referred to the improvement substantially as
described with reference to Figure 2 and for the purposes specified.
2. In the telephone system herein described the method of connecting the
metallic loop at the subscriber's end to the ground circuit substantially as described
with reference to Figure 3, and for the purpose specified.
3. In the telephone system herein described the two polarised electro-magnetic
switches at the exchange in connection with a subscriber's circuit and in combination

page_text: with the battery or other source of electricity and reversing keys at the sub-
scriber's end substantially as described with reference to Figure 4, and for the
purpose specified.
4. In a metallic circuit telephone exchange system means whereby one wire of
a metallic loop may be momentarily earthed before the other wire for the purpose
of multiplying distinctive signalling or calling combinations, substantially as
described.
5. In a metallic circuit telephone exchange system the improvements whereby a
subscriber is able to call at will to either of two operators at the central station
without employing a battery or other source of electricity at his end of the line,
substantially as described.
6. In a metallic circuit telephone exchange system the improvements whereby
subscriber is able to call at will to any of four operators at the central station,
substantially as described.
7. The improvement in metallic circuit telephone exchange systems substantially
as described with reference to Figure 15 or to Figure 16 in combination with the
devices described with reference to either Figure 17 or Figure 18; and the
further improvement described with reference to Figure 19 or to Figure 20 in
combination with the devices described with reference to Figure 21, for the purposes.
specified.
8. In electro-magnetic switches and relays designed to close either of two local
circuits the combination of two electro-magnetic switches in one instrument with a
locking bar between the armatures substantially as described with reference to
Figures 13 and 14 and for the purpose specified.
9. In electro-magnetic switches and relays designed to close either of two local
circuits the combination of two electro-magnets in one instrument each electro-
magnet operating one end of a balanced armature pivoted at its centre, substantially
as described for the purposes specified.
10. In electro-magnetic switches and relays such as those herein described the
insulating cross-piece and contact springs in combination with an armature of
ordinary construction, substantially as described with reference to Figures 5, 6.
and 7 or to Figures 8, 9 and 10, and for the purposes set forth.
Dated this 6th dox of February 1806
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicants.