Electrical Signalling Apparatus and Circuits.
Year: 1893

page_text: Date of Application (in United Kingdom), 13th May, 1893
Complete Specification Left, 12th Feb., 1894-Accepted, 28th Apr., 1894
PROVISIONAL OF MOTIVATION.
Electrical Signalling Apparatus and Circuits.
We, EDWARD JULIUS HALL, of Morris, in the County of Morris and State of
New Jersey, and FRANK ALBERT PICKERNELL of Newark in the County of
Essex and State of New Jersey United States of America do hereby declare the
nature of this invention to be as follows:-
This invention relates to call generators for telephone exchanges, to their
circuits, and to devices for graduating, controlling and differentiating their
currents.
It frequently becomes necessary and more frequently desirable in the operation
of telephone circuits to have a magneto receiving telephone, and a call bell in
circuit at the same time, so that whether words or calling currents are transmitted
at the distaut station, either may without delay be received and attended to; this
contingency however requires that the telephone shall be at the ear of the
attendant.
In the Specification of a separate application for Letters Patent filed of even
date herewith by Edward J. Hall and describing a system of divided switchboards,
with office trunk conductors, and means for operating and interconnecting a series
of substation circuits upon said switchboards, such a desirability is adverted to and
as one mode of carrying out the operation of signalling the substation called for,
apparatus is shown whereby as soon as the operator at one switchboard has called
for a line at the other, the call generator terminals by means of a suitable key or
switch at the first switchboard may be united to the trunk conductors to which the
line at the second switchboard is to be united.
As soon therefore as the second switchboard connection is made, the bell of the
desired station is rung, while the telephone at the calling station which has been
introduced into the circuit to give the order is still held to the ear of the person
desiring communication; and not only is this the case but after the attendant at
the second substation has brought his telephone into the circuit to see what is
wanted and to exchange conversation, the call generator at the central station may
remain connected with the talking circuit and continue to send call signals over the
line and through both substation telephones until the operator, having finished
other business taken up ad interim returns to his connection, and turns the generator
switch thus disconnecting the call generator.
Heretofore when a receiving telephone has either deliberately or inadvertently
been left in circuit during the operation of sending a call signal by means of a
magneto generator, the telephone has uniformly been fully responsive to said
generator and the instrument has been so affected by the circulation of the call

page_text: currents through its helices as to emit intensely loud and rattling sounds, representing
such currents and productive of great discomfort to the person at whose ear the
said telephone is held.
The purposes of our present invention are twofold :-
The first is to provide means for ringing polarized bells by means of alternating
current magneto electric generators or equivalent apparatus without materially
affecting speech receiving instruments included in the same circuit; and the second
is to furnish efficient means whereby a call generator common to a number of
switchboard connecting cords, some of which may be channels for voice currents,
and others simultaneously forming conductors for the call currents of said generator,
may be employed without involving telephonic interference or the transit of voice
currents between any two such cords.
We attain the desired object by associating with the circuit including the bell
which is to be affected, and the telephone which is not to be affected a call
generator graduated by the suitable application of retardation coils or electro-
magnetic resistance and condensers in such a manner that the currents it developes
have the crests of their alternations so rounded, that while continuing to efficiently
operate polarized bells, they produce no material sound in telephones.
We connect the condenser between the two generator main conductors near the
terminals thereof, so that it forms an electrostatic shunt therefor; and between each
of the said terminals, and the junction of the condenser shunt, we include in circuit
a suitably proportionate retardation coil or electromagnetic resistance having few
convolutions and therefore little real resistance, but also containing in its core and
casing a large amount of iron, and therefore a high apparent resistance due to
self induction.
To carry out the second part of the invention, the generator main conductors.
have auxiliary or branch conductors, leading in pairs, to keys having each a
connection with some one of a number of switchboard connecting cords which
are used to unite any two circuits for through communication; and in the
circuit of both conductors of each pair of such auxiliary conductors are placed
retardation coils or electromagnetic resistances wound with a comparatively large
number of convolutions, so as to offer a relatively high real resistance; but
containing comparatively little iron, whereby they are enabled to offer an apparent
resistance attributable to self-induction relatively high to voice currents, and
relatively low to calling currents.
It may here be explained that helices or coils of wire which surround or are
surrounded by iron offer by reason of their self induction a high retardation or
apparent resistance both to the call currents and to voice currents since these both
undergo a corstant change generally by alternating their direction; this apparent
resistance largely depends upon the amount of iron contained in the coil.
But the rate of change is much higher in the voice currents than it is or can be
in the call current and the apparent resistance offered by a given construction of
coil is also largely dependent on such rate; hence though by reducing the amount
of iron contained in the coils, the apparent resistance they offer to the call currents
which have a low rate of change can be greatly diminished, until in fact it closely
approximates the real resistance only, the said reduction of iron does not materially
diminish the apparent resistance offered to voice currents whose rate of change is so
much higher.
The graduation electromagnetic resistances in the generator mains which are to
affect the call currents are for this reason made to contain a large amount of iron,
while the circuit differentiating electro magnetic resistances in the auxiliary
conductors which are intended to oppose the passage of the voice currents only
while affording an unopposed passage to call currents, are therefore made to contain
little iron.
In the drawing which illustrates and forms a part of this Specification,
Figure 1 is a diagram showing the invention applied to a simple telephone circuit
of two stations

page_text: Figure 2 is a similar diagram indicating conventionally a compound telephone
circuit extending between two stations through a third.
Figure 3 is a detail diagram indicating in full the connections of call generator
by means of suitable call keys and connecting cords with telephone circuits.
Figure 4 is a diagram showing a converter interposed between the generator
proper and its working circuits.
Figure 5 is a diagram illustrative of the second feature only of the invention.
In Figure 1 we have an electric circuit C, having direct and return conductors L
and L 2, and extending between two telephone stations A and B.
At A a graduated magneto generator M is included in the circuit and at B there
is a polarized bell 6 and receiving and transmitting telephone t t 2. The direct
conductor L at B connects at u with the usual automatic telephone switch s on the
book of which the receiver t is hung, the circuit being supposed to be at rest.
The telephone being thus hung on the switch, the circuit continues through the
said switch to the contact s 2 forming the terminal of the brauch 6 which joins
the return main conductor L2 at the point z and in which is connected the bell b.
The telephone branch 7 extends from the terminal contact s 3 through the
telephones to the same point z, and is closed by the removal of the telephone from
the hook, the bell branch being at the same time opened.
с
At station A a condenser c has its terminals 2 and 3 united with the circuit
conductors Land L 2 respectively at a and y bridging them, and establishing an
electrostatic shunt round the generator; and an electromagnetic resistance or
retardation coil R is included in each of the generator mains 5 between the generator
terminals and the condenser junctions & and y.
The said retardation coils are made with a comparatively few turns of wire, but
contain in their cores and casings a relatively large amount of iron. We have found
coils having a real conductor resistance of about 40 ohms answer well. It is
necessary that the conductor resistance of these coils shall be low, in order that the
currents developed by the generator M may be of sufficient volume to supply as
many circuits as it may at any time be necessary to ring over at once.
And it is also necessary that there shall be a considerable amount of iron in and
about the coils, in order that their apparent resistance, or counter electromotive
force shall be sufficiently high to graduate the current, whereby it may be caused
to assume a character or form to which the telephone when in circuit is irresponsive.
The several terms "electromagnetic resistance," "inductive resistance ""retardation
33 60
coil," choking coil" and "self induction coil" have all been in the art applied to
such coils R, which are intended to oppose to currents traversing them an apparent
resistance which is composed of their real resistance and their inductance and we
understand the said terms to be interchangeable.
We have found condensers having a capacity of three microfarads to operate
satisfactorily; and such a condenser associated as described with the retardation
coils R efficiently achieves the desired graduation.
In Figure 2 the connections at both terminal stations are alike, and are identical
with those of station B in Figure 1. The telephone t at station A is however
hung on its hook, and the circuit there is through the bell b; while at station B the
telephone t is removed from the switch, and consequently is in circuit. The two
sections C and C 2 of the circuit are united at a central or intermediate station D to
form one compound circuit, having a bell in circuit at one station and a telephone
in circuit at another.
At D an alternating current call generator M graduated as described above by
retardation coils K and a condenser c is connected in derived circuit or in multiple
arc with the said compound telephone circuit, one of its main conductors 12 joining
the conductor L of such circuit at v, and the other 13 joining the conductor L2
at w. Under these conditions the alternating currents of the graduated generator M
will sound the call in the bell b at A, but will not disturb or produce sounds in the
telephone t at B though both alike are in the circuit and equally traversed by such
alternating currents.

page_text: Figure 3 indicates the connections of two pairs of switch cords F and F 2 with
the generator M. These may be regarded as being located either at different
sections of the switchboards or at the same section; but some of the arrangements
shown are necessary only where they are at different switchboards. Hence the
former view is the one to be preferred.
C and C2 are circuits leading from substations where are telephones t to the
central station D where they are united by the flexible switch-cord F, which has
conductors and
P P 2 and plug terminals P and P 2.
Other two circuits C3 and C4 are in like manner shown as being connected or
adapted to be connected with one another through a second switchcord F 2 its
conductors p and p2 and terminal plugs P and P 2.
M is the generator, 5 its main conductors, R its graduating retardation coils
and c its graduating condenser.
Branching from any points g h on the mains 5 are paired conductors 12 and 13
leading to the several switchcords; and the generator may be common to any
number of such pairs of conductors.
In the circuit of each member of each pair of conductors 12 and 13 is an
auxiliary retardation coil r. These retardation coils r contain a comparatively
small amount of iron, but are wound with a comparatively large number of turns of
wire. We have satisfactorily used coils wound up to a conductor resistance of
150 ohms. The construction adopted for the coils r readily permits the passage
of the alternating call current of the generator; but the more rapidly alternating
telephonic currents are strongly opposed; the apparent resistance offered by such
coils to voice currents being much greater than that offered to call currents. Their
position in the circuits of the branched conductors 12 and 13 is necessary, as
otherwise all circuits over which the ringing current was simultaneously being sent
would be telephonically cross-connected at the terminals of the retardation coils, R,
or at the branching points g h; but the interposition of the coils which may be
said to be opaque to voice currents presents an effectual bar to the passage of such
currents, and virtually prevents such cross connection so far as concerns telephonic
transmission.
1"
N is a three way cam and spindle switch which controls the connection with the
switchboard conductors of the operators telephones, the generator circuits, and the
disconnecting annunciator d.
When the said cam lever is turned to the side shown in connection with the
switchboard F, the operators telephones T T2 are connected through their
terminal contacts e and e 2, and the corresponding contacts m and m 2 of the bridge
conductors 31 and 30 between the switchboard conductors p and p 2.
When the cam is turned into the opposite extreme position, the generator
conductors 12 and 13 are by sub-branches 14 and 15 and contact springs 17 and 18
and corresponding contact springs n and n2 connected with the bridge con-
ductors 30 and 31, and thereby with the switchcord conductors; and when the
cam is caused to take the middle position, both telephones and generator are
disconnected from the cords, and the disconnecting drop d only is bridged across
the circuit.
Figure 4 differs only in slight particulars from the organization shown in
Figure 3. The cord and key connections are omitted as being identical, and a
converter J is interposed between the generator M and the retardation coils R
and r; one belix of the converter is joined up in a circuit o with the armature coils,
and the other has its terminals united to the main conductors 5. In this case, the
generator and converter together virtually constitute the working generator.
In some cases it is conceivable that the latter object of our invention namely the
isolation or differentiation telephonically of the several cord circuits of the
generator, is alone to be attained.
In such cases the retardation coil R and the condenser may be dispensed with,
and this is shown in Figure 5 where the generator mains divide their branch
conductors at the points g and h without any previously interposed resistances or

page_text: retardation coils; the coils
branch conductors 12 and 13.
We have so far exclusively spoken of a magneto electric call generator, but we
may of course substitute therefor any well known practical equivalent thereof such
as a battery and pole changer without departing from the spirit of our invention.
Dated this 13th day of May 1893.
being however connected as usual, in each of the
CARPMAEL & Co.,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Electrical Signalling Apparatus and Circuits.
We, EDWARD JULIUS HALL, of Morris, in the County of Morris and State
of New Jersey, and FRANK ALBERT PICKERNELL of Newark in the County of
Essex and State of New Jersey, United States of America, 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 :-
This invention relates to call generators for telephone exchanges, to their cir-
cuits, and to devices for graduating, controlling and differentiating their currents.
It frequently becomes necessary and more frequently desirable in the operation
of telephone circuits to have a magneto receiving telephone, and a call bell in
circuit at the same time, so that whether words or calling currents are transmitted
at the distant station, either may without delay be received and attended to; this
contingency however requires that the telephone shall be at the ear of the
attendant.
In the Specification of a separate application for Letters Patent filed of even
date herewith by Edward J. Hall and describing a system of divided switchboards,
with office trunk conductors, and means for operating and interconnecting a series
of substation circuits upon said switchboards, such a desirability is adverted to and
as one mode of carrying out the operation of signalling the substation called for,
apparatus is shown whereby as soon as the operator at one switchboard has called
for a line at the other, the call generator terminals by means of a suitable key or
switch at the first switchboard may be united to the trunk conductors to which the
line at the second switchboard is to be united.
As soon therefore as the second switchboard connection is made, the bell of the
desired station is rung, while thé telephone at the calling station which has been
introduced into the circuit to give the order is still held to the ear of the person
desiring communication; and not only is this the case, but after the attendant at
the second substation has brought his telephone into the circuit to see what is
wanted and to exchange conversation, the call generator at the central station may
remain connected with the talking circuit and continue to send call signals over the
liné and through both substation telephones until the operator, having finished
other business taken up ad interim, returns to his connection, and turns the generator
switch thus disconnecting the call generator.
Heretofore when a receiving telephone has either deliberately or inadvertently
been left in circuit during the operation of sending a call signal by means of a
magneto generator, the telephone has uniformly been fully responsive to said
generator and the instrument has been so affected by the circulation of the call
currents through its helices as to emit intensely loud and rattling sounds representing
such currents and productive of great discomfort to the person at whose ear the
said telephone is held.
The purposes of our present invention are twofold :
The first is to provide means for ringing polarized bells by means of alternating
current magneto electric generators or equivalent apparatus without materially
affecting speech receiving instruments included in the same circuit; and the second

page_text: is to furnish efficient means whereby a call generator common to a number of
switchboard connecting cords, some of which may be channels for voice currents,
and others simultaneously forming conductors for the call currents of said generator,
may be employed without involving telephonic interference or the transit of voice
currents between any two such cords.
Electrical impulses succeeding one another at a comparatively low rate of speed,
say fifteen per second as usually the case with those employed in call-signals for
telephone stations are when regular and uniform virtually inaudible in a telephone.
The reason why with an ordinary generator they are audible, is that the curve
representing the electromotive force is irregular and rapidly changing, so that
instead of fifteen impulses per second, a very much larger number is produced, the
sharp and ragged points in the curve of electromotive force correspond to
.harmonics.
We attain the desired object by associating with the circuit including the bell
which is to be affected, and the telephone which is not to be affected a call
generator graduated by the suitable application of retardation coils or electro-
magnetic resistance and condensers in such a manner that the currents it develops
have the crests of their alternations so rounded, that while continuing to efficiently
operate polarized bells, they produce no material sound in telephones.
We connect the condenser between the two generator main conductors near the
terminals thereof, so that it forms an electrostatic shunt therefor; and between
each of the said terminals, and the junction of the condenser shunt, we include in
circuit a suitably proportionate retardation coil or electro-magnetic resistance
having few convolutions and therefore little real resistance, but also containing in
its core and casing a large amount of iron, and therefore a high apparent resistance
due to self induction.
To carry out the second part of the invention, the generator main conductors
have auxiliary or branch conductors, leading in pairs, to keys having each a
connection with some one of a number of switchboard connecting cords which are
used to unite any two circuits for through communication; and in the circuit of
both conductors of each pair of such auxiliary conductors are placed retardation
-coils or electromagnetic resistances wound with a comparatively large number of
convolutions, so as to offer a relatively high real resistance; but containing com-
paratively little iron, whereby they are enabled to offer an apparent resistance
attributable to self-induction relatively high to voice currents, and relatively low
to calling currents.
It may here be explained that helices or coils of wire which surround or are
surrounded by iron offer by reason of their self induction a high retardation or
apparent resistance both to the call currents and to voice currents since these both
undergo a constant change generally by alternating their direction; this apparent
resistance largely depends upon the amount of iron contained in the coil.
But the rate of change is much higher in the voice currents than it is or can be
in the call current and the apparent resistance offered by a given construction of
-coil is also largely dependent on such rate; hence though by reducing the amount
of iron contained in the coils, the apparent resistance they offer to the call currents
which have a low rate of change can be greatly diminished, until in fact it closely
approximates the real resistance only, the said reduction of iron does not materially
diminish the apparent resistance offered to voice currents whose rate of change is
so much higher.
The graduation electromagnetic resistances in the generator mains which are to
affect the call currents are for this reason made to contain a large amount of iron,
while the circuit differentiating electromagnetic resistances in the auxiliary
conductors which are intended to oppose the passage of the voice currents only
while affording an unopposed passage to call currents, are therefore made to
.contain little iron.
In the drawing (left with the Provisional Specification) which illustrates and
forms a part of this Specification,

page_text: Figure 15 aagram showing one "PP
of two stations.
"P
Figure 2 is a similar diagram indicating conventionally a compound telephone
circuit extending between two stations through a third.
Figure 3 is a detail diagram indicating in full the connections of a call generator-
by means of suitable call keys and connecting cords with telephone circuits.
Figure 4 is a diagram showing a converter interposed between the generator
proper and its working circuits.
Figure 5 is a diagram illustrative of the second feature only of the invention.
In Figure 1 we have an electric circuit C, having direct and return conductors L.
and L, and extending between two telephone stations A and B.
At A a graduated magneto generator M is included in the circuit and at B there
is a polarized bell and receiving and transmitting telephone t t. The direct
conductor L at B connects at u with the usual automatic telephone switch s on the
hook of which the receiver t is hung, the circuit being supposed to be at rest.
The telephone being thus hung on the switch, the circuit continues through the
said switch to the contact forming the terminal of the branch 6 which joins
the return main conductor L' at the point and in which is connected the-
bell b.
The telephone branch 7 extends from the terminal contact 3, through the
telephones to the same point z, and is closed by the removal of the telephone from:
the hook, the bell branch being at the same time opened.
At station A a condenser c bas its terminals 2 and 3 united with the circuit.
conductors L and L³ respectively at x and y bridging them, and establishing an
electrostatic shunt round the generator; and an electromagnetic resistance or
retardation coil R is included in each of the generator mains 5 between the
generator terminals and the condenser junctions x and y.
The said retardation coils are made with a comparatively few turns of wire, but
contain in their cores and casings a relatively large amount of iron. We bave
found coils having a real conductor resistance of about 40 ohms answer well. It is.
necessary that the conductor resistance of these coils shall be low, in order that
the currents developed by the generator M may be of sufficient volume to supply
as many circuits as it may at any time be necessary to ring over at once.
And it is also necessary that there shall be a considerable amount of iron in and
about the coils, in order that their apparent resistance, or counter electromotive-
force shall be sufficiently high to graduate the current, whereby it may be caused
to assume a character or form to which the telephone when in circuit is irresponsive..
The several terms "electro magnetic resistance," "inductive resistance,'
"retardation coil," "choking coil and self induction coil" have all been in the-
art applied to such coils R, which are intended to oppose to currents traversing
them an apparent resistance which is composed of their real resistance and their
inductance and we understand the said terms to be interchangeable.
We have found condensers having a capacity of three microfarads to operate-
satisfactorily; and such a condenser associated as described with the retardation.
coils R efficiently achieves the desired graduation.
In Figure 2 the connections at both terminal stations are alike, and are identical
with those of station B in Figure 1. The telephone t at station A is however bung
on its hook, and the circuit there is through the bell b; while at station B the
telephone t is removed from the switch, and consequently is in circuit. The two
sections C and C² of the circuit are united at a central or intermediate station D to
form one compound circuit, having a bell in circuit at one station and a telephone.
in circuit at another.
At D an alternating current call generator M graduated as described above by
retardation coils R and a condenser c is connected in derived circuit or in multiple.
are with the said compound telephone circuit, one of its main conductors 12 joining
the conductor L of such circuit at v, and the other 13 joining the conductor L2 at w...
Under these conditions the alternating currents of the graduated generator M will.

page_text: sound the call in the bell b at A, but will not disturb or produce sounds in the
telephone at B though both alike are in the circuit and equally traversed by
such alternating currents.
Figure 3 indicates the connections of two pairs of switch cords F and F with
the generator M. These may be regarded as being located either at different
sections of the switchboards or at the same section; but some of the arrangements
shown are necessary only where they are at different switchboards. Hence the
former view is the one to be preferred.
C and C are circuits leading from substations where are telephones t to the
central station D where they are united by the flexible switch cord F, which has
conductors P and p' and plug terminals P and P³..
Other two circuits C3 and C are in like manner shown as being connected or
adapted to be connected with one another through a second switchcord F' its
conductors P and p and terminal plugs P and P.
M is the generator, 5 its main conductors, R its graduating retardation coils and
C its graduating condenser.
Branching from any points g h on the mains 5 are paired conductors 12 and 13
leading to the several switchcords; and the generator may be common to any
number of such pairs of conductors.
In the circuit of each member of each pair of conductors 12 and 13 is an auxiliary
retardation coil r. These retardation coils contain comparatively small amount
of iron, but are wound with a comparatively large number of turns of wire. We
have satisfactorily used coils wound up to a conductor resistance of 150 ohms. The
construction adopted for the coils readily permits the passage of the alternating
call current of the generator; but the more rapidly alternating telephonic currents
are strongly opposed; the apparent resistance offered by such coils to voice
currents being much greater than that offered to call currents. Their position in
the circuits of the branched conductors 12 and 13 is necessary, as otherwise all
circuits over which the ringing current was simultaneously being sent would be
telephonically cross-connected at the terminals of the retardation coils R, or at the
branching points g h ; but the interposition of the coils which may be said to be
opaque to voice currents presents an effectual bar to the passage of such currents,
and virtually prevents such cross connection so far as concerns telephonic trans-
mission.
r
N is a three way cam and spindle switch which controls the connection with the
switchboard conductors of the operators telephones, the generator circuits, and the
disconnecting annunciator d.
When the said cam lever is turned to the side shown in connection with the
switchboard F, the operators telephones T T are connected through their terminal
contacts e and, and the corresponding contacts m and m² of the bridge
conductors 31 and 30 between the switchboard conductors p and p².
When the cam is turned into the opposite extreme position, the generator
conductors 12 and 13 are by sub branches 14 and 15 and contact springs 17 and 18
and corresponding contact springs n and n² connected with the bridge conductors 30
and 31, and thereby with the switchcord conductors; and when the cam is caused
to take the middle position, both telephones and generator are disconnected from
the cords, and the disconnecting drop d only is bridged across the circuit.
Figure 4 differs only in slight particulars from the organization shown in
Figure 3: The cord and key connections are omitted as being identical, and a
converter J is interposed between the generator M and the retardation coils R
and one helix of the converter is joined up in a circuit o with the armature
coils, and the other has its terminals united to the main conductors 5. In this
case, the generator and converter together virtually constitute the working
.generator.
In some cases it is conceivable that the latter object of our invention namely the
isolation or differentiation telephonically of the several cord circuits of the
generator, is alone to be attained."

page_text: In such cases the retardation coil R and the condenser may be dispensed with,
and this is shown in Figure 5 where the generator mains divide their branch
conductors at the points 9 and without any previously interposed resistances or
retardation coils; the coils r being however connected as usual, in each of the
g
branch conductors 12 and 13.
We have so far exclusively spoken of a magneto electric call generator, but we
may of course substitute therefor, any well known practical equivalent thereof
such as a battery and pole changer without departing from the spirit of our
invention.
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. The combination of an electric circuit and a polarized bell and magneto
telephone included therein; with an alternating current generator graduated to
produce electrical currents adapted to operate said bell but to which the said
telephone is irresponsive.
2. In an electric circuit, the combination substantially as hereinbefore described,
of a polarized electro magnetic bell; and a magneto telephone; with an alternating
current call generator; and graduating devices therefor, consisting of a condenser
shunting the said generator, and an electromagnetic resistance included in the
circuit between each pole of the generator and the condenser.
3. A telephone circuit extending between two terminal stations through an
intermediate or central station; a receiving telephone and a call bell connected
with said circuit at the said terminal stations; combined with an alternating current
call generator connected with said circuit at the intermediate station, and
graduating devices therefor, comprising a condenser constituting an electro-static
shunt for the said generator, and an electromagnetic resistance or retardation
coil interposed between each terminal of said generator and the condenser
whereby the currents developed by said generator are enabled to operate said bell
without the production of disturbing sounds in the said telephone, substantially as
described.
4. The combination substantially as hereinbefore described of an electric circuit;
a polarized electromagnetic bell; and a magneto telephone, included therein, with
a magneto electric generator, and graduating devices therefor comprising a
converter or induction coil having its secondary connected with the said electric
circuit and its primary included in a closed circuit with said generator; a condenser
bridging or shunting the said secondary; and an electromagnetic resistance included
in circuit between the terminals of said secondary and the terminals of said
condenser bridge, substantially as described.
5. The combination with a series of telephone circuits, and call sending keys
therefor, of a common call generator having conductors extending in pairs to said
call keys; and a retardation coil in each of the said generator conductors for
preventing the passage of telephonic currents between circuits simultaneously
connected with any two pairs of the said conductors, substantially as described.
6. The combination with a series of telephone circuits, and call sending keys
therefor; of a common magneto call generator a series of pairs of conductors
extending from the poles thereof to said call keys; and an inductive resistance or
retardation coil constructed to offer relatively low apparent resistance to call
currents and a relatively high apparent resistance to voice currents included in each
of the said generator conductors, substantially as described.
7. The combination with a series of telephone circuits, and call sending keys
therefor, of an electric call generator common to the series, having conductors
extending to said call keys, and means as indicated for preventing the passage of
telephone currents through their respective call keys, generator conductors and
common portions of the said generator, circuit between any two telephone circuits
over which calls are simultaneously being sent.

page_text: 8. The combination of a series of telephone main circuits converging to a central
station; switchboard connecting cords at said station for uniting any two circuits;
-call sending keys one for each connecting cord included in circuit therewith; a
common magneto electric call generator having conductors extending in pairs to
the said keys and adapted to be thereby connected with the connecting cord circuit;
and an electromagnetic or retardation coil included in the circuit of each of the
said paired conductors, the said coils being so constructed as to offer a relatively
low inductive resistance to call currents, and a relatively high inductive resistance
to voice currents, substantially as and for the purposes specified.
9. The combination of a series of telephone circuits, each extending from a
substation to a central station; a telephone and call bell at each substation; switch-
board conducting cords at the central station for uniting any two circuits; call keys
one for each cord, connected in circuit therewith; a magneto call generator common
to the series of circuits, having branch conductors in pairs extending from its
terminals to said call keys; main conductors connecting the generator terminals
respectively with their several branches; a condenser shunting the generator, a
retardation coil in each main between the generator terminal and the condenser ;
and an auxiliary retardation coil in each branch conductor, substantially as
described and for the purposes specified.
Dated this 7th day of February 1894.
CARPMAEL & Co.,
Agents for the Applicants.