Year: 1896

page_text: I SYDNEY EVERSHED of Woodfield Works Woodfield Road Harrow Road in the
County of London Electrical Engineer do hereby declare the nature of this invention
to be as follows:-
This invention relates to a system for Telegraphic Communication between two or
more places by means of the mutual magnetic induction between electric circuits,
and its objects are to enable the required mutual induction to be produced with a
minimum expenditure on the provision of the necessary circuits and apparatus, to
enable communication by Induction Telegraphy to be carried on at greater distances
than have hitherto been possible, and to provide means by which the attention of
the distant operator may be called when a message is to be transmitted.
According to our invention the electric Circuits at the transmitting and receiving
stations are laid as nearly as possible in a circular form either by means of
continuously insulated wire laid on the ground or by means of an ordinary land line
of bare wires carried on insulators attached to posts so that the plane of each circuit
is parallel with the surface of the earth. The area enclosed by each Circuit must be
made as large, and as nearly circular as local conditions will permit, in order that the
Minimum weight of Conductor may be required. Another condition for obtaining
the maximum induction with a Minimum expenditure is that the two Circuits should
be of equal area, but where for any reasons the area of one circuit is limited (for
example in an Induction Telegraph between an island and the main land), the other
Circuit will have to be either increased in area or an increased weight of Conductor
must be employed.
Signals by means of the Morse Code are made by connecting the transmitting
Cireuit. throngh an ordinary telegraph key, to an apparatus adapted to produce
interrupted or alternate currents. These siguals are made audible at the receiving
station by attaching telephonic receivers to the receiving Circuit. With the well
known Gower-Bell telephone receiver the limit of audibility is reached when the
maximum induction threading the receiving Circuit is equal to about 20 C.G.S.
lines and the signalling current sent into the transmitting circuit must he
calculated to produce at least this amount of induction in the receiving Circuit, in
practice four or five times this amount will be found necessary.
The Currents set up in the receiving Circuit are too feeble to operate any ordinary
circuit closing relay, and in order that the transmitting station may be able to call
the attention of the receiving station by ringing a bell or otherwise a relay must be
employed in which the current causes a vibration in a reed or wire, the amplitude
of such vibration attaining the maximum when the frequency of the receiving Current
is equal to the natural frequency of the vibrating part of the relay.
attainment of such synchronism the amplitude of the vibrator is sufficient to bring it
against a fixed contact, thus momentarily closing a local circuit, and in accordance,
with our invention we place in this local circuit the coil of a small electro inagnet
On the

page_text: the magnetic Circuit of which is normally closed by means of an armature attracted
to the poles of the magnet and held against them by means of the magnetic
induction due to the coercive force of the iron. The momentary current is caused
to traverse the coil of the magnet in such a direction and is of such a strength as
shall reduce the coercive force and therefore the attraction on the armature to zero.
A sinall spring attached to the latter is then able to draw it away from the pole
pieces and bring it against a fixed contact. This fixed contact and the magnet
Armature form part of a second local circuit containing a battery and a bell and on
the release of the armature from the pole pieces this circuit becomes closed and the
bell rings until the armature is replaced. To replace the armature a comparatively
large momentary current is caused to traverse the coil of the magnet in the reverse
direction to the releasing current, the armature is then forcibly attracted against the
poles the current being strong enough to magnetise the iron to Saturation. Thus
the armature is again brought into the condition to receive the releasing current from
the vibratory relay..
Since the alternate or interrupted currents sent into the transmitting circuit for
the purpose of calling attention at the receiving station must be brought into
synchronism with the vibratory relay, in order that it may attain sufficient amplitude
to close the local circuit, special apparatus for producing currents of the required
frequency must be provided. One method is to cause a vibrator similar to a tuning
fork to automatically interrupt the transmitting current. This vibrator being tuned
to the saine frequency as the vibratory relay the required condition would be fulfilled,
but as it is difficult to maintain perfect synchronism, between the transmitting
vibrator and the vibratory relay owing to differences of teinperature and other causes
we prefer to provide an apparatus by which synchronisin is automatically obtained
independently of any conditions as to temperature or otherwise. For example
according to our invention the calling current is made to transverse an ordinary
interrupter having a rotating contact wheel, carrying alternate insulating and
conducting segmenta, on its periphery against which a metallic spring or brush is
pressed in order to close and open the circuit with a frequency depending on the
number of conducting segments and speed of rotation of the wheel. The driving
mechanism which may be operated either by clockwork by hand or by an electro
motor is capable of being un-coupled from the contact wheel while running allowing
the latter to come to rest in a time dependent on its inertin and friction. The
operation of calling attention consists in raising the contact wheel by means of
the driving mechanisin to a speed greater than that required for synchronism with the
vibratory relay. It is then released from the driving mechanism and at the same time
the battery provided for producing the calling current is switched into the circuit
thus as the speed of the contact wheel diminishes an interrupted current of a
gradually diminishing frequency is sent into the transmitting circuit and at some
instant during the gradual retardation the interruptions will have exactly the same
frequency as the vibratory relay. The latter will then reach its maximum amplitude
and close the local circuit releasing the armature of the aforesaid electro-magnet and
thus closing the circuit of the call bell. It is desirable to make the retardation take
place as slowly as possible and with this object we either arrange that the contact
wheel shall have a large amount of inertia or if this is not convenient we attach a
heavy By-wheel to its axle.
As an alternative method for bringing the calling current to the required frequency
automatically we cause the current from an alternate current dynamo to traverse the
transmitting cirenit and having mised the speed of the dynamo until the frequency
is in excess of the required value we release the dynamo from the driving mechanism
and leave it to come gradually to rest so that the frequency may at some instant
during the retardation be exactly equal to that. of the vibratory relay and in order to
bring about a sufficiently gradual retardation of the dynamo we find it convenient to
attach a heavy fly-wheel to its axle. During the time the dynamo is being brought 4
up to speed it is preferable to reduce the work being done as much as possible and
we therefore arrange that the machine shall he left with its field magnets unexcited

page_text: until the moment when the armature axle is released from the driving mechanism
thus the only work done is that required to overcome friction and to provide for the
kinetic energy in the fly wheel and other moving parts.
FELL & JAMES,
1 Queen Victoria Street, London, E.C.,
Agents for the Applicant.
I, SIDNEY EVERSHED, of Woodfield Works, Woodfield Road, Harrow Road, in the
County of London, Electrical Engineer, 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 a system for Telegraphic Communication between two or
more places, by means of the mutual magnetic induction between electric circuits;
and its objects are to enable the required mutual induction to be produced with a
minimum expenditure on the provision of the necessary circuits and apparatus; to
enable communication by Induction Telegraphy to be carried on at greater distances
than have hitherto been possible; and to provide means by which, the attention of
the distant operator inay be called when a message is to be transmitted.
According to our invention, the electric circuits at the transmitting and receiving
stations are laid nearly as possible in a circular forin, either by means of continuously
ingnlated wire laid on the ground, or by means of an ordinary laud line of bare wires
carried ou insulators attached to posts, so that the plane of each circuit is parallel
with the surface of the earth. The area enclosed by each circuit must be made as
large and as nearly circular as local conditions will pornit, in order that the minimum
weight of conductor may be required. Another condition for obtaining the maximum
induction with a minimum expenditure is that the two circuits should be of equal
area, but where for any reason the area of one circuit is limited-for example, in an
Induction Telegraph between an island and the main land; the other circuit will
either have to be increased in area, or an increased weight of conductor must be
employed.
Signals by means of the Morse Code are made by connecting the transinitting
circuit through an ordinary telegraph key to an apparatus adapted to produce
interrupted or alternate currents; these signals are made audible at the receiving
station by attaching telephonic receivers to the receiving circuit. With the well
known Gower-Bell telephone receiver, the limit of audibility is reached when the
maximum induction threading the receiving current is equal to about 20 G.C.S. lines,
and the signalling current sent into the transmitting circuit must be calculated to
produce at least this amount of induction in the receiving circuit; in practice four
or five times this amount will be found necessary.
The currents set up in the receiving circuit are too feeble to operate any ordinary
circuit closing relay, and in order that the transmitting station may be able to call
the attention of the receiving station by ringing a bell or otherwise, we employ a
relay, in which the current causes a vibration in a reed or wire, the amplitude of such
vibration attaining the maximum when the frequency of the receiving current is
equal to the natural frequency of the vibrating part of the relay. On the attaining
of such synchronisin, the amplitude of the vibrator is sufficient to bring it against
a fixed contact, thus inomentarily closing a local circuit, and in accordance with our
invention we place in this local circuit the coil of a small electro-magnet, the

page_text: magnetic circuit of which is normally closed by means of an armature attached to
the poles of the magnet, and held against them by means of the magnetic induction
due to the coercive force of the iron. The current due to the momentary closing of
the aforesaid local circuit is caused to traverse the coil of the magnet in such a
direction, and is of such a strength, ns shall reduce the coercive force, and therefore
the attraction of the armature to zero. A small spring attached to the latter is
then able to draw it away from the pole pieces and bring it against a fixed contact.
This fixed contact, and the magnet armature form part of the second local circuit,
containing a battery and a bell, and on the release of the armature from the pole.
pieces, this circuit becomes closed, and the bell rings until the armature is replaced.
To replace the armature a comparatively large current is caused to traverse the coil
of the magnet for a short time in the reverse direction to the releasing current;
the arinature is then forcibly attracted against the poles, the current being strong
enough to magnetise the iron to saturation. Thus the armaturo is again brought
into the condition to receive a releasing current from the vibratory relay.
Since the alternating and interrupted currents sent into the transmitting circuit,
for the purpose of calling attention at the receiving station, must be brought into
synchronism with the vibrating relay, in order that it may obtain sufficient
amplitude to close the local circuit, special apparatus for producing currents of the
required frequency must be provided. One method is to cause a vibrator similar to
a tuning fork to automatically interrupt the transmitting current. This vibrator
being tuned to the same frequency as the vibmtory relay, the required condition
would be fulfilled, but as it is difficult to maintain perfect synchronism between the
transmitting vibrator and the vibratory relay, owing to the difference of temperature,
and other causes, we prefer to provide an apparatus by which synchronisan is
automatically obtained independently of any condition as to temperature or
otherwise. For example, according to our invention, the calling current is made to
traverse an ordinary interruptor having a votating contact wheel carrying alternate
insulating and, conducting segments on its periphery, against which a metallic spring
or brush is pressed in order to close, and open the circuit, with a frequency depending
on the number of conducting segments, and speed of rotation of the wheel. The
driving mechanism which may be operated either by clockwork, by hand, or by au
electro motor, is capable of being uncoupled from the contact wheel while running,
allowing the latter to come to rest in a time dependent on its own inertia and
friction. The operation of calling attention consists in raising the contact wheel by
means of the driving mechanism to a speed greater than that required for
synchroniem with the vibratory relay. It is then released froin the driving
mechanism and at the same time the battery provided for producing the calling
current is switched into the circuit; thus, as the speed of the contact wheel
diminishes, an interrupted current of a gradually diminishing frequency is sent into
the transmitting circuit, and at the same instaut during the gradual retardation, the
interruptions will have exactly the same frequency as the vibratory relay. The latter
will then reach its maximum amplitude and close the local circuit, releasing the
armature of the aforesaid electro inagnet and thus closing the circuit of the call bell.
It is desimble to make the retardation take place as slowly as possible, and with this
object we either arrange that the contact wheel shall have a large amount of inertia,
or if this is not convenient, we attach a heavy fly wheel to its axle.
As an alternative method for bringing the calling current to the required frequency
automatically, we cause the current from an alternative current dynamo to traverse
the transmitting circuit aud having' raised the speed of the dynamo until the
frequency is in excess of the required value, we release the dynamo from the driving
mechanism and leave it gradually to come to rest so that the frequency may, nt some
instant during the retardation, be exactly equal to that of the vibratory relay; and
in order to bring about a sufficiently gradual retardation of the dynamo, we find it
convenient to attach a heavy fly-wheel to its axle. During the time the dynamo is
being brought up to speed, it is preferable to reduce the work being done as much
possible, and we therefore arrange that the machine sha.l be left with its field magnets

page_text: unexcited until the moment when the armature axle is released from the driving
mechanism; thus the only work done is that to overcome friction, and to provide for
the kinetic energy in the fly wheel, and other moving parts.
The essential features of our invention are shown in the diagram accompanying
this specifiontion in which the size of the apparatus to the inductive circuits, and
parts of apparatus to one another are exaggerated for the sake of clearness.
Fig. 1 is a diagram of the transmissive and receptive circuits.
Fig. 2 is a detail of the receptive relay vibrator.
Fig. 3 is a detail of the transmissive interruption mechanism.
Fig. 4 is a modification of the same.
In Fig. 1, A and B represent two telegraph lines laid at or near the places between
which it is desired to communicate. These two lines are laid or erected in the plane
of the earth, and arranged to enclose as large an area as possible, thus forming two
electric circuits having as large a mutual induction as a given weight of wire will
permit. It is not essential that the whole of each circuit should be metallically
complete; for example, a certain length of wire may be saved by omitting the piece
of circuit B marked X Y Z and electrically completing the circuit B by means of
the earth plates P1 and 12 as indicated in dotted lines. One end of each of these
two circuits is connected to a 3-way switch 8, serving to connect the circuit either
to the speaking apparatus comprising a Morse Key K; Telephone T; and interruptor 1
with a battery E; or to a vibratory relay indicated by the letter R used to set a bell
ringing as described; or to the calling apparatus indicated by the letter C. The
switch S is shown in its normal position that is to say it connects the circuit to the
vibratory relay and is thus at all times ready to receive a signal, calling attention.
The details of the vibratory relay, electro-magnet and bell are shown in Fig. 2
where A and 8 represent the receiving circuit and 3-way switch as in Fig. 1. The
form of vibrator shown is that in which the received current traverses a rectangle of
fine wire V, one side of which is placed in the magnetic field of a magnet N. When
the received currents correspond in frequency with the natural period of the vibrator V
its amplitude is sufficient to inake momentarily the two contacta H, thus emploting
the circuit of a small battery (e) through the small electro-inagnet M. The coercive
force of M being thus destroyed the armature L is released, and heing capable of
rotation round a pivot (a) is drawn back by the spring F and so makes the contact H
closing the circuit of the bell G. The opemtor having thus had his attention called,
presses the key Q causing the current from the battery E to traverse the coils of M
in the reverse direction to the previous momentary current from (e); the armature L
is immediately attmcted and owing to the new coercive force of the magnet M
remains in contact with its poles after the koy Q has been mised to its original
position.
The means by which we bring the calling current in the transmitting circuit to the
required frequency are illustrated in Figs. 3 and 4. In Figure 3 a contact wheel W
having sufficient inertin to keep it in rotation for several ininutes after the driving
mechanisin has been disconnected from it serves to send au interrupted current from
the battery E into the transmitting cireuit B.
The contact wheel may be conveniently set in motion by hand, either by means of
a winch attached to its axle, or to another axle connected therewith by gearing.
There is then no necessity for any disconnection between the driving mechanisin and
the contact wheel.
In Fig. 4 an alternating current dynamo is shown in plan, its armature A is
connected to the transmitting cironit B, while the field magnet coils M' are connected
to the battery E and switch X; sufficient inertia in given to the armature axle by
means of a fly wheel D or otherwise. The armature having been brought to a speed
above that corresponding to the required frequency, the switch X is closed and the
field magnets become magnetised; the armature then sends an alternating current of
gradually diminishing frequency into the transmitting circuit B.
In operating the calling mechanism shown in Figures 3 and 4 we find it convenient
to attach to the contact wheel or armature axle, a speed indicator having a sufficient

page_text: range to show when the speed has reached a value sufficiently (say 10 per cent.) above
the required frequency, and the same amount below the required frequency. The
operator is then enabled to see at a glance when he has reached a sufficiently high
speed, aud also to know when the speed has fallen definitely below the required
frequency, and without waiting for the call device to come to rest, he is able to
connect his circuit with the telephonic speaking apparatus without delay, and wait
for the reply of the distant operator.
Having now particularly described and ascertained the nature of my said Invention
and in what manner the same is to be performed I declare that what I claim is,
1st. A system for telegraphy by magnetic induction consisting of, in combination,
mutually inductive circuits, disposed seperately, and apart from each other, arranged
in planes parallel to and over, under, or concident with the surface of the earth; the
necessary speaking apparatus; calling apparatus consisting of means for producing
interrupted, or alternate currents of gradually diminishing frequency in the
transinitting circuit; and a vibrating relay in connection with a circuit closing
device, substantially as and for the purposes described.
2nd. In a system for telegraphy by magnetic induction, the arrangement of the
mutually inductive circuits in planes parallel to, and over, under, or coincident with
the surface of the earth, substantially as described.
3rd.. In a system for telegraphy by magnetic induction, mechanism applied to the
transmitting circuit adapted to produce a gradually diminishing frequency of
interruption or alternation therein, from a maximum above that of the frequency
of the vibrator in the receptive circuit, thus passing automatically, and without
skilled attention, through a frequency equal to the natural frequency of the said
vibrator, substantially as described.
4th. In a system for telegraphy by magnetic induction, rotary contact breaking
and making apparatus of large inertia, adapted when running free, to interrupt
automatically the calling current in the transmitting circuit, at gradually diminishing
frequencies, substantially as and for the purposes described.
5th. In a system of Telegraphy by inagnetic induction, a dynamo adapted to
produce alternating currents in a transmitting circuit, and by its large inertia when
running free, to gradually and automatically diminish the frequency of the said
alternations, substantially as and for the purposes described.
6th. In a system of telegraphy by inagnetic induction, a circuit closing device,
disposed in the receptive circuit, and consisting of an electro magnetic, and an
armature and contacts adapted to close a circuit when a momentary current in the
coils of the electro-magnet destroys the coercive force of its core and arinature,
substantially as described.
FELL & JAMES,
1, Queen Victoria Street, London,
Agents for the Applicant.