Improvements in Magnetic Telegraphy and Telephony.
Year: 1897

page_text: Date of Application, 13th Dec., 1897
PROVISIONAL SPECIFICATION.
Improvements in Magnetic Telegraphy and Telephony.
I, OLIVER JOSEPH LODGE, D.Sc., F.R.S., of 2, Grove Park, Liverpool, in the
County of Lancaster, Professor of Physics, do hereby declare the nature of this
invention to be as follows:-
By this invention I propose to signal without connecting wires to any part of
the earth or sea, using magnetic impulses for the purpose.
As transmitter I use a condenser of large capacity in combination with a large
coil of wire; and I excite it either by means of a battery and sudden breaking
key, the key being either in series or more usually in parallel with condenser
and coil; or else by means of an alternating dynamo with a make and break
signalling key in series with condenser, dynamo and coil to start and stop the
current, or with a switch to divert the current from an operative to an inoperative
coil at will; or else I excite it with a Ruhmkorff or a Tesla coil or with an
influence machine or an alternating generator or transformer of any kind, or
some other suitable source. When a transformer is used, the condenser may be
inserted in both the primary and the secondary coil, or in either of them; and the
key too may be in either circuit when an alternating generator is employed.
The operative coil is to consist of a greater or less number of turns of insulated
wire forming a horizontal coil laid in or on the ground, or in some cases sup-
ported on posts or otherwise above the ground, but always in a horizontal plane
and enclosing as much area as possible; and it is to be connected in series with
the alternating generator, when one is used, and with the condenser of large capacity.
Such a circuit has a natural frequency of electric oscillation, and the frequency
of the dynamo or alternating generator (acting either directly or through a trans-
former) may be readily made to correspond therewith, by adjusting either the
coil or the condenser or the generator, in which case a moderate power will excite
very vigorous oscillations or alternations of current in the entire circuit, and there-
fore a strong alternating magnetic field perceptible at a distance.
Thus if the total self inductance of the operative coil and generator together
were 1 henry or secohm, and if the capacity of the condenser were one microfarad
the natural frequency of vibration would be 157 per second, or thereabouts; and
at this frequency the dynamo or other special alternating generator could easily
be run.
The receiving circuit is another condenser of large capacity connected with a
similar insulated coil of any desired number of turns arranged so as to enclose a
considerable horizontal area, and with a telephone or other detector of feeble or
of dying out alternating currents. Such a circuit has also a natural frequency of
electric oscillation; and, by arranging that the product of capacity and total
self-inductance shall be the same as in the emitting circuit, there will be syntony
between the emitter and the receiver, and an ear applied to the telephone will
hear a musical hum so long as the emitting circuit is kept completed and supplied
by an alternating generator. The adjustment to exact tuning may be made in
either sender or receiver by having a supplemental coil whose spires can be

page_text: approached or separated, or a coil divided into two portions whose relative aspect
or distance apart can be varied, by rotation or otherwise or a cylindrical coil with
a hollow core into which a bundle of fine iron wires can be inserted or withdrawn.
But I may use a still larger condenser or may shunt it out altogether in cases
where a closed circuit is advantageous.
A signalling key controls the making and breaking of the sending circuit,
and, by giving an intermittent hum of longer or shorter duration in the receiver
when the transmitter is excited by an alternator, the usual Morse alphabet can be
easily signalled.
Or, when a battery and a breaking or a discharging key is used, (the breaking
key being arranged to stop a current suddenly, by aid of surfaces separating under
alcohol or in a strong magnetic field) a series of dying out vibrations are excited
in the transmitter and induced in the distant receiver, where they can be detected
by their demagnetising effect on a steel needle, after the manner of Sayart, Henry,
and Mr. Rutherford, and can thereby furnish a tape record or deflect a spot of
light or work a relay.
~
7
Or again I may use a colierer as detector of the induced currents or condenser
charges, sometimes making them intermittent and jerky with a vibrating or
revolving key or cog-wheel arranged in the coherer circuit and connected either
in shunt or in scries, with the condenser in order to enable its electric oscillations
to affect the coherer more jerkily and therefore more powerfully. (A kind of inter-
mitter in the receiving circuit may also be useful when a tone telephone is
employed, as it assists hearing, especially in "calling up" before alphabetical
signalling has begun.)
2374
The coherer may be employed either for giving the messages, or for giving a
simple signal, as in "ringing up." The coherer is usually not to be in series
with the main coil and condenser and telephone, but is to be in a supplementary
circuit likewise connecting the terminals of the condenser and containing also a
weak battery and a detector, such as a telegraph instrument or electric bell or
relay, shunted if desirable with a supplementary small condenser .or a thin wire
to prevent its interference with the electric jerks. The telephone, may likewise
be connected in parallel instead of in series with the condenser and coil, especially
when it is a non-conducting or "condenser" telephone acting, by electro-static
attraction instead of by magnetic attraction; or preferably two telephones can
be used, one of high resistance connected to the terminals of the condenser,, the
other of low resistance in series with the condenser and the coil. For "ringing
up" and for, other cases where extreme sensitiveness is required, a special syntonised
reed or tuningfork telephone is to be employed, in conjunction with a sound board
or other suitable vibrating, surface, and its tone is to be adjusted so as to corre-
spond with that of both the sending and receiving circuits and with the generator.
If such a telephone is suitably damped it may be used also for Morse signalling,
or even for speech of a kind.
In order to have the load on the dynamo constant, when an alternating dynamo
of fixed or adjustable frequency is used, it is well to make the signalling key in
the form of a switch which transfers the current in the pauses or silences to a
circuit of corresponding electric properties, but with its magnetic circuit closed
upon itself so as not to transmit any magnetic field to a distance.
Iron, preferably subdivided, e.g. a vertical bundle or column of iron wires or
rods may be used as a core in either of these coils, usually long and straight in
the operative coil, but forming a closed ring or spiral in the inoperative one..
The same coil will do for either sender or receiver, according to its connections,
which are changed over from "sending" to receiving by a switch of special
'design.
"
For adjusting the frequency of a sending station to a particular receiving
station or vice versa, interchangeable condensers of different capacities can be used;
the capacity at any station being readily altered by plugs or by sliding contacts,
and the frequency of the alternating generator at a sending station can be like-

page_text: wise modified to correspond. The change of frequency at either station may also
be effected by the use of adjustable supplemental coils as already described, or
by employing different main coils, or by shunting out or disusing some of their
turns.
For attaining different frequencies in a generator, either its speed is to be
altered, or else a number of small alternations may be geared say with different
cog-wheels to a carefully governed constant-speed shaft, and any one of them may
be switched into action as desired. The power required is but small.
For lighthouses, the coils will consist of many turns of say gutta-percha covered
wire, round the inside of the base of the tower. For ships, if of wood, the coil will
be in the hold or embedded in the timbers all round one of the decks or it may be
placed outside the taffrail, or round all the deck-houses, or in any other convenient
place so as to give as much horizontal area as conveniently possible. If the ship
be of iron, the coil should be outside and as far from the iron as is practicable;
and if possible the continuous conductance of the iron all round the ship should
be at one place interrupted.
£4
I propose to use the multiple or Magpie" cables made for telephonic purposes,
and to connect their,insulated components in series, so as to make a virtual coil
of many turns which can be compactly and easily laid as a single cable round a
large area.
The effectiveness of a coil, other things being equal, whether for sending or
receiving is simply proportional to its area, and to the number of turns of wire;
it also varies inversely as the cube of the distance between a sending and a receiving
coil. No true electromagnetic waves of any noticeable energy are emitted, the
whole thing is a magnetic telegraph. Intervening insulators, solid or liquid or
gaseous, have no effect. Intervening magnetic substances have very little effect,
but so far as they are bad conductors they rather assist the transmission of signals
than hinder it. Neighbouring conductors cannot altogether stop signalling, but
if they are very near to either sending or receiving coil they will delay it, and
they will greatly weaken the distant effect of rapidly alternating impulses; they
may in fact entail special devices, to be subsequently described.
In case of neighbouring closed-circuit conductors, and in any other case when
convenient, the making and breaking of steady currents may be used to give the
impulses, instead of the make and break of a sinuously alternating current as
heretofore chiefly described. In that case a polarized receiver may be used at the
receiving station, and a current reverser employed at the sending station. Or,
instead of an alternating generator, a continuous-current dynamo or a battery,
with any form of commutator or any vibrating or intermittent contact, may be
used or I may use the discharge of suitable condensers or Leydens with sparks,
to give suddenness.
It is possible to convey articulate speech or at least vowel sounds in monotone,
over moderate distances across space by the use of a, suitable microphonic trans-
mitter in conjunction with the sending condenser and its coil, and by the use of
an appropriate telephonic receiver in conjunction with another condenser and its
coil. I propose to develop this magnetic transmission of speech without connect-
ing line wires.
For extremely distant signalling, as to the Antipodes, and in any case where
area is unlimited; it is preferable to use a large coil of few turns instead of a
smaller one with many turns; for instance only one turn round an area comparable
with that of England, with a similar collector in Australia, should be sufficient:
at least if too much capacity is avoided' by supporting the wire in the air, and if
the conducting power of the earth is not too great; or a less area will serve
(though it entails more wire) if the number of turns be increased in inverse pro-
portion to the area of the coil. When the sizes of sending and receiving coils are
different, more turns should be used on the smaller coil, in inverse proportion to
its diameter, so that both coils involve the same total length of wire: if a given
length of wire is to be distributed most economically.

page_text: The horizontal coils in different parts of the earth will present various aspects
to each other, but as all lie on the surface of a sphere they are always in a position
suitable for appreciating each others magnetic field, and for indicating its fluctua-
tions, when properly syntonised, by induced currents detected telephonically or
magnetically or in any other known way.
Improvements in Magnetic Telegraphy and Telephony.
I, OLIVER JOSEPH LODGE, D.Sc., F.R.S., of 2, Grove Park, Liverpool, in the
County of Lancaster, Professor of Physics, 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:-
My invention relates to an improved method of signalling across space by
magnetic induction, employing some form of alternating current generator at one
end and some form of telephonic or phonoporic detector at the other. The chief
feature of my invention consists in the use of a condenser or "Leyden" at both
sending and receiving station, in circuit with a coil or circuit of stout wire, so
as to have a definite natural frequency of electric vibration however it be stimulated,
and associated with an adjustable coil or appendage for precise tuning.
The coil or circuit, whenever space is available, is usually a single loop of very
stout insulated copper enclosing a large horizontal area, and either laid in the
ground or sea or supported on posts like a telegraph wire, well insulated from the
earth but not lead covered or otherwise protected from induction. When space is
constricted, for instance in lighthouses and ships, the circuit is a multiple coil
surrounding a horizontal area many times, and it may in some cases be wound all
over a tall cylinder packed full of thin iron strip, so as to constitute a great
vertical electro-magnet, which may be made something like a chimney and may
be provided with a flue for keeping the iron core hot, at some temperature below
its critical point.
The condenser is an ordinary instrument, constructed in some cases of alternate
sheets of glass and tin-foil when very high potentials are employed, but usually an
article such as are now sold for use with alternating currents or for ocean
telegraphy, with its capacity adjustable in the customary manner.
As current generator an alternating dynamo machine is selected or designed
so as to give a fairly sinuous curve with a frequency between 500 and 1000 per
second, preferably without iron in its armature, and usually driven by an electric
motor whose speed can be regulated and adjusted so as to give different frequencies
of electric alternation according to the speed at which it is run.
Where power is
not available a battery and revolving commutator may be substituted for the
dynamo.
The use of different frequencies is to enable messages to be sent to some one
or more stations without disturbing others: each of the receiving stations can
have a normal characteristic note in which the signals intended for it are to be
sent, and to which alone its apparatus will readily respond.
It is necessary to adjust the natural frequency of the circuit as well as that
of the dynamo, and this is done by two adjustments, one a coarse adjustment
obtained by varying the capacity of the condenser by a series of sliding or plug
contacts in the known way, the other a fine adjustment which may be managed

page_text: by aid. either of a small supplemental coil or of a pair of coils included in the
circuit, the pair of coils being movable relatively to one another so as to vary their
mutual inductive influence, or else the single coil having movable spires or a core
of iron wire or strip which can be inserted or withdrawn more or less for the same
purpose. One of these arrangements (the single coil and core) is indicated dia-
grammatically at p q in Figure 1 of the accompanying drawings, the other (the
pair of coils) is indicated at p 2 in Figure 2. This constitutes the final tuning
arrangement and the same can be used at either the sending or receiving end.
So also the main coil or circuit and the condenser may be used for either sending
or receiving.
Figure 1 shows the simplest form of sending circuit as now described; a being
an alternator, c the condenser, d the signalling key, and e the coil or circuit; and
Figure 2 shows the corresponding simplest form of receiving circuit, t being a
telephone.
In some places where a dynamo is inconvenient another current generator is
employed for instance a battery of high potential which charges and discharges
the condenser through a key, as shown in Figure 3 (arranged for sending or
receiving) long and short signals being given by the interval between charge and
discharge; or else a battery of low resistance giving a strong current through the
coil e which is then suddenly interrupted by a suitable break D) actuated by key d
and battery b¹ as shown in Figure 4, so as by self-induction to set up oscillations
in the coil and condenser circuit, after the manner of a Ruhmkorff primary, the
secondary of which in this case is the receiving circuit at a distance. Or again, as
another alternative, the same general arrangement but with a rapidly vibrating
properly timed break and other arrangements as in the primary, of a Tesla coil;
or once more by using the secondary of an ordinary Ruhmkorff R as an exciter
of the condenser (or in this case preferably a pair of condensers c c²) which
discharge across a spark gap U as shown in Figure 7 and thereby set up very rapid
oscillations in the coil e which can be heard as a momentary whistle or chirp in
the receiving circuit at a distance, whenever the sending key d and vibrator D
are put into action so as to cause sparks at knobs U.
Figure 6 is only a slight modification of Figure 3, where a reversing key u
is used instead of a Morse key.
When a regular alternator is feasible I prefer that, but it is possible to imitate
its effect with a battery and a vibrating string as employed by Dr. Pupin; and
this form of artificial alternator I have also employed. The arrangement is
shown in Figure 13 where is the "string" which must be a metal wire,
sounding its first harmonic, and stretched over monochord bridges on a frame,
being tightened and tuned by the lever and screw j at one end, with a peg ?
at the other end for coarse adjustment.
n is a mercury contact at the node and hand are amalgamated pins fixed
to the vibrating wire and dipping in and out of other mercury cups H and K
alternately, the mercury cups being supported on screw stands of adjustable height
not shown.
B is a battery. cc¹ are condensers. e is the coil, of which the middle must be
accessible, giving three terminals e¹, e² and e³ which are joined up as shown to
the condensers.
The signalling key d has for its function the transfer of the string and battery
contacts from an inactive circuit, composed of equivalent resistances r r³, to the
active circuit consisting of condensers and coil e. When the knob d is depressed,
the insulating cross piece d' attached thereto makes contact with the active circuit
by pressing its terminals on to the spring contacts ar; and immediately
breaks it with the inactive one, by pressing the contacts a downwards away
from the contacts r² 23: and immediately afterwards completes connection with
the contact of the middle terminal. by pressing thereon. A signal is given
and continued as long as the key d is held down. The string is kept vibrating all

page_text: the while under the action of the current, but the current only reaches and
stimulates the condenser circuit when the signalling key is depressed.
When the string is set in vibration in synchronism with the period of the
condenser and coil circuit its battery supplies energy to the circuit and main-
tains the electric. vibrations. The vibration of the string when once set up
is
maintained by a pair of permanent horseshoe magnets M M which have the string
passing freely between their poles, one magnet between n h, the other between
nk, both acting on the wire by reason of the current impulses passing through
it.
One other transmitting arrangement remains to be described; z. when the
signalling key instead of simply making or breaking the connection of the
alternator and condenser with the main circuit switches them on to, another but
inactive circuit, as depicted in Figure 5. Here the active circuit is represented
as a few of the turns of the coil e round a few iron wires of the vertical column wo;
the inactive circuit is a closed ring of iron wires also covered with insulated copper
wire indicated at .. The Morse key is used to switch the alternating current
supplied by a through c from one of these circuits to the other, thus leaving the
load on the dynamo constant, but only transmitting a signal to a distance when
the active circuit is on; the closed magnetic circuit . having no distant effect.
When it is attempted to transmit speech across space by induction, a microphonic
transmitter is used to excite the sending circuit, as shown diagrammatically in
Figure 8 or 9, either of which will serve as receiving circuit also; the telephone t
being connected directly as shown in Figure 9 when it is of low resistance, or
through a transformer as in Figure 8 when its resistance is high; the microphone
also being connected either directly as in Figure 8 or through a transformer z
as in Figure 9. By any of these transmitting arrangements an alternating or
intermittent magnetic disturbance is emitted across space, and its effects can be
detected at a distant station by another large circuit or horizontal wire-surrounded
area through which some of its lines of force pass, thereby inducing currents
of corresponding frequency. A condenser is essential to the sensitiveness of a
receiving circuit, so that it may have. a natural period of vibration which is
adjusted to correspond with that of the sending station. When this is properly
arranged the receiving circuit becomes very sensitive to otherwise imperceptible
magnetic fields, and the use of a condenser for this purpose is an essential feature
of my invention. As detector of the induced electric currents I employ some
form of telephone, preferably the magnifying telephone, or series of alternate
special telephones and microphones which forms the subject of another patent
application (Provisional No. 9712, 1898), but likewise any known form of telephone
and also the tone telephone now shortly to be described.
The telephone is connected either in series or in parallel with the condenser
of the receiving circuit, according to the wire with which it is wound. When
its wire is thick I place it in series as in Figure 2; when its wire is thin I place
it in parallel as in Figure 10; or else I connect it through a transformer as in
Figure 8, but I prefer a low resistance telephone connected in series direct.
A tone telephone is an instrument whose vibrating portion emits a musical
note and is therefore especially adapted to resound or respond to vibrations of a
definite frequency.
In Figure 11 the vibrating portion is a tuning fork 3 mounted on a sounding
board E to which the ear may be applied, or which may be extended over several
square feet in order to make a noise audible at a little distance. The pitch of
the fork can be adjusted by a movable load 7 on its prongs. The limbs N S of the
fork are magnetised so that it constitutes a horseshoe magnet, and between the
prongs a coil of wire 5 with a soft iron core. When this instrument is con-
nected to the receiving circuit by its terminals 6, 61, it readily indicates currents
of the desired frequency but is not much affected by others.
Figure 12 shows a slight modification, where 3 is a steel reed carrying a disc 4

page_text: whose motion is listened to by the ear-piece 2; 8 is the steel magnet, 9 the soft
iron core and 10 the receiving coil, whilst is the outer case of the instrument.
A tone telephone may also be employed as a tester of the state of adjustment of
a sending or receiving circuit; for if its vibrating portion be twitched or other-
wise sounded, it will induce feeble currents of standard frequency in its own coil,
and this current can be easily arranged to induce a current in the main condenser
circuit, of strength sufficient to excite its detector and give a signal if everything
is in correct adjustment for that particular frequency. For instance a tuning-
fork-telephone circuit might be permanently associated by induction with one of
the tuning coils already spoken of, p in Figures 1 and 2, so as to induce currents
in that coil whenever the magnetised tuning fork is twitched, and this disturbance
would be heard or otherwise felt in the main receiving instrument of the circuit
as soon as the tuning was correct. Thus it would afford means for keeping the
circuit properly tuned.
66
For purposes requiring greater power, such as calling or ringing up" or
obtaining messages recorded on tape, I employ tuned phonoporic receivers, arranged
according to the plans of Mr. Langdon Davies or some modification of those,
wherein a vibrating portion makes or breaks a local battery contact and so acts
as a relay. In connection with the "call" or "ringing up" also I employ the
magnifying telephone hereinbefore referred to, whereby imperceptible vibrations
are enabled to produce audible signals.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, declare that what I
claim is:-
1. A system of syntonic magnetic induction telegraphy wherein a set of magnetic
alternations of predetermined frequency are detected and utilised for telegraphic
purposes by apparatus adjusted to that same frequency, substantially as herein-
before described.
2. As transmitter in syntonic magnetic telegraphy the combination of a con-
denser in series with a coil or circuit of wire with tuning appliances, so that it
shall have a definite frequency of free electric vibration substantially as herein-
before set forth, and adapted to be excited by an alternator or by any other
means of exciting alternating or intermittent currents of definite frequency.
3. As receiver in syntonic magnetic telegraphy the combination of a condenser
in series with a coil or circuit of wire capable of exact attuning as set forth, and
having associated with it a telephone of suitable design for detecting feeble
electric oscillations.
4. As detector in a system of syntonic magnetic telegraphy a telephone as set
forth whose vibrating portion has a definite frequency of vibration so as to
resound more readily to a particular note than to any other.
5. In the transmitting circuit of any system of magnetic induction telegraphy
the combination of an inoperative closed magnetic circuit, and an operative open
magnetic circuit, and a Morse key capable of switching the current from one of
these circuits to the other, substantially as hereinbefore set forth.
6. In the transmitting circuit of magnetic induction telegraphy the combination
of condensers, coil, and spark gap, adapted to give a whistling spark when excited
by a Ruhmkorff coil and thereby to excite corresponding high-frequency oscilla-
tions in a distant similarly attuned circuit substantially as hereinbefore set forth.
7. In the receiving circuit of any system of magnetic induction telegraphy,
the application and use of a magnifying telephone, or series of telephones and
microphones, for purposes of a "call" substantially as hereinbefore set forth.
8. In a system of magnetic induction telegraphy the application and use of a
microphonic speech-transmitter in the sending circuit, and a magnifying telephone
in the receiving circuit, for the purpose of conveying speech to a moderate distance
without connecting wires, substantially as herein before set forth.
9. Means whereby a syntonic induction condenser circuit can be readily tested

page_text: for correct adjustment to standard frequency, comprising a tuning-fork-telephone;
or other magnetised standard vibrator, associated inductively with a coil and with
the receiving circuit, and acting as a feeble dynamo or alternating current generator
for testing purposes; substantially as herein before set forth.
10. The general construction, arrangement and combination of parts, taken as
a whole, forming my improved system of signalling across space by magnetic
induction, substantially as herein before described and illustrated.
Dated this 5th day of October 1898.
W. P. THOMPSON & Co.,
Patent Agents, of Liverpool, Manchester, Birmingham and London.