IMPROVEMENTS IN TELEPHONIC APPARATUS
Year: 1883

page_text: LETTERS PATENT to Thomas Henry Meatchem of Waterford in the County
of Waterford Ireland for an Invention of IMPROVEMENTS IN TELEPHONIC
APPARATUS"
PROVISIONAL SPECIFICATION left by the said Thomas Henry Meatchem at
the Office of the Commissioners of Patents on the 13th September 1883.
THOMAS HENRY MEATCHEM of Waterford in the County of Waterford [Ireland]
IMPROVEMENTS IN TELEPHONIC APPARATUS,"
These improvements relate to combined and compound or multiplying trans-
mitters and combined compound or multiplying receivers and devices connected
therewith used in a telephone the object being to attend the utility of the telephone
to increase its power of transmitting and receiving messages and generally to
increase the clearness and distinctness of the sounds rendered and the adaptability
under varying conditions of the apparatus
The first part of the invention consists essentially in the method of fixing and
arranging certain vibrators capable of being acted upon by articulate speech musical
sounds or other sounds or by signals that it may be necessary to convey over &
telephone or telegraph line or cable
The second part of the invention consists in the arrangement and connection
with each other and with the vibrators above mentioned of certain electrodes or
electric conductors capable of conveying one or more electric currents for telephonic
purposes
The third part of the invention relates to a method of employing more than one
magnet in connection with a diaphragm or several magnets in connection with
several diaphragms operating at the same time with or without a modified induction
coil and in connection with one or more local cells or batteries serving the purpose
of a telephone relay
I will now describe more fully the several parts of this invention
It is well known that if a thin plate of suitable élastic material be fixed at its
centre and made to vibrate the outer and free edges will vibrate more strongly
han the portions contiguous to the fixed point. Certain portions of the plite
alled nodal points or lines have little or no vibration. Taking advantage of this
Prise

page_text: circumstance for the purpose of this invention I take a thin plate of wood cork
iron or other suitable elastic material and fix it firmly at its centre to any convenient
support
A thin plate so fixed I call a vibrator and it can readily be fixed in any
convenient position and at any angle that may be required and this is of
considerable importance A cover may be placed over the vibrator support but
must not touch the vibrator
Two or more vibrators attached at their centres to proper supports and placed
side by side without touching can be actuated by the same sound
I will now describe a convenient method of so fixing and supporting two
Vibrators that they may both be acted upon at the same time by the same
sound.
An oblong box having an open front has four grooves, two in each of its opposite
sides. The spaces between the grooves which face one another are bridged.over by
means of two pieces of wood which slide rather tightly in and out in the grooves ;
each bridge carries a support at its centre to which the vibrators are secured.
The vibrators are so attached to the supports that they converge towards each
other at the back of the box and form a wide opening at its front and the vibrators
do not touch each other or the box at any part.
Four vibrators may be fixed in a box or frame for the purpose of being simul-
-taneously acted upon by the same sound This is effected by bridging the corners
or angles of a box or frame and fixing the vibrators to the supports in the centre
These vibrators may vary considerably in size and shape, they may be round
square or oblong
The angle which a vibrator forms with a horizontal line should not be too great
angles varying between say 30° and 45° are suitable
I will now describe the method of attaching the electrodes, e.g. carbon blocks and
pencils to the surface of the vibrator. And here I may observe that what appears
to be but a trifling difference between one microphone arrangement and another, is
often of the greatest consequence in the practical working of a transmitter.
As the result of numerous experiments I have discovered that, as near as possible,
the best position for fixing the carbon blocks on a quadrangular vibrator is found
in the manner following
Draw the diagonals; their point of intersection is the point at which the vibrator
is attached to its support. Through this point also draw two lines dividing the
surface into four equal parts. In each of the four divisions inscribe a circle
touching or nearly touching two of the sides of the vibrator, and at least one
dividing line and in each circle a square having one of its angles towards the corner
of the vibrator. At the centre of each circle place a carbon block and also one at
each angle of each square.
These blocks are suitably connected by insulated metallic strips and carbon
pencils. Having found the positions of the blocks on one vibrator the positions
for the blocks on other vibrators of the same dimensions can be readily taken from
this first one
Such vibrator with its carbon electrodes fixed to its support in any of the positions
herein before described I call a Simple duplex transmitter
Two simple duplex transmitters placed in one box I call a double or compound
duplex transmitter several such vibrators a multiplex transmitter
I will now describe how a simple duplex transmitter may be employed to send
a message over a telephone or telegraph line or cable.
Let two wires connect stations which I will call A and B. These wires may. be
on poles as ordinary telegraph lines or they may be insulated and then formed
into one line or cable.
Both the Zinc and copper (or carbon) of A's battery are connected with the
electrodes on the transmitter and also the zinc and copper or carbon of B's battery,
but in such a way that the line wire from A's copper or carbon is joined to the ziuc
of B's battery and B's carbon or copper is joined by means of the line wire with its

page_text: zinc element. Thus the currents flowing round this metallic circuit flow in opposite
directions through the line wires and the induced currents follow the same direction
as the primary currents'
A's receiver may be placed in the circuit so that the positive current passes.
through the coil before reaching the transmitter. B's receiver may be placed in a
like position at his end or they may be placed at other points.
•
Where only one line wire is available the battery is connected with the simple
duplex transmitter as if there were two line wires and then the zinc end of the
transmitter is put to earth in the ordinary way.
When it is desirable to transmit the same message at the same time to two
different stations, then two separate batteries are employed, the zincs to earth
and the carbons or coppers connected with the separate electrodes of the
transmitter.
When a double duplex transmitter is employed two different stations may be
communicated with at the same time, each station having double lines or cables,
Or four stations may be communicated with if only single lines be used.
A double duplex transmitter may be used as a simple duplex by joining up its
electrodes into two sets, using one for the positive and the other for the negative
element of the battery.
These transmitters may have their electrodes joined together or used separately
in various ways.
When it is desirable further to increase the working capacity of a transmitter I
proceed in the following manner
A circle as large as possible is described on the surface of a vibrator This circle
is, by drawing the diameters, divided into sectors. In each sector is placed a
number of carbon blocks and pencils corresponding in number and arrangement to
those of the squares in a simple duplex transmitter. The systems in opposite
Sectors are placed in metallic contact, the connections being insulated. Vibrators
of this kind may be made round and placed in the manner of a simple or double
duplex transmitter,
When a vibrator is made of iron or other conducting material it is necessary to
insulate the carbon blocks
It is well known that some sounds have less power of affecting a transmitter
than others. Such words as keys, weep, sweep & which may be called close
sounds, are difficult to distinguish in a receiver when they occur in a message sent
by the ordinary transmitter This defect is remedied almost entirely in my duplex
transmitter by means of the variation in the dimensions and weight of the carbon
pencils, the very sensitive nature of the vibrator and the double vibration working
in a metallic circuit.
Under certain circumstances I find it advantageous to use an ordinary condenser
(such as is used with an induction coil) with these transmitters. One end of the
condenser is attaced [sic] to the positive and the other to the negative end of the
battery. The condenser may be varied in size to suit the battery power and length
of circuit
Any of the ordinary receiving telephones may be employed with these
transmitters and generally it will be found with a very marked improvement in
intensity and clearness of sound
Both surfaces of the vibrators may be arranged with carbon electrodes, generally
however it is sufficient to use only one surface, leaving the unoccupied surface
presented to the sound waves.
In order to increase the receiving capacity in a telephone I employ one or other
of the following devices.
I prepare an induction coil of larger dimensions than the ordinary induction
coil used in telephone receivers. The secondary wire of this coil is wound in any
convenient number of sections.
The ends of the wire of each section are brought out separately and fastened
to binding screws,

page_text: The wires of the bobbins of the receiving magnets are put in metallic connection
with these binders
The magnets are made flat and circular and to each pole is attached a soft piece
of iron round which the fine wire is wound in the ordinary way. The magnet
with its diaphragm is inclosed in a wooden cup like receptacle which fits over the
ear. Each section of the coil has one or two of these receivers attached and they
are suspended in any convenient manner so as to be readily applied to the ear.
By using a coil of this kind very large battery power may be employed, and two
or more of the sections may be joined and used as one section when necessary.
In order to combine a magnet and induction coil in one instrument I take a
straight bar of soft iron of any convenient length The length may be say from
twelve to fourteen times the diameter of the bar. Each end is turned down and
near the shoulder of each end is a Screw, on which runs a nut, the bar forms the
core or magnet of the coil. The primary wire is wound round the centre of this
core in the ordinary way. The secondary wire is then wound on, in two or more
sections. Leaving the extended poles bare. The coil is then screwed up between
two supports and a bobbin of wire placed on each pole or on one pole only. The
ends of the secondary wire are attached to the ends of the wires forming the
bobbins placed on the extended poles. A current passed through the primary
magnetises the core and induces a current in the secondary which current is made
to re-act on the poles through the bobbins fixed thereon. A diaphragm may be
placed opposite each pole if required. And two, three or several such compound
coils may be arranged at an equal distance from each other between supports each
having its own diaphragm.
I have above set forth a device for forming a magnet and induction coil in one
instrument for the purpose of a telephone receiver Now several of these
instruments may be joined together and each made to act on its own diaphragm.
In order to arrange a number of diaphragms for a Compound Receiver I make
use of the following device. I take a plate of wood brass or other metal having
a sufficiently true surface. This plate is divided into a number of circles which
are turned out in a lathe or otherwise bored out leaving the plate with the number
of perforations corresponding to the number and size of the required diaphragms.
Another plate of the same dimensions is treated in the same manner, so that the
perforations of the one coincide with the perforations of the other. The thin plate
for forming the diaphragms is placed between these two and all three plates screwed
up tightly together.
The plates supporting the combined coil and magnet are screwed to the plates
containing the diaphragms which are adjusted at the required distance.
Instead of the compound magnet and coil herein above described I may use
straight bar magnets with bobbins fixed on in the ordinary way. The only
difference being, that in this case a cylindrical piece of wood must be bored out to
contain the several magnets as in the ordinary Bell receiver. Over each magnet is
fixed a diaphragm and its distance from the magnet is adjusted by a Screw passing
through the wood into the opposite end of the magnet. prefer however to use,
instead of straight bar magnets, horse shoe magnets. These may be so formed as
to present each a part of a circle and placed beneath the diaphragms. The
magnets are screwed to a board, and the diaphragms are fastened over the
perforations of another board, or brass plates and screwed down over the magnets.
These magnets and diaphragms can be arranged in various ways
A receiver essentially consists of a magnet coil of wire surrounding the poles of
the magnet, and a diaphragm, I have herein described how several magnets coils
and diaphragms may be combined to form one compound Receiver which may be
employed in different ways.
When all the magnets and coils are connected with the secondary wire of an
induction coil as herein described or directly to the line wires, then two or more
persons can receive the same message simultaneously.
When the different magnets and coils are connected with different Stations then

page_text: different messages can be received by different persons at the same time. Or the
magnets and coils may be grouped together to suit different Stations.
It is to be understood that a tube leads from each diaphragm, so that any one
or two may be applied to the ears. But in cases where it is necessary to increase
the sound each diaphragm may be covered by a short tube and then all these short
tubes made to unite in one tube or two tubes long enough to apply to the ears.
In this case the message comes from only one station. Or all the diaphragms may
be covered with a funnel shaped cap, the tube being attached to the pipe of the
funnel.
In order that a person may have both hands free to take down a message.
I make use of the following device. A soft band of flexible material, with an
elastic piece inserted encircles the head, another band goes over the head and under
the chin. On opposite sides of the band are placed two car flaps into which the
tubes coming from the diaphragm, are inserted. Should the strap under the chin
not be used the flaps may be kept close to the ears with a spring.
When a flat magnet receiver is used then elastic straps may be employed. It
is easy to adjust the length of the flexible cords by means of which the receivers
are suspended, so that the weight need only occasionally be borne by the head.
It sometimes happens that the sound of the voice may be heard in a receiver,
but the words are indistinct. This may arise from feebleness of current. I then
employ a local cell or battery as a Relay. The line wiro proceeding from the
copper or carbon of the transmitting battery is connected with the zinc element
of the local cell or battery, the other element continues the line through the
receiver. Or they may be otherwise connected according to the circuit employed
In this way the words are made clear and distinct. And generally a cell or battery
may be placed in any part of the circuit provided it is joined up in the manner
here indicated
The Cup-like receptacle above mentioned is conveniently constructed in three
parts. The centre portion is a ring of wood or brass and contains the circular
magnet. On the outside of this ring is formed a screw over which the ear piece
containing the diaphragm is screwed. The back portion may be flat, or it may be
a hollow hemisphere of wood. The inside of the hemisphere may be made smooth
with a coating of shellac. A ribbon of thin iron may be used instead of the
diaphragm
The usual switches and arrangements for closing and shutting off the battery
and live currents may be employed with these transmitters and receivers.
The compound coil and magnet as above described may also be made with a
horseshoe-shaped magnet of soft iron. Or the soft iron core may be part of
a circle, but in this case the poles are made re-entrant towards the centre of the
circle; Or the poles may be made of separate pieces fastened to the ends of the
ring and extended to its centre.
With a duplex transmitter and metallic circuit and particularly on short lines
only one battery need be used this battery may be placed in any suitable position
in the circuit. This obviates the necessity for using a battery at each end, or
placing the battery in a particular position.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Henry Meatchem in the Patent Office on the 13th March
1884.
THOMAS HENRY MEATCHEM of Waterford in the County of Waterford, Ireland
"IMPROVEMENTS IN TELEPHONIC APPARATUS
These improvements relate to combined compound or multiplying transmitters
and also to combined compound or multiplying receivers and devices connected
there with used in a telephone, the object being to extend the utility of the
telephone, to increase its power of transmitting and receiving messages and
generally to increase the clearness and distinctness of the sounds rendered and
the adaptability under varying conditions of the apparatus.
The first part of the invention consists essentially in the method of fixing and
arranging certain vibrators capable of being acted upon by articulate speech,
musical sounds or other sounds or by signals that it may be necessary to convey
over a telephone or telegraph line or cable.
The second part of the invention consists in the arrangement and connection
with each other and with the vibrators above mentioned of certain electrodes or
electric conductors capable of conveying one or more electric currents for telephonic
purposes.
The third part of the invention relates to a method of employing more than one
magnet in connection with a diaphragm or several magnets in connection with
several diaphragms operating at the same time, with or without a modified
induction coil and in connection with one or more local cells or batteries serving
the purpose of a telephone relay.
I will now describe more fully the several parts of this invention.
It is well known that if a thin plate of suitable elastic material be fixed at its
centre and made to vibrate, the outer and free edges will vibrate more strongly than
the portions contiguous to the fixed point. Certain portions of the plate called
nodal points or lines have little or no vibration. Taking advantage of this
circumstance for the purpose of this invention, I take a thin plate of wood, cork,
iron or other suitable elastic material and fix it firmly at its centre to any
convenient support.
A thin plate so fixed I call a vibrator and it can readily be fixed in any
convenient position and at any angle that may be required and this is of
considerable importance. Two or more vibrators attached at their centres to
proper supports and placed side by side without touching can be actuated by the
same sounds.
These vibrators may be square, oblong or circular, and may vary in size as may
be required.
To fix a vibrator, all that is necessary is to attach to a wall, desk, table, bracket
or other convenient support a piece of wood, iron, lead or other rigid body, the
general shape of which may be like A B in figure 1. The base B is screwed or
fastened to the support and the centre of the vibrator is screwed on at A. The
required inclination may be given to the vibrator by cutting the base support at A
obliquely or by tilting the base at B by means of a wedge. Figure 2 shows a
vibrator attached to a support, and also a circular vibrator fixed to a bracket-arm
capable of being moved round the centre C.
I will now describe a convenient method of so fixing and supporting two
vibrators, that they may both be acted upon at the same time by the same sound
(see Figures 3 and 4).

page_text: An oblong box having an open front has four grooves, two in each of its opposite
sides. The spaces between the grooves which face one another are bridged over by
means of two pieces of wood or metal which slide rather tightly in and out in the
grooves; each bridge carries a support at its centre 'to which the vibrators are
screwed. The vibrators are so attached to the supports that they converge towards
each other at the back of the box and form a wide opening at its front and they
do not touch each other or the box at any part
.
Figure 3 shews a front view looking into the box. v, v, are the vibrators
converging towards cach other at the back; 88 are the screws by means of which
the vibrators are fastened to the bridges. figure 4 shows a section of the box and
vibrators; v. v. vibrators; t. t. supports.
These vibrators may vary considerably in size and shape and the angle which
they form with a horizontal line should not be too great. Angles varying between
say 30° and 45° are suitable.
Four vibrators may be fixed in a box or frame for the purpose of being
simultaneously acted upon by the same sound. This is effected by bridging the
corners or angles of a box or frame and fixing the vibrators to the supports on the
centre of the bridges.
D. figure 5. shews a sectional elevation of such a box with bridges and supports
for four vibrators. The vibrators are fastened at their centres to the supports and
do not touch each other or the box.
I will now describe the method of attaching the electrodes e. g. carbon blocks
and pencils to the surface of a vibrator.
And here I may observe that what appears to be but a trifling difference
between one microphono arrangement and another is often of the greatest
consequence in the practical working of a transmitter.
As the result of numerous experiments I have discovered that, as near as
possible the best position for fixing the carbon blocks on a quadrangular vibrator
is found in the mannor following, illustrated by figure 6.
Draw the diagonals, their point of intersection is the point at which the vibrator
is attached to its support. Through this point also draw two lines dividing the
surface into four equal parts. In each of the four divisions inscribe a circle, each
circle touching two of the sides of the vibrator and at least one dividing line and
in each circle inscribe a square having one of its angles towards the corner of the
vibrator, the surface of which will then appear as in figure 6.
At the centre of each circle place a carbon block and also one at each angle of
each square-these blocks may be of moulded French carbon, each half an inch
high and half an inch in diameter but they may vary in size above or below these
dimensions according to the size and thickness of the Vibrator and the purpose for
which it is intended. These blocks will suit a vibrator of, say, seven inches by
six and one eighth of an inch thick or a vibrator much larger but may be smaller,
for smaller vibrators. The pencils eonnecting the blocks may be also of French
moulded carbon and may vary in diameter.
For a Vibrator of the size named and with half inch blocks, pencils sold as N° 5
each 0.273 inch diameter are suitable. Larger pencils may be used, and smaller
ones with smaller blocks.
Figure 7 shows one method of connecting these blocks and pencils. A hole is
drilled in each block through which a screw passes to fasten it to the vibrator.
The pencils are turned down at each end, as shown at P. figure 8. These turned
ends are inserted loosely in the holes drilled in the sides of the carbon blocks as
shewn in Fig 9. First the block at the centre is screwed on, then the block
towards the corner of the vibrator, which block is connected with the adjacent
blocks on the corners of the square these latter being connected with the centre
block which is connected with the block towards the middle of the Vibrator. The
one surface of the Vibrator therefore contains four separate systems of connected
blocks and pencils similarly arranged: Each system may be looked upon as a unit

page_text: of the whole system which contains twenty blocks, twenty pencils, and forty
points of loose contact. These separate units or systems may be connected in
different ways and I do not confine myself to any particular manner of connecting
the same.
The Systems when connected as in figure 7 by metallic insulated
connections, vizt, those in opposite corners give good results. M. M. are the
metallic connections which may be flat insulated stripes A. B. C. D. are the
units of the system; 8. is the central screw.
In the second method of connecting the blocks the arrangement is the same but
a double "rail "
or row of pencils is employed. For this purpose the blocks are
made say six eighths of an inch long and two holes are drilled in the side one above
the other instead of one hole as in the first method. The "rails" or pencils differ
slightly in weight, the heavier one being placed lowest-The unit system here
contains five blocks ten pencils and twenty points of loose contact, the whole
system when connected having twenty blocks forty pencils and eighty points of
loose contact.
A double rail is shewn at D. R. figure 9.
The third system is to omit the centre block and then connect the corner
blocks round the periphery of the figure by a double rail as in the second Case.
The figure here alluded to is a square on the corners of which the blocks, are
placed, the pencils running parallel to the sides.
A vibrator with its carbon electrodes attached and fixed to its support as
- herein described I call a "duplex" or "simple duplex" transmitter. Two duplex
transmitters placed in an ablong box as herein described I call a "double
"
or
'compound" duplex transmitter. When more than two transmitters are employed
at the same time and acted on by the same voice or sound such instrument I call
a "multiplex" transmitter.
There are various other ways of arranging and grouping the above mentioned
carbon blocks and pencils in the squares in which they are placed and I do not
confine myself to any one mode of arranging or grouping them.
I will now describe how a simple duplex transmitter may be employed to send
a message over a telephone or telegraph line or cable.
Let two wires connect stations which I will call A. and B. (figure 10). These
wires may be on poles as ordinary telegraph lines or they may be two cables
running side by side, or they may be insulated and then formed into one line
or cable.
At A. is a battery b and a simple duplex transmitter, both poles of the battery
are connected with the transmitter, one pole with one corner block and, the other
pole with the adjacent corner. block on the vibrator. At station B. is also a duplex
transmitter and a battery. c the connections are the same except that the poles of
the battery must be connected in the reverse order, say, the zinc pole at station B.
is connected with the carbon or copper line coming from station A. and the carbon
or copper pole of B's battery with the zinc line from station A.
Now taking
A's station it will be seen that the current coming from B's Battery crosses the
electrode on A's vibrator to the zinc-element, through the battery out by the
carbon, through the other electrode on the vibrator and by the line wire to
B's station where the current follows a similar course, twice passing through the
electrodes on the vibrator. I may speak of the current at each station as the
incoming current and the outgoing current, both currents pass through the
electrodes on the vibrator and are simultaneously affected by any sound that
affects the vibrator.
The receivers may be placed at the positions shewn in the drawing or at other
positions as may be most convenient,
In order to work a double duplex transmitter on a metallic circuit it is only
necessary to connect the electrodes on one vibrator with one line wire and also with
one pole of the battery, while the electrodes on the other vibrator are connected
with the remaining line and battery pole, taking care that the same poles of the
batteries at opposite stations are not connected with the same line wire. In this

page_text: case the incoming current passes through the electrodes on one vibrator, while the
outgoing current passes through those on the other vibrator. Each current has a
vibrator of its own and undergoes a greater number of sub-divisions than with a
simple duplex transmittor. It is to be understood that both in the case of the
single and double duplex transmitters, the electrodes may be coupled up and used
in various ways and I do not confine myself to any particular way of using them.
A trial or two will shew which is the best way of joining them to the line wires and
battery on any particular circuit. They may also be used with single line wires,
the zinc pole of the battery being put to earth in the ordinary way, or the zinc
pole may be joined to one end of the electrode on a vibrator and then the other end
of this electrode put to earth.
When it is desirable to transmit the same message at the same moment to two
different stations the double duplex transmitter may be used. One pair of line
wires is attached to the electrodes on one vibrator, and the other pair of line wires
to the electrodes on the other vibrator in the same manner as with a simple
duplex. Two batteries may be used one for each Station to which the message is
to be sent.
The connections exhibited in figure 19 show how a double duplex transmitter
may be employed on a metallic circuit. The line wires are each connected to the
electrodes on a vibrator, the other extremities of these electrodes being connected
with the battery poles as shown. With a multiplex transmitter it is easy to see
that more than two stations may be communicated with at the same time, each
station having double lines or a metallic circuit.
Or the same message may be sent along several lines to a station at the same
time and each received by a compound receiver as hereinafter described.
When it is desirable further to increase the working capacity of a transmitter
a circle as large as possible is described on the surface of the vibrator. This circle
is divided into sectors by drawing the diameters; in each sector is placed a
number of carbon blocks and pencils corresponding in number and arrangement to
those of the squares in a simple duplex transmitter. The systems in opposite
sectors are placed in metallic contact thus forming one electrode.
Figure 11 shews six sectors, and six systems of blocks and pencils forming three
separate electrodes.
Figure 12 shows a round vibrator having the same number of electrodes. It
will be readily understood that the number of electrodes on a vibrator may be
increased and that two quadrangular vibrators each containing three or more
electrodes, may be placed in a box in the same way as v. v figure 4. With two
such vibrators thus placed more than two stations could be communicated with at
the same time, or the electrodes can be coupled up and used as in figure 19.
I do not confine myself to any particular method of joining or using these
transmitters.
Circular vibrators have less tendency to warp than square or oblong vibrators.
Should it be found necessary to prevent these latter warping, two of them may be
glued together, the grain of the one running at right angles to, or across the grain
of the other, when thus fastened they may be reduced to the shape and thickness
required.
When the vibrators are made of iron or other conducting material, it is obviously
necessary to insulate the carbon blocks therefrom.
When the condenser is used in circuit with these transmitters all that is
necessary is to connect one pole of the battery with one pole of the condenser and
the line wire to same pole, the other pole of the battery, condenser, and other line
wire are joined in the same manner- -Figure 13 shows this arrangement, B battery,
C condenser. T transmitter.
As the result of numerous experiments I find that even without an induction
coil in circuit any of the above mentioned transmitters have great power of
transmitting what may be called close sounds; such words as keep, keys, sweep,

page_text: weep, which I have found to be very difficult to distinguish in other instruments
and which some people cannot distinguish at all, sound quite distinct when sent by
these transmitters. The above stated defect is almost entirely obviated in my
duplex transmitter by means of the variation in the dimensions and weight of the
carbon pencils, the very sensitive nature of the vibrator and the double vibration
working in a metallic circuit.
In order to increase the receiving capacity in a telephone I employ one or other
of the following devices. I prepare an induction coil of larger dimensions than the
ordinary induction coil used in telephone receivers
•
The secondary wire of this coil is wound in any convenient number of insulated
sections. The ends of the wire of each section or of two or more joined sections
are brought out separately and fastened to binding screws. The wires of the
bobbins on the receiving magnets are put in connection with these binders.
The primary wire of the coil is in connection with the line wires. Figure 14
shows an arrangement of this kind. C is the coil wound in divisions, R and R, the
receivers, each connected with two joined sections. B is a local battery which may
be placed in connection with the carbon line wire as shewn The zinc element of the
local battery is connected with the line wire coming from the carbon element of the
battery at the sending station and the carbon element of the local battery continues
the line through the primary wire of the coil. Another way of connecting up these
wires is to connect one end of the primary and one end of a secondary section each
to a line wire as in figure 16 the remaining end of the primary is put in connection
with one end of the bobbin wire on the magnet of receiver, while the other end of
the bobbin wire is united to the remaining end of the secondary section. When
there is only one line wire the connections must be placed to earth in the ordinary
way. Two or more persons may employ one each of the receivers to take down
the same message at the same time, which may be done when two or more copies
are required and which method will help in checking each report as taken down.
The magnets used in a receiver with a coil of this kind may be made flat and
circular and to each pole is attached a soft piece of iron round which the fine wire
is wound as in the ordinary magnets of this class. The magnet with its diaphragm
is inclosed in a wooden, cup like receptacle which fits over the ear. These
receivers may be suspended in any convenient position so as to be readily used
when required.
In order to combine a magnet and induction coil in one instrument, I take a
straight bar of soft iron of any convenient length, which length may be twelve or
fourteen times the diameter. Each end is turned off in a lathe say for an
inch or more. Near the shoulder runs a screw carrying a nut for the purpose
of fastening the bar between plates. Figure 15 shews the bar in this form.
The primary wire is wound between the shoulders in the ordinary way, and
the secondary in one, two or more divisions, leaving the extended poles bare. This
coil is now screwed up between two supports and a bobbin of wire placed on each
pole or on one pole only. A current passed through the primary magnetises the
core and induces a current in the secondary which current is made to re-act on the
poles through the bobbins placed thereon, the ends of the bobbin wire being placed
in contact with the ends of the secondary wire of the magnet. In working a coil
or magnet of this kind I prefer to proceed in the manner following. The bar or
rod of soft iron is made as above, the primary wire, which may be N° 24 B. W. G,
silk covered copper wire is wound on between the shoulders once or twice. The
wire is then continued round the one end only several times for about one third of
the bar. This end is now to act as the pole of the magnet--and on this pole only,
the bobbin of fine wire is used. The secondary wire is wound on as before, first
filling up the space left by the primary and then continuing the winding over the
whole primary. The end of the bar not intended to be used as a pole is screwed
into a soft iron support or plate, the polar end to a plate of brass or hard wood.
The diaphragm is placed opposite the pole carrying the bobbin, that is the pole to

page_text: which the wooden support is attached and round which the primary is several
times coiled. One method of joining up the ends of these several wires is as
follows one end of the bobbin wire and one end of the secondary are both joined
together and to the carbon element of a local battery, the other end of the bobbin
wire and secondary wire are joined to an end of the primary, while the remaining
end of primary is joined to the line wire, the remaining line wire is joined to the
zinc element of the local battery. It will be noticed in this arrangement that the
current from the local battery is divided, one portion flowing round the polar
bobbin through the primary and line wire while the other portion circulatos round
the secondary wire and primary to line wire. The power of the battery and
winding of the wire on the soft iron core may be varied to suit any particular
circuit. An instrument of this kind renders the vocal sounds particularly clear
and distinct. Figure 16 shews the several connections
Referring to figure 16 p. p is the soft iron plate, C the soft iron rod or core,
W W the the wooden plate support; bb the polar bobbin P¹ P₁ the primary
shown by large dots. S S the secondary indicated by small dots. B the battery
line, and zinc wires are shewn connected at O, bobbin, secondary and carbon wires
at t, remaining ends of bobbin and secondary and primary at x; also primary and
line at y. There are other modes of connecting the different wires above mentioned
and I do not confine myself to any particular manner of connecting them. For
the sake of distinction I call the combined coil and magnet as above described
“modifiod induction coil" or "compound coil and magnet" A ribbon of thin
iron fastened at two of its ends but otherwise free to vibrate may be used instead
of a diaphragm.
a
Two or more modified coils as above described may be joined together and made
to act on a large diaphragm, or each coil may act on its own diaphragm. Such
a receiver having two or more coils and magnets in operation at the same time
may be called a compound receiver.
In order to arrange a number of diaphragms for a compound receiver of this
kind I take a plate of wood, brass or other metal having a sufficiently true surface.
This plate is divided into a number of circles which are turned out in a lathe or
otherwise bored out, leaving the plate with the number of perforations corresponding
to the number and size of the required diaphragms. Another plate of the same
dimensions is treated in the same manner, so that when one plate is placed on the
other the perforations of the one coincide with those of the other A thin iron
plate for forming the diaphragms is placed between these two and all three plates
screwed up tightly together. Figure 17 shews a plate for six diaphragms, but
the arrangement may be different, and the number be varied as may be desirable.
These plates are supported and adjusted by means of four corner screws such as
are shewn at Figure 16 in which n. n. are the screws and D. D are the diaphragm
plates.
I may also employ straight bar permanent magnets with bobbins as follows
In a cylindrical piece of wood holes, a convenient distance apart, are bored out
to receive each a magnet. Over each magnet is placed a diaphragm and the
distance adjusted by a screw passing through the wood at the opposite end of the
magnet as in the ordinary Bell receiver, I prefer however horse shoe magnets
These may be formed as to present each a part of a circle screwed to a board and
placed beneath The diaphragms are fastened between two plates and adjusted
over the magnets as with the compound coil above described. In the case of the
straight bar permanent magnets or circular magnets above mentioned the wires
of the polar bobbins are joined in the ordinary way, that is, as ordinary Bell
receivers are joined together. A local battery may also be placed in the circuit,
taking care that the proper pole is connected with the proper line wire. It is to
be understood that a flexible tube leads from each diaphragm, so that any one or
two may be applied to the ears. But when it is necessary to increase the sounds
each diaphragm may be covered with a short tube and then all these short tubes

page_text: joined in one tube or two tubes long enough to apply to the ears. Or all the
diaphragms may be covered with a funnel shaped cap the tube being attached to
the pipe of the funnel. It is to be understood that this method for collecting the
sounds applies to all compound diaphragms herein described. Or the sounds may
be collected by using a cover same as the cover usually called the mouth piece
in a Bell receiver, only on a larger scale. It is also evident that when several
diaphragms are in operation at the same time in a compound receiver, two
or more persons can receive and take down the same message at the same timo.
In order to construct a circular modified induction Coil I take a soft iron bar
which may be about 8th of an inch in diameter and about nine inches long less
or more as may be required. This bar is turned into a circular form leaving
a space between the ends. Around the circular bar, except a space of about '/, an
inch at each end are wound two or more layers of insulated copper wire-
A sufficient quantity of wire is left attached at each end to form two or more
-layers round the pole-pieces when afterwards put on.
+
The fine or secondary wire is wound on a mandril in discs each about one
eighth thick and so that they will readily pass over the copper wire on the
circular core.
As the discs are being wound, the wire passes through melted
paraffin wax and the whole coil insulated with the same material in the
ordinary way.
The polar pieces containing the polar bobbins are now screwed on the ends of
the core and the spare primary wire coiled round them. The whole is placed in
a suitable circular wooden receptacle-The diaphragm may be fastend on over
the poles and round the edge in the ordinary way, or the diaphragm may be
fastened to the ear piece which may be screwed over the edge of the wooden
recptacle containing the coil or a thin ribbon of iron may be placed across the
poles and fastened at each end.
The wires in this coil are joined to each other and the line wires and local
battery in the manner described with reference to in Figure 16.
The
Figure 18 shews a circular coil and magnet of this form S S &c secondary
sections P P. primary (large dots) pp polar pieces, E E the soft iron core.
electrical connections are shewn and will be readily understood by electricians
In order that a person may have both hands free to take down a telegraphic
message the receivers or acoustic tubes may be kept close to the ears by means of
flexible elastic straps encircling the head
Figures 20. 20a and 20b show a method of forming an ear-holder for a
telephone receiver; ffis a circular piece of wood or leather which fits over the
ear and is held in position by means of flexible straps having elastic webs inserted.
These straps encircle the head as shewn. In the centre of the ear flap is an
aperture through which the end of the acoustic flexible tube is inserted; the end
of this tube has a little spring which, when pressed with the finger admits the
tube, and when released holds the tube in the ear flap. T is the tube coming from
a diaphragm and on its end is shewn the little spring S.
Another method is to insert a short piece of tube firmly in the ear flap-This
partly projects into the ear on the inside and on the outside is a little stud by means
of which the flexible tube coming from a diaphragm is fastened in the same manner
as a bayonet is fastened to a rifle. Figure 20 shews an arrangement of this kind
M shews the section of the ear flap with the fixed tube inserted Tis the tube with
slit for stud.
When a circular modified coil is used as above described as the receiver it may
be kept close to the ear by means of an elastic web encircling the head as in
figure 20. Such receiver may also be easily suspended above the head by elastic
cords and the web circlet or hoop attached so that it may be applied to the head
at a moments notice-Such holders are very useful when long commercial messages
are being received and they may be modified to meet the convenience of the user.
It is not necessary to use a battery at each end of a circuit with a duplex

page_text: transmitter A battery at one end only is often quite sufficient particularly where
as in a private dwelling it is not desirable to have a battery.
In a house telephone when a battery is objectionable in any room or apartment
a duplex transmitter plain or ornamental may be fixed in any of the above
mentioned ways in such room or apartment without a battery.
For this purpose the electrodes on the transmitter are united to the line wires at
one end, while the electrodes are joined together at the other end of the vibrator
as shewn at E figure 21. where they are placed in connection with the wires of the
receiver A-At B station the ends of the electrodes are joined to the battery poles
at one extremity and to the line wires at the other extremity the receiver being
placed in the circuit
This very simple and effective method of using these transmitters having obviated
the necessity of using a battery in rooms where likely to be objectionable also saves
the battery expense.
A switch board and bells can easily be employed with this arrangement-three
connecting insulating wires are used covered with differently coloured silk or cotton-
one may be called the line wire another carbon line and the third the Zinc line or
earth line-The zinc and line wires may form a double line e g each is insulated
and then over spun in one line
The construction of switch boards being well understood calls for no description
It is also evident that several rooms in a House may have each a duplex
transmitter and receiver without a battery, connected with a double duplex
transmitter or multiplex transmitter and battery placed in any convenient place
and easily accessible to persons with whom it may be necessary to communicate
In Figure 22 is shewn an arrangement by means of which this can be easily effected
A B. C and D are four duplex transmitters placed in four separate rooms numbered
respectively 2. 1. 4. 3-v and v are the vibrators of a double duplex transmitter
placed in a hall or other apartment used for the purpose; here also is placed the
battery B and switch S for the purpose of connecting any particular room or
transmitter with the battery and one electrode on the double duplex transmitter.
b. is a brass arm moveable round the pivot P with which is connected the Zinc
pole of the battery-1. 2. 3 and 4 are little brass plates with which are connected
the wires leading from the electrodes one from each on the double duplex
transmitter. A wire C connected with the carbon element of the battery leads to
the several rooms and is connected to each transmitter by a short wire leading from
one of the electrodes. The other electrode on each room transmitter is in connection
with one of the electrodes on the double duplex transmitter The remaining ends
of the electrode on each room transmitter are connected together at n n n n as
shewn-When the arm b is moved to 1 on the switch, then N° 1 room is in circuit
and no other, when it is moved to 2 then number 2 room, and no other is in circuit
and so on with 3 and 4-When the switch arm is placed as in the figure then none
of the rooms are in circuit The receiver may hang from this arm and serve to put
the battery out of circuit when not required.
The ordinary bells may be employed with this arrangement to shew which room
has called or electric Bells may be employed with room indicators. By this simple
and effective means the expense of several batteries is avoided, and the necessity
of employing them in any particular apartment obviated. It is evident that with
a double duplex transmitter, having on each vibrator three separate electrodes six
different rooms can be communicated with in the manner above described. It is
also plain that with a multiplex transmitter several rooms may be united in a
telephone system as above described. This system is particularly suitable where
it is not desirable to disturb the old wire pull bell.
The central flap of a telephone ear-holder when of hard material may be lined
or padded with flannel or rubber. This will keep the hard material from
pressing against the skin at the same time that it will deaden extraneous sounds.
It will be readily understood that, if desired, one of the electrodes in a

page_text: .
simple duplex transmitter, or several of these electrodes, in a double duplex
transmitter, may be thrown out of circuit or have an earth connection in the
ordinary way.
A battery may be employed in any part of the circuit with a duplex transmitter,
provided, the poles of each battery be not opposed to the like pole of any other
battery employed in that circuit, as is illustrated by Figure 23.
It has above been stated that the current passing through the electrodes on a
vibrator may be spoken of as the "incoming current". and the "out going
current the same terms namely-incoming and outgoing may be applied to the
electrodes conveying these currents.
"
Should the incoming current be too weak to work the receiver at any station
a local battery may be placed in the circuit where it is joined up to the incoming
electrode on the vibrator the other terminal of this electrode may be joined to the
zinc element of a second local battery to the carbon element of which is joined
a terminal of the secondary and bobbin wires of the modified induction coil
herein before described, one terminal of the primary of which is attached to the
outgoing electrode on the vibrator shown in Figure 16 Here the second local
battery and coil serve the purpose of a relay.
The local batteries, the transmitter and line wires may be connected in various
ways and I do not confine myself to any particular way of connecting them.
Having now described the nature of my said invention and the manner of
performing the same I claim.
First In a telephonic transmitter one or more centrally fixed suspended or
supported vibrators so constructed that all the sides and edges of vibrator or
vibrators may be free to move substantially as herein described and as illustrated
in the accompanying drawings.
Second: In a telephonic transmitter the two centrally supported vibrators in
a box so arranged that they converge towards each other at one extremity and
form a wide opening at the other without touching each other or the box, and
that they may be simultaneously acted upon by the same sound substantially as
herein described and shown in the accompanying drawings.
Third-In a telephonic transmitter the method of fixing centrally more than
two vibrators in a box or frame so that they may be simultaneously affected by
the sound substantially as set forth and shown in the drawings.
Fourth In a telephonic transmitter the arrangement and grouping on the
more strongly vibrating parts of a vibrator of groups systems or units composed
of symetrically arranged carbon blocks and single or double carbon pencil rails
and having the systems on opposite corners or sectors united by insulated metallic
strips and forming two or more separate electrodes substantially in the manner
herein described and shown in the drawings.
Fifth In a telephonic receiver the combination of a soft iron plate and soft
iron rod or bar wound with primary and secondary wire and carrying a polar
bobbin forming a modified induction coil as herein described and as illustrated in
the accompanying drawings
Sixth In a telephonic receiver the circular modified induction coil substantially
as described and shown in the drawings. .
Seventh-In a telephone system and metallic circuit the combination with a
condenser and a local battery of the duplex transmitter and modified induction
coil all substantially as and for the purposes herein described and illustrated in the
accompanying drawings.
Eighth In a telephone system the combination with two or more metallic
circuits and two or more batteries of a double duplex or multiple transmitter,
transmitting the same message at the same time to two or more stations all
substantially as herein described and for the purposes set forth.
Ninth A telephone ear-holder constructed and supported substantially as set
forth leaving both hands free as herein described.

page_text: Tenth In a telephone system the combination of one battery, one or more
simple duplex transmitters and double duplex transmitter substantially as
described.
In witness whereof I the said Thomas Henry Meatchem have hereunto set my
hand and seal this twenty first day of February in the year of our Lord One
thousand eight hundred and eighty four.
THOMAS HENRY MEATCHEM (L.S.)