Improvements in or relating to Telephonic Systems, and in Apparatus Employed therein.
Year: 1896

page_text: Date of Application, 14th Nov., 1896
Complete Specification Left, 26th Feb., 1897-Accepted, 29th May, 1897
Improvements in or relating to Telephonic Systems, and in
Apparatus Employed therein.
A communication from LA SOCIÉTÉ ANONYME DE TÉLÉPHONIE PRIVÉE, of
115 Boulevard de la Senne, Brussels, in the Kingdom of Belgium.
I, ALFRED JULIUS BOULT of 111 Hatton Garden in the County of Middlesex,
Chartered Patent Agent, do hereby declare the nature of this invention to be as
follows:-
The improved telephonic system with call by means of a battery, forming the
subject of the present invention, and chiefly destined to be used as a house or similar
installation is chiefly characterized by a special construction and arrangement of
telephonic apparatus whereby communication may be established without a central
switch and by a new granular microphone completing the telephonic apparatus.
In telephonic systems in which the call is made by means of a battery in house-
telephones, the electric circuits are generally constituted by movable or elastic
parts establishing the desired connections.
The number and the shape of the parts may vary and their arrangement depends
on the requirements of each individual case.
But in all cases, the proper working of the apparatus, depends on such con-
struction and arrangement. Thus too many springs cause, by their deformation
and other defects, more or less temporary disturbance, and the junctions or
connections through which the current has to pass may be very imperfect.
In the improved arrangement and construction of the apparatus these drawbacks
are remedied by reducing the number of parts to a minimum and by arranging
them so as to completely ensure proper working of the apparatus. For this
purpose the number of springs is reduced to one only; the hinge of the automatic
switch-hook forming no part of the circuit and the contact of the switch-lever is
effected by friction on the inclined faces of a stud.
The spring is connected to the line wire and at a contact point above the hinge
it is connected with the switch-hook which, when lowered or depressed, comes in
contact with the stud connected to the call-hell of the receiving apparatus.
A call-current from the line will therefore follow the circuit without passing
through the hinge of the switch hook.
In the same way if a knob is pressed to depress the spring in order to make a
call, the spring will move away from the hook and come into contact with the stud
connected to the battery used for calling up, the current of said battery passing
into the line without having previously to pass through the hinge of the switch
hook.
The spring has therefore two functions: first, to establish communication with
the line and secondly to effect a call, through tho stud connected to the battery
and without including the hinge of the switch hook in the electric circuit.
This spring has further another function, that of raising the hook when the
receiver is removed from it. Under such circumstances the bell is switched out of
the circuit and the hook is in contact with the upper studs.
In order to make such simultaneous double contact possible, it has been hithertu.
usual to make both these studs of elastic material.

page_text: According to the present invention, however, both the studs are made solid but
have inclined planes.
The joint or hinge not forming part of the electric circuit, may be made some-
what loose, thereby permitting the lever or hook to swing easily which hook being
raised by the spring is easily brought to bear against the two upper studs, and
passes in the hollow on one or on the other of their inclined planes.
It is clear therefore that only one spring is sufficient for the whole apparatus,
that the current does not pass through the hinge and that the studs with inclined
faces are sufficient to establish contact of the lever with said two studs.
One or the other or both of these studs are connected to the telephone, microphone
and to the battery when the apparatus is not provided with an induction coil.
They are connected in a different way when an induction coil is used.
These parts may be obviously utilised for other purposes. The switch-hook may
be insulated from the spring by an ebonite stud. These two parts, the hook and
the spring may therefore be connected to different circuits. The result will be
that when the hook is lowered, the spring will be in contact with the under stud
thus short-circuiting the telephone and microphone of the apparatus, whereas by
raising the hook these parts are switched into the circuit, the upper studs being at
the same time placed in contact by the hook, and complete the return-circuit of the
battery. This arrangement may be adopted when several sets have to use the
same battery and the same wires by means of the hereinbefore described parts.
When it is desired to establish communication between more than two apparatus
without having to use a central switch, all the apparatus are connected with each
other by wires terminating in similarly numbered 1, 2, 3, 4 &c. studs or terminals.
In apparatus in which a battery is used, and with transmitting apparatus without
an induction coil where communication has to be made in different directions, the
chief difficulty is to prevent the batteries of the transmitters from working in
opposition.
In order to satisfy this requirement, we arrange these batteries in similar
positions where are attached flexible cords terminating in plugs which are to be
introduced into the contact-holes 1, 2, 3, 4, when it is desirous to connect the
apparatus with any other of the apparatus of these numbers.
If the apparatus No. 1 is to be connected with the apparatus No. 2 for instance
the plug is introduced into the hole No. 2. By pressing on the call knob or button
the circuit of the battery for calling up, is closed by the line 2 and the conductor
and through the bell of the apparatus 2 which is thus called up.
If both the operators remove their instruments from the hooks, the circuit of the
battery will be closed by the conductors passing through the transmitters and
receivers.
Only the battery therefore of the apparatus will be in use in which the cord has
been operated which serves for the conversation or connection required. There is
therefore no possible opposition of current between the two apparatus connected
with each other.
Besides all these batteries being similarly placed it follows that in the common
return wire only currents of the same sign circulate and that thus there cannot
possibly be any interference with the communications exchanged simultaneously
through this conductor.
. A separate return wire for the currents for calling up may be employed but the
same conductor might be used if there were no danger of disturbing conversations
by intermittent currents produced by the bell-apparatus.
The conductor connected to the single battery may also be dispensed with if a
call battery is used with each apparatus instead of using one battery for all.
The better effect of the improved microphone of this apparatus is explained by
following considerations.
In a casing of the same kind as Hunnings of a certain diameter, the grains are
heaped in different degrees of density. The lowest layer is the one with the
greatest density or the most compressed; the middle layer is of a smaller density,

page_text: or is less compressed, and the density of the upper layer is very small or it is only
slightly compressed. It follows that if the diaphragm is directly or indirectly in
contact with the whole of the face of the microphone, the variations of pressure
are in consequence of the very great density of the lower layer much exaggerated
when they reach the upper layer, where they produce jumping or crackling so that
the normal working is obtained by means of the middle layer. The modulation of
the transmission which is perfect in a certain layer, is therefore considerably
affected by the imperfections of the transmission by adjoining layers and thereby
suffers.
It is clear from the above that if the injurious influence of the top and bottom
layers be excluded and the diaphragm actuated only by the middle layer a trans-
mission through a layer of uniform density of a desired degree of compression is
obtained without influencing the vibrations of the diaphragm and consequently the
perfection of the modulation.
This end is attained when the diaphragm touches the transmitting medium only
along the middle layer and it is sufficient to construct the parts in any suitable
manner to obtain the result.
A practical construction is to make the shape of the box or casing with a front
circular flange on a casing parallel to its bottom or rear side the flange covering
the upper and the lower layers and leaving open only the central layer which is
thus the only one in contact hy means of its grains, with the diaphragm the
vibrations of which do not therefore influence the layers of unequal density at the
same time the current passes through the whole granular mass and through the casing
made entirely of conducting material.
The casing of such shape may be made from a single block of conducting material
hollowed out and its shape may be differently formed as for instance the hollow may
be made taper or oval or of other desired shape, but we prefer the shape already
described, characterised by a cylindrical hollow with circular flange at a right angle
to the walls.
The new transmitter not only has the above explained microphonic advantages,
but is also of very simple construction and may be manufactured easily and
inexpensively the only adjustment required is that of a central screw on a support
included in the circuit.
1000
BOULT & WADE,
Agents for the Applicant.
Improvements in or relating to Telephonic Systems, and in
Apparatus Employed therein.
A communication from LA SOCIÉTÉ ANONYME DE TELEPHONIE PRIVÉE, of
115 Boulevard de la Senne, Brussels, in the Kingdom of Belgium.
1, ALFRED JULIUS BOULT of 111 Hatton Garden, in the County of Middlesex,
Chartered Patent Agent 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 :-
The improved telephonic systems with call by means of a battery forming the
subject of the present invention and chiefly destined to be used as a house or
similar installation is chiefly characterised by a special construction and arrange-
.ment of telephonic apparatus whereby communication may be established without

page_text: a central Switch, and by a new granular microphone completing the telephonic
apparatus.
In the accompanying drawing
Fig. 1 is a view of part of the telephonic apparatus showing the arrangement
of the spring and of the hook with corresponding accessories when the telephone
is on the hook.
Fig. 2 is the same arrangement the telephone being off the hook.
Fig. 3 is a cross section of contact studs with inclined faces.
Fig. 4 is a diagramı of a telephone system in which no induction coil is used.
Fig. 5 is a diagram of the same system with an induction coil.
Fig. 6 is a diagram of a modified arrangement.
Fig. 7 is a diagram of a system according to which communication may be
established between more than two apparatus on the same line and with the same
wires without necessitating the use of a central switch.
Fig. 8 is a diagram of the new granular microphone used in the improved
apparatus.
Fig. 9 is a cross section of the microphone casing with its diaphragm, on a
larger scale.
Figs. 10 and 11 show modified forms of said casing.
In the telephonic systems in which the call is made by means of a battery in
house telephones, the electric circuits are generally constituted by movable or
flexible parts establishing the desired connections.
The number and the shape of the parts may vary and their arrangement depends
on the requirements of each individual case.
But in all cases the proper working of the apparatus depends on such construc-
tion and arrangement. Thus too many springs cause by their deformation and
other defects, more or less temporary disturbance, and the junctions or connections
through which the current has to pass may be very imperfect.
In the improved arrangement and construction of the apparatus these drawbacks
are remedied by reducing the number of parts to a minimum and by arranging
them so as to completely ensure proper working of the apparatus. For this
purpose the number of springs is reduced to one only; the hinge of the automatic
switch hook forming no part of the circuit and the contact of the switch lever is
effected by contact on the inclined faces of a stud.
In Fig. 1 the spring LA B is connected at L tu the line wire and at a contact
point above the hinge of the hook B it is connected with the switch hook CD
which when lowered or depressed comes in contact with the stud S connected to
the call-bell of the receiving apparatus. A call current from the line will therefore
follow the circuit LA BS without passing through the hinge C of the switch
hook.
In the same way if a knob P is pressed to depress the spring in order to make
a call the spring LA B will move away from the hook C D and come into contact
with the stud E connected to the battery used for calling up, the current of said
battery passing into the line without having previously to pass through the hinge C
of the hook.
The spring has therefore two functions: first to establish communication with
the line and secondly to effect a call through the stud E connected to the battery
and without including the hinge in the electric circuit.
This spring has further another function that of raising the hook CD when the
receiver is removed from it Fig. 2. Under such circumstances the bell is
switched out of the circuit and the hook CD is in contact with the upper
studs M and N.
In order to make such simultaneous double contact possible, it has been hitherto
usual to make both these studs of elastic or flexible material.
According to the present invention, however, both the studs are made solid but
have inclined surfaces (see Fig. 3).
The joint or hinge C not forming part of the electric circuit may be made

page_text: somewhat loose thereby permitting the lever or hook CD to swing easily which
hook being raised by the spring A B is easily brought to bear against the two
upper studs M and N and passes in the hollow on one or on the other of their
inclined planes.
It is clear therefore that only one spring is sufficient for the whole apparatus,
that the current does not pass through the hinge and that the studs with inclined
faces are sufficient to establish contact of the lever with said two studs.
One or the other or both of these studs are connected to the telephone,
microphone and to the battery (Fig. 4) when the apparatus is not provided with
an induction coil.
They are connected in a different way (Fig. 5) when an induction coil is used.
These parts may be obviously utilised for other purposes, as is indicated in
Fig. 6. Here the switch hook CD may be insulated from the spring LA B by
an ebonite stud. These two parts, the hook and the spring, may therefore be
connected to different circuits. The result will be that when the hook is lowered,
the spring A B will come in contact with the under stud S thns short circuiting
the telephone and inicrophone of the apparatus, whereas by raising the hook these
parts are switched into the circuit L L the upper studs M and N being at the
same time placed in contact by the hook, and complete the return circuit of the
battery LL. This arrangement may be adopted when several sets have to use
the same battery and the same wires by means of the hereinbefore described
parts.
When it is desired to establish communication between more than two
apparatus without having to employ a central switch, all the apparatus are
connected with each other by wires terminating in similarly numbered 1, 2, 3, 4 etc.
studs or terminals as in Fig. 7. In the apparatus in which a battery is used and
with transmitting apparatus without an induction coil where communication has to
be made in different directions, the chief difficulty is to prevent the batteries, of
the transmitters from working in opposition.
In order to satisfy this requirement, these batteries are arranged in similar
positions relatively to the points 010 etc. Fig. 7 where flexible cords are attached
terminating in plugs FF which are to be introduced into the contact-
holes 1, 2, 3, 4 etc., when it is desired to connect the apparatus with any other of
the apparatus of these numbers.
If for example the apparatus No. 1 is to be connected with the apparatus No. 2
the plug F is introduced into the hole 2 (see dotted connection between the point O¹
aud the hole 2). By pressing on the call-knob or button B', the circuit of the
battery P for calling up, is closed by the line 2 and the conductor R' and through
the bell S of the apparatus 2, which is thus called up.
If both the operators remove their instruments from the hooks, the circuit of
the battery will be closed by the conductors 2 and R passing through the
transmitters m² m² and receivers T¹ T'.
Only the battery therefore of the apparatus will be in use in which the
connections have been made which serve for conversation. There is therefore no
possible opposition of currents between the two apparatus connected with each
other.
Besides all these batteries / being similarly placed it follows that in the
commou return wire R only currents of the same sign circulate and that thus
there cannot possibly be any interference with the communications exchanged
simultaneously through this conductor.
Fig. 7 shows how a separate return wire R' for the currents for calling up may
be employed; but the same conductor R might be used, if there were no danger
of disturbing conversations by intermittent currents produced by the bell-
apparatus.
The conductor P connected to the single battery P may also be dispensed with, if
a call-battery is used with each apparatus, instead of using one battery P¹ for all.
In such case, the call-batteries are arranged between a and b, as indicated by

page_text: dotted lines for the battery P'; and, of course, these batteries will be between a¹
and b, if the conductor R is comprised in the wire R.
The better effect of the improved microphone of our apparatus is explained by
the following considerations.
In a casing of the same kind as Hunnings of a certain diameter, the grains are
heaped in different degrees of density (as diagrammatically shown in Fig. 8). The
lowest layer is the one with the greatest density or the most compressed; the
-middle layer is of a smaller density, or is less compressed, and the density of
the upper layer is very small or it is only slightly compressed. It follows that if
the diaphragm is directly or indirectly in contact with the whole of the face of the
microphone, the variations of pressure are, in consequence of the very great density
of the lower layer much exaggerated when they reach the upper layer, where they
produce jumping or crackling so that the normal working is obtained by means of
the middle layer. The transmission of sound which is perfect in a certain layer is
therefore considerably effected by the imperfections of the transmission by adjoining
layers and thereby suffers.
It is clear from the above that if the injurious influence of the top and bottom
layers be excluded and the diaphragm actuated only by the middle layer, a
transmission through a layer of a uniform density and of a desired degree of
compression is obtained without influencing the vibrations of the diaphragm and
consequently the perfection of the instrument.
This end is attained when the diaphragm touches the transmitting medium only
along the middle layer in Fig. 8 at the part included within the dotted circle C
and it is sufficient to construct the parts in any suitable manner to obtain this
-result.
A practical construction is to make the shape of the box or casing in which the
grains will lie as indicated in Fig. 9 said construction being characterised by the
use of a front circular flange P³ on a casing B' parallel to its bottom or rear side
the flange covering the upper and the lower layers and leaving open only the
central layer which is thus the only one of the grains which of are in contact with
the diaphragın D³ the vibrations of which do not therefore influence the layers of
unequal density, at the same time the current passes through the whole granular
mass and through the casing made entirely of conducting material.
The casing of sucb shape may be made from a single block of conducting
material hollowed out and its shape may be formed in various ways as shown for
instance in Figs. 10 and 11 that is to say the hollow may be made taper or oval or
of other desired shape, but the shape already described and shown in Fig. 9 is
preferred characterised by a cylindrical hollow space and a circular flange at a right
angle to the walls.
This new transmitter not only has the above explained microphonic advantages,
but is also of very simple construction, and may be manufactured easily and
inexpensively the only adjustment or addition required is that of a central screw v
on a support T included in the circuit.
Having now particularly described and ascertained the nature of the said inven-
tion as communicated to me by my foreign correspondent, and in what manner the
same is to be performed, 1 declare that what I claim is :-
1. In telephonic apparatus in which calling up is effected by means of a battery
with or without an induction coil the employment of a single spring, acting as a
spring for raising the switch hook, as a spring opposing calling up, and as an
electric connection between the line, and the switch hook without the current
passing through its hinge substantially as described.
2. In telephonic apparatus the employment of contact studs having inclined
surfaces against which the pivotted switch hook strikes so as to produce double
contact of the switch-hook with the two rigid studs without the use of flexible
material, substantially as described.
3. In a telephonic system with call by battery in which transmitters without

page_text: induction coil are employed and in which communication is to be made as desired'
between various apparatus the arrangement of the batteries of the transmitters-
relatively to numbered coils or contact wires in order to establish communication
with any desired apparatus and putting in circuit only the hattery of the desired
apparatus during conversation, thus avoiding the production of opposing currents.
and producing by the uniformorientation, currents of the same sign in the return.
conductor, thus avoiding all interference with conversations taking place at the
same time on this return conductor, substantially as described.
4. In telephone systems and apparatus of the kind described, a microphonic
transmitter having a modulating granular medium consisting of a casing constructed
so as to prevent the diaphragm from touching directly or indirectly the upper and'
lower layers of the granular material, in order to cause it to act exclusively on the
middle layer so that the layers excluded cannot disturb the vibrations of the.
diaphragm either directly or indirectly, substantially as described.
5. A construction of the transmitter described consisting of a casing containing
the granular material having a circular flange covering the upper and lower layers.
of the granular filling and allowing the diaphragm to come in contact only with
the grains of the middle layer, substantially as described.
6. A casing as described formed of a single piece of conducting material so.
that the flange is in one piece with the body of the casing, substantially as
described.
7. In telephonic apparatus the arrangement of the switch hook and contact parts.
substantially as described and illustrated in Figs. 1, 2 and 3 or in the modifications
Fig. 4 or Fig. 5 or Fig. 6 of the accompanying drawings.
8. In telephonic apparatus the arrangement of parts substantially as and for the-
purpose described and illustrated in Fig. 7 of the accompanying drawings.
Dated this 26th day of February 1897.
BOULT & WADE,
Agents for the Applicant.