Year: 1889

page_text: I, ALFRED ROSLING BENNETT of 8 Duddingston Park, Portobello, in the County of
Midlothian, Telegraph Engineer do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
The object of my Invention is to facilitate rapidity of switching in a central telephone
exchange and the invention is intended for use chiefly in combination with a calling
wire exchange system, that is to say, a system which in addition to the usual wire to
a subscribers station, provides special supplementary wires, by means of which the
subscribers communicate their wishes to the Exchange operators. Two well known
systems of this type are termed the Law system of New York and Mann's circuit
system.
The diagrams up to, and inclusive of, Figure 10, together with the descriptions
relating to those figures, have reference to the invention as combined with such a
Calling wire Exchange system; and the figures from 11 to 17 together with the
descriptive matter, have reference to the invention as applied to the more ordinary
methods of Exchange working by which the subscribers' communications with the
operators are conducted on the same wires as the correspondence between
themselves.
According to the first part of my invention each subscriber's wire on being brought
into the Exchange is connected to a number of metallic blocks which are fixed in
different parts of the same room in such positions as may be most suitable. These
blocks are formed with grooves in their under sides, which grooves are made to fit the
shape of the switch pegs or plugs. The blocks are sufficiently numerous to allow of
one or other of them being within reach of every operator, or of as many operators as
may be considered desirable. Each block thus in connection with a subscriber's line
has beneath it, but not in electrical contact with it, a second metallic block which is
grooved on its upper side, so that when a switch peg is inserted between the two
blocks it will remain in firm contact with them both, being retained in position by the
groove on the underside of one and the groove on the upper side of the other. The
switch peg being of metal puts the two blocks in electrical contact so long as it
remains between them. A front view of two sets of three blocks cach is shown in
figure 1, representing the connections for two subscribers' lines. B₁ B2, B3, are the

page_text: upper blocks and 61 62, 63 the lower blocks connected with Line 1, and B4, B5, B6, the
upper blocks and . 65, 66, the lower blocks connected with Line 2. Instead of
three blocks to each line there may be thirty or any required number, the parts merely
being duplicated to the necessary extent. Each subscriber's line has a branch to
each upper block of its set, and all the lower blocks of each set are connected
together.
A pair of the switch pegs is shown in Figure 2, the two pegs being connected by a
flexible conductor. The pegs are made preferably, but not necessarily, of cylindrical
hollow metal, which tapers slightly from the insulating haft or handle, and is split, as
shown in the figure, for some distance from its smaller end. The object of the splitting
is to ensure a firm contact between the peg and the blocks between which it is inserted.
When the peg is pushed home the taper will cause the split halves to be pressed together
and the firm contact will result from the tendency of the metal to resist this compression.
This result may be further ensured by placing a metallic spring or an india-rubber core
inside the hollow cylinder of the peg. Such an india rubber core is shown at I
Figure 2 where T is the metallic part of the peg and H the insulating haft or
handle.
It will be understood that if such a peg is inserted between any of the blocks in
connection with Line 1 (Figure 1) that peg will be in electrical contact with that sub-
scriber's line; also, if the second peg which is attached to the first by means of a
flexible conductor, inserted in any block connected to Line 2 (Figure 1), the two
lines will be in electrical communication through the blocks, pegs and flexible conductor,
and the two subscribers will be able to signal each other by means of electrical currents
and converse together by means of their telephones. Their two lines, in fact, for the
time being, are made one. By this method any two lines amongst several hundreds
or thousands which are connected to sets of blocks may be temporarily joined
together.
It will be further apparent that whenever a peg is inserted it connects the upper
blocks to the lower blocks of the same set and as all the upper blocks are permanently
connected together by a wire and all the lower blocks are similarly joined, the insertion
of a peg connects all the upper and all the lower blocks together so that a current sent into
one will pass into all the others. By applying a current to the lower block nearest to
him an operator can, with the help of suitable apparatus discover whether any of the
blocks connected to the same subscriber's line in any other part of the room is in
contact with a peg.
Figure 3 shows an appartus by which he can do this, V being a vultameter composed
of two conducting plates, placed close together but not touching, in a glass vessel
containing acidulated water or other chemical solution traversable by an electric
current. One of the conducting plates is connected to earth through a voltaic battery G.
The other conducting plate is connected to a flexible conductor which terminates in a
metallic point or pin P. To discover whether any particular subscriber's line is in
contact with a switching peg in another part of the room, the operator applies the
Fin P to the lower part of the pair of blocks of that set nearest to him, say to 62
(Figure 1). If no peg is inserted anywhere the voltameter will remain quiescent, for
no current will pass; if the line is in contact with a peg anywhere say at 63
(Figure 1) bubbles of gas will immediately rise from the conducting plates of the
voltameter, for an electrical circuit has been established by the application of the pin
and a current has passed from G through V, the pin P (Figure 3) the lower block b³,
the wire connecting the lower blocks together the lower block 63, the peg the upper
block B³ and Line 1 connected thereto (Figure 1).
Instead of being made cylindrical the grooves in the blocks may be rectangular as
shown in Figure 4. In this case the pegs must be made to fit the grooves.
Another plan for enabling an operator to discover whether a subscriber's line is or
is not in use is to employ a peg having two metallic parts insulated from each other,
one part being at the top and the other at the bottom, so that when inserted in a
rectangular hole, the one makes contact with the top and the other with the bottom
block. The flexible conductor which joins, the two pegs contains in this case two

page_text: distinct wires insulated from each otlier, one wire joining the top metallic part of one
peg to the top metallic part of the other. The other wire joins the two bottom parts
and is connected also to a voltaic battery. This arrangement is shown in Figures 5
and 6 where T and T2 are respectively the top and bottom metallic parts of the peg;
H the haft; I the rubber core; W and We the wires of the flexible conductor and G
the voltaic battery. Instead of being connected as in Figure 3 the voltameter is in
this case connected as per Figure 7.
tho
The action is as follows. When Line 1 and Line 2 are joined by a pair of pegs
being inserted in any of the block's to which they are connected, the signalling and
conversation between them goes on through one of the upper blocks of Line 1, say BB
(Figure 4), T of one peg, W1 of the flexible conductor, T of the second peg and one
of the upper blocks say B12 of Line 2. It will be seen that the lower blocks of both
Line 1 and Line 2 will be in connection with each other by T2 of the first peg, W2 of
the flexible conductor and T of the second peg. So long as the lower blocks are not
touched no current will flow from the battery G, nor will any current flow when no
pegs are inserted. But if an operator applies the pin P of the voltameter V
(Figure 7) to any of the lower blocks while a peg is inserted in the same set in any
part of the room a current will flow from G through W, T (Figure 6) the lower
block in contact with the peg, the lower block touched by the operator, the pin P,
voltauneter V (Figure 7) to carth. Bubbles rising from the conducting plates will
show that a peg is in and that the line is engaged. With this method it is essential
that the upper part T₁ of the peg be always placed in contact with the upper block
and never with the lower. Means must consequently be taken to prevent the possi
bility of an operator reversing a peg when inserting it. This may be accomplished
by making the grooves in the upper and lower blocks dissimilar in shape so that the
peg will only enter if properly applied. The rectangular grooves in the upper and
lower blocks may be made of different sizes; one groove may be made circular and
the other rectangular; or one may be made V-shaped and the other rectangular or
circular. Figure 8 indicates the nature of these variations, B, b, being the two blocks
and TT, the point of a peg. The voltameter as connected in Figure 3 may be used
with equal effect if the wire W in figure 6 be connected to the earth instead of to the
battery G, for it is evident that the positions of the earth and of the battery may be
reversed without altering the effect.
Another modification of the peg is shown in Figure 9. The peg contains two
metallic parts, T1, T2, an upper and a lower, insulated from each other. To the lower
surface of the upper metallic part, T', and insulated from it by a piece E of suitable
material such as ebonite, a small metallic contact C is attached. This contact is
connected to one wire W2 of a flexible conductor containing two wires. When out
of use the position of the contact C in respect to T is as shown in Figure 9; but
when inserted between two blocks the parts are pressed together and C makes contact
with T. The application of the pin P in Figure 3 enables the operator to tell
whether or not a peg is inserted in any of the blocks of that set, for on the pin
touching any of the lower blocks of a subscriber's line the voltameter remains
unaffected if no peg is in, but if the line is in use a current will flow from the
battery G, through V, the pin P (Figure 3) T2, C, W2 to earth (Figures 9 and 10).
In this case also the position of the earth and battery may be reversed, that is to say,
a battery may be connected to the wire W (Figure 10) instead of the earth, and the
voltameter may be user connected as in Figure 7.
As described up to this point my invention is adapted for employment only when
independent wires are provided for communications between the subscribers and the
operators.
According to the second part of my invention, by which it is adapted to the more
ordinary methods of switching, the arrangeinents are modified in the following
manner.
Each subscriber's line is connected to metallic blocks as B3, B4, B¹³, and
B6, B1, B18 in Figure 11, but the blocks are, in this case, of sucli a construction
that, either the upper or the lower, or both, are kept in their normal position of

page_text: contact with each other by means of springs or elastic pads. The peg is solid and its
insertion separates the upper from the lower blocks by compressing the springs which
hold them together. Each lower block is composed of three parts. One part 0,
(Figure 11) is of ebonite or other insulating material; the others R and X, are of
metal and are insulated from each other by intervening layers of suitable material.
The part R of each lower block is connected to earth through an electro-magnet
possessing a high magnetic inertia or degree of self induction and, preferably, wound
with fine wire to a high resistance. When no pegs are inserted it will be seen that a
current arriving from Line 1 or Line 2 (Figure 11) will traverse all the upper blocks
in connection with it, passing thence through the small contacts S to the metallic
part R of the lower blocks and then traversing all the electro-magnets to earth.
A form of peg which may be used is shown in Figure 12 and a pair of such pegs
connected by a flexible conductor at Figure 13. The peg is composed of a circular
piece of metal T containing an insulated core through which a wire W³ is led to a
metallic tip Q. The metal T of the peg is connected to the wire W¹. The insertion
of a pair of pegs between any of the blocks, say B and B (Figure 11) connected to
lines 1 and 2, separates the top and bottom portions of the blocks and connects the
two lines together through B1, T of the first peg, W₁ of the flexible conductor, T of
the second peg, and B. A current from one line will consequently pass to the
other, but it will be seen that such a current will also have other paths open to it, for
the upper blocks 1314, B16 B1 and B18 are still in contact with the portions R of their
lower blocks and through them and the corresponding electro-magnets M to earth.
But as these electro magnets are possessed of a high magnetic inertia, the undulatory
speaking currents will not pass through them with facility and the talking between
the lines 1 and 2 will not be materially weakened by the fact that the unpegged
blocks afford other paths for the current. For the purpose of enabling the subscriber
to signal the Exchange, one of the electro-magnets connected to each line must be
caused to actuate an armature so as to produce a visible signal in response to the
calling current sent from the subscriber's instrument, according to one or other of the
many devices that are employed for that purpose. In order to signal the termination
of a conversation the circuit of W1 of the flexible conductor joining the two pegs may
be caused to pass through an indicator of any one of the many well-known patterns,
or such an indicator may be connected to WI,
as a shunt to earth in the manner well
understood by telephonists.
The insulating portion of the lower blocks (Figure 11) may be omitted. In
this case the insertion of the peg will not put the upper and lower blocks out of
electrical contact, but the effect will only be that the current will traverse the
electro-magnet in connection with the pegged blocks as well as those connected
with the unpegged blocks and so have two additional paths to earth through the
electro-magnets of the pegged blocks. By the adoption of this plan two blocks
separated from each other are rendered unnecessary, a mere hole in a piece of
metal fitted to receive the peg (Figure 14) being all that is required.
But if a
mere hole is employed it is preferable to use a split peg in lieu of a solid one.
This plan enables the indicator in the circuit of the wire, W', to be dispensed with,
since the signal terminating a conversation may be given on the same electro-
magnet as the signal to begin one, for that electro-magnet is not now cut out when
the pegs are inserted.
The function of the metallic tip Q in connection with the insulated wire W
which traverses the peg (Figure 12) is to enable an operator to discover whether
any particular line is in use or not. Figure 15 is a side view of one of the blocks,
say B3 of Figure 11. Behind the block and opposite the aperture into which the
peg fits is a metallic contact Z backed by a spring or elastic pad and connected by
wires, not shown in the diagrams, permanently to all the insulated metallic sections
of the blocks marked X in Figures 11 and 14, that are proper to that particular
subscriber's line. The insertion of the peg puts the tip Q against the contact
(Figure 15). On the operator touching any of the sections ✗ with the pin P of
Figure 7 a current will flow from, the battery G by W², T, Q, (Figure 13) Z

page_text: (Figure 15) X (Figure 11 or 14) P, V, and earth (Figure 7). If no peg is inserted
no current will flow and the absence of bubbles in the voltameter will show that
the line is disengaged. As in the preceding cases the positions of the battery and
earth may be reversed.
It must be understood the voltaic battery G shown throughout this specification
may be replaced by any other source of electricity such as a magneto, dynamo, or
thermo-pile. The voltameter may likewise be replaced by any of the many devices
for producing a visible or an audible signal on the passage of a current through the
pin P of Figures 3 and 7. Amongst such devices may be enumerated the sound
of an electro-magnetic bell or vibrator; of a telephone; the deflection of a needle;
the dropping of a shutter; the movement of a disc or flag, or of a strip of metal
foil; the divergence or collapsing of the leaves of an electroscope; the closing of
a relay; the shock from an induction coil; the heating of a wire and the glowing of
an incandescent lamp.
If the shapes of the grooves in the blocks be made as in Figure 8 so that the same
side of the peg must always be inserted in the same position, the shape of the peg in
Figure 12 may be modified. Instead of being cylindrical it may be rectangular or
one side may be rectangular and the other V-shaped or round. Its connections may
then be modified as in Figure 16 where the under metallic part T which is insulated
from the upper, is in connection with the wire W and is extended and turned up at
the point, the turned up portion taking the place of the tip Q in Figure 12. Or
the peg may be arranged as in Figure 17, where the under part is of insulating
material, the tip Q being attached to a strip of metal which traverses the
from the upper metallic part and connected to the wire W2.
peg, insulated
The blocks connected to a subscriber's line have been described as distributed
throughout a room but it is not necessary that they should all be in the same room
or even in the same building.
I do not confine myself to the form of apparatus shown in Figure 15. The blocks
may be kept in contact by springs applied in various other ways. The essential
feature of the invention consists more in the production of the described effects
following the insertion of a peg than in the arrangement of the blocks and springs,
which is susceptible of many variations.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what I
claim is :-
--
1. In telephonic switching apparatus the provision of devices substantially as
hereinbefore described for making connections between subscriber's lines and indi-
cating when subscribers are engaged.
2. In telephonic switching apparatus connecting the sabscribers' lines to or
through the upper and lower contact blocks or spring-jacks in parallel circuit, sub-
stantially as described, instead of in series as by the ordinary method.
Data ihir Riftranth daer af Fabra 1880
CRUIKSHANK & FAIRWEATHER,
62, Saint Vincent Street, Glasgow,
Agents.