Improvements in Electric Telephone Apparatus.
Year: 1893

page_text: Date of Application, 17th Jan., 1893-Accepted, 18th Mar., 1893
COMPLETE SPECIFICATION.
Improvements in Electric Telephone Apparatus.
A communication by CARL CHRISTIAN ERNST LESENBERG, of Rostock, in the
Empire of Germany, Consul.
I, WILLIAM PHILLIPS THOMPSON F.C.S. M.I.M.E. of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6 Bank Street,
Manchester, both in the County of Lancaster, and 323 High Holborn in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :—
Several switching devices have been designed in recent years for the telephonic
connection of several points within works, and private and business houses, which
shall allow of any point being automatically connected with any other of the
same system without the intervention of a third.
As such systems are only employed over a place of very limited extent, there
are combined in a switching device of this kind the advantages which short
distances afford for telephonic communications.
This problem is far better solved by this improved switching device than by
those hitherto known. It allows of a hitherto unattained strength of tone of the
conversation being conveyed, and exhibits peculiar properties which prevent any
error in the use of the apparatus connected with one another by this system.
Without doubt, the best conveyance of speech is obtained by such a switching
device, owing to the very small resistance of the lines in question, in which device
the microphone at one point, having a separate source of current, acts directly on
the telephone of the corresponding point, avoiding any intermediate apparatus
such as inductors between telephone and microphone at the corresponding points.
The plan shown in Figure 2, Sheet 1, of the accompanying drawings, fulfils
this condition. By inspecting this plan, the invention is thoroughly explained.
In the figures, M denotes the carbon microphone: T the telephone: K the bell
(this is seen in Figure 1), B and B2 batteries of two to four manganese elements.
Let it be supposed that such a plan exists with the customary successive
switching of both the telephones and microphones of two points, a battery common
to both being employed. If this latter be adopted, which already means a low
price and a simple mode of working, then three wires must be employed for calling
up. If the battery as well as the apparatus be divided over the two loops of the
wire, the switching device shown in Figure 2 is obtained. It is to be understood
that in the following Specification AF means difference.
1
The superiority of the same to the successive switching is best shown by figures.
Within small limits, the strength of tone is proportionate to the size of the variation
of current (AF) caused by the microphone. If this (AF) be calculated for a
fixed alteration of resistance of 1 ohm of the microphone on the successive
switching on of four elements, as well as for a loop of the new switching device
with two elements, the desired proportion of tone strength is approximately.
obtained in that of the (AF). In both cases, the use of similar apparatus and
similar resistances in the wires is presumed. If the resistance of the wire amounts
to 3 ohms, that of a telephone to 4 ohms, of a microphone 15 ohms and of a
battery 5 ohms; the electromotive force of such will be 1.5 volts.
By the successive switching in, the total resistance in a state of rest is, 30 ohms
(2 microphones) + 8 ohms (2 telephones) + 3 ohins (wires) + 2 ohms (4 elements).
43 ohms in the other cases, 43 - 1 = 42 ohms.

page_text: 6
6
The strengths of current are then
43
-
= 0.140 ampères and
140003 ampères.
=
42
0.143 ampères.
(AF) is therefore 143.
= 23 ohms; in
In this new switching device, the resistance of a circuit is 15 ohms (1 microphone)
+4 ohms (1 telephone) + 3 ohms (wire) + 1 ohm (2 elements)
the other case, 22 ohms.
0.130 =
3
=
3
22
0.130 ampères and
23
0.006 ampères.
The strengths of the currents are therefore
0.136 ampères (AF) is therefore 0.136
The variations of current are approximately in the proportion of 3: 6 that is to
say although the battery is halved, the telephones, on the assumed proportions,
sound almost twice as loud with the new switching as with the ordinary successive
switching.
In larger establishments, of course, not 2 but 3 or 4 elements are employed in
the two loops, and thereby an unusually loud sound is obtained.
Figure on Sheet 1 shows a connection of 4 places on the plan hereinbefore
explained. Each place has a separate wire which is carried close to all the places.
All the places are also connected with 4 other wires which are each attached to
one pole of the two common sources of current B and B². A branch wire, the
end points of which are indicated on the drawing by 0, 1, 2, 3, 4 and a, b, c, d, is
provided from each main wire at each place. When not working, all the receivers
hang on their switches, by which means these form contact on their under side.
All the places are connected with the branches o a and b by detachable connections,
in the manner shown at points II III and IV. If point I wishes to speak to
point III, the previous connection with the wires must be severed, and contact
established with 3 c and d. A current then flows from B¹ through K' and T III
and another current from B2 through KIII and T I.
The bells and telephones at both places make a sound. When the telephone
receiver has been taken off the switch, the latter makes contact on its upper side,
and the bells are replaced by the carbon microphones M. When the conversation
is ended and the telephones have been hung on their switches, I is continuously
requested, by the noise of his own bell and telephone to re-establish the former
inactive condition, until this is done. If, during the conversation, II should wish
to call up point 1, he would be automatically informed by the silence of the
telephone that I is engaged, as the bell of I is disconnected. It is, of course,
desirable that the switching of a to c and b to d should always take place
automatically as soon as the connection with O is broken, or automatically again
re-established with the same. This may be practically carried out in various
ways.
Sheet 2 shows the construction of an arrangement by which the line which is
provided with such a switching device can be selected out. This selecting device
is described and shown as being applicable for use in connection with point II
(Sheet I, Figure 1).
The stopper S, which is shown broken off, is, in the figure, placed over the
contact pin and presses, by means of the insulating piece F, the two contact
springs e and on a and b. This corresponds to the inactive position. If point II
wishes to speak with III, it draws the stopper S from off O and pushes it over the
contact pin III. The springs e and f are released and make contact with c and d.
It is, of course, not at all necessary that all points of an establishment shall be
connected with each wire.
C
If one point is at a considerable distance from the others, it is frequently
preferable to carry to this point only the wires of the battery belonging thereto,
and perhaps 1 or 2 other wires.
If then this point should require to call up one of the others
no connecting wire, it may employ any other suitable point
directly in connection as intermediary, by calling up the desired
former, and requesting to be connected with its wire.
with which it has
with which it is
point through the

page_text: Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is
A switching apparatus for connecting electric telephone places without a central
exchange being necessary, characterised by the arrangement that the separate
points work with two sources of current common to all the points, which, when two
points are connected for conversation, connect the same by two separate circuits
into which only the telephone of the one point and the microphone of the other
are switched.
Dated this 16th day of January 1803
WM. P. THOMPSON & Co.,
Agents for the Applicant.