IMPROVEMENTS IN THE METHOD OF APPLYING AND IN THE ARRANGEMENTS OF THE CONDUCTING WIRES CONVEYING ELECTRICITY TO BE USED IN SENDING TELEPHONIC MESSAGES."
Year: 1877

page_text: LETTERS PATENT to Alexander Graham Bell, of 38, Southampton Buildings,
London, Professor of Vocal Physiology in the University of Boston, United
States of America, for the Invention of "IMPROVEMENTS IN THE METHOD OF
APPLYING AND IN THE ARRANGEMENTS OF THE CONDUCTING WIRES CONVEYING
ELECTRICITY TO BE USED IN SENDING TELEPHONIC MESSAGES."
PROVISIONAL SPECIFICATION left by the said Alexander Graham Bell at the
Office of the Commissioners of Patents on the 20th November 1877.
ALEXANDER GRAHAM BELL, of 38, Southampton Buildings, London, Professor of
Vocal Physiology, in the University of Boston, United States of America.
"IM-
PROVEMENTS IN THE METHOD OF APPLYING AND IN THE ARRANGEMENTS OF THE
CONDUCTING WIRES CONVEYING ELECTRICITY TO BE USED IN SENDING TELEPHONIC
MESSAGES."
In the application of the ordinary conducting wires to the practical use of the
electric telephone, for which I obtained Letters Patent in England under the
Number 4765, A.D. 1876, December 9th, certain difficulties have occurred in sending
the messages from the wire itself being affected by currents passing along the
neighbouring wires; the result is that the Morse or other instruments at work on the
neighbouring wires occasion sounds in the telephone that distract the attention of
those operating the instrument.
Now I have discovered that if in place of sending the message by one wire and
using the earth to complete the circuit two conductors or wires are used-with the
telephone, one of which is the return wire, that all disturbances from neighbouring
wires may be prevented by attending to this, the principle of the Invention, namely,
that these two conductors shall be within a much shorter distance of each other
than the distance to the wire or wires or conductors from which the disturbance is
expected, the reason being that the currents induced in the one wire are neutralized
[Priest.J7

page_text: by those induced in the other wire when the two wires are equally distant from the
wire or wires from whence the disturbance comes. In practice therefore I use
two insulated conductors separated from one another by as slight a space as
possible.
A convenient form may be made by taking two copper or other wires properly
insulated with any convenient material, and then forming them into one strand by
lapping or covering them with any convenient material, or even by twisting them
together; the compound wire may then be suspended as usual. For underground
purposes I prefer to cover them with gutta percha, but any other material suitable
may be employed.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
1 the said Alexander Graham Bell in the Great Seal Patent Office on the 18th
May 1878.
ALEXANDER GRAHAM BELL, of 38, Southampton Buildings, London, Professor of
Vocal Physiology in the University of Boston, United States of America.
"IM-
PROVEMENTS IN. THE METHOD OF APPLYING AND IN THE ARRANGEMENTS OF THE
CONDUCTING WIRES CONVEYING ELECTRICITY TO BE USED IN SENDING TELEPHONIC
MESSAGES."
In the application of the ordinary conducting wires to the practical use of the
electric telephone for which Letters Patent were obtained in England under the
Number 4765, A.D. 1876, December 9th, certain difficulties have occurred in sending
the messages, arising from the wire itself being affected by currents passing along
the neighbouring wires; the result is that the Morse or other instruments at work
in connection with the neighbouring wires occasion sounds in the telephone that
distract the attention of those operating the instrument.
Now I have discovered a practically successful and convenient method of obviating
all difficulties arising from induction caused by the interference of currents
passing along wires adjoining those employed in working telephonic apparatus.
In place of sending telephonic messages by one wire and using the earth to complete
the circuit I employ two conductors or wires connected with the telephone, one of
which acts as the return wire, and thereby all disturbance from currents passing
along neighbouring wires may be prevented by attending to this, the principle of
the Invention, that is to say, by so arranging the two conductors or wires that
they shall be within a much shorter distance of each other than the distance
from the wire or wires from which disturbance from interfering currents may
be expected, and practically at an equal distance from the disturbing wire or
wires.
The two telephone wires as employed by me are arranged in a common strand,
and are thereby placed at such a relative distance that the space between them is
practically so much less than that which intervenes between either wire and any
other wire from which there is any risk of disturbance, that the telephone wires
may be considered equally distant from the disturbing wire or wires, and the currents

page_text: induced in one of the telephone wires by any neighbouring independent wire, are
neutralised by those induced in the other telephone wire. In practice therefore I
use two conductors insulated from one another and as close together as possible.
A convenient form of arranging the two telephone wires will be found in practice
to be to manufacture a compound insulated conductor in the following manner :-I
take two copper or other conducting wires, one or both of which should be covered
in the usual way with an insulating material, such as cotton or silk soaked in paraffine.
These wires I twist together and cover with a covering of the ordinary kind, such
as tarred tape or gutta percha or india-rubber. It should be observed that the
external covering though advantageous may be omitted. Again the two wires may
he laid side by side without being twisted, but the twisted arrangement is more
advantageous because the mean distance of the twisted telephone wires from any
neighbouring disturbing wire may be regarded as constantly the same while they
are constantly as close as possible to one another, thereby securing the best conditions
required to operate the telephonic apparatus, notwithstanding the disturbing
influences of neighbouring independent wires. The employment of a fibrous
insulator for the twisted telephone wires will obviate the risk of the insulating
material being cut, and so allowing of contact
By employing in connection with telephonic apparatus, such as is described in the
Specification of the said Patent of 1876, my compound conductors having wires
arranged as above described, I not only succeed in obviating all difficulty arising
from external induction, but I intensify and improve the action of the telephone
itself by increasing the amplitude of the electrical undulations, and thus rendering
the resulting sounds more loud and distinct.
When the telephone is employed upon a circuit consisting of two wires very
close together the current due to the telephone passes at the same time in opposite
direction in the two wires, and the secondary current induced in one of the wires
by the influence of the other reinforces the primary current when it is increasing in
intensity, and opposes it when it is decreasing in intensity. The difference between
the maximum and minimum intensity of the current is thus increased, that is, the
amplitude of the electrical undulations is increased and the resulting sound becomes
louder.
I am aware that two wires have been before used in working telegraphic instru-
ments in place of sending the return current by the earth, and I do not lay claim
to the use of two wires generally, or otherwise, than when they are used in the
manner I have described with the object of obviating the difficulties that have
hitherto been experienced in working telephonic apparatus arising from the
disturbing currents induced by other wires, that is to say, I claim the use of the
compound conductor wherein telephone wires are arranged, substantially in the
manner and for the purpose as above described.
In witness whereof, I, the said Alexander Graham Bell, have hereunto set my
hand and seal, this Seventeenth day of May, in the year of our Lord One
thousand eight hundred and seventy-eight.
ALEXANDER GRAHAM BELL. (L.S.)