AN IMPROVED METHOD OF, AND MEANS FOR, WORKING TELEPHONIC AND TELEGRAPHIC APPARATUS
Year: 1882

page_text: LETTERS PATENT to Amos Emerson Dolbear of Somerville, Massachusetts,.
United States of America now of Queen Victoria Street in the City of London
SEAL APEL FA4 WAD KING
PROVISIONAL SPECIFICATION left by the said Amos Emerson Dolbear at
the Office of the Commissioners of Patents on the 21st March 1882.
AMOS EMERSON DOLBEAR of Somerville, Massachusetts, United States of America,
now of Queen Victoria Street in the City of London AN IMPROVED METHOD
OF, AND MEANS FOR, WORKING TELEPHONIC AND TELEGRAPHIC APPARATUS
"
In all telegraphic and telephonic systems hitherto employed, arrangements have
been provided for bringing the instruments into an electric circuit which is com-
pleted either with a return wire or by the earth or through a condenser of sufficient
capacity to the earth.
I have discovered that it is possible to work such instruments as telephones and
the like, when entirely disconnected with any source of electricity or circuit by the
varying strength of an electric field. An electric field is created about every
substance or body that is electrified and all objects within this field are attracted
towards this electrified body. With a constant source or supply of electricity this
field varies in strength and in form with, or according to, the form and extent of
surface of the electrified body and the form and character of other bodies in its
neighbourhood. The lines of force that make up this electric field are seldom
straight lines but are generally a complicated system or series of curves. The
electric field may be created in any room or space by placing therein a metallic body
in connection with a battery or other source of electricity.
In order to employ this electric field for this purpose of my invention in con-
nection with a telephone, I place a suitable conductor such as a wire say from one
foot to three feet in length so that its two ends shall extend into parts of the
electric field having different strength. Therefore any change in the strength of

page_text: the field resulting from a change in the clectric tension of the body or bodies in
electrical connection with the variable source of electricity, will give rise to electrical
manifestations in the said wire or other conductor resulting in a transient current
of electricity in the conductor or the usual phenomenon of the attraction of
neighbouring bodies by the said conductor. If then an electric telephone-receiver
be connected to one end of the short wire or conductor in such a manner that the
other end of the same shall be in a part of the field, of a strength different from that
occupied by the telephone receiver, then any electric change that takes place in the
field will so affect the plates of the receiver as to make them attract each other
with greater or less force in proportion to the change or variation of the field. If
the body which is to effect or create the electrical field (whether the same be the
end of a wire or a metallic surface of any form and extent) is in electrical con-
nection with the secondary wire of an induction coil having an ordinary transmitter
and battery in its primary circuit, any change or variation of the current in the
primary circuit will result in charging the line and its terminal bodies with
electricity, and create in their neighbourhood a field which will vary with the
strength of the electrical variations in the coil and hence one may, by listening at
the receiver, hear words spoken at the transmitter.
If, instead of an electric telephone-receiver a magnetic telephone-receiver be
substituted and the terminals be made to assume the proper positions, as above
stated, in the electric field the speaking may be heard as with the first named
instrument, and with either of these instruments these effects may be observed at a
distance of several feet from the metallic terminals of the same.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Amos Emerson Dolbear in the Great Seal Patent Office on the
21st September 1882.
"
AMOS EMERSON DOLBEAR, of Somerville, Massachusetts, United States of
America, now of Queen Victoria Street in the City of London "AN IMPROVED
METHOD OF, AND MEANS FOR, WORKING TELEPHONIC AND TELEGRAPHIC APPARATUS.”
In the telegraphic and telephonic systems hitherto employed the instruments
have been arranged, in or connected with, an electric circuit. But I have discovered
that it is possible to work such instruments as telephonic receivers and the like by
the varying strength of an electric field when such instruments are not in, or con-
nected with a circuit. And my invention relates to this novel method of electric
communication, and is carried into practice by means of telephonic receivers or
other delicate instruments provided with suitable conductors which connect two
surfaces of different potentials in the electric field of a charged body which is in
communication with the transmitting instruments.
My invention is illustrated in the accompanying drawing in which,
Figure 1 is a diagram illustrating the existence of equi-potential surfaces in the
electric field produced by a body charged with electricity.
Figure 2 is a diagram illustrating the manner of using disconnected receivers in
the electric fields of charged bodies.
A is an insulated body connected to a wire B by which it can be charged with
electricity as desired; the dotted lines in Figure 1 represent equi-potential surfaces
in the electric field of the charged body A, as they exist when that field is unaffected
by other bodies.
It has long been known that an electrified or electrically charged body will excite
all neighbouring bodies even at considerable distances. The space within which
this electric excitation takes place, is called the "electric field." If an electrometer
be brought into the neighbourhood of a charged body it will manifest electric
excitation, and if another body, in the vicinity of this charged body, is found to be
electrified it is said to be in the electric field of the charged body. The electric
field may be considered as consisting of a series of equipotential surfaces extending
around the charged body, the potentials of these surfaces differ according to their
distances from the charged body, and if the ends of a conductor attached to the
instrument be placed in surfaces of different potentials, electricity will flow from
one end to the other of the said conductor. It has been thought, heretofore, that
these electric effects were too feeble to be of any utility, except when an uncharged
body was brought quite close to the charged body.
I have discovered, however, that the electric field produced by a body charged to
a high potential, even if that body be exceedingly small in comparison with its
electric field, (for instance as the ends of small wire in proportion to a room twenty
feet square and fourteen feet from floor to ceiling) can be utilized for operating
telephone receivers and other delicate electrical instruments.
In Figure 2. A represents a wire which is insulated from the wall F of the room, F¹
representing the floor of the said room. T represents a telephone receiver say of
the kind described in the specification of Letters Patent dated March 29th AD. 1881
No. 1395.
Now if A be charged to a high potential, (say by connecting the wire B with
one terminal of the induction coil described in the said former specification) the
whole room will be in the electric field of A. Now as this field will vary with the
electric potential of A. the electric condition of the telephone-receiver T will vary

page_text: with it, as a whole, just as the electric condition of any other body in the room
and of the walls, floor and ceiling of the room will vary. But if one of the plates t
or t¹ of the telephone T have a conductor such as t say of a length of twelve
inches or more, the end t* of this conductor will occupy a surface of the electric
field which has a potential very different from that of the surface occupied by any
point in plate t' or in plate t, and I have discovered that the telephone receiver T
will under these conditions, re-produce speech transmitted through the line wire B
whether the said receiver is held in the farthest part of the room F, F, or in close
proximity to the terminal A. Moreover the movement of the receiver T from one
part of the room to another has but a very slight effect, so that the listener may
walk about the room and yet distinctly hear all that is spoken to the transmitter
with which the line-wire B is connected especially if there be a number of electrified
bodies A in different parts of the room, each forming a terminal of the line wire B.
Furthermore the number of receivers in the room seems to be immaterial so that
many persons in one room, each holding a receiver to his ear, and each walking
about the room can hear distinctly. When a magneto-telephone receiver such as
that shown at T is used the conductor t² should be in electric connection with one
end of the helix therein. In practice I usually employ a wire extending about
three feet from one plate of my receiver or from one end of the coil of the magneto-
receiver. When receivers are to be used in various parts of a large room, the line-
wire should have a number of terminals each brought into the neighbourhood of
the place where a receiver is most likely to be used as in figure 2, where A A' A³ A³
represent four terminals of the line-wire, brought into the room F F¹. Or I may
use metallic bodies connected with the ground such as gas-chandeliers or brackets
in place of the aforesaid terminals.
Having thus fully described my said invention and the manner of performing the
same I wish it understood that I Claim,
The improved method of providing for electric communication consisting in
utilizing the difference of potential existing at different parts in the electric field of
a charged body by means of a telephone-receiver or other suitable instrument pro-
vided with a conductor so arranged that its terminals can be in surfaces having
different potentials in the electric field as and for the purposes specified.
In witness whereof I the said Amos Emerson Dolbear have hereunto set my
hand and seal this First day of September in the year of, our Lord One
thousand eight hundred and eighty two.