IMPROVEMENTS IN TELEPHONIC APPARATUS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the Office
of the Commissioners of Patents on the 31st August 1882. Communi-
cated to him from abroad by Doctor Arsène D'Arsonval of Paris in the
Republic of France.
"
JOHN HENRY JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman "IMPROVEMENTS IN TELEPHONIC APPARATUS a communication to
me from abroad by Doctor Arsène D'Arsonval of Paris in the Republic of
France
This Invention has for its object an improved construction of telephone which is
distinguished by the employment of a coil moving in an annular magnetic field.
The two poles of the magnet are utilised one pole being in the form of a solid
cylinder encircled by the other pole which takes the form of a ring. The poles are
consequently concentric and the space between them constitutes an annular magnetic
field of equal intensity.
A coil wound on a hollow core attached to the vibrating plate or diaphragm of
the telephone moves in this magnetic field under the influence of the vibrations of
sound or speech transmitted to it by the said plate which in this case may be of
other material than iron.
In carrying out this invention the two ends of the magnet are brought together
by bending the magnet into the form of a spiral or V. These forms are the most
practical but the magnet may be made in any other convenient form.
The spiral magnet when such is employed is secured in position by two brackets
on a plate let into the board which supports the whole apparatus. One of the
poles of the spiral magnet is constituted by a solid cylinder which is screwed into
one leg of the inagnet and extends into the interior of a ring forming part of a
plate attached to the other leg of the magnet. This ring constitutes the other pole
of the magnet and by this arrangement the two poles are placed concentrically to
each other so as to form an annular space between them. In this annular space
there is arranged a coil whose axis coincides with that of the concentric poles.
The inner or solid pole is surrounded by the coil which is attached to the diaphragm
or vibrating plate of the telephone and moves relatively to the poles when the said
diaphragm or vibrating plate is set in motion.

page_text: This plate or diaphragm is held between plate carrying the magnet and another
plate provided with a screwed socket to which is screwed a branch pipe commu-
nicating with suitable bearing or speaking tubes.
Instead of employing a single moveable coil as hereinbefore described two coils
may be employed fixed respectively upon the two poles of the magnet these coils
are concentric and the vibrating plate or diaphragm must in this case be of soft
iron but the arrangement firstly hereinbefore described is preferred on account of
its greater power and the advantage of not requiring adjustment.
The annular magnetic field may also be obtained by employing a tubular electro
magnet in place of the permanent magnet.
When a V shaped magnet is employed one pole is formed by a solid cylinder
extending through a corresponding opening or ring on or attached to the other leg
of the magnet and a coil attached to the plate or diaphragm of the telephone is
placed in the annular magnetic field formed between the solid cylinder and the ring
which constitutes the other pole of the magnet.
In this as in the case firstly hereinbefore described the coil is fixed to the
diaphragm or vibrating plate which is supported betweeen the end of the speaking
or hearing tube and a corresponding ring or flange on the telephone case. The bow
or lower part of the magnet is provided with a handle for convenience holding the
instrument.
In all modifications of the improved apparatus the magnetic field is of an annular
or equivalent form obtained by means of a permanent magnet one of the poles of
which encircles or surrounds the other pole. The coil being placed in this annular
space all its parts are exposed to induction thus avoiding unnecessary resistance and
enabling the apparatus to produce a maximum of useful effect with a minimum of
weight.
This apparatus may either be applied directly to the ear or may be provided
with a branched or double bearing or speaking tube admitting of listening with
both ears with a single receiving instrument or it may be provided with a trumpet
mouth for enabling the sound to be heard at a distance
The coil may be fixed and independent of the vibrating plate which in this case
must be of soft iron.