IMPROVEMENTS IN. ELECTRO-MAGNETS."
Year: 1883

page_text: LETTERS PATENT to John Henry Johnson of 47 Lincoln's Inn Fields, in the
County of Middlesex, Gentleman for an Invention of "IMPROVEMENTS IN.
ELECTRO-MAGNETS." Communicated to him from Ernest Fréderic Recordon
person resident at Geneva in the Republic of Switzerland
a
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 9th October 1883.
"1
4
JOHN HENRY JOHNSON of 47 Lincolns Inn Fields, in the County of Middlesex, .
Gentleman, IMPROVEMENTS IN ELECTRO-MAGNETS" '-a communication to me
from Ernest Frederic Recordon a person resident at Geneva in the Republic of
Switzerland
This Invention relates to improvements in Electro-Magnets whereby the mass of
metal and length of wire required to produce a given effect is considerably reduced
and the Electric current is more advantageously utilised than in ordinary Electro-
Magnets, which latter do not utilise the Electric current in the most efficient
manner possible for the following reasons.-These magnets as heretofore constructed
in what is known as the horseshoe form are constituted by two coils or reels of
wire and consequently one of the poles of the cores of each of these coils, that is to
say, one end of each coil cannot be utilised. A considerable quantity of energy is
also wastefully expended in consequence of the great length of the iron core, a
great part of which is magnetised by the current without producing any useful
effect whatever.
The arrangement of the ordinary horseshoe Electro-Magnet also involves the
employment of two reels of wood or brass, because without these reels it would be
impossible to wind the wires upon the cores. These reels being interposed between
the core and the wire further lessen the effect of the Electricity
In the improved Electro-Magnets hereinafter described the tendency of magnetism
to collect at the surface of the iron is utilised and a core is employed constituted by
r

page_text: a soft iron tube similar to a piece of gas pipe-By this means a large surface is
obtained with a relatively small mass of metal.
This property possessed by iron tubes of readily transmitting the magnetic
action of an Electric current flowing round the tube is well known, but the novelty
in the employment of these tubes according to this Invention consists in employing
these tubes as the core of a true electro-magnetic coil whereby the two extremities
of the tubes when provided with polar enlargements in the form of iron cheeks or
discs as hereinafter described become receivers of two contrary magnetisations of
opposite denominations. By simply connecting these two cheeks or discs with a
suitable armature (preferably flat) the two poles are utilised, although only one coil
is employed, and the insulating wooden reels ordinarily employed are dispensed
with.
It is desirable to paste a sheet of paper over the core and over the inner surfaces
of the cheeks in order to prevent any possibility of the metal of the core coming
in contact with the insulated wires of the coil but by dispensing with the wooden
reels the layers of wire are brought considerably nearer to the core.
In the Recordon Electro-Magnets the base or bridge piece usually employed to
connect the cores of horse shoe Electro-Magnets is dispensed with
The Recordon Electro-Magnet can be constructed with great facility especially
on a large scale and with a corresponding saving of labour-It takes up less room
and requires three or four times less insulated wire than ordinary Electro-Magnets
for an equal intensity of magnetisation, consequently less resistance is opposed to
the passage of the Electricity and less battery power is required-In the case of
the Recordon Electro-Magnet facility is afforded for fixing the magnet to a support
in any desired position by means of brass screws or by means of feet or brackets
fitted to the sides of the cheeks or engaging with the tube-One or more flat
surfaces may be formed at any part of the periphery of the cheeks or discs to form
the poles, another flat surface being employed to form a bearing.
The cheeks of this improved Electro-Magnet simply transmit to and collect at
their surface the magnetisation produced in the tubular core and they do this so
effectually that when a current is passing in the coil the tube itself does not act as
a magnet
One of the improved Electro-Magnets may be used with several armatures and
thus caused to give a greater effect by forming several flat surfaces on the circum-
ferences of the cheeks and coupling the armatures together by means of levers or
otherwise or by causing the armatures to act independently-Or a number of
discs or cheeks may be formed on the same core thereby forming any desired
number of poles.
One of the wires proceeding from the coil may be connected to one of the cheeks
of the Recordon Electro-Magnet by a screw, one of the conducting wires leading
from the battery being connected also by a screw to one of the cheeks or to the
core of this Electro-Magnet without touching the wire from the coil. This arrange-
ment enables one of the terminals to be dispensed with, as a single screw fixed to
any part of the iron of the magnet may be employed to connect the battery wire
to that of the coil-Holes may also be made in the cheeks in order to diminish
the mass of iron at this part without reducing the thickness at the circumference
In order to diminish the residual magnetism the cheeks of the Electro-Magnet
may be composed of thin iron washers rivetted together by iron or copper pins,
there being as many of such washers employed as are necessary to form the requisite
thickness of metal-Copper plugs may also be inserted in the poles in order to
neutralise the effect of the residual magnetism as in the case of ordinary Electro-
Magnets.
The mass of iron in the cheeks composed of washers of sheet iron may be
diminished by perforating them or by an arrangement consisting in employing
entire washers for the inner part aloue in order to support the wire of the coil,
and in the case of the end or polar part removing all the metal that does not
contribute to the formation of the poles.

page_text: All of the washers may be cut out in like manner, except the first washer which
must be entire and consist of ebonite, wood or other insulating material to carry
the coils of wire.
The same object may also be attained by splitting the tube and cheeks of the
Recordon Electro-Magnet throughout their entire length or part of their length
thereby enabling the magnetisation and demagnetisation to take place more
quickly-The centre or neutral joint in the Recordon Electro-Magnet having no
magnetic effect the wire may be wound so as to form two cones or fusees, having
their bases or thicker ends turned towards the cheeks or poles.
The mass of iron in the cheeks may also be diminished by means of a circular
groove or channel of a suitable depth. The recessed surfaces of both of these
cheeks may be turned either inwards or outwards or one may be turned inwards
and the other outwards as found most convenient.
In the construction of large Recordon Electro-Magnets the diameter of the
core tube may be made sufficient to enable a small or secondary magnet of the
same construction to be contained in the first, so that the cheeks of the inner
magnet fill the hollow in the core of the outer or larger magnet. The circum-
ferences of the cheeks of these secondary Electro-Magnets being in contact with
the internal surface of the cheeks of the main Electro-Magnet, the magnetism
produced in the secondary cheeks passes into the cheeks of the main Electro-
Magnet and is transmitted to the poles of the latter
In this case the wires of the two coils may be arranged to lead from one
extremity or pole to the corresponding pole of the battery, or the two wires of the
same denomination of the two coils (the inner and the outer coil) may be joined,
in which case the other pair of wires are connected to the respective poles of the
battery.
The Recordon Electro-Magnets may also be manufactured by casting them
The improved Electro-Magnets with solid discs or cheeks are susceptible of very
strong induction when passed between the pole of permanent or Electro-Magnets
The poles of the Recordon Electro-Magnets as hereinbefore described are
constituted by a flat surface upon the circumference of the cheeks, but they may
be made to project from this circumference in the form of a projection or
prolongation of suitable length terminating in a straight or flat surface before
which the armature or keeper is presented-The cheeks of the Recordon Electro-
Magnet may also be cut out in the form of a star in order to act upon several
armatures simultaneously or for the purpose of enabling the said Magnet to be
employed as a motor-Residual magnetism may also be entirely or partially
obviated by means of specially constructed armatures
The armature may be made in several pieces; in this case the pieces are
presented flatwise to the poles of the Electro-Magnet.
The armature may be in the form of a tube slightly flattened, being split
throughout its entire length on one side only, the unsplit side of the armature
being presented to the poles of the Electro-Magnet.
In order to preserve the attracting power of the Electro-Magnet as much as
possible, the armature may be constituted by a second and similar Electro-Magnet
presenting a flattened surface facing the poles of the principal Electro-Magnet-
The wire of the coil of the Magnet acting as an armature being wound in the
opposite direction to that in the main coil and one current being caused to pass
through both coils simultaneously-The poles of each coil being presented to the
pole of opposite denomination
This arrangement is peculiarly suitable for telegraphic apparatus
The Recordon Electro-Magnet may be formed by a series of coils connected
together by discs or cheeks common to all the series-This arrangement is
preferable to single magnets of large size when great power is required
In order to facilitate the operation of winding the wire upon these coils the
tubes may be provided with cheeks of thin sheet iron which may be either removed
or left in position after the coils have been placed between the cheeks. One or

page_text: '
more flat surfaces may be formed on the circumference of the disc for attracting one
or more armatures either within or without its periphery.
The reel which forms the core of the Magnet may be turned out of an iron
cylinder, the central part being bored out in order to obtain the necessary tubular
form
A species of reciprocating influence is produced in the Recordon Electro-Magnet
between the magnetism of the cheeks and that of the core the interior of which
does not evince any magnetisation during the passage of the current and promotes
the magnetisation
The Recordon Electro-Magnet may be employed in dynamo and magneto Electric
machines and in all cases where an Electro-Magnet is required.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Henry Johnson in the Patent Office on the 9th April 1884.
JOHN HENRY JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman "IMPROVEMENTS IN ELECTRO MAGNETS" a communication to me from
Ernest Frederic Recordon a person resident at Geneva in the Republic of
Switzerland
This Invention relates to improvements in electro magnets whereby the mass of
metal and length of wire required to produce a given effect is considerably reduced
and the electricity is more advantageously and economically utilised than in electró
magnets as heretofore constructed and arranged. Electro magnets with two legs or
branches such as ordinary horse shoe magnets fail to produce a maximum of useful
effect for the following reasons.
They are provided with two bobbins or coils of wire of which only one end or
pole of each is utilised so that in magnetizing the iron core a great part of the
magnetism is lost. Also two spools are necessary to facilitate the winding on of
the wire and owing to the substance of the sides of these spools being interposed
between the iron cores and the wire the action of the electric current is impeded.
The tendency of magnetism to be most powerful at the surface of the core and
to diminish gradually towards the inner parts of the iron is well known-To
utilize this tendency tubes of soft iron preferably of about the form and size of gas
service pipes are employed as hereinafter described in the construction of electro
magnets according to this Invention being provided at both ends with plates
or discs also of soft iron and forming the poles: This construction obviates the
employment of a larger mass of iron and presents an extensive area of surface.
And in order that the said Invention may be fully understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the annexed sheet of Drawings the same letters of reference
indicating corresponding parts in all the corresponding figures.
Figures 1 and 2 represent respectively a longitudinal section and a plan of an
improved electro magnet constructed according to this Invention and consisting of
a soft iron tube n with soft iron plates or discs a a¹ at both ends thus forming a
reel or bobbin. The insulated conducting wire is wound upon this bobbin a
covering of paper or equivalent material being previously applied round the tube
and inside the plates or discs a and a¹ in order to prevent contact between these
parts and the conducting wire.
In order to apply an armature shewn at 6 to this electro-magnet a portion of the
rim of each of the plates or discs a a¹ is formed flat or cut or filed away so as to
form a flat surface a'; these flat surfaces form the poles proper. Similar flat
surfaces may be formed on the plates or discs diametrically opposite to ¹to
facilitate the attachment of the electromagnet to a support or frame as shewn for
example at vu in figures 3 and 4. Other means of attaching the electromagnets are
represented by figures 5 and 6. The facility afforded by this system of construction
for securing the electro magnets firmly in position is obvious. To fix them in a
vertical position (as shewn in figure 5) a screw S with a washer 8 sunk into the
upper plate or disc a may be employed.
According to the arrangement illustrated in figure 0 the screws for fixing thé
brackets are inserted from below.
In the electro magnet constructed according to this Invention the magnetism
generated at the surface of the tube n is concentrated at the circumferences of the

page_text: plates or discs a a¹ to such an extent that the interior of the tube n does not
indicate any magnetic power. The armature is attracted by the two flat or polar
surfaces xx¹ and is thus presented to the improved electro magnets in a position
parallel to the axial line of the coil or core and moves at right angles thereto
whereas in electro magnets of ordinary construction the armature is placed at
right angles to the axis of the coil and moves in line with the axial lines of
the coils.
The flat polar surfaces on the plates or discs are of great importance for an
armature of curved or rounded form corresponding to the periphery of the circular
plates or discs such as is shewn at b figure 2^ exhibits scarcely half the power
gained by a flat armature (as represented in figures 1 and 2) corresponding to the
flat portions xxl even when the flat armature is of less width than the curved
armature. The practical advantage of the flattened form of the poles is made
apparent when the rounded armature is presented to the electromagnet with flat
poles (figure 2) the attraction being then much more powerful than when the same
armature is presented to the rounded poles and this notwithstanding the
diminished area of surface opposed.
In order to diminish the mass of iron in the plates or discs a a¹ holes t of any
convenient size and number may be drilled therein as shown by figure 8 so as to
remove a portion of the metal without reducing either the thickness or the diameter
of the said discs
In some cases, where remanent magnetism causes inconvenience the plates or
discs may each be made up of a number of thin plates or discs of sheet iron rivetted
together or the ends of the tube n may each be provided with one thin plate a
figures 9 and 10 acting simply as retaining discs for the wire and the other sheet s
iron polar plates a a¹ being outside and made of the form indicated in the
said figures 9 and 10 so that all the metal of the discs or washers that does not
contribute to the formation of the poles a al is dispensed with. In lieu of the
circular metal plates a' two discs of hard rubber or vulcanite or the like may be
employed.
The middle part of the coil being neutral does not produce magnetic power and
in winding these electromagnets the wire may be economised by winding it in the
form indicated in figure 7 so as to constitute two cones or semi elliptical pieces ff
having their bases turned towards the cheeks a a¹. The mass of iron in the polar
plates or discs may be reduced by turning one or more circular grooves g in the
inner or outer surfaces of the cheeks (for instance as shewn by figure 11) Care
should however be taken that the grooves are not turned so close to the inner rim
as to diminish the thickness of the plates or discs at this point and consequently
the area of surfaces in contact with the tubes or cores n.
When the cores are composed of tubes of large diameter the core may contain a
similar electromagnet of smaller dimensions so arranged that the outer edges of
the polar plates or discs of the small or secondary electromagnet touch the inner
rims or edges of the plates or discs of the larger electromagnet. The magnetism
of the smaller electromagnet is thus caused to pass into the poles of the larger
magnet and add its power to the magnetism developed by the latter.
The tubes and plates or discs of the improved electro magnets may be made of
malleable cast iron.
The electro magnets constructed according to this Invention are susceptible of a
strong magnetization when placed between the poles of two permanent magnets and
are so sensitive that when two of the improved electro magnets are attached to the
ends of a shaft or bar rotating in the direction of the meridian having previously
connected the poles of these electro magnets with a galvanometer the latter
indicates the presence of an electric current when the shaft in rotating is placed -
vertically to the terrestrial axis.
In figure 12 an electro magnet is represented having its plates or discs cut out in
form of a star so as to obtain a certain number of poles to each of which an armature
may be applied. This form is well adapted for motors.

page_text: According to another arrangement several armatures may be employed by filing
a number of flat surfaces on the edges of the cheeks as indicated in figure 13.
In some cases the tube n and the plates or discs a may be cut open or split
throughout the whole or part of the length or at one end of the magnet only whereby
the magnetization and demagnetization is accelerated.
In the arrangements herein before described the poles of the electro magnets are
in the form of flat surfaces x x¹ filed in the edges of the plates or discs but the
poles may also be formed by prolonging the plates or discs in a radial direction as
indicated in Figures 14 and 15 which show in end and side elevation respectively an
electro magnet with plates or discs provided with prolongations a³. This form is
suitable for telephones.
Figures 16 and 17 represent forms preferably employed for electro motors.
Figure 16 is an end view of a revolving electro magnet a around which a series of
stationary electro magnets are fixed one of which is indicated at b. The cheeks of
the electro-magnet a have projections c c in the form of teeth being slotted so far
as the edges of the cheeks. The stationary electromagnets 6 have projections don
their pole plates on each side of which the slotted projections c pass during
the rotation of the magnet a. Figure 16ª shows in side elevation the form of the
teeth d.
This arrangement of the discs or cheeks whereby the projections on one magnet
are enabled to pass the projections on the other produces a great amplification of
the motion in the magnetic field. As the attractive power acts from a considerable
distance; it commences to act when the outer edges of the poles pass one another
and continues until the poles are completely in juxtaposition. To produce a
powerful compound electromagnet a number of the core tubes and coils may be
combined with one pair of pole plates or discs
Figures 18 and 19 represent a powerful electro magnet thus constituted made up
of seven coils connected to two plates or discs a a¹ common to all. Considerable
power may also be produced by increasing the dimensions of the electro magnets,
but where the distance between the outer layer of wire and the core would be too
great it is preferable to employ an arrangement like that shewn by figures
18 and 19. The plates or discs a a¹ in this compound arrangement may be
provided with one or more flat surfaces x x¹, the armatures being in all cases
situated parallel to the axes of the bobbins or coils instead of at right angles
thereto as with ordinary electro magnets. To facilitate the winding of the coils
thin retaining plates may be fixed on the ends of the tubes or cores n which plates
may be removed or allowed to remain when the coil is placed between the plates or
discs a a¹ figure 19.
It is important to construct the different parts of the improved electro magnet of
the proper proportions. The following I believe to be best. The diameter D of
the cheeks or discs a al should be equal to twice the external diameter (d)
of the tube n, D=2 d-The thickness W of the plates or discs a a¹ should be equal
to twice the thickness (w) of the sides of the tube n, W=2 w. The length (1) of
the tube n between the plates or discs a a¹ should be equal to two thirds of the
diameter of the said plates or discs, b= D.
By following these directions the maximum effect from a given source of
electricity will be obtained with a minimum length of wire and powerful
electromagnets can be manufactured very economically.
Having now described and particularly ascertained the nature of the said
Invention and the manner in which the same is or may be used or carried into
effect I would observe in conclusion that what I consider to be novel and original
and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent is
An electro magnet composed of an iron tube or of a number of iron tubes forming a
core or cores and provided at each ond with iron cheeks discs or plates formed or

page_text: provided with a flat surface or flat surfaces constituting the poles of the magnet
substantially as hereinbefore described and also illustrated under several
modifications by the accompanying drawing.
In witness whereof I the said John Henry Johnson have to this my Specification
set my hand and seal this ninth day of April One thousand eight hundred and
eighty four,
J. HENRY JOHNSON (L.B.)