IMPROVEMENTS IN ELECTRO MAGNETS AND ARMATURES THEREFOR FOR ELECTRO MECHANICAL, TELEGRAPHIC, AND OTHER PURPOSES
Year: 1882

page_text: LETTERS PATENT to William Phillips Thompson of the Agency for Foreign
Patent Solicitors 6 Lord Street, Liverpool, in the County of Lancaster, and
of 323, High Holborn, in the County of Middlesex, Civil Engineer, for
an Invention of "IMPROVEMENTS IN ELECTRO MAGNETS AND ARMATURES
THEREFOR FOR ELECTRO MECHANICAL, TELEGRAPHIC, AND OTHER PURPOSES."
-A communication from abroad by Gerritt Smith, of Astoria, in the State of
New York, one of the United States of America.
"
PROVISIONAL SPECIFICATION left by the said William Phillips Thompson
at the Office of the Commissioners of Patents on the 7th March 1882.
WILLIAM PHILLIPS THOMPSON of the Agency for Foreign Patent_Solicitors
6 Lord Street Liverpool in the county of Lancaster and of 323 High Holborn in
the county of Middlesex Civil Engineer "IMPROVEMENTS IN ELECTRO-MAGNETS
AND ARMATURES THEREFOR FOR ELECTRO-MECHANICAL, TELEGRAPHIC, AND OTHER
PURPOSES."-A communication from abroad by Gerritt Smith, of Astoria, in the
State of New York one of the United States of America.
The object of this invention is to attain a greater degree of rapidity of vibration
in the armatures of electro-magnets, such as are employed in telegraphic receiving
instruments and other like mechanism than has been possible with apparatus of
this kind constructed in the usual manner. The invention is principally useful in
connection with telegraphic apparatus, particularly in cases where unusual rapidity
of signaling is necessary, as in Wheatstone's and other automatic systems. The
invention consists in actuating the armature of the electro-magnet and its necessary
mechanical attachments, through the instrumentality of a constant mechanical
power whose action is controlled by electro magnetism, in lieu of causing the
armature and its attachments to be actuated solely by the direct attractive force
of the electro-magnet as heretofore. I make use of a cylinder or disk of magnetic
metal, such as iron or steel, which is so mounted as to rotate upon an axis within a
magnetizing helix. An armature of iron or steel is maintained in permanent

page_text: magnetic contact with the surface of said cylinder, and is so mounted as to be
capable of receiving motion therefrom by friction. In some cases I provide
spring or other retractor which tends to exert a constant force upon said armature
in a direction opposed to that which it derives from its frictional contact with the
moving cylinder. Fixed stops, which are preferably made adjustable, are provided
for the purpose of limiting the movement of the armature in each direction. The
magnetizing helix which surrounds the cylinder is included in an electric, or
telegraphic circuit, and a suitable key or transmitter may be placed at some point
in said circuit which acts to alternately increase and decrease the strength of
current traversing said circuit. In some cases I prefer to employ two separate
magnetic cylinders or disks which are mechanically united together so as to move
with equal rapidity but in opposite directions, and to arrange the magnetizing
helix in such a manner that it will induce contrary magnetic polarity in or upon
the moving surfaces of the two cylinders or disks respectively. In this connection
I prefer to employ a polarized armature which is so mounted as to remain in
permanent magnetic contact with the moving surfaces of both cylinders or disks
and is capable of receiving motion from either cylinder by friction. Under this
arrangement the transmitter is preferably so organized as to be capable of
transmitting electrical currents or pulsations alternately of positive and negative
polarity through said circuit. I prefer to construct the polarized armature in two
sections mechanically united but magnetically insulated from each other, said
sections being respectively maintained in permanent frictional contact with the
moving surfaces of the rotating magnetic cylinder or disk. A permanently
polarized artificial magnet or an electro-magnet may be employed for imparting
magnetic polarity to both sections of the polarized armature. Another and
preferable form of constructing and arranging the apparatus is to make use of two
magnetically united polarized armatures which are arranged to receive unlike
polarity respectively, by induction from a permanent magnet, and which are
maintained in permanent frictional contact with the moving surface of a rotating
magnetic cylinder or disk which surface moves in opposite directions but at the
same rate of speed at the respective points of contact of the armatures therewith.
This mode of construction renders it possible to impart a positive motion to the
armature system in each direction by means of a single magnetic cylinder or disk
and magnetizing coil. In this case I prefer to mount the axes of the armature
system in slotted or grooved bearings which permits the weight of the armatures to
rest at all times upon the moving surface. When employed in connection with a
telegraphic relay or translating apparatus the armature may be provided with
electrical contacts whereby a local or other independent circuit may be opened,
closed, or otherwise controlled. When employed as a receiving instrument upon
the principle of the direct working ink-writer, the marking point, pen, or wheel,
may be attached directly to the movable armature system. The invention is also
applicable to various other purposes for which electro-magnets with movable
armatures may be required.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed.
by the said William Phillips Thompson in the Great Seal Patent Office on
the 6th September 1882.
WILLIAM PHILLIPS THOMPSON of the Agency for Foreign Patent Solicitors
6, Lord Street Liverpool, in the county of Lancaster and of 323, High Holborn, in
the county of Middlesex, Civil Engineer " IMPROVEMENTS IN ELECTRO-MAGNETS
AND ARMATURES THEREFOR, FOR ELECTRO-MECHANICAL, TELEGRAPHIC AND OTHER
PURPOSES." A communication from abroad by Gerritt Smith, of Astoria, in the
state of New York, one of the United States of America.
The object of this invention is to attain a greater degree of rapidity of vibration
in the armatures of electro-magnets, such as are employed in telegraphic receiving
instruments and other like mechanism, than has been possible with apparatus of
this kind constructed in the usual manner. The invention is principally useful
in connection with telegraphic apparatus, particularly in cases where unusual
rapidity of signalling is necessary, as in Wheatstone's and other automatic
systems.
The invention consists in actuating the armature of the electro-magnet and its
necessary mechanical attachments, through the instrumentality of a constant
mechanical power whose action is controlled by electro-magnetism, in lieu of
causing the armature and its attachments to be actuated solely by the direct
attractive force of the electro-magnet as heretofore. Use is made of a cylinder or
disc of magnetic metal, such as iron or steel, which is so mounted as to rotate upon
an axis within a magnetizing helix. An armature of iron or steel is maintained in
permanent magnetic contact with the surface of said cylinder, and is so mounted as
to be capable of receiving motion therefrom by friction. In some cases a spring or
other retractor is provided which tends to exert a constant force upon said
armature in a direction opposed to that which it derives from its frictional contact
with the moving cylinder. Fixed stops, which are preferably made adjustable, are
provided for the purpose of limiting the movement of the armature in each
direction. The magnetizing helix which surrounds the cylinder is included in an
electric or telegraphic circuit, and a suitable key or transmitter may be placed at
some point in said circuit, which acts to alternately increase and decrease the
strength of current traversing said circuit. In some cases it is preferred to employ
two separate magnetic cylinders or discs, which are mechanically united together
so as to move with equal rapidity but in opposite directions, and to arrange the
magnetizing helix in such a manner that it will induce contrary magnetic polarity
in or upon the moving surfaces of the two cylinders or discs respectively. In this
connection it is preferred to employ a polarized armature which is so mounted as
to remain in permanent magnetic contact with the moving surfaces of both
cylinders or discs and is capable of receiving motion from either cylinder by
friction. Under this arrangement the transmitter is preferably so organized as to
be capable of transinitting electrical currents or pulsations alternately of positive
and negative polarity through said circuit. It is preferred to construct the
polarized armature in two sections, mechanically united, but magnetically insulated
from each other, said sections being respectively maintained in permanent frictional
contact with the moving surfaces of the rotating magnetic cylinder or disc.
Alpermanently polarized artificial magnet or an electro-magnet may be employed
for imparting magnetic polarity to both sections of the polarized armature. Another.
and preferable form of constructing and arranging the apparatus is to make use of
two magnetically united polarized armatures which are arranged to receive unlikė

page_text: polarity respectively, by induction from a permanent magnet, and which are
maintained in permanent frictional contact with the moving surface of a rotating
magnetic cylinder or disc, which surface moves in opposite directions but at the
same rate of speed at the respective points of contact of the armatures therewith.
This mode of construction renders it possible to impart a positive motion to the
armature system in each direction by means of a single magnetic cylinder or disc
and magnetizing coil. In this case it is preferred to mount the axes of the
armature system in slotted or grooved bearings which permit the weight of the
armatures to rest at all times upon the moving surface. When employed in con-
nection with a telegraphic relay or translating apparatus the armature may be
provided with electrical contacts whereby a local or other independent circuit may
be opened, closed, or otherwise controlled. When employed as a receiving instru-
ment upon the principle of the direct working ink-writer, the marking point, pen
or wheel, may be attached directly to the movable armature system. The invention
is also applicable to various other purposes for which electro-magnets with movable
armatures may be required.
In the accompanying drawings, figure 1 is a plan view of an apparatus illustrating
one method of carrying out the invention, in which a part of the apparatus is
broken away to exhibit the internal construction; and figure 2 is a transverse
vertical section taken in the plane of the dotted line 2, 2, in figure 1.
Referring to figures 1 and 2, A represents a suitable base upon which the various
parts of the apparatus are mounted; B is a helix or coil of thin insulated wire
which is wound upon a hollow bobbin b, the lower flange of 61, of which should be
formed of ebonite or other insulating material. C is a cylinder of soft iron, fitting
closely within the central opening of the hollow bobbin b, but capable of rotating
freely upon its longitudinal axis. The cylinder C forms the magnetic core of the
helix B. It preferably has an enlargement or flange c, (figure 2) formed upon its
upper end.
Upon the lower end of the cylinder C is fixed a small pulley D
which revolves beneath the base A. A belt or band D 1 passes around the small
pulley D, and also around a larger pulley E, which is also mounted in the same
plane beneath the base A, as shown in dotted lines in figure 1. A crank F, is
affixed to that portion of the shaft e, of the pulley E which projects above the
base A by means of which crank it may be turned by the hand of the receiving
operator in the direction indicated by the arrow. When the crank F is thus
turned, the soft iron cylinder C constituting the core of the hollow helix B, is
caused to rotate rapidly in the direction indicated by the arrow in figure 1.
The upper surface of the soft iron cylinder C is polished, and is moreover
carefully turned and fitted, so as to revolve as accurately as possible in a horizontal
plane. His an armature preferably formed of a thin flat disc of soft iron, a small
portion of the periphery of which rests upon the upper surface of the cylinder C,
near the edge of the flange, as shown in figures 1 and 2. The disc or armature H
is capable of moving freely in a horizontal plane upon its vertical pivot or axis h,
but the extent of this horizontal motion is limited by a rigid arm or lever I,
affixed to the armature and moving with it, which plays between fixed stops J
and K. These stops may with advantage be rendered adjustable by mounting
them upon screws or other well known equivalent devices as shown in figure 1.
The stop J is mounted upon a standard L upon the base A, and the stop K is
mounted upon a bracket, secured to but insulated from the standard L. The
retractor M consists of a spiral spring attached to the armature H preferably at a
point in its periphery diametrically opposite to the point of attachment of the
The retractor is capable of adjustment by means of the milled-head and
spindle M 1, or other suitable means, so as to exert a constant force of any required
amount upon the armature H. The helix B terminates in the projecting wires ww
which are electrically connected to the binding screws W 1 W 2, and serve to form
a connection with the main line.
arm I.
The apparatus thus constructed is placed at a receiving station in the circuit of
a telegraph line, the connections being completed in the ordinary manner by means

page_text: of a wire w 1, connecting the terminal post W 1 with the earth at the receiving
station, while the line wire w 2, coming from the transmitting station is attached
to the terminal post W 2. The key at the transmitting station may either be
arranged to open and close the circuit of the main battery T as shown at Q 1, or it
may be inserted in the manner shown at Q 2 so that when closed it will shunt a
constant resistance R normally interposed in the line, and thus act simply to
alternately increase and decrease the strength of current in the line without
interrupting the circuit.
The operation of the apparatus is as follows:-When a telegraphic communi-
cation is to be received upon the instrument the cylinder C which forms the core
of the coil B is caused to rotate upon its axis in the direction indicated by the
arrows, which may be effected by turning the crank F as herein before explained.
So long as no electric current traverses the coil B the friction between the
cylinder C and the armature H which rests lightly upon it; will be so small that
the cylinder will have but a slight tendency to drag the armature along with it,
and this tendency will be overcome by the resistance of the spring M, so that the
armature will remain in its normal position, (shown in figure 1) the arm I resting
in contact with the rear stop K. When, however, an electric current is transmitted
through the line, as by the depression of the key Q1, the cylinder C instantly
becomes magnetic by the inductive influence of the coil B, and attracts the
armature H which rests upon its periphery. The pressure produced by this
magnetic attraction increases the friction between the two surfaces to such an
extent that the antagonistic force of the retracting spring M is overcome, and the
armature H is caused to turn upon its axis by the force imparted thereto by the
friction of the rotating cylinder C. Hence the arm I is brought into contact with
the stop J, in which position it remains so long as the electric current from the
transmitting station continues to traverse the coil B.
When the current is interrupted by the raising of the key Q1, the attraction
between the cylinder C and the armature H ceases, whereupon the recoil of the
spring M instantly restores the armature H and its attached arm I to their normal
position.
In case it is desired to operate the apparatus by an alternate increase or decrease
in the strength of a constant current, as for example, by manipulating the key Q2,
the tension of the retracting spring M is so adjusted that the friction due to the
magnetism induced by the normal or minimum strength of current is not quite
sufficient to overcome its tension, but any increase of friction beyond the normal
amount will overcome the spring and instantly communicate a lateral movement
to the armature H in the manner hereinbefore explained.
The apparatus is shown in figure 1, in a form particularly adapted for use as a
relay or repeater, in which case the terminal wires of an independent receiving
instrument and an independent battery o are connected to the terminals X
and Y, and the independent circuit will be closed in the same manner as by the
lever of an ordinary relay instrument whenever the arm I is brought into contact
with the stop J, thus adapting the apparatus for use as a repeater or translator for
either long or short lines.
Figures 3 and 4 illustrate a plan of constructing the apparatus, wherein the
armature is moved to and fro, in both directions by the mechanical action of the
constant motor, thereby dispensing with the retracting spring; the direction of
the mechanical action being controlled by an electric current of alternating polarity
as from a double-current or reversing key. Figure 3 is a plan view of the
apparatus, a part of the receiving instrument being broken away to exhibit the
internal construction. The electric connections are shown in diagram. Figures 4
and 5 represent certain details of construction. In this form of the apparatus, the
single helix B and the cylindrical core C shown in figure 1, are replaced by two
coils or helices B1 and B2 and cylinders C1 and C2, similar in construction to
those herein before described in connection with figures 1 and 2. From the lower
end of each cylinder projects a spindle as shown at c 1 in figure 5, upon which are

page_text: fixed pinions d 1 and d 2 respectively. These pinions are mechanically secured to
the respective soft iron cylinders C1 and C2, as shown in dotted lines in figure 3,
so as to turn with them. The two pinions have each an equal number of teeth
and engage with each other. A toothed driving-wheel ƒ engages with the pinion d 2
and is provided with a crank F, whereby it may be caused to revolve, as in the
apparatus first described. When the crank F is thus turned the soft iron
cylinders C1 and C2 are caused to rotate rapidly in opposite directions as
indicated by the arrows in figure 3, and at a like speed. In place of the disc-
shaped armature shown in figure 1, it is preferred to employ a V-shaped plate of
soft iron H, (figure 3) the extremities of which rest upon and in permanent
frictional contact with the upper surfaces of the respective cylinders C1 and C2
⚫near the edge of the flanges. This armature may be constructed of a single piece
of soft iron, but it is much better, especially when great rapidity of action is
required, to construct it in two separate parts h1 and h2 as shown in figures 3
and 4. These parts are magnetically insulated from each other and at the same
time mechanically united by means of an interposed arm I of brass or other
suitable non-magnetic metal. The armature H is capable of moving freely in a
horizontal plane upon its vertical pivot or axis h, but the extent of this horizontal
motion is limited by the rigid arm I which is mechanically a part of the armature
and consequently moves with it. This arm plays between fixed stops J and K,
mounted upon standards attached to the base-board or pedestal A which supports
the apparatus. The armature H, whether single or compound, is supported by or
rests upon a stationary polarizing magnet, best seen in the detached sectional view,
figure 4. The polarizing magnet is preferably constructed of a cylindrical soft iron
core G surrounded by a magnetizing helix G 1, through which passes a constant
current from a local battery o1 (shown in diagram in figure 3) and is connected
with the terminals of the helix G 1, by means of the wires jj underneath the base
of the instrument as indicated by the dotted lines. The helices B1 and B2 are
united together in the same circuit, but are so connected with each other that the
magnetizing current passes in opposite directions around the respective cores C1
and C 2. The terminal wires w1 w 2 of the helices are extended to the terminal
posts W 1 and W 2, and serve to form a connection with the earth and with the
main line.
The apparatus thus constructed is included in the circuit and the connections
are arranged in the same general manner as herein before described in connection
with figure 1. Instead however, of being operated by a simple make-and-break
key or transmitter, or by a key adapted to transmit currents of constant polarity
but of varying strength as described in connection with figure 1, a double-current
or reversing key Q is employed for transmitting alternate positive and negative
currents from the battery T and T1 respectively, in a well known manner, so that
while the key is depressed a positive current is sent to line, and while it is raised
a negative current is sent.
When signals are to be received upon an instrument constructed in this
manner, the cylinders or cores C1 and C2 are caused to rotate upon their
respective axes in opposite directions as indicated by the arrows. So long as no
electric current whatever traverses the coils B1 and B2, the friction between the
rotating surfaces of the cylinders and the extremities h1 and 2 of the
armature H1 which rest lightly upon them, will be very slight, and moreover
the friction of the cylinder C2, tending to drag the armature in one direction
will be counteracted by an equal and similar tendency on the part of the other
cylinder C1 to drag it in the opposite direction, and the armature will therefore
tend to remain in a position midway between the limiting contact stops J and K,
as shown in figure 3. When however an electric current is transmitted through
the line as by the depression of the key at the transmitting station, the
cylinders C1 and C2 instantly become magnetic under the inductive influence of
their enveloping coils, one of them, as for example the cylinder C 1, manifesting
north polarity and the other cylinder C2 south polarity. The armature H resting

page_text: upon and being in magnetic contact with the core of the inducing or polarizing
magnet G (as herein before explained, and shown in figure 4) receives by induction
magnetic polarity therefrom, both its extremities however being of the same
polarity, for example, south. The effect of the contrary magnetization of the
respective cores is therefore that a mutual attraction is exerted between the
rotating cylinder C1 and the extremity h1 of the armature H in consequence
of their magnetic polarity being unlike, while on the other hand the cylinder C 2,
rotating in the opposite direction, tends to repel the extremity h 2 of the armature,
and thus diminishes the normal friction; the arm h1 of the armature is there-
fore instantly carried along in the direction of its motion by the cylinder C1,
until arrested by the arm I coming in contact with the stop J, in which position
it remains so long as a current of unchanged polarity continues to traverse the
coils B1 and B2, or until the action is reversed by the transmission of a current
of opposite polarity from the battery T 1. When such a reversal of the direction
of the current upon the line takes place, the former action of the receiving instru-
ment is reversed; the extremity 2 of the armature H is now attracted by the
cylinder C2, and the other extremity 1, repelled by the cylinder C 1, and hence
the armature is moved in the direction of the arrow by the friction of the
cylinder C2, and the arm I is brought into contact with the stop K.
Another and preferable method of constructing an apparatus for receiving
electric currents of alternating polarity is shown in figures 6, 7 and 8. The
general principle of construction of this apparatus is similar to that described in
connection with figures 3, 4 and 5, but it differs therefrom in certain details
relating to the mechanical organization of the apparatus whereby its construction
is rendered more simple, its moving parts of less weight, and its operation more
rapid and efficient. Figure 6 is a plan view of the apparatus, figure 7 is a vertical
transverse section of the same taken in the plane of the dotted line 7, 7, and
figure 8 is a section taken in the plane of the dotted line 8, 8. In this apparatus a
single helix of insulated wire provided with a soft iron core similar in construction and
forin to the corresponding parts hereinbefore described in connection with figures 1
and 2 is employed. The core is caused to rotate, in the direction indicated by the
arrow, in the manner already described. Two small upright armatures n and 8
preferably of soft iron are supported upon the surface of the upper flange of the
core C, and are mechanically united together, and by brazing or other suitable
means, secured to the interposed rigid arm I of brass or other non-magnetic metal,
which also serves to magnetically insulate them from each other. The lower ends
of both armatures rest upon, and are in frictional contact with, diametrically
opposite points upon the surface and near the periphery of the cylinder, and these
ends may with advantage be made slightly convex, as best seen in figure 7. An
axis i is inserted into the armatures n and s at the point where they are affixed to
the arm I and the extremities of this axis turn in vertical slots g g' which are
formed in the faces of the poles N S of a stationary permanent artificial magnet. It
is obvious that the armature system, being thus mounted in slotted bearings will be
supported by the cylinder C, and hence that there will exist at all times a frictional
contact between the armatures n und 8 and the surface of the cylinder C, while at
the same time any lateral motion of the axis i will be prevented. The arm I
vibrates between fixed limiting stops J and K in the usual manner. Thus the
armatures n and 8 together with the rigid arm I to which they are attached, are
capable of moving freely in a vertical plane upon the horizontal pivot or axis i but
the extent of this motion is limited by the fixed stops J and K. The armatures
n and s are magnetically polarized by induction, receiving north and south polarity
respectively from the poles N and S of the permanent magnet by reason of their
proximity thereto.
The circuit connections are the same in this apparatus as in that already
described in connection with figure 3. The operation is as follows:-When tele-
graphic signals are to be received upon the apparatus the soft iron cylinder Cis caused
to rotate in the direction indicated by the arrow, as hereinbefore explained. It is

page_text: obvious that so long as no electric current whatever traverses the coil B the friction
between armatures n and s and the rotating surface of the cylinder C will be that
due to the weight of the armature system alone, in addition to the attractive force
derived from its polarization by the permanent magnet N S; hence the friction of
the moving cylinder tending to drag the armature n in one direction will be
counteracted by an equal tendency on the part of the same cylinder to drag the
armature s in an opposite direction, inasmuch as they respectively rest upon
diametrically opposite points upon its periphery. The compound armature system
and its attached arm I will therefore tend to remain in a position midway between
the extreme limits of movement as determined by the position of the contact stops
J and K. When however an electric current is transmitted through the line, the
cylinder instantly becomes magnetic under the inductive influence of its
enveloping coil. If we assume the cylinder C to exhibit north polarity under the
influence of this current, the attraction between it and the armature 8 will be
increased, as the two are now of unlike polarity, while the direction between it
and the armature will be simultaneously diminished for the reason that the
latter are now of like polarity. Hence the friction between the armature 8 and
the periphery of the cylinder will be augmented, and the former will be dragged
in the direction of the arrow until the arm I is arrested by its contact with the
stop K.
When the current is reversed upon the line, the mechanical action of the
instrument is also reversed, for the reason that the cylinder C now assumes south
polarity and tends to attract the armature n and repel the armature 8; and the
arm I will thus be brought into contact with the stop K. The operation of the
apparatus, it will be seen, is essentially the same as that of the apparatus shown in
figure 3 with the exception that the armatures are placed in contact with portions
of the same surface moving in opposite directions, instead of being placed in
contact with corresponding parts upon the two revolving surfaces.
The apparatus may be constructed in many other forms without departing from
the general principle; thus the armature may be made to revolve by mechanical
power and the core of the electro-magnet placed in frictional contact with it, so as
to receive its motion therefrom.
In all the modifications which have been described it is usually found preferable
in practice to employ a train of wheel-work of well-known construction driven by
a coiled spring or other maintaining power, for producing the necessary rotation of
the core cylinders as shown at vin figure 3, and thus the attendant by throwing
the wheel-work into gear by means of a lever v may be relieved from the necessity
of turning the crank during the reception of a communication.
It is evident that each of the forms of apparatus described may be employed
either as a relay or as a translator or repeater, by connecting the terminal wires of
an independent main or local circuit (including a sounder, inkwriter, register or
other receiving instrument) to the terminal posts X and Y. When arranged in this
manner the independent circuit, whether local or main, will be opened or closed in
the same manner as by the armature-lever of an ordinary telegraphic relay. The
knife-edge or marking point, pen or wheel of an ink-writer may be attached
directly to the arm I, and the speed of its vibration may thus be made exceedingly
great.
It is obvious that the ordinary telegraphic signals may be distinguished by the
ear, while the instrument is in operation in the manner heretofore practiced by
expert telegraphists, the requisite sounds being produced by the vibration of the
arm attached to the armature between the fixed stops.
The invention is also applicable to various other purposes for which electro-
magnets with movable armatures may be required.
Having thus described the nature of the said invention and the manner in
which the same is to be performed as communicated to me by my foreign
correspondent I claim:
First. The herein before described method of causing the armature of an electro-
magnet to vibrate to and fro between fixed stops, through the instrumentality of a

page_text: constant mechanical power whose action upon said armature is controlled by
electro-magnetism.
Second. One or more polarized armatures receiving magnetism by induction from
a constant or permanent magnet and maintained in permanent frictional contact
with the surfaces of one or more iron cylinders or discs, in combination with a
magnetizing belix, and mechanism for communicating motion to the armature or
to the magnet, the direction of said motion being determined by the polarity of the
magnetizing current.
In witness whereof I the said William Phillips Thompson have hereunto set
my hand and seal this Twenty ninth day of August in the year of our Lord
one thousand eight hundred and eighty two.