IMPROVEMENTS IN ELECTRIC CURRENT GENERATORS AND MOTORS."
Year: 1882

page_text: LETTERS PATENT to Silvanus Phillips Thompson, of University College,
Bristol, Professor of Experimental Physics, for an Invention of "IMPROVEMENTS
IN ELECTRIC CURRENT GENERATORS AND MOTORS."
PROVISIONAL SPECIFICATION left by the said Silvanus Phillips Thompson
at the Office of the Commissioners of Patents on the 27th October 1882.
SILVANUS PHILLIPS THOMPSON, of University College, Bristol, Professor of
Experimental Physics, "IMPROVEMENTS IN ELECTRIC CURRENT GENERATORS AND
MOTORS
"
The first part of my present invention relates to a type of dynamo-electric machine
which can be used either as a generator or as a motor, and is an improvement upon
an early machine described by Faraday. The second part of my invention relates
to an improved form of dynamo-machine to serve as a generator or motor, wherein
the castings which serve as cheeks and cores for the field-magnets also form the
bed-plate of the machine, and wherein also I make use of a quadruplex armature
which is a modification of the simple longitudinal shuttle-shaped armature described
in the provisional specification of Siemens No. 2107 of 1856.
The improved machine forming the subject of the first part of my invention is a
modification of Faraday's machine of 1831 wherein a simple copper disc rotated by
mechanical means between the poles of a magnet or electro-magnet generated
continuous currents which flowed from a collector (or spring) in contact with the
axis to another collector in contact with the periphery, or vice versa according to
the sense of the rotation. This machine is unsuitable for practical work for the
following reasons, viz firstly; there is excessive friction when contact is made at
the periphery of the rotating disc armature by a contact spring. Secondly; the
currents are very feeble owing to the small intensity of the magnetic field. Thirdly;
when a simple disc armature is thus rotated between a pair of magnet poles at
some point on either side of it there are currents generated (the so-called Foucault
currents) which merely circulate wastefully and internally on the disc and do not
reach the external circuit but only run round in closed paths in the disc and
heat it.

page_text: '
I therefore inodify Faraday's machine in the following manner, that is to say,
firstly I employ two such discs rotating about a common axis, and connect their
peripheries by bridges or cross-bars or laticed rims of iron, copper, or other suitable
metal; and I arrange the contact springs or collecting brushes in contact with the
hubs of the discs or with small pulleys in contact with the hubs thereby avoiding
the excessive friction due to the peripheral contact. It is essential that the
respective hubs or pulleys should be insulated from direct electrical contact with
one another and one or both should be insulated from contact with the axis, in
order that the currents may flow as hereinafter described. Secondly, I arrange
powerful field magnets in groups of two or more on each side of this double-disc
armature, so that there shall bo similar poles opposite two, three, or more points of
the periphery. These poles are joined by stout flat rings or annular iron pole
pieces on either side so that the double disc armature rotates in a very intense
imagnetic field between two parallel cheeks; moreover I intensify this field by
placing plates or discs of soft iron within the interior of the double disc armature.
Thirdly, I get rid of useless Foucault-currents which might otherwise circulate in
the discs, by slitting the said discs radially and by arranging the conditions of the
magnetic field so that it is equally intense concentrically with the discs, that is to
Buy, though the field may be more intense at the circumference than at the centre
it is equally, or nearly equally, intense all round the circumference; this object is
accomplished by using as pole-pieces to the field-magnets the aforesaid stout flat
iron rings. The result of using these annular polar surfaces will be to cause the
equipotential surfaces of the flow in the discs to be also concentric, and the currents
themselves to be truly radial in direction.
In order that the currents generated in the discs shall follow the course herein-
after described it is necessary that both the opposing pole-pieces shall be of the
same sign, that is to say, both north, or both south in polarity. The discs rotate
like a loose pulley upon a fixed shaft or axis-of-iron-or-steel. This shaft is a part
- of the electro-magnets, the middle point of the axis being a double-pole of opposite
Bign to that of the pole pieces of the peripheral magnets. In order that the lines
of force of the field may be cut more squarely by the rotating disc-armature I place
-one or more circular plates of soft iron at the middle point of the iron shaft within
the rotating disc armature: The compound disc armature may then be said to
consist of three parts, the discs, the bridges, and an internal mass of iron which,
though an important and essential feature of the armature, need not rotate with
the other parts. By these means each of the two discs rotates, as in Faraday's
machine, between magnetic poles. But since the motion, as viewed from the two
ends of the axis, is of one disc a right-handed rotation, while that of the other disc
is a left-handed rotation, the induced radial currents will flow, in one disc from
centre to circumference, and in the other from circumference to centre as required
for the action of the machine, which thus generates continuous currents flowing
radially from the hub of one disc outward to its periphery across the bridges to the
periphery of the other disc, and thence radially inward toward its hub and to
the contact spring or brush. The frame-work of the field-magnets may be cast
in one or more pieces so as to serve also as a bed-plate and frame-work for the
machine.
The field-magnets may be wound and excited as in other dynamo machines, the
coils being joined either in series with, or as a shunt to, the external circuit, or they
may be separately excited, or they may be excited in any combination of these
ways. I sometimes use permanent steel magnets. The bridges uniting the discs
may be made either of magnetic or non-magnetic metal, and may be either solid or
laminated or may take the form of a continuous lattice work or of a continuous
rim pierced with holes. In some instances I make these sufficiently heavy to
steady the action of the machine by acting as a fly-wheel
I sometimes provide my machine with more discs than two in pairs upon a
common axis, pole-pieces being introduced between each pair, thereby increasing
the effective action of the machine.

page_text: In another form or modification of the said machine the two discs, instead of
being placed side by side on one axis, are placed edge to edgo upon parallel axes,
their rims being in rolling contact with each other at one point and being made
broad and heavy. In this modification of my invention the polar surfaces must be
of opposite signs on the two sides of the discs, and the lines of force must cross
both discs in the same direction. In this machine the currents will flow from the
hub of one disc to its periphery, thence through the point of contact to the
periphery of the other disc, and so to the hub of the other; In this case the rims
should not be slit.
The improved dynamo electric machine forming the subject of the second part of
my invention is designed primarily as a motor, but is capable of being used also as.
a generator. It may be used in conjunction with a machine of the class first
herein described, or independently. The field-magnets of this improved machine
are electromagnets, the coils being wound upon cast iron cores. These cores aro so
constructed in form as to be capable of being cast in one or two pieces, the cores,
cheeks, and bed-plate being all cast together. The general forin given to tho
electromagnet is similar to that known as Joule's. The armature which I employ
I designate as a " quadruplex armature" because of the peculiar manner of grouping
the two pairs of coils across one another; it is a modification of the longitudinal
armature of Siemens, which though eminently well suited for small motors, has but
one coil of wire and has therefore dead-points. The modification which I havo
devised consists in arranging two such coils, one within, and at right angles to, the
other, along one spindle; the two coils being, for convenience in winding, each
divided into two parts on opposite sides of the spindle. The commutator is also
duplicated. It may be arranged either in the form of a single copper tube split
into four segments, or there may be two copper collars each split into two segments.
If I use the single tube arrangement the two pairs of coils are connected to the
segmental bars in such a manner that the current, after traversing half of one coil,
runs to one segment of the commutator, then enters one half of the coil at right-
angles to it, and thence to another segment of the commutator, and so forth. If
the two split collars be adopted for the commutator the two coils will remain
entirely disconnected from each other. Each coil will have its two ends connected
with the two halves of its own collar; the two collars being placed so that the
slits of one collar are ninety degrees from the slits of the other. In either case
there will be but one pair of contact springs or collecting brushes or wheels, but
these, in the second manner of arranging the commutator, must be broad enough to
press simultaneously against both collars. The core of the arinature is sometimes
inade of malleable iron cast or forged upon a steel spindle. In other cases the core
is made up of plates of iron cut out to a cross-shape and strung side by side upon
a steel axis. In some larger machines the cross-shaped plates of iron are replaced
by a pair of strips of sheet iron separated from one another by varnish, and Inid
upon one another crosswise. The bearings of the axis are of gun metal or other
non-magnetic metal, and are integral with the end-plates which are screwed on to
the end faces of the cast-iron field-magnet frame-work of the machine.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Silvanus Phillips Thompson in the Great Seal Patent Office on
the 27th April 1883.
SILVANUS PHILLIPS THOMPSON, of University College, Bristol, Professor of
Experimental Physics, "IMPROVEMENTS IN ELECTRIC-CURRENT GENERATORS AND
MOTORS
"
The first part of my present invention relates to a type of dynamo-electric
machine which can be used either as a generator or as a motor, and, is an improve-
ment upon an early machine described by Faraday in papers read by him before
the Royal Society in the year 1831 and since published in the work entitled
"Faraday's experimental researches in electricity."
The second part of my invention relates to an improved form of dynamo-machine
to serve as a generator or motor, wherein the castings which serve as cheeks and
cores for the field-magnets also form the bed-plate of the machine, and wherein I
make use of an armature which is a modification of the simple longitudinal shuttle-
shaped armature described in the specification of Letters Patent granted to Charles
William Siemens in 1856 (N° 2107.)
The improved machine forming the subject of the first part of my invention is a
modification of Faraday's machine of 1831, wherein a simple copper disc rotated by
mechanical means between the poles of a magnet or electro-magnet generated
continuous currents which flowed from a collector (or spring) in contact with the
-axis-to another-collector in contact-with-the-periphery, or vice versa, according to
the direction of the rotation. This machine is unsuitable for practical work, for
the following reasons, viz:-Firstly, excessive friction is caused by the contact of
the spring, or collector with the periphery of the rotating disc armature. Secondly,
the currents are very feeble by reason of the small intensity of the magnetic
field. Thirdly, when a simple disc-armature is thus rotated between a pair of
inagnet poles at some point on either side of it, there are currents generated (the
so-called Foucault currents) which merely circulate wastefully, not reaching the
external circuit, but running round in closed paths in the disc and heating the same.
I therefore modify Faraday's machine in the following manner, that is to say,
Firstly, I employ two such discs rotating about a common axis, and connect their
peripheries by bridges, cross bars or latticed rims of iron, copper, or other suitable
metal; and I arrange the contact springs or collecting brushes in contact with the
hubs or bosses of the discs, or with small pulleys in contact with the hubs, thereby
avoiding the excessive friction due to the peripheral contact. It is essential that
the respective hubs or pulleys should be insulated from direct electrical contact
with one another, and one or both should be insulated from contact with the shaft
or axle in order that the currents may flow as hereinafter described. Secondly, I
arrange powerful field magnets in groups of two or more on each side of this
double disc-armature, so that there shall be similar poles opposite each other at
two, three, or more points of the periphery. These poles are joined by stout flat
rings, or annular iron pole-pieces on either side, so that the double disc-armature
rotates in a very intense magnetic field between two parallel cheeks. Moreover, I
intensify this field by placing plates or discs of soft iron within or between the
two discs or plates of the double disc-armature. Thirdly, I get rid of useless
Foucault" currents, which might otherwise circulate in the discs, by slitting the
said discs raidally and by arranging the conditions of the magnetic field so that it
is equally intense concentrically with the discs; that is to say, though the field
may be more intense at the circumference than at the centre, it is equally, or nearly
equally, intense all round the circumference of the discs; this object is accomplished
at

page_text: esult of using these ring or
otential surfaces of the flow in the discs to be concentric and the currents
hemselves to be truly radial in direction. Fourthly, in order that the currents
generated in the aforesaid discs shall follow the course hereinafter described, it is
ecessary that both the opposing pole-pieces shall be of the same sign, that is to
ay, both north or both south in polarity. :
The machine, constructed upon the above principles, I term a
dynamo." It is shown in Figures 1, 2, 3 and 4 of the drawings.
Figure 1 is a side elevation.
Figure 2 is a vertical longitudinal section, and
Figure 3 is an end elevation of the said machine.
Figure 4, is a side view of one of the armature discs.
The remaining Figures of the drawings are hereinafter referred to.
"
circumpolar
The discs D' L' are preferably of copper and are cut or slit radially as in Figure 4.
and may be strengthened at the back with radial ribs. The said discs are joined at
the periphery by bridges D* as shown in Figures 1 and 2, and rotate together (like
a loose wheel or pulley) upon a fixed shaft or axle S of iron or steel. This shaft is
a part of the electro-magnets, and in some cases coils are placed on one or both of
its ends to induce magnetism in it. The middle part of the said shaft must be a
pole of opposite sign to that of the pole-pieces N, N, of the peripheral field magnets.
These peripheral magnets are arranged, as shown, with their cores B parallel to the
shaft S, and are united into two groups, one on the right, the other on the left of
the machine, being held in their places between the circular iron cheeks or pole-
pieces N, N, and the end-plates A of the machine, through which the cores pass
and are secured by screw-nuts as shewn. The circular pole-pieces N may be
connected at their peripheries by iron plates or masses so that the rotary armature
will be enclosed thereby.
In order that the lines of force of the field may be cut squarely by the rotating
disc-armature, one or more circular plates C of soft iron are placed on the middle
part of the said shaft S, within, or between, the two discs of the armature," The
compound disc-armature may then be said to consist of three parts, viz. the discs,
the bridges, and an internal mass of iron, which, though an important and essential
feature of the armature, need not rotate with the other parts thereof. In this
arrangement, each of the two discs rotates as in Faraday's machine between
magnetic poles. But, since in my machine the motion as viewed from the respective
ends of the axis is, of one disc a right-handed rotation, and of the other disc, a left-
banded rotation, the induced radial currents will flow, in one disc from centre to
circumference and in the other disc from circumference to centre as required;
Tubular or other suitable attachments must, therefore, be added to the discs for the
conveyance of the currents; One or both of the said tubular attachments must be
insulated from the aforesaid shaft or axle by the insertion of an interior tube of
non-conducting material such as vulcanized fibre; and upon the outer surface of
such insulated attachment, or a smooth metal pulley placed thereon presses &
"brush" which I provide to collect the currents. In some cases one such brush
only is used, the attachment of the second disc being uninsulated, so that the current
enters or leaves through the shaft or axle of the machine; In such a case the said
shaft or any part of the machine in metallic contact with it may be used as a
second terminal. The frame-work of the field-magnets at either end may be cast
in one piece with their cores B and the united framework may serve also as &
bed-plate for the machine.
The field-magnets may be wound and excited in any of the ways adopted in
ordinary dynamo-machines, the coils being joined either in series with, or as a shunt
to the external circuit; or they may be separately excited, or they may be excited
by any method involving a combination of these ways; or by any of the modified
methods of winding the coils hereinafter described. Or they may be replaced by
permanent magnets. The bridges D* uniting the discs are represented in the
.

page_text: drawings as consisting merely of short thick bars of metal keyed firmly by their
ends to the said discs; but they may be of many other forms. In some cases, I use
flat strips of metal; in other cases, I use laininated plates. I also employ, in certain
cases, actual coils of wire as the bridges; Where a greater electro-motive force is
required, I employ, as bridges, pieces of metal formed into a loop or coil the inner
portion of which, or that which is nearest the axis, is formed of iron, the two arms
of the loop being made of copper and united, after crossing one another, with two
points on the peripheries of the two discs.
Figure 4a shews one of these pieces the part a being of iron and the parts 6 of
copper.
I, in some instances, modify my invention by employing more than two dises
combined in pairs upon a common axis, pole-pieces being introduced between each
pair, thereby increasing the effective action of the machine.
In Figures 5 and 6 I have shown another form of machine, Figure 5 being a
side elevation and Figure 6 a plan or top view. In this machine, the two discs D,
instead of being placed side by side on one axis, are placed edge to edge upon parallel
axes R, R, their rims D' being in. rolling contact with one another at one point, and
being made broad and heavy. In this case, the polar surfaces must be of opposite
signs on the two sides of the discs, and the lines of force must cross both discs in
the same direction. As thus arranged, the currents will flow from the hub of one
disc to its periphery, thence at the point of contact to the periphery of the other
disc, and so to the hub of the other. The rims of the discs should not be slit,
though the discs themselves may be. In this modification of the machine also it is
advisable, though not absolutely essential, that the pole-pieces of the field magnets
be arranged so that the field is symmetrical round the axis of each disc, as in the
first form of machine described above. It is evident that such symmetry of arrange-
ment may be obtained in a variety of ways by employing circular pole pieces set
round with a number of similar poles; and the magnets for producing these poles
may be set either with their axes parallel to the axis of the armature, or radially; or-
in any equivalent manner.
The-second part of my invention is illustrated in figures 7, 8, 9 and 10. Figure 7
is a longitudinal vertical section, Figure. S is a plan or top view, and Figure 9 is
partly an end view and partly a transverse section of one machine, Figure 10 is
partly an end view and partly a transverse section of another machine.
This part of my invention relates to an improved dynamo-electric machine designed
primarily as a motor, but capable of being used also as a generator. It may be
used in conjunction with the above described machine, or independently. The field-
magnets of this machine are electro-magnets, the coils being wound upon cores of
malleable cast iron. These cores are of such form that the cores and cheeks (the
latter serving, in some cases, as bed-plates also) can be cast in one piece or in two
or more pieces. The particular form of machine shewn in Figure 10 is adapted for
casting in one piece. For larger machines the form shewn in Figures 7,8 and 9 is
adopted, that is to say, I provide two iron pole-pieces T with cores T¹ above them,
united at the top by bolts with a third piece of iron T. In the smaller machines
an arched form of electro-magnet is preferred. The field-magnets, whether made of
one piece or of several pieces, may serve also as a firm frame-work and bed-plate
for the machine. The said field-magnets may be wound and excited in any of the
ways adopted in the construction of ordinary dynamo machines, the coils being
joined either in series with or as a shunt to, the external circuit, or they may be
separately excited, or they may be excited by any combination of these ways.
In some cases, the machines are wound with two coils, upon one core, as shewn in
Figure 11, where one coil is connected in series, and a separate coil is wound on
the same core as a shunt, the proportions of the coils being adapted to the
⚫ conditions of the supply of electric energy, to the size of the machine, and to the
speed it is required to be run at; I find that machines thus arranged may be made
to give more constant results than machines wound with a shunt-coil only, or with a
series-coil only. When such machines are used as motors, the two separate coils

page_text: must, for the purpose of controlling the speed of armature, be so connected that the
magnetism induced by one opposes that induced by the other; whereas, when used
as generators, the connections must be such that the magnetism of one coil helps
that of the other. In the case of some of the larger machines, it is convenient that
one of the two cores shall receive the shunt-coils whilst the other receives the series-
coils, as shewn in Figure 12, wherein the coil M is the series-coil and N the shunt
coil. In some cases, the second coil is not connected, oither in series or in shunt,
to the supply circuit, but is entirely separate and receives its curront from an
independent battery, or from another source, such as an accumulator or a dynamo;
Such an auxiliary method of separately exciting the whole or a portion of the
magnetism in the field magnet is convenient for regulating the action of the machine
when used either as motor or generator. Another way of combining a shunt-coil
and a series-coil in the machine is indicated in Figure 13, wherein also is a switch
to enable the connections to be changed at will. I am aware that dynamo-electric
machines have been constructed in which a series-coil and a shunt-coil have been
combined, and that such machines have been used both as generators and as motors ;
I am also aware that dynamo-electric machines have been described or constructed
wherein magnetism of the field-magnets was derived partly or wholly from an
independent source of current, such as a local battery, and that such machines have
been used as generators of currents; but not that they have been described or used
as motors. This part of my improvements, consisting in tho application, in a
dynamo machine used as a motor, of magnetisın derived wholly or partially from an
independent local battery or accumulator or other source of currents different from
that which supplies the armature of the machine whether such auxiliary magnetism
is applied to augment or oppose the magnetism derived from the current which
supplies the armature of the machine, is new, and it is applicable not only to the
particular forms of dynamo-electric machines described in this specification but to
dynamo-electric machines in general, in their use as motors. In some cases, I excite
the separate coils of the electro-magnet from accumulators, such accumulators being
charged by the same supply that brings current to the motors. In some cases,
unite two machines both of them being series-wound or both of them shunt-wound,
their armatures having a common axis of rotation, and I 'arrange them so that in
one machine there shall be inany more coils on the field-maguot than are requisite
for the magnetising of the iron cores when the current is at its strongest, whilst in
the other machine there are many fewer coils than are requisite to magnetise the
iron core or cores. This result can be accomplished by constructing the cores and
pole-pieces of one machine to contain very little iron, whilst those of the other
machine contain an abnormally great mass; and such coupled machines can be
used to run at a more uniform speed than single machines wound only in shunt, or
only in series. I find that this arrangement is susceptible of many modifications
and is applicable to motors with all kinds of armatures. I sometimes couple up
the two machines with connections in series, sometimes with connections parallel.
Instead of the above specified arrangements, I sometimes employ a novel
arrangement of winding the field-magnets with one continuous coil.
with the coils of galvanometers, so with the coils of field magnets, the
wire should not be of one gauge but should increase in size from the inmost
windings of the coil outwards, as shewn in Figure 15. As it is impracticable
to manufacture wire of uniformly varying diameter. I approximate to it by
employing three, four, or more different sizes of wire; all the various sections
being united into one continuous coil. This arrangement is shewn in the diagram
Figure 14 where the coil consists of six sections A, B, C, D, E, F; the section A
is formed of many turns of thin wire, the section B of a sinaller number of
turns of somewhat thicker wire, and so on to the section F, which is the thickest
part of the coil and is formed of comparatively few turns of wire. At the junctions
of the different sections of the coil I attach connections to separate contact pieces G ;
and I employ a lever-handle L, by whose adjustment the current can be caused to
enter at either or any section. I thus provide for regulating the amount of current
As

page_text: supplied and the power of the motor. Such a device constitutes a controlling
switch very convenient for enabling a motor to be used under varying circumstances
of electric supply, and enabling the user of the machine to readily change the
speed at which it is being driven.
Another modification of this part of my invention consists in employing a
continuous coil wound in sections, but having the thinnest wire in the middle and
the thickest wire at the ends of the coil. Such coils are shewn in diagram in
Figures 16 and 17. In these cases also, contact pieces G are attached at the
junctions of the various sections as, and for, the purpose above specified. In the
arrangement shewn in Figure 16, the coil is arranged as a shunt to the armature,
and the current is introduced by connecting the positive main with one of the
contact pieces, and the negative main with another contact piece, the connections
being, as above described, adjustable to suit the conditions of the electric supply
and to give, at will, either a slow or a rapid speed to the motor. In the arrange-
ment shewn in Figure 17, the connections are reversed, and the current is introduced
to the armature by so bringing it into connection with the contact-pieces of the
sections of the coil that the current in one or more sections of the coil is shunted
through the armature.
An armature which I have devised is shewn in longitudinal section in Figure 7,
and is a modification of the well known shuttle-wound simple armature of
Siemens. To avoid dead-points I embed as it were two such armatures within one
another along a common spindle, but at right angles to one another. In some cases;
for convenience of winding, the two coils are each divided into two parts on
opposite sides of the spindle, the connections being made as. in Figure 18, this
figure and figures 19 and 20 being end views of armatures illustrating different
windings. Since the armature is thus duplicated the commutator or collector must
be also duplicated. It may be arranged either in the form of a single metal collar
or tube split into four segments, as shewn, in Figure-8 and also in Figures 22
and 23 Figure 22 being a side elevation of this commutator, and figure 23 a
transverse section of the same; or there may be two metal collars or tubes each
split into two segments. In the former arrangement, the two coils are connected
to the segmental bars in such a manner that the current after traversing half a, a',
of one coil runs to one segment of the collector or cominutator (as shewn in
Figure 18) then enters one half b, b', of the coil at right-angles to the former,
thence to another segment of the collector or commutator and so forth. If the
second arrangement be adopted for the duplicated commutator, the two coils will
remain, as shewn in Figure 19, entirely disconnected from each other. Each coil
will have its two ends connected respectively with the two halves of its own collar;
the two collars being so placed that the slits of one collar are 90 degrees from the
slits of the other collar. In either case, there will be but one pair of contact-
springs or collecting brushes or wheels; but these, in the second manner of
arranging the commutators, must be broad enough to press against both collars at
once. In some cases, I wind the two halves of each coil upon the opposite edges
of the longitudinal core-pieces, and virtually use them as four coils. This arrange-
ment and the connections for it are shewn in Figure 20. In some larger machines
I increase the number of parts by embedding within one another more than two
coils, and connect them similarly to those described for two coils, but with the
corresponding multiplication of parts.
The core of the armature is sometin s made of malleable iron, cast or forged
upon a steel spindle. In other cases, the core is made up of plates of thin iron
cut cross-shaped and strung side by side upon a steel axis. In some larger
machines, the cross-shaped plates of iron are replaced by a pair of strips of sheet-
iron separated from one another by varnish and laid on one another cross-wise as
shewn in Figure 9. The bearings of the shaft or axle are of gun-inetal or other
non-magnetic metal, and may form one continuous part with the end-plates of the
machine.
I employ several devices as reversing-gear for the above described motors, such

page_text: devices being applicable to electric motors generally. One form of my reversing-
gear is shewn in diagram in Figure 21, wherein there are three brushes or contact
springs, one of which B' is placed to make contact on the median line between the
field-magnet poles. The other two brushes of springs B and B³ are placed at the
opposite side of the collector, but one has a lead given it to the right, and the other
to the left of the median line. As the sense of the rotation depends on the direction
of the lead, the motor can be reversed by switching the current from B2 to B³, for
which purpose I provide the switch S*. If desired, contact-wheels may be
employed, instead of contact-brushes or springs. When brushes or springs are used
they are sometimes held at both ends, but bent so as to spring with the requisite
pressure against the collector. In some cases, instead of switching the current from
B³ to B³, B' and B³ are both mounted upon one metallic frame, and this frame is fixed
upon a stiff spring, by bending which spring slightly to one side or the other,
either B or B can be made at will, to press upon the collector so that the lead is
given through that brush which is pressed against the collector; Or a similar
arrangement may be applied both above and below the the collector in the same
machine, so as to give a lead to the left below at the same time as a load is given to
the right above, and vice versa.
I have shewn another device for a reversing gear in figures 22 and 23. Figure 22
being a side elevation and Figure 23 a transverse section.
In this case, I obtain the requisite change of lead by the employment of a
collector composed of a tube slit, as described, into four parts, these parts being,
however, helicoidally cut, and the splits e between the parts being carried spirally
through at least a quarter of a revolution round the tube. The brushes B* are
attached to a frame or plate fitted to slide between guides f parallel to the spindle
of the armature, and, by bringing the said brushes into contact with either the
anterior or the posterior part of the tube-collector, they will get the requisite lead
to the right or the left as the case may be. The sliding motion is given to the frame
which carries the brushes by a suitable lever, or other convenient means. This
device also serves to regulate, at will, the speed of the motor, since the action will be
affected by the degree of lead given to the brushes.
Another device for reversing gear consists of the apparatus shewn in side and
end elevation in Figures 24 and 25; this apparatus is arranged for giving a lead in
either direction. A, B, C, D are the four segments of a straight-slit four-part
collector, projected in a plane in Figure 24. for the sake of tracing the connections.
They are shewn in their true relative positions in Figure 25. Behind them, on the
same cylindrical mounting, are set four plates, a, b, c, d, connected to the former as
shewn, that is to say, a to A, b to B, and so on. Between the posterior plates a, b, c, d,
and the plates or segments A, B, C, D, are four bars of copper or brass m, n, o, p,
sliding in brass supports which are connected respectively to the four attachments
1, 2, 3, 4, of the armature coils. The sliding bars, as shewn in the drawing, connect
the four attachınents with the posterior plates, so that D is in communication
with 1, A with 2, B with 3 and U with 4. If now the sliding bars are drawn
forward A will be made to communicate with 1, B with 2, C with 3, and D with 4,
thus altering the lead by of a rotation; and if set, in the first instance, to
have lead in one direction, the shifting of the four bars will give lead in the
other direction. It is possible by connecting A and b, B and c, and so on, to change
the lead from in one direction to in the other direction. For convenience the
four bars are connected rigidly by a ring of non-conducting material (as shewn in
Figure 25) by which they can be shifted when it is desired to reverse the rotation
of the motor.
A modification of this arrangement is shewn in Figures 26 and 27. which are
views similar to Figures 24 and 25. In this modification, I place behind the four
segments A B, C, D, and alternating in position with them, four plates 1, 2, 3, 4,
connected with the four attachments of the coils. The four sliders m, n, o, p, in this
case are capable of being rotated round the collector to the position shewn by
the dotted lines. This arrangement enables the plate -1 to-be-brought into

page_text: communication with either A or B; plate 2 with either B or C, and so on, thus.
changing the lead. As above described, the four slides may be conveniently
mounted in a ring of non-conducting material indicated in Figure 27.
Having thus fully described my said invention and shown how the same may
be conveniently and advantageously carried into practice, I wish it understood that
I am aware that prior to the date of my invention it has been attempted to
combine two or more discs in an armature for a dynamo-electric machine, I
therefore do not claim, generally or irrespectively of my improvements as herein
specified, the construction or employment of an armature with two or more discs,
that is to say, I do not claim the employment of such an armature otherwise than 1
in or for machines wherein the magnetic field is arranged concentrically as above
described, but I claim :-
First. In a dynamo-electric machine, the combination of a double disc-armature
with external concentrically arranged field-magnets or pole-pieces, the polarity of
such external pole-pieces being alike on both sides of the armature and contrary to 1
that developed between or within the discs, for the purpose specified.
Second, The employment of bridges or conductors to unite the two discs of the
said double disc-arinature, substantially as, and for the purpose, specified.
Third, In the armature of a dynamo-electric machine, the employment of loops
or coils the innermost portions of which are made of iron or other magnetizable
metal, the outermost portions of the same being made of copper or other non-
magnetizable metal, for the purpose specified.
Fourth, The modification of the double disc dynamo-electric machine wherein
the two discs are arranged in rolling contact at their peripheries between
cheeks or pole-pieces arranged to produce concentric magnetic fields, substantially
as described.
Fifth, In the armature of an electric motor, the combination of cross-shaped iron
plates or pieces or of crossed pairs of iron strips with the double longitudinal coil,
substantially as described.
Sixth. The improvements relating to an electric motor so constructed that in its
use the magnetism of the field-magnet may be partially derived from the circulation
in some or all of its coils of a current from a source separate from, and independent
of the electric supply which is applied to drive the armature.
Seventh. The employment, in connection with an electric motor, of an accumu⚫
lator or accumulators, charged by the main current which feeds the armature-part
of the motor, to excite an independent magnetisation of its field-magnets in coils
entirely separate from the primary coils supplied by the main current, whether
such primary coils be connected in series with the armature or as a shunt to the
same.
Eighth. The combination, on one common driving shaft or axle, of two motors,
which are both series-wound or both shunt-wound, and both of which are
united either in series or in parallel to a common electric supply, the field-magnets
of one motor being arranged so as to be completely saturated when those of the
other are far from saturation, for the purpose set forth.
Ninth. The use, in an electric motor of a single coil wound in sections of
different thickness as and for the purpose set forth.
Tenth. The reversing gear or device whereby, in an electric motor, the current
can be switched at will into one or more contact-brushes or pieces having different
degrees of lead at the commutator.
Eleventh. The reversing-gear or device consisting in the combination of two
contact brushes having opposite leads with a stiff spring holder permitting either
brush to be pressed more strongly than the other upon the commutator, substantially
as described.
Twelfth. The reversing-gear or device consisting in the combination of an
obliquely or helicoidally cut commutator or collector with brushes capable of
sliding in ways or guides parallel to the axis of the commutator or collector,
substantially as set forth

page_text: Thirteenth. The reversing-gear or device illustrated in Figures 24, 25, 26, and 27
for altering the connections between the armature-coils and collector segments so
as to change the lead of the brushes, substantially as described.
In Witness whereof I the said Silvanus Phillips Thompson have hereunto set
my hand and seal this Twenty sixth day of April in the year of our Lord
One thousand eight hundred and eighty three
SILVANUS PHILLIPS THOMPSON (2.5.)