Year: 1887

page_text: Date of Application, 23rd Feb., 1887
Complete Left, 23rd Dec., 1887
Complete Accepted, 23rd. Feb., 1888
I JOHN GRICE STATTER, of 49, Finsbury Pavement, in the city of London,
Electrical Engineer do hereby declare the nature of this invention to be as follows:-
In order to maintain a constant current in the circuit or circuits fed by a dynamo
electric machine (in which variations in the resistance of those circuits or moderate
variation of speed or both exist) it is necessary to vary the electro-motive force
generated by the dynamo electric machine hereinafter called the dynamo.
My invention consists in effecting this automatically so as to enable such dynamo
to maintain a constant current under varying conditions of resistance in the circuit
or circuits fed by it or varying rates of speed or both.
It is well known that in continuous current dynamos which have many part
commutators, such as Gramme's, Siemen's, Edison's and others, if the brushes be
moved from the position of least sparking forward in the direction of rotation of the
armature there will be a diminution in the electro-motive force generated by the
dynamo and this electro-motive force will be reduced to zero when the brushes, in
a two pole dynamo, have been moved round, in the direction of rotation, through an
angle of about ninety degrees so that by simply moving the brushes round it becomes
possible to obtain any desired' electro-motive force from the aforesaid dynamo between
the maximum for which it is constructed and zero. But in dynamos, as hitherto
constructed it would be impracticable to reduce the electro-motive force in this way
because violent sparking would take place at the brushes which would soon destroy
them. One of the causes of sparking is the self induction of the coils of the
armature of the dynamo as the following explanation will show when a dynamo of
any of the before mentioned classes is put to work. Through any coil of the
armature the current passes in a definite direction as the coil travels from one brush
to another which direction becomes reversed suddenly as soon as the leading section
of the commutator belonging to the aforesaid coil has passed the latter brush. This
sudden reversal generates by the self induction of the current a momentary electro-
motive force (hereinafter called the electro-motive force of self induction)
tending to produce a current opposite in direction to the direction of the now

page_text: reversed current and depending in amount on the strength of the current passing
and on the number of turns in the coil. This self induction electro-motive force
tends to prevent the proper current of the machine from arriving at or leaving the
brush as the case may be by passing through the coil in question, which would be its
course if there were no self induction present, and if sufficiently great will cause a
spark indicating that part of the current has sparked across from the above mentioned
leading section of the commutator to the brush instead of passing through the coil.
Any coil of the armature in which the current has just been reversed and in which
there is generated an electro-motive force of self induction I shall hereinafter call
a self induction coil.
The electro-motive force of a dynamo having more than two poles can also be
reduced by moving the brushes round as herein above mentioned with the difference
that it will not be necessary to move them through so great an angle as ninety
degrees to reduce the electro-motive force to zero, the said angle depending upon the
angular distance of the poles from one another. The foregoing remarks concerning
self induction in the coils of the armature apply equally to dynamos having more
than two poles.
In dynamos having many part commutators as hitherto constructed, where the self
induction of the armature coils is considerable as for instance in those dynamos used
for arc lighting, in order to prevent sparking it has been necessary to move the
brushes round the commutator into such a position that a self induction coil shall
actually be passed through the magnetic field existing between the armature core and
the pole piece (hereinafter called the magnetic field) and so having an electro-motive
force generated in it opposite in tendency to the electro-motive force of self induction
and moreover the self induction coil must be passing through a portion of the
magnetic field of such intensity that the amount of this electro-motive force shall be
approximately equal to the amount of the electro-motive force of self-induction so
that the two electro-motive forces shall neutralise one another and consequently will
neither aid nor hinder the passage of the proper current of the machine from
reaching or leaving the brush through the self-induction coil. But in such dynamos
if the brushes were moved from this position violent sparking would take place
because the magnetic field is not of equal intensity throughout its extent and a coil
at the time of reversal of its current would be passing through a portion of the
magnetic field of a greater or less intensity than that necessary to produce an
electro-motive force equal and opposite to the self-induction electro-motive force.
If however a magnetic field could be provided in which the magnetic intensity
throughout its whole extent was equal then altering the position of the brushes
would not cause sparking providing that the intensity of such field was sufficient to
produce an electro-motive force equal to that momentarily set up in a self induction
coil and the electro-motive force of the dynamo could then be altered by moving the
brushes.
According to our invention we make that portion of the magnetic field through
which a self induction coil is passing so that it shall always be of the requisite
intensity to neutralize the electro-motive force of self induction in that coil. This
can be done either
(1). By providing a magnetic field of the requisite intensity and making this
intensity the same over the whole extent of this magnetic field, for which purposo
we remove portions of the sides of the pole pieces which embrace the armature
(hereinafter called the inner. sides of the pole pieces) at places where the intensity of
the magnetic field is greatest, the position of these places varying somewhat with
the form of field magnets and pole pieces employed, or we shape the inner sides of the
pole pieces to such a curve as shall give the desired result, or wrought iron cores
may be employed in the field magnets with cast iron pole picces and allowing the
wrought iron to reach the inner surfaces of the pole picces at places where it is
desired to keep up the intensity of the magnetic field.
(2). By varying the intensity of the magnetic field as a whole, by altering the
exciting power or other suitable means so that no matter where the self induction

page_text: coil is the intensity of the magnetic field in that place is always sufficient to
neutralize the electro motive force of self induction. For instance if the dynamo
electric machine were giving out its maximum electro motive force and we desired
to reduce this electro motive force, we should move the brushes forward but by so
doing we should bring the self induction coil into a part of the magnetic field which
is not of the intensity requisite to neutralize the electro motive force of self induction
and to bring this intensity to the required amount we increase or decrease, as the
case may be, the intensity of the whole field by increasing or decreasing the exciting
power or other suitable means.
(3). By combining the first and second methods. For instance we may make the
magnetic field of as nearly uniform intensity as possible by the first method and
adjust any small differences which may still exist by the second method.
Suitable means are provided for moving the brushes automatically. For example
we may take a solenoid through the coils of which the current generated by the
machine is passed. The core of this solenoid is attached by suitable means to the
arm carrying the brushes so that alterations in the current strength can move
the brushes as desired, or the brushes can be moved by suitable gearing driven from
any source of power, the solenoid being used only to determine in which direction
they shall be moved.
We may also use an electro magnet in place of a solenoid.
In the case in which the second or the third method of regulating the intensity of
the magnetic field, hereinbefore described, is employed we make the solenoid, electro-
magnet, or other regulator vary the strength of the magnetic field as may be required
in addition to moving the brushes.
For the purposes of our invention the armatures of the dynamos should be
constructed and the coils thereon should be so wound as to give considerable self
induction, since it will be obvious that a stronger magnetic field may be employed
where the electro motive force of self induction is greatest.
1
1
ד
1007
G. F. REDFERN,
4, South Street, Finsbury, London,
Agent for the Applicant.

page_text: I, JOHN GRICE STATTER of 49 Finsbury Pavement in the City of London,
Electrical Engineer do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement:-
My invention relates to improvements in or applicable to dynamo-electric machines.
These improvements have for their object the maintenance of a constant current
through a variable resistance or a constant current when the machine is driven at
varying speeds. In attaining such objects these improvements require the position of
the brushes on the commutator to be altered; and they enable such brushes to be
moved round the commutator through a large angular distance, say 90°, without the
production of sparking. I do not herein specify any particular means whereby the
brushes are moved. They can be moved by hand or by any suitable known automatic
device.
In carrying the principles of my invention into effect for the purpose of obtaining
a machine capable of acting as above mentioned, I find it necessary to maintain
constant the product of the magnetic intensity affecting those coils of the armature
which are at any moment passing under the brushes, expressed in any suitable units
such for example as Gramme-Centimetre-Second units, and the length of the
conductor of such coils as is directly acted upon by the field magnets, expressed say in
centimetres. This magnetic intensity must be of a certain value as the following
explanation will show. For the purpose of this explanation I shall assume that I
employ an armature of the drum or ring type, and field magnets such as those shown
in the accompanying drawings, it being understood that the accompanying drawings
show ordinary pole pieces modified according to the present invention as will be
hereinafter described. A coil on the armature, in passing from a position imme-
diately behind to one immediately in front of the brushes, experiences a sudden
reversal of the current which it is carrying. This causes a momentary electromotive
force of self induction to take place in the said coil, which if not neutralised will
cause a current to leap between that plate of the commutator connected to the coil
which has just passed from under a brush and the brush which the plate has just left:
in other words sparking is produced. By so placing the brushes that the magnetic
intensity of the field magnets shall affect this coil to a suitable extent, this electro-
motive force is neutralised by the electro-magnetic induction on this coil. In order
to be able to move the brushes through a large angular distance, say 90° around the
commutator, without producing sparking, it is necessary that the inductive effect of
the field magnets upon that part of the armature, upon which the coils passing under
the brushes are wound, shall be constant throughout such angular distance, and shall be
sufficient to neutralise the electromotive force of self induction hereinbefore referred to.
In constructing my improved machine, say for the production of a high tension
current of 10 ampères at a maximum electromotive force of 2000 volts, 1 employ a
quantity of iron relatively large to the quantity of wire in both the field magnets and
the armature, and having a depth of armature core say three to four times the depth

page_text: of the external winding on the same, and having in the field magnets a mass of iron
preferably wrought iron, considerably in excess of the mass of the iron in the
armature.
Having constructed such a machine with a ring armature in the usual way, that is,
so as to have the pole pieces solid and. concentric with the armature, and with just
sufficient clearance between the pole pieces and the armature, I put it into operation,
and close the circuit through such a resistance as will enable the machine to give out
its normal current; and I set the brushes at the position where no sparking occurs.
I now take an apparatus which I may for convenience term an exploring apparatus,
and which consists of a voltmeter of any convenient type with flexible conductors
attached thereto; which flexible conductors terminate at their other extremities in two
small brushes or plates of metal insulated from one another, and suitably distanced
apart. With this apparatus 1 obtain relative indications of the electromotive force of
the current (which are also relative indications of the resultant magnetic intensity
produced by the mutual action upon each other of the field magnets and the armature)
flowing through the coils whose circuit I complete by means of the exploring
apparatus: and this I do by bringing the brushes of the exploring apparatus (herein-
after for the sake of convenience termed the exploring brushes) in contact with
adjacent segments of the commutator, which, it must be understood, is revolving at
the time, and the machine giving out its normal current. The object of obtaining
such indications is to enable me to alter the shape of the pole pieces in such a way
that when the pole pieces are so altered the product of the magnetic intensity, affecting
those coils of the armature which are at any moment passing under the brushes, into
the length of the conductor of such coils as is directly acted upon by the field magnets,
shall be constant. This alteration I effect by incising or boring the pole pieces, so as
to produce orifices or cavities of certain definite shape and size, such shape and size
being determined in the manner following.
I determine the shape by plotting out the electromotive forces indicated by the
voltmeter of the exploring apparatus. I set out such electromotive forces as ordinates,
and as abscissæ I set out the angular distances corresponding with the positions which the
exploring brushes, at the time of a reading being obtained upon the voltmeter, occupy
upon the commutator. These angular distances are set out from a vertical line
midway between the poles, and are diagramatically represented in Figure 3, where it
will be seen that angular distances, equal to 45°, are marked passing in the direction
of the arrow. It will be noticed that these angular distances are represented as angles
from 0° to 180° on one side of the said vertical line, and repeated as 0° to 180° on the
other side. In this Figure the exploring brushes are shewn in connection with the
voltmeter, and in contact with the commutator segments at an angle of 20° from
the part where the said vertical line cuts the top of the armature, the main brushes,
that is the brushes connected with the external circuit fed by the machine, being one
at this point and the other at the corresponding angular distance from the part where
the vertical line cuts the bottom of the armature and diametrically opposite, these
being the positions which the brushes would naturally occupy in a machine as
ordinarily constructed. In the immediately preceeding sentence I mention that the
exploring brushes are at the same point as the main brushes. This is not strictly
correct, since no reliable readings can be obtained by the exploring apparatus when
the exploring brushes are exactly in line with the main brushes on account of the
continual short circuiting of adjacent sections of the commutator by the main brushes.
I therefore take readings with the exploring brushes immediately behind and imme-
diately before the main brushes; and am able to draw the curve hereinafter described
with sufficient accuracy without having taken a reading exactly under the main
brushes. The electromotive force at this angle is thus obtained, and electromotive
forces are similarly obtained at all parts, the whole of the commutator being explored
for this purpose, and the indications obtained plotted out in curves as shewn in
Figure 1, the main brushes in connection with the external circuit remaining in the
same position during such exploration, and the speed at which the machine is driven,
and the resistance of the said external circuit, being maintained constant. Referring to

page_text: Figure 1 it will be seen that CCCC shews a curve of electromotive forces as
obtained by exploring the whole commutator. It will be seen that the curve when
the main brushes are at an angle of 20° is thus displayed. I then change the position
of the main brushes to 60°, and in the same manner plot out the curve D D D D.
Again, I shift the main brushes to an angle of 90°, and obtain the indications which
enable me to plot out the curve E E E E. Upon the curves as shown in Figure
C (on the curve CCCC represent the positions of the main brushes when they
are at an angle of 20°; the points D1 D2 on the curve D D D D represent the
positions of the main brushes when they are at an angle of 60°; and the points E¹ E²
on the curve E E E E represent the positions of the main brushes when they are at
an angle of 90°. It will be seen that when the main brushes are in the positions
shewn on the curve C C C C there is no sparking. When in the positions shewn on
the curve D D D D it will be seen that there is sparking, the electromotive force in
the coil short circuited by the main brushes being represented by the length of the
ordinate L (this ordinate being obtained as herein described) which electromotive
force represents the excess of the inductive effect as herein before mentioned over the
self-inductive effect in the coil passing under the brushes at the time of observation.
Similarly in the case of the curve E E E E it will be seen that there is sparking at
the brushes, the ordinate K (this ordinate being obtained as herein described) repre-
senting this as described in the last case. In figure 11 have only plotted out three
curves, these being representations of results obtained during explorations with the
brushes in three different positions. In practice, however, instead of making three
explorations I make a considerable number, say ten or twelve, and plot the curves
obtained by this means in the same manner as are those shewn in Figure 1. These
curves I shall call for the purposes of this specification exploration curves.
exploration curves I utilise to obtain a new curve which for convenience I shall
hereinafter refer to as the shaping curve. The shaping curve is obtained as follows.
On the horizontal line (see Figure 1), and at the point corresponding with the angle
at which the main brushes are at the time when the exploration curve CCCC is
obtained, I set up an ordinate cutting the said exploration curve C C C C. On the
horizontal line, and at the point corresponding with the angle at which the main
brushes are when the exploration curve D D D D is obtained, I set up the ordinate L,
cutting the said exploration curve D D D D. On the horizontal line, and at the point
corresponding with the angle at which the main brushes are when the exploration
curve E E E E is obtained, I set up the ordinate K, cutting the said exploration
curve E E E E. These three points C₁ D' and E' I join by a line and so obtain the
shaping curve desired, it being of course understood that to obtain such a shaping
curve as would be desirable in practice instead of having only three curves (the result
of explorations in three positions of the main brushes). I should as before mentioned
plot out a larger number of curves, and so obtain additional points, by the connection
of which I would obtain my desired shaping curve. This shaping curve represents the
excess of the inductive effect as hereinbefore mentioned over the self inductive effect
in the coil passing under the main brushes at different positions of these with respect
to the before mentioned vertical line. This curve also indicates where and to what
extent the magnetic intensity of the field exceeds the definite valve hereinbefore
referred to. I therefore utilise such indications as are shown by the shape of this
curve to guide me in determining the shape of a part of the metal of the pole pieces
to be removed as hereinbefore mentioned.
These
To determine the amount of metal to be removed, or the size of the cavities or
orifices to be made, I have recourse to experiment, as I know of no definite method
approaching accuracy by which I can obtain this information. A rough guide
however exists in the length of the ordinates which represent the excess of the
inductive effect over the self inductive effect as before mentioned.
I shall now proceed to explain how I employ the information yeilded by the shape
of this shaping curve to guide me in altering the form of my pole pieces. For this
purpose I shall first of all refer to one form of modified pole piece, namely that in
which a groove is cut parallel to the armature shaft; and thereafter I shall refer to

page_text: other forms of modified pole pieces which may be constructed according to my
invention.
in
Having obtained the shaping curve as before mentioned, I proceed to cut out
grooves in the pole pieces of a shape resembling that of the shaping curve, and in
a direction parallel to the armature shaft. Such a groove is represented in Fig. 2,
the position of the said groove being indicated by the shape of the curve and corre-
sponding with the angles as shown in Figs. 1 and 3. Having cut out this groove as
aforesaid I replace the armature, and run the machine again, using the exploring
apparatus and again plotting out curves as before. In order not to confuse the
diagrams shown in Fig. 1 by having too many curves, I represent only one exploration
curve obtained after the removal of some of the iron from the pole pieces, and this
exploration curve, which is taken with the main brushes at an angle of 90° with the
vertical line above referred to, is shown in the dotted line F. It will be seen that this
new exploration curve cuts the ordinate K corresponding with the angular position of
the brushes on the horizontal line, and that there is no excess of electromotive force
as before mentioned when the main brushes are in this position, and therefore no
sparking. Such cutting of the ordinates at the horizontal line and consequent absence
of sparking at all positions of the brushes, would show that the shape and size of the
groove is of sufficiently approximate accuracy in order to obtain the desired purpose.
If however it had not been so, it would have been necessary to alter the groove
accordance with this second shaping curve, and then to obtain another shaping curve,
and so alter the groove as to make it correspond therewith, and so on, shaping curves
being obtained, and the grooves altered in accordance therewith, until it were found
that the machine could be run as before mentioned, and curves be taken which should
cut, on the horizontal line, the ordinates corresponding with the positions of the main
brushes at all angular positions. Figs. 2, 3 and 3 a illustrate pole pieces modified in
the manner just described, that is so as to have grooves cut in them in a direction
parallel to the armature shaft, and incised in accordance with the form of the shaping
curve. Having now described one form of modified pole piece, namely that in which
a groove is cut parallel to the armature shaft, I shall proceed to describe some other
forms of modified pole pieces, that is to say, pole pieces modified by the formation of
cavities or orifices differing from the form just described. A large number of such
modifications could be made, and I desire it to be understood that I do not limit
myself to any particular form of cavity or orifice, as the essence of my invention
consists in the modification of the pole pieces by the formation of cavities or orifices
for the purpose either of varying the magnetic intensity, or of varying the length of
conductor acted upon, as previously mentioned, and in accordance with what is shown
to be necessary by the form of the shaping curve. Figs. 4, 5 and 6 illustrate pole
pieces modified in different manners. Fig. 4 illustrates a case closely resembling that
herein before described with reference to Figs. 2, 3 & 3a, the difference being that
instead of the groove being cut across the whole face of the pole piece as shown in
Figs. 2, 3 and 3 a, it is cut in an interrupted manner. In the figure, namely figure 4,
it will be seen that two cavities are cut, but if the metal between and at the sides of
these cavities were cut away it will be seen that cavities of the same form would be
attained as in Figs. 2, 3 and 3a. Fig. 5 shows another modification. In this case
an orifice is bored right through the pole piece in a direction at right angles to the
armature shaft; and the resemblance between this form of orifice, as it would be
shown in cross section, with the shaping curve, or a groove such as is shown in Fig. 2,
will be apparent. At the angular distance with reference to the commutator where
the ordinate is highest (see Fig. 1) or the cavity is deepest (see Fig. 2) the orifice of
Fig. 5 is broadest. It is not necessary that the orifice should be bored the whole way
through as shown in the Figure. It may be merely a cavity of a shape similar to the
orifice shown. Fig. 6 illustrates another form of pole piece modified in accordance
with my invention. It will be seen that this form of modified pole piece differs from
that shown in Fig. 4 chiefly in the fact that the cavities instead of being incised at or
near the central part of the pole pieces are incised at the ends thereof.
It will be noticed that of these Figures, illustrating modified forms of pole pieces,

page_text: Figs. 2, 3 and 3 a are the best illustrations of the case wherein the magnetic intensity,
as previously described, is varied; whereas Fig. 6 illustrates probably in a better
manner than the other Figures the case wherein the length of conductor acted upon
by the field magnets is varied. Figs. 4 & 5 may be taken as being good illustrations
of cases which are as it were a compromise between those illustrated in Figs. 2 and 6
respectively. Such compromise might be introduced still further in making other
forms of modified pole piece: for example a form of pole piece might be made differing
from that shown in Fig. 2 in that the grooves might be shallower towards the centre
than at the ends of the said grooves, or vice versa; and other modifications will readily
suggest themselves.
Inasmuch as it is generally necessary to obtain more than one shaping curve, and
as modifications in the cavity or orifice have to be made in accordance with each
additional shaping curve obtained after the first one, I find it expedient in incising
the metal of the pole pieces for the purpose of obtaining cavities or orifices to incise
the metal to a less extent than the shaping curve would appear to warrant, and so
leave myself a margin of metal to work upon.
I would remark that hitherto I have assumed that the commutator plates are at the
same angular position on the armature as the coils with which they are in connection.
But this is not always the case, for in some armatures the coils, instead of being
connected to commutator plates at the same angular position, are connected to
commutator plates at a different angular position. This is the case with the
well known Edison armature; and when my invention is applied to machines
having such armatures I cut away my pole pieces at the places indicated with respect
to the coils, and not at the places indicated with respect to the commutator plates with
which such coils are connected.
curves.
I have herein before described my invention as applicable to a machine having a
single horse-shoe field magnet and a ring armature. My invention is not however
restricted to such a machine, but is applicable to other types of machine, namely to
any two or four pole machine whose field is capable of suitably acting upon an
armature of the ring or drum type and having many coils (say twelve or more and a
corresponding number of commutator plates) connected up in a single circuit, as is for
example the well known Gramme armature. It is to be understood however that
though my invention is not applicable to machines having many poles, still should the
diameter of the armature be large the number of such poles might be increased say to
six or eight. In the case of such types of machine as I have just indicated I proceed
as hereinbefore described; that is I take readings enabling me to plot out shaping
curves, and afterwards remove the metal as shown to be necessary by such shaping
In order to explain more clearly the application of my invention in the case
of other known types of machine as aforesaid I shall proceed to consider what the
action of single horse-shoe magnets must be upon a ring armature in order that there
may be no sparking at the brushes, whatever may be their position on the commutator.
It will be understood that in a single horse shoe field magnet as usually constructed
the magnetism of the pole pieces at the part nearest the field magnet coils is stronger
than at the part most remote therefrom, therefore as the current is taken off the
armature at different positions with respect to the two pole pieces, in one of them.
nearer the field magnet coils and in the other further away from them (see figure 3),
the shaping curves indicated with respect to the two pole pieces will differ from one
another as will the shape of the part to be cut away from each pole piece. This will
he readily seen by reference to the two shaping curves shown in figure 1, where they
will be seen to differ. In a drum armature as is well known each coil is simultaneously
acted upon by both pole pieces, so that in exploring after the manner hereinbefore
mentioned round one half of the field I would in reality have explored both halves of
the field, and the diagram I would take would only be one half of such an one as is
shown in figure 1. The shaping curve would indicate the resultant effect of both pole
pieces on one coil; and in carrying my invention into effect I might either cut away
one pole piece only or cut away both to such an extent that the sum of the grooves
cut in them would equal the groove cut if on one pole piece only.

page_text: By the employment of pole pieces cut away or incised as hereinbefore specified,
together with a suitable device for altering the position of the brushes, I am able to
maintain a constant current through a variable resistance or a constant current when
the machine is driven at varying speeds.
It is not necessary that separate shaping curves should be obtained for every
individual machine constructed, for one shaping curve will apply to all machines made
to one pattern but any alteration of pattern that would sensibly alter the strength of
the field, such as an alteration in the winding of the field magnets or armature, would
entail the obtaining of a new shaping curve, and the cutting away or incision of the
pole pieces in accordance therewith.
Having thus specified the nature of my invention and the best manner of carrying
it into effect with which I am acquainted, I would add that modifications of a
mechanical nature may be introduced without departing from the essence of my
invention. For example instead of incising a pole piece such as is shewn in figure 5
one might bore a number of small holes through the pole piece, the number of such
being greatest where the orifice is broadest (see figure). Modifications of such a
nature would readily, suggest themselves to an ingenious mind, but they would be mere
self evident variations of the invention hereinbefore set forth.
In practice I find that a convenient form of modified pole piece to employ is that
shewn in figure 4, and that a convenient form of device for altering the position of
the brushes is that referred to in the provisional specification accompanying my appli-
cation for Letters Patent No. 13,320 of the year 1887.
I am aware that before this date pole pieces have been modified in form for various
purposes. For example modified forms, which may be looked upon as pole pieces of
ordinary type cut away or incised, have been described by Houston and Thompson, by
Trouvé, by Wissendanger, by Weston, by Joel, by Lever, and by E. & J. Hopkinson
& J. Platt; but such modified forms of pole piece as they describe differ essentially
from mine, and have different objects in view. I therefore desire it to be understood
that I make no claim whatever to such modified forms of pole piece as they describe ;
but what I do claim is :-
1. The improvement in or applicable to dynamo-electric machines, consisting in the
employment, together with a suitable device for altering the position of the brushes,
of pole pieces cut away or incised substantially as and for the purposes herein set
forth.
2. The improvement in or applicable to dynamo electric machines, consisting in the
combination, with a suitable known device. for altering the position of the brushes, of
a pole piece or pole pieces cut away or incised substantially as and for the purposes
herein set forth.
3. The improvement in or applicable to dynamo-electric machines, consisting in a
pole piece or pole pieces modified substantially as and for the purposes herein set
forth.
4. In dynamo-electric machines, the improvements, substantially as and for the
purposes herein set forth, consisting in the specific forms of modified pole piece shown
respectively in figures 2, 4, 5 and 6 and any combination thereof.
Dated this 22nd day of December 1801.
For the Applicant,
J. G. LORRAIN, M.S.T.E., M. Inst. M.E.,
Consulting Electrician & Patent Agent,
Norfolk House, Norfolk Street,
London, W.C.