Improvements in Electricity Meters, Parts of which Improvements + are Applicable to Dynamo Electric Generators and Motors.
Year: 1887

page_text: This Specification was, upon the 14th day of February 1889, Amended under
Sections 18 to 21 of the Patents, Designs, and Trade Marks Act, 1883.
Improvements in Electricity Meters, Parts of which Improvements
+
are Applicable to Dynamo Electric Generators and Motors.
I GEORGE HOOKHAм of Nos. 7 and 8 New Bartholomew Street Birmingham in the
County of Warwick Manufacturer do hereby declare the nature of this Invention to
be as follows:-
My invention consists of the improvements hereinafter described in electricity
meters parts of the said improvements as hereinafter pointed out being also applicable
to dynamo electric generators and motors.
I will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant or
nearly constant field the armature carrying the current to be metered and an electric
brake consisting of a mass of metal in the form of a disc cylinder or other figure of
rotation rotating in a magnetic field in such a manner as to have "eddy" or so called
"Foucault currents generated in it. When all other work done by the motor is
negligible compared with that done against "eddy" currents the speed of rotation of
its armature is directly proportional to the armature current.
The electro motor may be of any convenient kind or form. It may for instance
have a drum ring or disc armature. Or it may consist of a simple solid disc or
cylinder rotating between magnetic poles. In the latter case however I prefer to use
two thicknesses of metal in the disc or cylinder the one carrying the current to be
measured being insulated from the other except near the centre. And in order to
confine the current to a narrow field the said disc or cylinder may be slit in directions
at right angles to the motion in the field or instead of a disc or cylinder so slit insulated
wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached to
the armature so as to rotate in the same field or it may be independent of the armature
and rotate in a separate field or a separate brake may be used in addition to an
armature brake.
In order that other work done by the motor may be very small compared with the
work done on the electric brake special means to reduce friction are adopted. If the

page_text: axis of the motor armature is horizontal the spindle is supported on friction wheels
and if vertical or nearly vertical on hardened points and in both cases I use mercury
contacts or commutators where practicable.
If the spindle of the motor is horizontal I forin a double commutator consisting of
two sets of insulated spokes or projections placed side by side each set dipping into a
mercury trough the mercury troughs being connected one with each terminal of the
machine. Each commutator spoke is put in connection with the one opposite to it on
the other half of the double commutator so that the mercury troughs though both on
the same side act as ordinary brushes act when placed on opposite sides of the com-
mutator. If the spindle is vertical I take advantage of the high surface tension of
mercury in virtue of which it may be made to stand above the level of the vessel
containing it. The ends of wires or metallic strips from the vertical armature can
thus cut the mercury without touching the vessel.
When I use a motor consisting of a simple solid disc or cylinder I may in order to
economise magnetising force corrugate the disc or cylinder in concentric rings and
form the magnet poles to correspond in a manner analogous to that described in the
provisional specification of the application for patent made by me on the sixth day of
January 1887 No. 187 and thereby not only lessen the resistance of the non magnetic
space but in this case also increase the efficiency of the driving current.
If in any case it is found impracticable to render friction or other disturbing causes
inappreciable I nay "compound-wind" the magnets of the motor or if they are
separate of the electric brake or both.
In cases where iron is used in the armature or the electric brake I may so
dispose the magnets as to counteract gravity and thereby lessen friction or if the
spindle is vertical I form it of iron and place it in the axis of a solenoid having a
similar action.
For alternating currents the magnet cores and if of iron the armature core must
be finely divided into wires or metal strips.
The revolutions of the meter are registered by means of counting apparatus of an
ordinary type.
The double commutator and the corrugation of the disc or cylinder herein before
described are applicable to dynamo electric generators and motors.
Dated this Twentyfirst day of March 1887:
W. T. WHITEMAN,
Agent for the Applicant.
30

page_text: are Applicable to Dynamo Electric Generators and Motors.
I GEORGE HOOKHAM of Nos. 7 and 8 New Bartholomew Street, Birmingham in the
County of Warwick, Manufacturer do hereby declare the nature of my 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 consists of the improvements hereinafter described in electricity
meters, parts of the said improvements, as hereinafter pointed out, being also applicable
to dynamo-electric generators and motors.
I will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant or
nearly constant field, the armature carrying the current to be metered and an electric
brake consisting of a mass of metal in the form of a disc, cylinder or other figure of
rotation, rotating in a magnetic field in such a manner as to have "eddy" or so called
"Foucault" currents generated in it. When all other work done by the motor is
negligible compared with that done against "eddy" currents the speed of rotation of
its armature is directly proportional to the armature current.
The electro motor may be of any of the ordinary forms now in use. It may for
instance have a drum, ring or disc armature. Or it may consist of a simple solid
disc or cylinder rotating between magnetic poles. In the latter case however I may
use two thicknesses of metal in the disc or cylinder, the one carrying the current to
be measured being insulated from the other except near the centre. And in order to
confine the current to a narrow field the said disc or cylinder may be slit in directions
at right angles to the motion in the field; or instead of a disc or cylinder so slit,
insulated wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached to
the armature so as to rotate in the same field, or it may he independent of the
armature and rotate in a separate field; or a separate brake may be used in addition
to an armature brake.
In order that other work done by the motor may be very small compared with the
work done on the electric brake, special means to reduce friction are adopted. If the
axis of the motor armature is horizontal, the spindle is supported on anti friction
wheels and if vertical or nearly vertical on hardened points and in both cases I use
mercury contacts or commutators where practicable.
If the spindle of the motor is horizontal I form a double or divided commutator
consisting of two sets of insulated spokes or projections placed side by side each set
dipping into a mercury trough the mercury troughs being connected one with each
terminal of the machine. Each commutator spoke is put in connection with the one
opposite to it on the other half of the double commutator so that the mercury troughs
though both on the same side act as ordinary brushes act when placed on opposite
sides of the commutator. If the spindle is vertical I take advantage of the high

page_text: surface tension of mercury in virtue of which it may be made to stand above the level
of the vessel containing it. The ends of wires or metallic strips from the vertical
armature can thus cut the mercury without touching the vessel.
When I use a motor consisting of a simple solid disc or cylinder I may in order to
economize magnetising force, corrugate the disc or cylinder in concentric rings and
form the magnet poles to correspond and thereby not only lessen the resistance of the
non-magnetic space but also increase the efficiency of the driving current. If in any
case it is found impracticable to render friction or other disturbing causes inappre-
ciable I may compound-wind" the magnets or armature of the motor or if it is
separate of the electric brake.
In cases where iron is used in the armature or the electric brake, I may so dispose
the magnets as to counteract or partially counteract gravity and thereby lessen friction.
For alternating currents the magnet cores and if of iron the armature core must be
finely divided into wires or metal strips.
The rotations of the axis of the armature of the meter are registered by means of
counting apparatus of an ordinary type.
The double commutator and the corrugation of the disc or cylinder and pole pieces
herein before described are applicable to dynamo electric generators and motors.
Having described the nature of my said invention I will proceed to describe with
reference to the accompanying Drawings the manner in which the same is to be
porformed.
Figure 1 represents in side clevation an electricity meter constructed according to
one form of my invention; Figure 2 represents a plan of the same; Figure 3 is an
end elevation of the same partly in section taken at the commutator end and Figure 4
is an elevation of the opposite end; Figure 5 represents the armature in elevation
and Figure 6 is a diagram illustrating the course of the electrical current as
bereinafter explained.
The armature consists of a series of metallic sectors marked respectively 1 to 16
both inclusive in Figure 5. These sectors make up a circular disc with radial slits by
which slits the said sectors are electrically insulated from one another. These sectors
do not extend to the axis a of the machine as seen in Figure 5. The said sectors are
carried by the circular disc b which is mounted on the axis a and constitutes the
brake of the meter as hereinafter explained. The sectors are connected to the disc or
brake by means of the pins or pegs a made of ivory or wood or other insulating
material. Between the brake band the sectors is a dise of brown paper 7 by which
the said sectors are electrically insulated from the brake be is the magnet between
the pole pieces and y of which the armature and brake rotate. The sectors are
electrically connected with each other in the manner best seen in Figure 5. The
connections are effected by flat wires or bands of copper covered with silk ribbon or
other insulating material and are carefully insulated from one another. The sector
marked 1 is connected to the sector marked 8 by the outer band one end of which
is soldered to the sector 1 and the other end is soldered to the sector S. The inner
end of the sector 8 is electrically connected by the inner band / to the inner end of
the sector 15. By tracing the several outer and inner bands, it will be seen that the
several sectors are connected in the following manner.
The sector 1 is connected to the sector S and the sector 8 to the sector 15. The
sector 15 is connected to the sector 6 and the sector 6 to the sector 13. The sector 13
is connected to the sector 4 and the sector 4 to the sector 11. The sector 11 is con-
nected to the sector 2 and the sector 2 to the sector 9. The sector 9 is connected to
the sector 16 and the sector 16 to the sector 7. The sector 7 is connected to the
sector 14 and the sector 14 to the sector 5. The sector 5 is connected to the sector 12
and the sector 12 to the sector 3. The sector 3 is connected to the sector 10 and the
sector 10 to the sector 1.
Referring to Figure 51 will assume that the sectors 7 to 13 are for the moment
situated between the pole pieces ƒ and g Figure 1; that is, are in a strong magnetic
field. By tracing an electric current entering at the inner or small end of the
sector 14 it will be seen, as indicated by the arrow head, that the said current in part

page_text: passes to the marginal end of the said sector 14 and in part passes to the inner end or
the sector 5.
I will first indicate the path of the current which passes to the marginal part of the
sector 14. The said current passes from the sector 14 to the sector 7 the current in
the said sector 7 travelling inwards that is from the marginal part to the central or
inner part and then by the inner connection of the said sector 7 it passes to the inner
part of the sector 16 where it travels outwards. By the outer connection of the
sector 16 the current passes to the outer or marginal part of the sector 9, in which
sector the current travels inwards. By pursuing this part of the current it will be
found that it travels outwards in the sectors 14, 16, 2 and 4 and that it travels
inwards in the sectors 7, 9, 11 and 13 which latter namely 7, 9, 11 and 13 are in the
magnetic field while the sectors 14, 16, 2 and 4 carrying the outward currents are out
of the magnetic field.
I will now indicate the path of that part of the current entering the sector 14 which
part of the current passes by the inner connection of the sector 14 to the inner end
of the sector 5 in which sector it travels outwards. From the sector 5 the current
passes to the marginal end of the sector 12, in which sector 12 it travels inwards.
By means of the inner connection of the sector 12 the current passes to the inner end
of the sector 3 in which it travels outwards. By further tracing this part of the
current it will be seen that it passes outwards in the sectors 5, 3, 1 and 15 and passes
inwards in the sectors 12, 10, 8 and 6. It will thus be seen that in the sectors 7, 8, 9,
10, 11, 12 and 13 which are all in the magnetic field the currents are all passing in
the same direction namely inwards and that all the currents in the other sectors
excepting sector 6 pass outwards and are outside the magnetic field. The result is
that the sectors 7, 8, 9, 10, 11, 12 and 13 are urged from between the pole pieces f
and g of the electro magnet e communicating a rotary motion to the axis a of the
armature. As the armature rotates the sectors which were in the magnetic field and
were traversed by currents travelling inwards pass in succession out of the magnetic
field when the direction of the currents in them is changed by the commutator as
hereinafter explained and the sectors coming into the magnetic field also have the
direction of their currents changed from outwards to inwards by the action of the
commutator. The normal state of the currents in the sectors is illustrated by
the diagram Figure 6 by which diagram it will be seen that the current in eight of
the sectors is flowing in one direction and that the current in the other eight is
flowing in the opposite direction. The line of commutation is marked A, A and it
will be noted that all the currents on the right of the line will be flowing inwards as
indicated by the arrow heads and all the currents on the left of the line are flowing
outwards. In tho said diagram Figure 6 the path of the current is represented in
part in continuous and in part in dotted lines by which method of indication the path
of the current will be the more readily traced.
The commutator consists of two series of insulated sectors j, k fixed a short distance
apart on the axis a of the armature, the marginal portions of the several sectors
dipping in turn as the axis a rotates into the mercury troughs 1, m respectively.
The series of sectors j, k exactly resemble in their action an ordinary commutator the
highest and lowest sectors respectively carrying the incoming and outgoing current.
But in order to avoid the friction of a brush or spring upon the two opposite sectors
and to effect the transmission of the current through mercury which is practically
frictionless each of the sectors of the series is connected by one of the wires p with
the sector diametrically opposite to it on the series so that the opposite sectors of the
series are respectively connected with the mercury in the two troughs and m.
The wires and s are the conductors by which the electric current to be metered is
conveyed to and from the meter.
If for any reason I desire to make the axis of the meter vertical I may make use of
the high surface tension of mercury to form a nearly frictionless commutator by
means of two cisterns of mercury filled so completely that the surface of the mercury
at a little distance from the side of the vessel stands higher than the edge of the
vessel. In such case the segments of the commutator will revolve horizontally and

page_text: then the commutator need not be divided but may consist of horizontal sectors moving
in one horizontal plane.
The brake consists of a metallic disc preferably of copper fixed on the axis a and
consequently rotating with it. As the said disc b travels between the pole pieces f, y
electric currents (commonly known as "eddy" ог "Foucault" currents) are generated
in the said disc 6 the resistance they cause to the motion of the disc being proportional
to its velocity.
It is of importance to increase as far as possible the magnitude of these eddy
currents. In order to do this I form the pole pieces f and g with grooves in them
radial or nearly radial to the axis of rotation of the armature as shown in Figures 1,
2 and 3. The said grooves increase the retarding action of the brake disc b. They
may be either made in both of the pole pieces and y as shown or only in the pole
piece nearest the brake disc b. Though these grooves are advantageous they are
not essential as both the pole pieces may be without grooves.
The special means I employ for reducing the friction of the axis a on its bearings
to a minimum consists of the arrangement of anti friction wheels and adjuncts
represented in the Drawings. Each of the reduced ends of the axis a bears upon the
summit of the anti friction wheel and the axis of the said wheel bears upon the
summits of the wheels and v¹. The end of the axis a is preserved in position on
the summit of the wheel t, that is, lateral and end motion in the said axis a is
prevented by the conical termination of the said axis a engaging in the V shaped
vertical groove to as illustrated in the detached detail of Figure 1. The axes of the
wheels t are kept in position by a similar arrangement.
The rate of rotation of the axis a and the current passing through the meter are
measured by the transmission of the rotary motion of the said axis a to an ordinary
indicating apparatus. To effect this a worm is made on the axis a which worm is
geared with a worm wheel (not shown in the Drawings) which worm wheel by its
rotation drives a train of toothed wheels the axes of which carry fingers or pointers
which indicate on dials the amount of electric current which has passed through the
meter. I do not confine myself to the use of any particular indicating apparatus.
In order to standardise the meter the strength of the magnetic field may be
modified by varying the resistance of the shunt circuit; or I may in place of or in
addition to varying the resistance of the shunt circuit partially short circuit the
magnetic field by a bar or bars of iron connecting the poles whose section or proximity
to the magnet can be adjusted. This method is applicable to permanent magnets
whose field may be increased at intervals if it falls off by removing one or more of the
iron bars.
In the meter I have described and represented the armature is divided into sectors
in order that the current to be measured may pass several times across the magnetic
field and the sensitiveness of the meter may be thereby proportionately increased. I
wish it however to be understood that I do not limit myself to the use of an armature
divided into sectors as a continuous disc may be employed in which the current
travels only between the axis and periphery. This arrangement although inferior in
sensitiveness to the arrangement described may be conveniently employed when
heavy currents are to be measured.
In the meter described and represented the main current passes through the
armature and the shunt through the field magnet but similar results may be obtained
by reversing this arrangement in which case the use of iron in the armature is
preferable.
In order to enable the meter to measure current the field must be constant or else
the armature must be of constant magnetic power and the current to be measured
must in such latter case pass round the field magnets. To obtain this constancy in
electro magnets they must be saturated and the magnetising force and the dimensions
of the core must be so proportioned as to secure this. The constancy of the field in
which the brake moves (in the case in which it moves in a separate field) may be
secured in an analogous way. In electrical circuits in which the electro-motive force
is practically constant this degree of saturation in Electro-magnets is not essential.

page_text: But 1 prefer to have as field magnets both of the electro motor and of the brake
permanent magnets as they can be made to be very powerful and very constant by the
following means.
In place of electro magnets as described and represented I prefer using for smaller
installations permanent magnets, a number of bar magnets being substituted for the
electro magnet represented in the drawings though I may use magnets of other shape
or configuration but in all cases in which I use permanent magnets whether for the
field of the motor or of the brake the pole pieces should have their surfaces very
large compared with their distance apart as represented in the drawings so as to form
a narrow slit in which the disc armature revolves. When this is done the permanent
magnets are practically constant and this arrangement essential to the constancy of
permanent magnets unless the disc is of iron which is objectionable on other grounds.
The power and constancy of these permanent magnets are increased by magnetising
them when in position which is easily done by wrapping wire round them and passing
a powerful current through the coil so formed. I prefer to make the ratio between
the area of the pole pieces and the distance apart of the said pole pieces at least
seventy times as great as the ratio between the sectional area of the steel maynets
and the length of the said magnets. For example if the length of the steel magnet
bars be si inches and their sectional area four square inches the area of each of the
pole pieces may be sie square inches and their distance apart one eighth of an inch.
Or the area of each of the pole pieces may be three square inches and their distance
apart one sixteenth of an inch. When these proportions are adopted a powerful and
stable field is obtained.
If iron is used in the armature however pure and soft the said iron may be there
is still a constant drag due to the work expended on magnetisation and de-magnetisa-
tion. In such cases this drag may be overcome by compound winding the armature
with a shunt current having separate commutator and brush arrangements. This is
proportioned so as just to balance the magnetic drag and enable the meter to start
with the required (small) current. Or may pass the greater part of the shunt
circuit round the armature and a small part round the magnets which in this case
are wound with the thicker conductor carrying the current to be metered the said
small part of the shunt serving the above mentioned purpose.
I have not thought it necessary to represent an electricity meter in which the
disc or cylinder and magnetic poles are corrugated as I believe this modification will
he understood. It is only necessary to remark that the corrugations in the disc or
cylinder are concentric with the axis of rotation and that the corrugations in the
pole pieces of the magnet or magnets are the counterparts of those in the disc or
cylinder. The said corrugations not only diminish air resistance but the increase in
the length of the conductor cutting the field increases the driving force.
Neither do I think it necessary to represent and describe a dynamo electric generator
or motor having a commutator and corrugations as I believe the application of the
commutator and corrugations to dynamo-electric generators and motors will be
sufficiently understood by the description hereinbefore given of their application to an
electricity meter. Mercury being inadmissable for high speed dynamos I employ the
ordinary brushes but placed side by side one on each part of the divided commutator
the parts of which are connected as described and represented.
Although I have described only that form of electric brake which I prefer to
employ yet I do not limit myself to that form as it may be replaced by any electrical
generating machine having a constant field and working on constant resistance or
stated generally by any arrangement involving the motion of a conductor relatively
to a magnetic field the strength of the field being maintained constant and the current
in the conductor being proportional to the rate of rotation.
The armature itself may be made to act as an efficient brake and the brake disc
dispensed with by making the sectors of thick copper and of considerable breadth as
compared with the teeth or projections of the pole pieces.
Although I prefer generally to use only one pair of poles I may use a second pair
of similar poles symmetrically disposed on the opposite side of the axis.

page_text: Having now particularly described and ascertained the nature of my invention
and the manner in which the same is to be performed I declare that I claim as my
invention of "Improvements in electricity meters, parts of which improvements are
applicable to dynamo-electric generators and motors."
First An electricity meter for measuring currents consisting of an electro motor
with constant field arranged substantially as herein before described and illustrated in
the accompanying drawings, the said electro motor being combined with an Electric
brake also moving in a constant or nearly constant field preferably the same field as
that in which the armature rotates substantially as herein described and illustrated in
the accompanying Drawings.
Secondly-Compensating for magnetic drag or friction or both by compound
winding either the armature or the magnets.
Thirdly In electricity meters the obtaining a constant field either for the brake or
the armature or both by the use of electro magnets of such construction and dimensions
that they become saturated while in use in the circuits of the kind for which they are
designed substantially as herein described.
Fourthly In electricity meters the use for the purpose of procuring a powerful
and constant magnetic field of permanent magnets arranged as described with very
large polar surfaces closely fronting each other so as to form a narrow slit in which
the disc armature revolves, whether the same be magnetized in position or
otherwise and the means described for regulating the same when or if necessary
substantially as herein described and in part illustrated in the accompanying
Drawings.
Fifthly In electricity meters the construction and arrangement of parts forming
a divided commutator making contact by means of mercury placed in insulated vessels
substantially as herein before described and illustrated in the accompanying drawings
and the use of the divided commutator in and in connection with dynamo machines or
electro motors as described.
Sixthly The construction and arrangement of parts forming a commutator making
contact by means of mercury placed in insulated vessels the axis of revolution of the
commutator being vertical substantially as herein described.
Seventhly Making grooves in the pole pieces of the electro magnet or permanent
magnet of an electricity meter for the purpose of increasing the action of the
brake substantially as herein before described and illustrated in the accompanying
drawings.
Eighthly The method hereinbefore described and illustrated in the accompanying
Drawings of combining the disc armature or insulated sectors with the continuous
disc constituting the brake.
Ninthly The arrangement and combination of parts herein before described and
illustrated in the accompanying drawings for diminishing the friction of the rotating
axis of the meter in its bearings.
Tenthly-An electricity meter constructed substantially as herein described and
illustrated in the accompanying Drawings.
Dated this Nineteenth day of December 1887.

page_text: Date of Application, 21st Mar., 1887
Complete Left, 21st Dec., 1887
Complete Accepted, 2nd Mar., 1888
are Applicable to Dynamo Electric Generators and Motors.
I GEORGE HOOKHAM of Nos. 7 and 8 New Bartholomew Street Birmingham in the
County of Warwick Manufacturer do hereby declare the nature of this Invention to
be as follows:-
My invention consists of the improvements hereinafter described in electricity
meters parts of the said improvements as hereinafter pointed out being also applicable
to dynamo electric generators and motors.
I will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant or
nearly constant field the armature carrying the current to be metered and an electric
brake consisting of a mass of metal in the form of a disc cylinder or other figure of
rotation rotating in a magnetic field in such a manner as to have eddy" or so called
Foucault" currents generated in it. When all other work done by the motor is
negligible compared with that done against "eddy" currents the speed of rotation of
its armature is directly proportional to the armature current.
The electro motor may be of any convenient kind or form. It may for instance
have a drum ring or disc armature. Or it may consist of a simple solid dise or
cylinder rotating between magnetic poles. In the latter case however I prefer to use
two thicknesses of metal in the disc or cylinder the one carrying the current to be
measured being insulated from the other except near the centre. And in order to
confine the current to a narrow field the said disc or cylinder may be slit in directions
at right angles to the motion in the field or instead of a disc or cylinder so slit insulated
wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached to
the armature so as to rotate in the same field or it may be independent of the armature
and rotate in a separate field or a separate brake may be used in addition to an
armature brake.
In order that other work done by the motor may be very small compared with the
work done on the electric brake special means to reduce friction are adopted. If the

page_text: axis of the motor armature is horizontal the spindle is supported on friction wheels
and if vertical or nearly vertical on hardened points and in both cases use mercury
contacts or commutators where practicable.
If the spindle of the motor is horizontal I form a double commutator consisting of
two sets of insulated spokes or projections placed side by side each set dipping into a
mercury trough the mercury troughs being connected one with each terminal of the
machine. Each commutator spoke is put in connection with the one opposite to it on
the other half of the double commutator so that the mercury troughs though both on
the same side act as ordinary brushes act when placed on opposite sides of the com-
mutator. If the spindle is vertical I take advantage of the high surface tension of
mercury in virtue of which it may be made to stand above the level of the vessel
containing it. The ends of wires or metallic strips from the vertical armature can
thus cut the mercury without touching the vessel.
When I use a motor consisting of a simple solid disc or cylinder I may in order to
economise magnetising force corrugate the disc or cylinder in concentric rings and
form the magnet poles to correspond in a manner analogous to that described in the
provisional specification of the application for patent made by me on the sixth day of
January 1887 No. 187 and thereby not only lessen the resistance of the non magnetic
space but in this case also increase the efficiency of the driving current.
"
If in any case it is found impracticable to render friction or other disturbing causes
inappreciable I may <
compound-wind the magnets of the motor or if they are
separate of the electric brake or both.
In cases where iron is used in the armature or the electric brake I may so
dispose the magnets as to counteract gravity and thereby lessen friction or if the
spindle is vertical I form it of iron and place it in the axis of a solenoid having a
similar action.
For alternating currents the magnet cores and if of iron the armature core must
be finely divided into wires or metal strips.
The revolutions of the meter are registered by means of counting apparatus of an
ordinary type.
The double commutator and the corrugation of the disc or cylinder herein before
described are applicable to dynamo electric generators and motors.
Dated this Twentyfirst day of March 1887.
W. T. WHITEMAN.
Agent for the Applicant.

page_text: are Applicable to Dynamo-electric Generators and Motors.
I GEORGE HOOKHAM of Nos. 7 and 8 New Bartholomew Street, Birmingham in the
County of Warwick, Manufacturer do hereby declare the nature of my 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 consists of the improvements hereinafter described in electricity
meters, parts of the said improvements, as hereinafter pointed out, being also applicable
to dynamo-electric generators and motors.
I will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant or
nearly constant field, the armature carrying the current to be metered and an electric
brake consisting of a mass of metal in the form of a disc, cylinder or other figure of
rotation, rotating in a magnetic field in such a manner as to have "eddy or so called
"Foucault" currents generated in it. When all other work done by the motor is
negligible compared with that done against "eddy" currents the speed of rotation of
its armature is directly proportional to the armature current.
The electro motor may be of any of the ordinary forms now in use. It may for
instance have a drum, ring or disc armature. Or it may consist of a simple solid
disc or cylinder rotating between magnetic poles. In the latter case however I may
use two thicknesses of metal in the disc or cylinder, the one carrying the current to
And in order to
be measured being insulated from the other except near the centre.
confine the current to a narrow field the said disc or cylinder may be slit in directions
at right angles to the motion in the field; or instead of a disc or cylinder so slit,
insulated wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached to
the armature so as to rotate in the same field, or it may be independent of the
armature and rotate in a separate field; or a separate brake may be used in addition
to an armature brake.
In order that other work done by the motor may be very small compared with the
work done on the electric brake, special means to reduce friction are adopted. If the
axis of the motor armature is horizontal, the spindle is supported on anti friction
wheels and if vertical or nearly vertical on hardened points and in both cases I use
mercury contacts or commutators where practicable.
If the spindle of the motor is horizontal 1 form a double or divided commutator
consisting of two sets of insulated spokes or projections placed side by side each set
dipping into a mercury trough the inercury troughs being connected one with each
terminal of the machine. Each commutator spoke is put in connection with the one
opposite to it on the other half of the double commutator so that the mercury troughs
though both on the same side act as ordinary brushes act when placed on opposito

page_text: sides of the commutator. If the spindle is vertical I take advantage of the high
surface tension of mercury in virtue of which it may be made to stand above the level
of the vessel containing it. The ends of wires or metallic strips from the vertical
armature can thus cut the mercury without touching the vessel.
When I use a motor consisting of a simple solid disc or cylinder I may in order to
economize magnetising force, corrugate the disc or cylinder in concentric rings and
form the magnet poles to correspond and thereby not only lessen the resistance of the
non-magnetic space but also increase the efficiency of the driving current. If in any
case it is found impracticable to render friction or other disturbing causes inappre-
ciable I may compound-wind" the magnets or armature of the motor or if it is
separate of the electric brake.
:
In cases where iron is used in the armature or the electric brake, I may so dispose
the magnets as to counteract or partially counteract gravity and thereby lessen friction.
For alternating currents the magnet cores and if of iron the armature core must be
finely divided into wires or metal strips.
The rotations of the axis of the armature of the meter are registered by means of
counting apparatus of an ordinary type.
The double commutator and the corrugation of the disc or cylinder and pole pieces
herein before described are applicable to dynamo electric generators and motors.
Having described the nature of my said invention I will proceed to describe with
reference to the accompanying Drawings the manner in which the same is to be
performed.
Figure 1 represents in side elevation an electricity meter constructed according to
one form of my invention; Figure 2 represents a plan of the same; Figure 3 is an
end elevation of the same partly in section taken at the commutator end and Figure
is an elevation of the opposite end; Figure 5 represents the armature in elevation
and Figure 6 is a diagram illustrating the course of the electrical current as
hereinafter explained.
The armature consists of a series of metallic sectors marked respectively 1 to 16
both inclusive in Figure 5. These sectors make up a circular disc with radial slits by
which slits the said sectors are electrically insulated from one another. These sectors
do not extend to the axis a of the machine as seen in Figure 5. The said sectors are
carried by the circular disc b which is mounted on the axis a and constitutes the
brake of the meter as hereinafter explained. The sectors are connected to the disc or
brake by means of the pins or pegs c made of ivory or wood or other insulating
material. Between the brake and the sectors is a disc of brown paper d by which
the said sectors are electrically insulated from the brake b;e is the magnet between
the pole pieces and g of which the armature and brake rotate. The sectors are
electrically connected with each other in the manner best seen in Figure 5. The
connections are effected by flat wires or bands of copper covered with silk ribbon or
other insulating material and are carefully insulated from one another. The sector
market is connected to the sector marked 8 by the outer band one end of which
is soldered to the sector 1 and the other end is soldered to the sector S. The inner
end of the sector 8 is electrically connected by the inner band to the inner end of
the sector 15. By tracing the several outer and inner bands, it will be seen that the
several sectors are connected in the following manner.
The sector 1 is connected to the sector S and the sector 8 to the sector 15. The
sector 15 is connected to the sector 6 and the sector 6 to the sector 13. The sector 13
is connected to the sector 4 and the sector 4 to the sector 11. The sector 11 is con-
nected to the sector 2 and the sector 2 to the sector 9. The sector 9 is connected to
the sector 16 and the sector 16 to the sector 7. The sector 7 is connected to the
sector 14 and the sector 14 to the sector 5. The sector 5 is connected to the sector 12
and the sector 12 to the sector 3. The sector 3 is connected to the sector 10 and the
sector 10 to the sector 1.
Referring to Figure 5 I will assume that the sectors 7 to 13 are for the moment
situated between the pole pieces and y Figure 1; that is, are in a strong magnetic
field. By tracing an electric current entering at the inner or small end of the

page_text: sector 14 it will be seen, as indicated by the arrow head, that the said current in part
passes to the marginal end of the said sector 14 and in part passes to the inner end of
the sector 5.
I will first indicate the path of the current which passes to the marginal part of the
sector 14. The said current passes from the sector 14 to the sector 7 the current in
the said sector 7 travelling inwards that is from the marginal part to the central or
inner part and then by the inner connection of the said sector 7 it passes to the inner
part of the sector 16 where it travels outwards. By the outer connection of the
sector 16 the current passes to the outer or marginal part of the sector 9, in which
sector the current travels inwards. By pursuing this part of the current it will be
found that it travels outwards in the sectors 14, 16, 2 and 4 and that it travels
inwards in the sectors 7, 9, 11 and 13 which latter namely 7, 9, 11 and 13 are in the
magnetic field while the sectors 14, 16, 2 and 4 carrying the outward currents are out
of the magnetic field.
I will now indicate the path of that part of the current entering the sector 14 which
part of the current passes by the inner connection of the sector 14 to the inner end
of the sector 5 in which sector it travels outwards. From the sector 5 the current
passes to the marginal end of the sector 12, in which sector 12 it travels inwards.
By means of the inner connection of the sector 12 the current passes to the inner end
of the sector 3 in which it travels outwards. By further tracing this part of the
current it will be seen that it passes outwards in the sectors 5, 3, 1 and 15 and passes
inwards in the sectors 12, 10, 8 and 6. It will thus be seen that in the sectors 7, 8, 9,
10, 11, 12 and 13 which are all in the magnetic field the currents are all passing in
the same direction namely inwards and that all the currents in the other sectors
excepting sector 6 pass outwards and are outside the magnetic field. The result is
that the sectors 7, 8, 9, 10, 11, 12 and 13 are urged from between the pole pieces f
and g of the electro magnet e communicating a rotary motion to the axis a of the
armature. As the armature rotates the sectors which were in the magnetic field and
were traversed by currents travelling inwards pass in succession out of the magnetic
field when the direction of the currents in them is changed by the commutator as
hereinafter explained and the sectors coming into the magnetic field also have the
direction of their currents changed from outwards to inwards by the action of the
commutator. The normal state of the currents in the sectors is illustrated by
the diagram Figure 6 by which diagram it will be seen that the current in eight of
the sectors is flowing in one direction and that the current in the other eight is
flowing in the opposite direction. The line of commutation is marked A, A and it
will be noted that all the currents on the right of the line will be flowing inwards as
indicated by the arrow heads and all the currents on the left of the line are flowing
outwards. In the said diagram Figure 6 the path of the current is represented in
part in continuous and in part in dotted lines by which method of indication the path
of the current will be the more readily traced.
The commutator consists of two series of insulated sectors, & fixed a short distance
apart on the axis a of the armature, the marginal portions of the several sectors
dipping in turn as the axis a rotates into the mercury troughs 1, m respectively.
The series of sectors j, k exactly resemble in their action an ordinary commutator the
highest and lowest sectors respectively carrying the incoming and outgoing current.
But in order to avoid the friction of a brush or spring upon the two opposite sectors
and to effect the transmission of the current through mercury which is practically
frictionless each of the sectors of the series j is connected by one of the wires with
the sector diametrically opposite to it on the series so that the opposite sectors of the
series are respectively connected with the mercury in the two troughs I and m.
The wires and s are the conductors by which the electric current to be metered is
conveyed to and from the meter.
?
If for any reason I desire to make the axis of the meter vertical I may make use of
the high surface tension of mercury to form a nearly frictionless commutator by
means of two cisterns of mercury filled so completely that the surface of the mercury
at a little distance from the side of the vessel stands higher than the edge of the

page_text: vessel. In such case the segments of the commutator will revolve horizontally, and
then the commutator need not be divided but may consist of horizontal sectors moving
in one horizontal plane.
The brake consists of a metallic disc preferably of copper fixed on the axis a and
consequently rotating with it. As the said disc travels between the pole pieces f, g
electric currents (commonly known as "eddy" or "Foucault" currents) are generated
in the said disc b the resistance they cause to the motion of the disc being proportional
to its velocity.
It is of importance to increase as far as possible the magnitude of these eddy
currents. In order to do this I form the pole pieces and g with grooves in them
radial or nearly radial to the axis of rotation of the armature as shewn in Figures 1,
2 and 3. The said grooves increase the retarding action of the brake disc b. They
may be either made in both of the pole pieces and g as shown or only in the pole
piece nearest the brake disc b. Though these grooves are advantageous they are
not essential as both the pole pieces may be without grooves.
The special means I employ for reducing the friction of the axis a on its bearings
to a minimum consists of the arrangement of anti friction wheels and adjuncts
represented in the Drawings. Each of the reduced ends of the axis a bears upon the
summit of the anti friction wheel and the axis of the said wheel bears upon the
summits of the wheels e and o¹. The end of the axis a is preserved in position on
the summit of the wheel t, that is, lateral and end motion in the said axis a is
prevented by the conical termination of the said axis a engaging in the V shaped
vertical groove to as illustrated in the detached detail of Figure 1. The axes of the
wheels are kept in position by a similar arrangement.
The rate of rotation of the axis and the current passing through the motor aro
measured by the transmission of the rotary motion of the said axis a to an ordinary
indicating apparatus. To effect this a worm is made on the axis a which worm is
geared with a worm wheel (not shown in the Drawings) which worm wheel by its
rotation drives a train of toothed wheels the axes of which carry fingers or pointers
which indicate on dials the amount of electric current, which has passed through the
meter. I do not confine myself to the use of any particular indicating apparatus.
In order to standardise the meter the strength of the magnetic field may be
modified by varying the resistance of the shunt circuit; or I may in place of or in
addition to varying the resistance of the shunt circuit partially short circuit the
magnetic field by a bar or bars of iron connecting the poles whose section or proximity
to the magnet can be adjusted. This method is applicable to permanent magnets
whose field may be increased at intervals if it falls off by removing one or more of the
iron bars.
In the meter I have described and represented the armature is divided into sectors
in order that the current to be measured may pass several times across the magnetic
field and the sensitiviness of the meter may be thereby proportionately increased. I
wish it however to be understood that I do not limit myself to the use of an armature
divided into sectors as a continuous disc may be employed in which the current
travels only between the axis and periphery. This arrangement although inferior in
sensitiveness to the arrangement described may be employed when heavy currents are
to be measured.
In the meter described and represented the main current passes through the
armature and the shunt through the field magnet but similar results may be obtained
by reversing this arrangement in which case the use of iron in the armature is
preferable.
In order to enable the meter to measure current the field must be constant or else
the armature must be of constant magnetic power and the current to be measured
must in such latter case pass round the field magnets. To obtain this constancy in
electro magnets they must be saturated and the magnetising force and the dimensions
of the core must be so proportioned as to secure this. The constancy of the field in
which the brake moves (in the case in which it moves in a separate field) may be
secured in an analogous way. But I prefer to have as field magnets both of the

page_text: electro motor and of the brake permanent magnets as they can be made io be very
powerful and very constant by the following means.
In place of electro magnets as described and represented I profer using for smaller
installations permanent magnets, a number of bar magnets being substituted for the
electro magnet represented in the drawings though I may use magnets of other shape
or configuration but in all cases in which I use permanent magnets whether for the
field of the motor or of the brake the pole pieces should have their surfaces very
large compared with their distance apart as represented in the drawings so as to form
a narrow slit in which the disc armature revolves. When this is done the permanent
magnets are practically constant and this arrangement is essential to the constancy of
permanent magnets unless the disc is of iron which is objectionable on other grounds.
The power and constancy of these permanent magnets are increased by magnetising
them when in position which is easily done by wrapping wire round them and passing
a powerful current through the coil so formed.
If iron is used in the armature however pure and soft the said iron may be there
is still a constant drag due to the work expended on magnetisation and de-magnetisa-
tion. In such cases this drag may be overcome by compound winding the armature
with a shunt current having separate commutator and brush arrangements. This is
proportioned so as just to balance the magnetic drag and enable the meter to start
with the required (small) current. Or may pass the greater part of the shunt
circuit round the armature and a small part round the magnets which in this case
are wound with the thicker conductor carrying the current to be metered the said
small part of the shunt serving the above mentioned purpose.
I have not thought it necessary to represent an electricity meter in which the
dise or cylinder and magnetic poles are corrugated as I believe this modification will
be understood. It is only necessary to remark that the corrugations in the disc or
cylinder are concentric with the axis of rotation and that the corrugations in the
pole pieces of the magnet or magnets are the counterparts of those in the disc or
cylinder. The said corrugations not only diminish air resistance but the increase in
the length of the conductor cutting the field increases the driving force.
Neither do I think it necessary to represent and describe a dynamo electric generator
or motor having a commutator and corrugations as I believe the application of the
commutator and corrugations to dynamo-electric generators and motors will be
sufficiently understood by the description herein before given of their application to an
electricity meter. Mercury being inadmissible for high speed dynamos I employ the
ordinary brushes but placed side by side one on each part of the divided commutator
the parts of which are connected as described and represented.
Although I have described only that form of electric brake which I prefer to
employ yet I do not limit myself to that form as it may be replaced by any electrical
generating machine having a constant field and working on constant resistance or
stated generally by any arrangement involving the notion of a conductor relatively
to a magnetic field the strength of the field being maintained constant and the current
in the conductor being proportional to the rate of rotation.
The armature itself may be made to act as an efficient brake and the brake disc
dispensed with by making the sectors of thick copper and of considerable breadth as
compared with the teeth or projections of the pole pieces.
Although I prefer generally to use only one pair of poles I may use a second pair
of similar poles symmetrically disposed on the opposite side of the axis.
Having now particularly described and ascertained the nature of my invention
and the manner in which the same is to be performed I declare that I claim as my
invention of "Improvements in electricity meters, parts of which improvements are
applicable to dynamo-electric generators and motors."
First An electricity meter for measuring currents consisting of an electro motor
with constant field arranged substantially as hereinbefore described and illustrated in
the accompanying drawings, the said electro motor being combined with an Electric
brake also moving in a constant field preferably the same field as that in which the

page_text: armature rotates substantially as herein described and illustrated in the accompanying
Drawings.
Secondly Compensating for magnetic drag or friction or both by compound
winding either the armature or the magnets.
Thirdly In electricity meters the obtaining a constant field either for the brake or
the armature or both by the use of electro magnets of such construction and dimensions
that they become saturated while in use in the circuits of the kind for which they are
designed substantially as herein described.
Fourthly In electricity meters the use for the purpose of procuring a constant
magnetic field of permanent magnets arranged as described with very large polar
surfaces closely fronting each other, whether the same be magnetized in position or
otherwise and the means described for regulating the same when or if necessary
substantially as herein described and in part illustrated in the accompanying
Drawings.
Fifthly In electricity meters the construction and arrangement of parts forming
a divided commutator making contact by means of mercury placed in insulated vessels
substantially as herein before described and illustrated in the accompanying drawings
and the use of the divided commutator in and in connection with dynamo machines or
electro motors as described.
Sixthly The construction and arrangement of parts forming a commutator making
contact by means of mercury placed in insulated vessels the axis of revolution of the
commutator being vertical substantially as herein described.
Seventhly Making grooves in the pole pieces of the electro magnet or permanent
magnet of an electricity meter for the purpose of increasing the action of the
brake substantially as hereinbefore described and illustrated in the accompanying
drawings.
Eighthly The method hereinbefore described and illustrated in the accompanying
Drawings of combining the disc armature or insulated sectors with the continuous
disc constituting the brake.
Ninthly The arrangement and combination of parts hereinbefore described and
illustrated in the accompanying drawings for diminishing the friction of the rotating
axis of the meter in its bearings.
Tenthly An electricity meter constructed substantially as herein described and
illustrated in the accompanying Drawings.
Dated this Nineteenth day of December 1887.

page_text: The decision of the Chief Examiner, acting on behalf of the Comptroller, of the
14th day of August. 1895, allowed, under Section 18 of the Patents, &c.
Act; 1883, a further Amendment of this Specification.
Date of Application, 21st Mar., 1887
Complete Specification Left, 21st Dec., 1887-Accepted, 2nd Mar., 1888
PROVISIONAL SPECIFICATION.
Improvements in Electricity Meters, Parts of which Improvements
are applicable to Dynamo Electric Generators and Motors.
1 GEORGE HOOKHAM of Nos. 7 and 8 New Bartholomew Street Birmingham in
the County of Warwick Manufacturer do hereby declare the nature of this
invention to be as follows:
My invention consists of the improvements hereinafter described in electricity
meters parts of the said improvements as hereinafter pointed out being also
applicable to dynamo electric generators and motors.
I will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant
or nearly constant field the armature carrying the current to be metered and an
electric brake consisting of a mass of metal in the form of a disc cylinder or
other figure of rotation rotating in a magnetic field in such a manner as to have
eddy." or so called Foucault currents generated in it. When all other work
done by the motor is negligible compared with that done against eddy
"
"
"
"
currents
the speed of rotation of its armature is directly proportional to the armature
current.
The electro motor may be of any convenient kind or form. It may for
instance have a drum ring or disc armature. Or it may consist of a simple solid
disc or cylinder rotating between magnetic poles. In the latter case however I
prefer to use two thicknesses of metal in the disc or cylinder the one carrying
the current to be measured being insulated from the other except near the centre.
And in order to confine the current to a narrow field the said disc or cylinder
may be slit in directions at right angles to the motion in the field or instead of
a dise or cylinder so slit insulated wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached
to the armature so as to rotate in the same field or it may be independent of
the armature and rotate in a separate field or a separate brake may be used in
addition to an armature brake.
In order that other work done by the motor may be very small compared with
the work done on the electric brake special means to reduce friction are adopted

page_text: If the axis of the motor armature is horizontal the spindle is supported on friction
wheels and if vertical or nearly vertical on hardened points and in both cases I
use mercury contacts or commutators where practicable.
If the spindle of the motor is horizontal I forin a double commutator consisting
of two sets of insulated spokes or projections placed side by side each set dipping
into a mercury trough the mercury troughs being connected one with each ter-
minal of the machine. Each commutator spoke is put in connection with the
one opposite to it on the other half of the double commutator so that the mercury
roughs though both on the same side act as ordinary brushes act when placed
on opposite sides of the commutator. If the spindle is vertical I take advantage
of the high surface tension of mercury in virtue of which it may be made to stand
above the level of the vessel containing it. The ends of wires or metallic strips
from the vertical armature can thus cut the mercury without touching the vessel.
When I use a motor consisting of a simple solid dise or cylinder I may in
order to economise magnetising force corrugate the disc or cylinder in concen-
trie rings and form the magnet poles to correspond in a manner analogous to
that described in the provisional specification of the application for patent made
by me on the sixth day of January 1887 No. 187 and thereby not only lessen
the resistance of the non magnetic space but in this case also increase the
efficiency of the driving current.
If in any case it is found impracticable to render friction or other disturbing
causes inappreciable I may compound-wind" the magnets of the motor or if
they are separate of the electric brake or both.
In cases where iron is used in the armature or the electric brake I may so
dispose the magnets as to counteract gravity and thereby lessen friction or if
the spindle is vertical I form it of iron and place it in the axis of a solenoid
having a similar action.
For alternating currents the magnet cores and if of iron the armature core
must be finely divided into wires or metal strips.
The revolutions of the meter are registered by means of counting apparatus
of an ordinary type.
The double commutator and the corrugation of the disc or cylinder herein
before described are applicable to dynamo electric generators and motors.
Dated this Twentyfirst day of March 1887.
W. T. WHITEMAN,
Agent for the Applicant.

page_text: The decision of the Chief Examiner, acting on behalf of the Comptroller, of the
14th day of August 1895, allowed, under Section 18 of the Patents, &c.
Act, 1883, a further Amendment of this Specification.
Improvements in Electricity Meters, Parts of which Improvements
are applicable to Dynamo Electric Generators and Motors.
1. GEORGE HOOKHAM of No. 7 and 8 New Bartholomew Street, Birminghaun in the
County of Warwick, Manufacturer do hereby declare the nature of my 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 consists of the improvements hereinafter described in electricity
meters, parts of the said improvements, as hereinafter pointed out, being also applicable
to dynamo-electric generators and motors.
1 will describe my invention as applied to an electricity meter.
My said electricity meter consists essentially of an electro motor with constant or
nearly constant field, the armature carrying the current to be metered and an electric
brake consisting of a mass of metal in the form of a disc, cylinder or other figure of
rotation, rotating in a magnetic field in such a manner as to have "eddy" or so called
Foucault" currents generated in it. When all other work done by the motor is
negligible compared with that done against "eddy" currents the speed of rotation of
its armature is directly proportional to the armature current.
It may for
The electro motor may be of any of the ordinary forms now in use.
Or it may consist of a simple solid
instance have a drum, ring or disc armature.
disc or cylinder rotating between magnetic poles. In the latter case however I may
use two thicknesses of metal in the disc or cylinder, the one carrying the current to
And in order to
be measured being insulated from the other except near the centre.
confine the current to a narrow field the said disc or cylinder may be slit in directions
at right angles to the motion in the field; or instead of a dise or cylinder so slit,
insulated wires or metal strips may be used.
The electric brake may be formed by the armature itself or it may be attached to
the armature so as to rotate in the same field, or it may be independent of the
armature and rotate in a separate field; or a separate brake may be used in addition
to an armature brake.
In order that other work done by the motor may be very small compared with the
work done on the electric brake, special means to reduce friction are adopted. If the
axis of the motor armature is horizontal, the spindle is supported on anti friction
wheels and if vertical or nearly vertical on hardened points and in both cases I use
mercury contacts or commutators where practicable.
If the spindle of the motor is horizontal I form a double or divided commutator
consisting of two sets of insulated spokes or projections placed side by side each set
dipping into a mercury trough the mercury troughs being connected one with each

page_text: terminal of the machine. Each commutator spoke is put in connection with the one
opposite to it on the other half of the double commutator so that the mercury troughs
though both on the same side act as ordinary brushes act when placed on opposite
sides of the commutator. If the spindle is vertical I take advantage of the high
surface tension of mercury in virtue of which it may be made to stand above the level
of the vessel containing it. The ends of wires or metallic strips from the vertical
armature can thus cut the inercury without touching the vessel.
When I use a motor consisting of a simple solid disc or cylinder I may in order to
economize magnetizing force, corrugate the disc or cylinder in concentric rings and
fortn the magnet poles to correspond and thereby not only lessen the resistance of the
non-magnetic space but also increase the efficiency of the driving current.
If in any
case it is found impracticable to render friction or other disturbing causes inappre-
ciable may "compound-wind" the magnets or arinature of the motor or if it is
separate of the electric brake.
In cases where iron is used in the armature or the electric brake, I may so dispose
the magnets as to counteract or partially counteract gravity and thereby lessen friction.
For alternating currents the magnet cores and if of iron the armature core must be
finely divided into wires or metal strips.
The rotations of the axis of the armature of the meter are registered by means of
counting apparatus of an ordinary type.
The double commutator and the corrugation of the disc or cylinder and pole pieces
herein before described are applicable to dynamo electric generators and motors.
Having described the nature of any said invention I will proceed to describe with
reference to the accompanying Drawings the manner in which the same is to be
performed.
1
Figure represents in side elevation an electricity meter constructed according to
one form of my invention; Figure 2 represents a plan of the same; Figure 3 is an
end elevation of the same partly in section taken at the commutator end and Figure 4
is an elevation of the opposite end; Figure 5 represents the armature in elevation
and Figure 6 is a diagram illustrating the course of the electrical current as
hereinafter explained.
The armature consists of a series of metallic sectors marked respectively 1 to 16
both inclusive in Figure 5. These sectors make up a circular disc with radial slits by
which slits the said sectors are electrically insulated from one another. These sectors
do not extend to the axis a of the machine as seen in Figure 5. The said sectors are
carried by the circular disc b which is mounted on the axis a and constitutes the
brake of the meter as hereinafter explained. The sectors are connected to the disc or
brake by means of the pins or pegs a made of ivory or wood or other insulating
material. Between the brake and the sectors is a disc of brown paper by which
the said sectors are electrically insulated from the brake b; e is the magnet between
the pole pieces and g of which the armature and brake rotate. The sectors are
electrically connected with each other in the manner best seen in Figure 5. The
connections are effected by flat wires or bands of copper covered with silk ribbon or
other insulating material and are carefully insulated from one another. The sector
marked 1 is connected to the sector marked 8 by the outer band one end of which
is soldered to the sector 1 and the other end is soldered to the sector 8. The inner
end of the sector & is electrically connected by the inner band h² to the inner end of
the sector 15. By tracing the several outer and inner bands, it will be seen that the
several sectors are connected in the following manner.
The sector is connected to the sector 8 and the sector 8 to the sector 15. The
sector 15 is connected to the sector 6 and the sector G to the sector 13. The sector 13
is connected to the sector 4 and the sector 4 to the sector 11. The sector 11 is con-
nected to the sector 2 and the sector 2 to the sector 9. The sector 9 is connected to
the sector 16 and the sector 16 to the sector 7. The sector 7 is connected to the
sector 14 and the sector 14 to the sector 5. The sector is connected to the sector 12
and the sector 12 to the sector 3. The sector 3 is connected to the sector 10 and the
sector 10 to the sector 1.

page_text: 5
Referring to Figure 5 I will assume that the sectors 7 to 13 are for the moment
situated between the pole pieces f and y Figure 1; that is, are in a strong magnetic
field. By tracing an electric current entering at the inner or small end of the
sector 14 it will be seen, as indicated by the arrow head, that the said current in part
passes to the marginal end of the said sector 14 and in part passes to the inner end of
the sector 5.
I will first indicate the path of the current which passes to the marginal part of the
sector 14. The said current passes from the sector 14 to the sector 7 the current in
the said sector 7 travelling inwards that is from the marginal part to the central or
inner part and then by the inner connection of the said sector 7 it passes to the inner
part of the sector 16 where it travels outwwards. By the outer connection of the
sector 16 the current passes to the onter or marginal part of the sector 9, in which
sector the current travels inwards. By pursuing this part of the current it will be
found that it travels outwards in the sectors 14, 16, 2 and 4 and that it travels
inwards in the sectors 7, 9, 11 and 13 which latter namely 7, 9, 11 and 13 are, in the
magnetic field while the sectors 14, 16, 2 and 4 carrying the outward currents are out
of the magnetic field.
I will now indicate the path of that part of the current entering the sector 14 which
part of the current passes by the inner connection of the sector 14 to the inner end
From the sector 5 the current
of the sector 5 in which sector it travels outwards.
passes to the marginal end of the sector 12, in which sector 12 it travels inwards.
By means of the inner connection of the sector 12 the current passes to the inner end
of the sector 3 in which it travels outwards. By further tracing this part of the
current it will be seen that it passes outwards in the sectors 5, 3, 1 and 15 and passes
inwards in the sectors 12, 10, 8 and 6. It will thus be seen that in the sectors 7, 8, 9,
10, 11, 12 and 13 which are all in the magnetic field the currents are all passing in
the same direction namely inwards and that all the currents in the other sectors
excepting sector 6 pass outwards and are outside the magnetic field. The result is
that the sectors 7, 8, 9, 10, 11, 12 and 13 are urged from between the pole pieces
and g of the electro inagnet e communicating a rotary motion to the axis of the
arinature. As the armature rotates the sectors which were in the magnetic field and
were traversed by currents travelling inwards pass in succession out of the magnetic
field when the direction of the currents in them is changed by the commutator as
hereinafter explained and the sectors coming into the magnetic field also have the
direction of their currents changed from outwards to inwards by the action of the
commutator. The normal state of the currents in the sectors is illustrated by
the diagram Figure 6 by which diagram it will be seen that the current in eight of
the sectors is flowing in one direction and that the current in the other eight is
flowing in the opposite direction. The line of commutation is marked A, A and it
will be noted that all the currents on the right of the line will be flowing inwards as
indicated by the arrow heads and all the currents on the left of the line are flowing
outwards. In the said diagram Figure 6 the path of the current is represented in
part in continuous and in part in dotted lines by which method of indication the path
of the current will be the more readily traced.
The commutator consists of two series of insulated sectors, j, fixed a short distance
apart on the axis of the armature, the marginal portions of the several sectors
dipping in turn as the axis a rotates into the mercury troughs l, m respectively.
The series of sectors j, exactly resemble in their action an ordinary commutator the
highest and lowest sectors respectively carrying the incoming and outgoing current.
0 But in order to avoid the friction of a brush or spring upon the two opposite sectors
and to effect the transmission of the current through mercury which is practically
frictionless each of the sectors of the series j is connected by one of the wires p with
the sector diametrically opposite to it on the series so that the opposite sectors of the
series are respectively connected with the inercury in the two troughs / and m.
5 The wires rands and the conductors by which the electric current to be metered is
conveyed to and from the meter.
If for any reason I desire to make the axis of the meter vertical I may make use of

page_text: the high surface tension of mercury to form a nearly frictionless commutator by
means of two cisterns of mercury filled so completely that the surface of the mercury
at a little distance from the side of the vessel stands higher than the edge of the
vessel. In such case the segments of the commutator will revolve horizontally and
then the commutator need not be divided but may consist of horizontal sectors moving
in one horizontal plane.
The brake consists of a metallic disc, preferably of copper fixed on the axis a and
consequently rotating with it. As the said disc travels between the pole pieces J, y
electric currents (commonly known as "eddy" or "Foucault" currents) are generated
in the said disc b the resistance they cause to the motion of the disc being proportional
to its velocity.
It is of importance to increase as far as possible the magnitude of these eddy
currents. In order to do this form the pole pieces and with grooves in them
radial or nearly radial to the axis of rotation of the armature as shewn in Figures 1,
2 and 3. The said grooves increase the retarding action of the brake disc b. They
may he either made in both of the pole pieces and gas shown or only in the pole
piece f nearest the brake disc b. Though these grooves are advantageous they are
not essential as both the pole pieces may be without grooves.
The special means I employ for reducing the friction of the axis a on its bearings
to a minimum consists of the arrangement of anti friction wheels and adjuncts
represented in the Drawings. Each of the reduced ends of the axis hears upon the
summit of the anti friction wheel and the axis of the said wheel bears upon the
summits of the wheels and e¹. The end of the axis a is preserved in position on
the summit of the wheel t, that is, lateral and end motion in the said axis
prevented by the conical termination of the said axis a engaging in the V shaped :
vertical groove w as illustrated in the detached detail of Figure 1. The axes of the
wheels are kept in position by a similar arrangement.
is
The rate of rotation of the axis a and the current passing through the meter are
measured by the transinission of the rotary motion of the said axis a to an ordinary
indicating apparatus. To effect this a worm r is made on the axis a which worm is
geared with a worm wheel (not shown in the Drawings) which worm wheel by its
rotation drives a train of toothed wheels the axis of which carry fingers or pointers
which indicate on dials the amount of electric current which has passed through the
meter. I do not confine myself to the use of any particular indicating apparatus.
In order to standardise the ineter the strength of the magnetic field may be
modified by varying the resistance of the shunt circuit; or I may in place of or in
addition to varying the resistance of the shunt circuit partially short circuit the
magnetic field by a bar or bars of iron connecting the poles whose section or proximity
to the magnet can be adjusted. This method is applicable to permanent magnets
whose field may be increased at intervals if it falls off by removing one or more of the.
iron bars.
T
In the meter I have described and represented the armature is divided into sectors
in order that the current to be measured may pass several times across the magnetic
field and the sensitiveness of the meter may be thereby proportionately increased.
wish it however to be understood that I do not limit myself to the use of an armature
divided into sectors as a continuous disc may be employed in which the current
travels only between the axis and periphery. This arrangement although inferior in
sensitiveness to the arrangement described may be conveniently employed when
heavy currents are to be measured,
In the meter described and represented the main current passes through the
armature and the shunt through the field magnet but similar results may be obtained
by reversing this arrangement in which case the use of iron in the armature is
preferable.
In order to enable the meter to measure current the field must be constant or else
the armature must be of constant magnetic power and the current to be measured
must in such latter case pass round the field magnets. To obtain this constancy in
electro magnets they must be saturated and the magnetising force and the dimensions

page_text: of the core must be so proportioned as to secure this. The constancy of the field in
which the brake moves (in the case in which it moves in a separate field) may be
secured in an analogous way.
In electrical circuits in which the electro-motive force
is practically constant this degree of saturation in Electro-magnets is not essential.
But I prefer to have as field magnets both of the electro motor and of the brake
permanent magnets as they can be made to be very powerful and very constant by the
following means.
In place of electro magnets as described and represented I prefer using for smaller
installations permanent magnets, a number of bar magnets being substituted for the
electro magnet represented in the drawings though I may use magnets of other shape
or configuration but in all cases in which I use permanent magnets whether for the
field of the motor or of the brake the pole pieces should have their surfaces very
large compared with their distance apart as represented in the drawings so as to form
a narrow slit in which the disc armature revolves. When this is done the permanent
magnets are practically constant and this arrangement is essential to the constancy of
perinanent magnets unless the disc is of irou which is objectionable on other grounds.
The power and constancy of these permanent magnets are increased by magnetising
them when in position which is easily done by wrapping wire round them and passing
a powerful current through the coil so formed. I prefer to make the ratio between
the area of the pole pieces and the distance apart of the said pole pieces at least
seventy times as great as the ratio between the sectional area of the steel magnets
and the length of the said magnets. For example if the length of the steel magnet
bars be six inches and their sectional area four square inches the area of each of the
pole pieces may be six square inches and their distance apart one eighth of an inch.
Or the area of each of the pole pieces may be three square inches and their distance
apart one sixteenth of an inch. When these proportions are adopted a powerful and
stable field is obtained.
If iron is used in the armature however pure and soft the said iron may be there
is still a constant drag due to the work expended on magnetisation and de-magnetisn-
tion. In such cases this drag may be overcome by compound winding the armature
with a shunt current having separate commutator and brush arrangements. This is
proportioned so as just to balance the magnetic drag and enable the meter to start
with the required (small) current. Or 1 may pass the greater part of the shunt
circuit round the armature and a small part round the magnets which in this case
are wound with the thicker conductor carrying the current to be inetered the said
small part of the shunt serving the above mentioned purpose.
I have not thought it necessary to represent an electricity meter in which the
disc or cylinder and magnetic poles are corrugated as I believe this modification will
be understood. It is only necessary to reinark that the corrugations in the disc or
cylinder are concentric with the axis of rotation and that the corrugations in the
pole pieces of the magnet or magnets are the counterparts of those in the disc or
cylinder. The said corrugations not only diminish air resistance but the increase in
the length of the conductor cutting the field increases the driving force.
Neither do I think it necessary to represent and describe a dynamo electric generator
or motor having a commutator and corrugations as I believe the application of the
commutator and corrugations to dynamo-electric generators and motors will be
sufficiently understood by the description herein before given of their application to an
electricity meter. Mercury heing inadmissible for high speed dynamos I employ the
ordinary brushes but placed side by side one on each part of the divided commutator
the parts of which are connected as described and represented.
Although I have described only that form of electric brake which I prefer to
employ yet I do not limit myself to that form as it may be replaced by any electrical
generating machine having a constant field and working on constant resistance or
stated generally by any arrangement involving the motion of a conductor relatively
to a magnetic field the strength of the field being maintained constant and the current
in the conductor being proportional to the rate of rotation.
The armature itself may be made to act as an efficient brake and the brake disc

page_text: dispensed with by making the sectors of thick copper and of considerable breadth as
compared with the teeth or projections of the pole pieces.
Although I prefer generally to use only one pair of poles I may use a second pair
of similar poles symmetrically disposed on the opposite side of the axis.
Having now particularly described and ascertained the nature of my invention
and the manner in which the same is to be performed I declare that I claim as
my invention of "Improvements in electricity meters, part of which improvements are
applicable to dynamo-electric generators and motors."
First An electricity meter for measuring currents consisting of an electro motor
with constant field arranged substantially as herein before described and illustrated in
the accompanying drawings, the said electro motor being combined with an Electric
bake also moving in a constant or nearly constant field preferably the same field as
that in which the armature rotates substantially as herein described and illustrated in
the accompanying Drawings.
Secondly Compensating for magnetic-drag-or-friction-or--both-by-compound
winding either-the-armature-of-the-magrets.
Thirdly Secondly-In electricity meters the obtaining a constant field either for
the brake or the armature or both by the use of electro magnets of such construction
mud dimensions that they become saturated while in use in the circuits of the kind
for which they are designed substantially as herein described.
Fourthly Thirdly-In electricity meters the use for the purpose of procuring a
powerful and constant magnetic field of permanent magnets arranged as described
with very large polar surfaces closely fronting each other so as to form a narrow
slit in which the disc armature revolves whether the same be magnetized in
position or otherwise and the means described for regulating the same when or if
necessary substantially as herein described and in part illustrated in the accompanying
Drawings.
Fifthly Fourthly-In electricity meters the construction and arrangement of
parts forming a divided commutator making contact by means of mercury placed
in insulated vessels substantially as herein before described and illustrated in the
accompanying drawings and the use of the divided commutator in and in connection.
with dynamo machines or electro motors as described.
Sixthly Fifthly-The construction and arrangement of parts forming a com-
mutator making contact by means of mercury placed in insulated vessels the axis
of revolution of the commutator being vertical substantially as herein described.
Seventhly Sixthly-Making grooves in the pole pieces of the electro magnet or
permanent magnet of an electricity meter for the purpose of increasing the action
of the brake substantially as herein before described and illustrated in the accompanying
drawings.
Eighty Seventhly-The method hereinbefore described and illustrated in the
accompanying Drawings of combining the disc armature or insulated sectors with
the continuous disc constituting the brake.
Ninthly Eighthly-The arrangement and combination of parts hereinbefore
described and illustrated in the accompanying drawings for diminishing the friction
of the rotating axis of the meter in its bearings.
Tenthly Ninthly-An electricity meter constructed substantially as herein described
and illustrated in the accompanying Drawings.
Dated this Nineteenth day of December 1887.
GEORGE HOOKHAM.