Improvements in Electric Meters.
Year: 1889

page_text: Date of Application, 27th Apr., 1889
Complete Specification Left, 27th Jan., 1890-Accepted, 8th Mar., 1890
PROVISIONAL SPECIFICATION.
Improvements in Electric Meters.
I, ROBERT SNOWDON of the Staveley Iron Works, Chesterfield in the County of
Derby, Engineer, do hereby declare the nature of this invention to be as
follows:-
This Invention relates to that type of electric meters known as "motor meters,”
and these Improvements consists in the construction of the meter in such a manner
that the motion of the motor is retarded or resisted by a viscous fluid resistance, and
so also that the current or currents passing through the armature of the meter is or
are exclusively the current or parts of the current to be measured, as and for the
purposes hereinafter described.
The meter as arranged for measuring continuous currents may have permanent
field magnets or electro-magnets energised by the current. The opposition of the fluid
viscous resistance will cause the rate of revolution to be proportional to the current
in the armature, and the instrument will be an ammeter or ampere hour meter.
If the field coil or coils are included in a shunt between the leads, or from one
of the leads to earth, the other conditions remaining the same, the torque will vary
as the product of the armature current into the field current, and the instrument will
be a Watt or Erg meter. The shunt coil in this case is connected to the leads on the
side of the apparatus further from the source of current so that the whole of the
current deviated through the shunt shall pass through the meter. This form of
the apparatus may be employed to measure alternating, intermittent or pulsating
currents if the iron in the field is laminated or omitted.
The viscous resistance may be obtained by the movement of suitable devices
operated by the motor in a highly viscous liquid such as oils, glycerine, molasses, and
gum or resin solutions, but a similar and suitable resistance may be obtained from
ordinary non-viscous fluids such as water by constructing the part or device moving
therein of wire or filaments and causing them to nove in contiguity with stationary
surfaces. In any case the object of the viscous resistance is to keep the rate of
rotation of the moving part of the motor as low as convenient. Variations in the
viscosity of the liquid employed may be compensated by a corresponding regulation
of the depth of immersion of the part moving in the fluid or by an alteration of its
position relatively to the fixed surfaces within the fluid. This regulation or move-
ment of the moving part within the fluid may be effected by means of a metallic
This automatic controlling
thermometer, by an air thermometer, or by like means.
or regulating device may advantageously be immersed in the fluid so as to acquire its
temperature.
When a fluid such as mercury, which is not ordinarily regarded as viscous, is
employed, the friction opposed to the moving part therein will vary in proportions
between the first and the second powers of the speed except when the motion is very
slow, (not as the second power of the speed). When the motion is very slow, and
when also the moving part is filamentous or constructed of wire, the friction will vary
almost exactly as the first power of the speed. The total fluid friction may be
regarded as consisting of a viscous component and another component which vary
respectively as the first and as the second powers of the speed, and I have experi-
mentally determined that the relative value of the viscous component may be
accurately calculated. In order therefore to construct an accurate ammeter, it is
necessary to make use of a field which also consists of two components, one
constant and one varying as with the current to be measured. These field components
are calculated to correspond with the friction components, and so that the constant
component of the field shall contribute by its reaction on the armature current a

page_text: torque just sufficient to overcome that component of the total fluid resistance which
varies directly as the speed and so that the other coil which is in series with the
armature current will contribute a moment equal to the component of the fluid
friction which varies as the square of the speed.
The coil which is employed to excite the constant component of the field being in
shunt on the side of the apparatus further from the source of current, it is obvious
that in the event of any fluctuation in the pressure in the mains, the instrument will
not give an accurate reading either as an ammeter or as an ergmeter, but an
intermediate result. That component of the field which varies as the current to be
measured may be produced by means of a coil in series with the armature, or in a
coil parallel with the armature or, in the case of alternating currents, an induced
current bearing a known relation to the current which traverses the armature may be
employed to excite this coil.
The unipolar type of electro-motor is the one which lends itself most conveniently
to the use of the fluid resistance and I therefore prefer to use such a motor.
One arrangement of this kind consists of an unbroken thread or circuit of mercury or
other conductive liquid contained in a tube of small diameter some part of which is
in the magnetic field. The current which energises the magnetic field passes also
through the conductive liquid, and, obviously, at right angles to the lines of force.
Whenever a current passes therefore, the conductive liquid will tend to be driven
through its containing tube and the liquid current so set up may be employed to
drive a small turbine or other equivalent device the motion of which is employed to
drive the counting apparatus. If a reciprocating device such as a balanced lever is
employed, the current may be reversed at the end of each stroke so as to drive the
conductive liquid in the opposite direction or, the field magnets may be wound in
parallel with two coils each of which has an equal but opposite magnetising effect.
Either of these coils may be provided with an adjustable resistance, and they are so
arranged that the coil which carries the stronger current during the movements in one
direction shall carry the weaker current during the opposite movements. When the
viscous resistance is required, obstructions to the easy flow of the fluid may be used
for the purpose of keeping the speed slow.
The unipolar motor, instead of having a fluid armature may have an armature of
the disc, star, wheel or other suitable form immersed in mercury and surrounded by
the exciting coils arranged in such a manner that the lines of force shall traverse the
armature at right angles to the plane of its motion. The current is led into the
armature near to its centre and out near the periphery so that as much as possible of
the current shall traverse the disc without being shunted through the mercury.
The resistance of the alternative mercury path may be increased by affixing to the
armature a series of concentric open tubes and in the vessel containing the mercury
a similar system of concentric tubes or recesses so that the armature tubes may enter
and rotate between the fixed tubes. The walls of the vessel and the tubes are
insulated or constructed of insulating material. The spindle of the armature is
employed to drive the recording apparatus through a tangent screw or other suitable
gearing.
Various forms of the armature may be employed as for example, it may consist of
a disc turned down at its periphery and having a tubular centre so that a
section of a radius of the armature resembles an inverted flattened U. The parts
corresponding to the extremities of the limbs of the U are immersed in or float upon
two annular baths of mercury. Or, the armature may more nearly approach as to its
radial section, an inverted L. In either of these cases flanges or collars may be
affixed to the vertical part of the armature and enter and rotate between corresponding
recesses in the containing chamber. Two or more armatures upon the same spindle
may in some cases be advantageously employed. Instead of a solid armature thus
arranged, the space otherwise occupied by it may be filled with mercury into which
vanes extend from a central spindle so as to be driven round by the mercury and so
drive the spindle and the recording mechanism.
The armatures of the motors last described rotate in a horizontal plane; the motor

page_text: may however be constructed so that the armature rotates in a vertical plane between
the poles of a magnet. In this case the bottom edge of the armature may be caused
to dip into mercury contained in an insulated vessel. The current is caused to pass
radially through the armature from the mercury to the centre, whence it is led off by
suitable contacts or by a collar dipping into a second bath of mercury.
the passage of the current in a radial direction in the armature, it may have a disc
shape, and have radial slits cut through it, these slits being filled with insulating
material.
To ensure
Any form or type of electric motor may be employed in combination with the
herein before described viscous fluid resistance, and when the ordinary type having
brushes is used, it may be preferable to pass the current to be measured (or a
derivation from this current) through the field coils, and the shunt or steady current
through the armature coils. The commutator segments of the armature may be then
arranged to come successively into contact with mercury contained within two
insulated troughs. The arrangement of the currents may be reversed, that is to say,
the shunt or steady current may pass through the field coils and the current to be
measured or a current proportional to the current to be measured may pass through
the armature.
When mercury is employed in any of the forms of motor for making contact, and
particularly when the viscous fluid is in contact with the mercury, the metallic
contacts are platinised or otherwise suitably prepared or treated so as to be wetted by
the mercury and to prevent electrolytic action in the film between the surfaces and
for the further purpose of preventing the access of dirt to this capillary space as
well as access of the viscous liquid when this is in contact. The free surfaces of
the mercury may be covered with a fluid consisting of or containing a substance
which will protect the mercury from corrosion.
For the purpose of overcoming the inertia of the recording system a slight
tremulous motion may be imparted to the first wheel by means of a high resistance
electro vibrator or by means of a vibrator actuated by a weight or spring or some
equivalent driving force is applied in order to assist the movement of the armature
or to enable the armature to rotate without being retarded by the resistance of the
recording apparatus.
Dated this 26th day of April A.D. 1889.
WILLIAM E. HAYS,
Agent for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Electric Meters.
I, ROBERT SNOWDON, of the Staveley Iron Works Chesterfield in the County of
Derby, 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:—
"
"
motor meters
This Invention relates to that type of electric meters known as
and these Improvements consist in the construction of the meter in such a manner
that the motion of the motor is retarded or resisted by a viscous fluid resistance,
and so also that the current or currents passing through the armature of the meter
is or are exclusively the current or parts of the current to be measured, as and for
the purposes berinafter described.
The meter as arranged for measuring continuous currents, may have permanent
field magnets or electro-magnets energised by the current. The opposition of the
fluid viscous resistance will cause the rate of revolution to be proportional to the
current in the armature, and the instrument will be an ammeter or ampere hour
meter.
If the field coil or coils are included in a shunt between the leads, or from one of
the leads to earth, the other conditions remaining the same, the torque will vary as
the product of the armature current into the field current, and the instrument will

page_text: be a Watt or Erg meter. The shunt coil in this case is connected to the leads on
the side of the apparatus further from the source of current so that the whole of the
current deviated through the shunt shall pass through the meter. This form of the
apparatus may be employed to measure alternating, intermittent or pulsating currents
if the iron in the field be laminated or omitted.
The viscous resistance may be obtained by the movement of suitable devices
operated by the motor in a highly viscous liquid such as oils, glycerine, molasses, and
gum or resin solutions, but a similar and suitable resistance may be obtained from
ordinary non-viscous fluids such as water by constructing the part or device moving
therein of wire or filaments and causing them to move in contiguity with stationary
surfaces. In any case,
the object of the viscous resistance is to keep the rate of
rotation of the moving part of the motor as low as convenient. Variations in the
viscosity of the liquid employed may be compensated by a corresponding regulation
of the depth of immersion of the part moving in the fluid, or by an alteration of its
position relatively to the fixed surfaces within the fluid. This regulation of move-
ment of the moving part within the fluid may be effected by means of a metallic
thermometer, by an air thermometer, or by like means, and this automatic con-
trolling or regulating device may advantageously be immersed in the fluid so as to
acquire its temperature.
When a fluid such as water or mercury, which is not ordinarily regarded as viscous,
is employed, the friction opposed to the moving part therein will vary in proportions
between the first and the second powers of the speed except when the motion is very
slow, (not as the second power of the speed). When the motion is very slow, and
also when the moving part is filamentous or constructed of wire, the friction will vary
almost exactly as the first power of the speed. The total fluid friction may be
regarded as consisting of a viscous component and another component which vary
respectively as the first and as the second powers of the speed, and I have
experimentally determined that the relative value of the viscous component may
be accurately calculated. In order therefore to construct an accurate ammeter, it is
necessary to make use of a field which also consists of two components, one constant
and one varying as with the current to be measured. These field components are
calculated to correspond with the friction components, and so that the constant
component of the field shall contribute by its reaction on the armature current a
torque just sufficient to overcome that component of the total fluid resistance which
varies directly as the speed and so that the other coil which is in series with the
armature current will contribute a moment equal to the component of the fluid friction
which varies as the square of the speed.
The coil which is employed to excite the constant component of the field being in
shunt on the side of the apparatus further from the course of current, it is obvious
that in the event of any fluctuation in the pressure in the mains, the instrument will
not give an accurate reading either as an ammeter or as an ergmeter, but an
intermediate result. That component of the field which varies as the current to be
measured may be produced by means of a coil in series with the armature, or in a
coil parallel with the armature or, in the case of alternating currents, an induced
current bearing a known relation to the current which traverses the armature may be
employed to excite this coil.
The unipolar type of electro-motor is the one which lends itself most conveniently
to the use of the fluid resistance and I therefore prefer to use such a motor.
One
arrangement of this kind consists of an unbroken thread or circuit of mercury or
other conductive liquid contained in a tube of small diameter, some part of which is
in the magnetic field. The current which energises the magnetic field passes also
through the conductive liquid and obviously, at right angles to the lines of force.
Whenever a current passes therefore, the conductive liquid will tend to be driven
through its containing tube and the liquid current so set up may be employed to drive
a small turbine or other equivalent device the motion of which is employed to drive
the counting apparatus. If a reciprocating device such as a balanced lever is
employed, the circuit may be reversed at the end of each stroke so as to drive the

page_text: conductive liquid in the opposite direction, or, the field magnets may be wound in
parallel with two coils each of which has an equal but opposite magnetising effect.
Either of these coils may be provided with an adjustable resistance, and they are so
arranged that the coil which carries the stronger current during the movements in
one direction shall carry the weaker current during the opposite movements.
the viscous resistance is required, obstructions to the easy flow of the liquid may be
used for the purpose of keeping the speed slow.
When
The unipolar motor, instead of having a fluid armature may have an armature of
the disc, star, wheel, or other suitable form immersed in mercury and surrounded by
the exciting coils arranged in such a manner that the lines of force shall traverse the
armature at right angles to the plane of its motion. The current is led into the
armature near to its centre and out near the periphery so that as much as possible
of the current shall traverse the disc without being shunted through the mercury.
The resistance of the alternative mercury path may be increased by affixing to the
armature a series of concentric open tubes, and in the vessel containing the mercury,
a similar system of concentric tubes or recesses so that the armature tubes may enter
and rotate between the fixed tubes. The walls of the vessel and the tubes are
insulated or constructed of insulating material. The spindle of the armature is
employed to drive the recording apparatus through a tangent screw or other suitable
gearing.
Various forms of the armature may be employed, as for example, it may consist of
a disc turned down at its periphery and having a tubular centre so that a section of
a radius of the armature resembles an inverted flattened U. The parts corresponding
to the extremities of the limbs of the U are immersed in or float upon two annular
baths of mercury.
Or the armature may more nearly approach as to its radial
section, an inverted L. In either of these cases flanges or collars may be affixed to
the vertical part of the armature and enter and rotate between corresponding recesses
in the containing chamber. Two or more armatures upon the same spindle may in
some cases be advantageously employed. Instead of a solid armature thus arranged
the space otherwise occupied by it may be filled with mercury into which vanes
extend from a central spindle so as to be driven round by the mercury and so drive
the spindle and the recording mechanisın.
The armatures of the motors last described rotate in a horizontal plane; the motor
may however be constructed so that the armature rotates in a vertical plane between
the poles of a magnet. In this case the bottom edge of the armature may be caused
to dip into mercury contained in an insulated vessel. The current is caused to pass
radially through the armature from the mercury to the centre, whence it is led off by
suitable contacts or by a collar dipping into a second bath of mercury. To ensure
the passage of the current in a radial direction in the armature, it may have a disc
shape and have radial slits cut through it, these slits being filled with insulating
material.
Any form or type of electric motor may be employed in combination with the
herein before described viscous fluid resistance, and when the ordinary type having
brushes is used, it may be preferable to pass the current to be measured (or a derivation
from this current) through the field coils, and the shunt or steady current, through
the armature coils. The commutator segments of the arinature may then be arranged
to come successively into contact with mercury contained within two insulated
troughs. The arrangement of the currents may be reversed, that is to say, the shunt
or steady current may pass through the field coiis and the current to be measured or
a current proportional to the current to be measured may pass through the armature.
When mercury is employed in any of the forms of motor for making contact, and
particularly when the viscous fluid is in contact with the mercury, the metallic
contacts are platinised or otherwise suitably prepared or treated so as to be wetted by
the mercury and to prevent electrolytic action in the film between the surfaces, and
for the further purpose of preventing the access of dirt to this capillary space as well
as of the viscous liquid when this is in contact. The free surfaces of the mercury

page_text: may be covered with a fluid consisting of or containing a substance which will protect
the mercury from corrosion.
For the purpose of overcoming the inertia of the recording system, a slight
tremulous motion may be imparted to the first wheel by means of a high resistance
electro vibrator or by means of a vibrator actuated by a weight or spring or some
equivalent driving force is applied in order to assist the movement of the armature or
to enable the armature to rotate without being retarded by the resistance of the
recording apparatus.
I will proceed to more particularly describe my said Invention with reference to
the accompanying drawings.
Fig. 1 is a vertical section and Fig. 2 is a plan of a motor meter in which the
armature A floats upon the mercury contained in two annular baths B B'. The disc
armature is kept central by means of the vertical pin which passes through a bearing
in an insulating piece I. The inner annuiar bath is connected with the terminal T
and is contained within the lower part of the field magnet by means of an insulating
bush D and a cylindrical ring E both of which are constructed and arranged to form
fluid tight joints. N and S are respectively the pole pieces of the field magnet and V
is the electric vibrator for communicating a tremulous motion to the indicating train.
The terminals of the vibrator may be connected to any suitable source of current and
the vibrator is insulated from the meter. The space in which the armature revolves
is filled with the viscous liquid and if this is of such a nature that its viscosity is
diminished with a rise of temperature the depth of the mercury is so arranged that
the lower pole piece S is always nearer to the armature than the upper one. With this
arrangement the armature will rise and fall slightly with variations of temperature
and will thus vary the fluid friction between the disc and the lower pole piece more
than that between the disc and the upper pole piece.
C is the exciting coil the ends of which are connected to the main leads. The
current to be measured may enter for example, at the terminal T whence it
successively traverses the lower pole piece, the mercury in the outer bath, the
armature radially, the neck connecting the armature with the bulb F, the mercury in
the inner bath, and thence out through the terminal T. The bulb F it will be under-
stood acts as a float for the armature. The side bolts which hold the apparatus
together are insulated from the apparatus as by means of insulating collars W; they
also serve to support the meter on a suitable base or foundation as indicated at U Fig. 1.
A similar arrangement may be employed without the viscous liquid provided that
the magnets are compound wound so as to satisfy the law of friction for a non-viscous
liquid like mercury.
It will of course be understood that any suitable counting or indicating train may
be employed and be connected to the armature spindle in the usual manner.
Fig. 3 represents in sectional elevation and Fig. 4 in sectional plan a type of motor
meter in which a vertical armature spindle A' is formed in two halves respectively
screwed or secured to the insulating piece I. This shaft runs in bearings offering
the least possible resistance and the upper portion carries the rotating part G of the
friction apparatus which may be constructed almost heavy enough to overcome the
bouyancy of the armature which is completely submerged in mercury and consists of
the disc or wheel A secured to the spindle A¹. To the periphery of the disc there are
secured the vertical strips H H which are slightly recessed on each side at the middle
of their length and let into narrow slots in the rim of A where they may be secured
by a surrounding of wire laid in the outer recesses. The sides of the strips H are
enamelled or insulated so as to laminate the mercury radially. NS is the upper
and N¹ S' is the lower field magnet, each of them being built up of radial plates of
soft iron tapered as shewn on their outer edges so as to be tightly bound together by
forcing on the tapered hoops J J' which are constructed with flanges through which
the side bolts pass. These side bolts may also serve to connect the meter with the
base as described with reference to Fig. 1. Owing to the radial disposition of the
plates, they will not, unless made to a radial cross section, fit compactly together

page_text: except at their inner edges, and suitable thickness strips are therefore interposed
between the larger plates as indicated at K Fig. 4. The plates may alternatively be
packed in groups with a thickness piece between each group and in either case, a thick
wedge of insulating material may be inserted, in holes through which the terminals of
the exciting coils may be passed and a tube to permit the escape of air when filling the
mercury chamber.
The tapered boop Jis prolonged upwards and is constructed so as to form or include
the trough L which contains the stationary friction apparatus G', the viscous fluid,
and a set of (for example four) metallic thermometers M upon which the stationary
friction apparatus rests so as to be raised and lowered with changes of temperature.
The liquid must be deep enough to submerge the friction apparatus and the thermo-
meters.
B and B' are the upper and the lower parts of the mercury chamber in which the
armature revolves, and the walls of this chamber are formed of ebonite or other
suitable insulating material. Pis an annular piece of similar material. O is a flat ring
of copper from the inner end of which strips O' of the same metal pass upwards
through grooves in the outer cylindrical surface of P and make contact with the
mercury above the armature. Q is a similar flat ring from which similar metallic
strips lead to the bottom of the mercury chamber.
The rings OQ are tightly clamped between P and B and B¹, the joint being made
good with cement. To each of the rings OQ one or more terminals T T' are fixed to
form a means for connecting the meter to the mains.
C and C are the exciting coils which may be in series or in parallel and which
combine to magnetise the space between them both in the same direction.
Assuming the current to enter by the terminals 1' it will successively traverse the
ring O the strips O¹ to the top of the armature strips and intervening mercury the
lower contact strips and the ring Q to the terminals T. In traversing the armature
space which is magnetised to an extent proportional to the pressure in the mains, it
induces rotation in the armature and mercury.
If the viscous fluid be not employed, the exciting coils must consist both of series
and shunt coils the relative proportions of which will be determined by the relative
values of the two components of the friction of the mercury and in this case it may be
advantageous to confine the series coils to one of the two inagnetic circuits in order to
avoid the effects of mutual induction.
For the purpose of avoiding air locking when filling the mercury chamber, one of
the grooves in P may be left open and a capillary duct from this groove may be
formed through the substance of the flange of B.
Fig. 5 is a sectional elevation and Fig. 6 is a sectional plan of an alternative form
of construction of a motor ineter in which the armature consists of two discs A A.
The mercury in which the armature. rotates is contained within an insulated
chamber B B P. The metallic contact rings O and Q are tightly clamped between P
and B and B so as to make a fluid tight joint. The ring O is in metallic connection
with the radial strips O'Q which form inward projections from the rings R R' which
carry the terminals T T for connection to the mains. The current therefore passes
from terminal T through R to the upper disc A through the armature boss, the lower
disc, the contact ring Q and thence through A' to the terminal T¹. The lower disc A
carries an annular projection F which rotates within a corresponding recess formed
in the insulation P. The whole surface of the armature except the peripheries of
the discs and the surface of the annular projection F are enamelled or insulated so
as to limit the current and therefore the torque to the armature as much as possible.
The armature is also slit radially as indicated in Fig. 6 for the purpose of minimising
Foucault currents. The space between the upper and lower flanges of the insulator P
is packed with vertical radial lamina of soft iron kept in place by a strap V and
bolt X. The dise of the first wheel of the counting train is of ivory or similar material
and the top bearing of the spindle A' is jewelled so that the armature is completely
insulated. The friction arrangement consists of the rotating part G and the stationary
part G. The depth of immersion is varied so as to compensate for variations of

page_text: viscosity from variations of temperature by means of a large vessel L containing the
same liquid alone or with air. The liquid in G¹ and in L respectively is at liberty to
pass from one chamber to the other through small ducts L'. The construction other-
wise will be understood by reference to the description of Figs. 3 and 4, similar
letters of reference being employed to denote the details.
Fig. 7 is a sectional end view and Fig. 8 a longitudinal sectional view of a friction
arrangement applicable to an ordinary motor. G G are four discs fixed on the
spindle A' and having the lower parts of their peripheries rotating in a trough I.
divided by partition plates G¹ rigidly connected together and resting upon three rods
of ebonite M connected by a pin. When these rods are heated they expand and lift
the plates G¹ so as to increase the friction. The motion of the spindle may
be communicated to the counting train by direct gearing or by rolling contact as
indicated in Fig. 8.
An equivalent arrangement to that represented in Figs. 7 and 8 is shewn in Fig. 9
but with the spindle of the motor vertical. The cylindrical trough is constructed of
an insulating material having a high coefficient of expansion for heat. I is an inner
vessel resting by a flange on its upper end upon the top edge of L and having
apertures near the bottom through which two or more levers Y Y pass. These levers
have their outer ends below projections on the inside of L and they are provided with
adjusting screws upon which rests the stationary part of the friction apparatus
consisting of the disc G' through the boss of which a guide can pass so that G¹ may
slide vertically thereon. The footstep or bearing of the spindle A' is carried in the
top of Z. The disc G' carries by means of light rods three tapered rings D which
enter corresponding recesses in the rotating part G so that whenever the length
of L'alters relatively to that of L the tapered rings D are raised or lowered
thus varying the friction as required. In this and the previously described
arrangements the weight of the moving parts of the meter may be reduced by
partly or entirely floating the armature, by means of bulbs fixed upon the spindle
or by immersing the armature itself if a liquid which is a good insulator be
employed.
In the arrangement illustrated in Figs. 10 and 11 of which Fig. 10 is a side
elevation and Fig. 11 a plan, both partly in section, a pair of vesselsvare
supported on a rocking lever which is carried by trunnions bearing in slots in the
pillars p p. The two vessels v1 are connected by means of a continuous tubular
connection which starts from v as a small vulcanite tube, bent at e to give it
elasticity, after which it passes through a clamp f at which point it is firmly
clamped against the inside of the pillar p thence it leads to g which is a mass of
copper carrying the terminal T. A channel is formed in the interior of which
continues the tube to the centre of the metallic and preferably non-magnetic spiral i
which is capable of being wetted by inercury. This spiral is clamped between the
insulations and as shewn in the half sections of this portion of the apparatus.
The space between the convolutions of this spiral continues the tube to the outside
whence it passes upwards through the space left around the edge of the insulating
disc and enters the upper spiral which is exactly similar to i. This continues the
tube to the channel formed in the interior of the copper contact g₁ which corresponds
with g and carries the other terminal T. Communicating with the channel in g' is
the tube e' which leads from g' to the clamp f when it is clamped firmly to the
pillar p'; it is then bent similarly to e to give it flexibility and then leads directly to
the vessel v. C is the shunt excited coil and N and S the upper and lower parts of
the field magnet the construction of which will readily be understood from the
descriptions of Figs. 3, 4, 5, and 6. The joint between the upper and lower insulating
discs is formed by means of a tapered turned and bored joint as shewn, the surface
being wetted with glue and just tightening together, at the same time as the joints of
the spirals and have become sufficiently tightened. It is clear that if the current
to be measured is passed in at the terminal T it will traverse the lower spiral radially
outwards and propel the mercury between its convolutions in a given direction within
the spiral; it then passes radially inwards across the convolutions of the upper spiral

page_text: so as to propel the mercury in the opposite direction and add to the pressure developed
in the lower spiral, so that the mercury is displaced from one of the vessels v vi to the
other according to the direction of the current. This displacement of liquid over-
balances the lever supporting the vessels v v¹ and causes it to move upon the trunnions.
In order that the rate of movement shall be proportional to the current passing a
pendulous weight w is attached to it of such mass that acting in conjunction with the
elasticity of the tubes e e' the system shall practically be in equilibrium in any position
of the lever.
In order to reverse the movement at the end of each excursion of the lever, a
tumbling lever o which rocks about the centre o¹ is provided with set screws s 8¹ which
come into contact alternatively with the arm q fixed rigidly upon a prolongation of the
trunnions which extension passes through a bearing q in an insulating slab of ivory r
and carries a loose lever of ivory into the boss of which are screwed two small
platinum wing pieces t t¹. These wing pieces are connected each by a flexible
insulated wire with one extremity of the exciting coil, and enter slots in the two
halves u and w of a metallic ring each half of which is screwed to the insulating slab r
and each half being respectively connected with the two terminals from which the
magnetising current is derived. The whole forms a switch which reverses the
direction of the current in the field coil every time the lever 1 is pushed from one
side to the other which happens each time the tumbling lever o overbalances, as this
brings one of the screws into contact with the switch lever, the weight of o then
carries this lever over with it until the motion of o is arrested by the arin q when it is
slowly moved back again. The drawing represents the main lever at the extremity of
an excursion with the lever o just ready to overbalance. An upright frame = carries
the recording mechanism the first wheel of which consists of a ratchet which is worked
by a pawl y connected to a small projecting hinge on the ivory boss of the switch
lever.
The meters herein before described are all, except that illustrated in Figs. 1 and 2
adapted for alternating currents. A much simpler but precisely analogous con-
struction will serve for the measurements of direct currents, and lamination being
unnecessary, the faces of the field magnet may be enamelled instead of employing the
insulating cells.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed, I declare that what I
claim is,
(1) In an electric motor meter the current or currents passing through which is or
are the current or parts of the current to be measured or a current or currents induced
thereby, a viscous fluid resistance constituted and arranged substantially as and for the
purpose herein before described.
(2) In an electric motor meter, operating the meter by the joint reactions of two
currents one of which passes through the armature and the other through the field
coils and retarding the subsequent notion of the armature by means of a viscous fluid
resistance, substantially as and for the purpose herein before described.
(3) In an electric motor meter for continuous currents the combination and
arrangement of a permanent magnetic field, an armature through which the current
or a proportional part of the current to be measured or a current induced thereby,
passes, and a viscous fluid resistance all constructed and arranged substantially as
and for the purpose herein before described.
(4) In an electric motor meter in which the motion of the armature is retarded by
a fluid resistance, constructing the motor field with two components one of which
is constant and the other of which varies as the current to be measured, substantially
as and for the purpose hereinbefore described.
(5) In an electric motor meter, a metallic thermometer or equivalent thermometric
device operating to compensate for variations in the viscosity of a fluid resistance
with variations of temperature, substantially as hereinbefore described.

page_text: (6) In an electric motor meter, an electrical or mechanical vibrator substantially
as and for the purpose herein before described.
.
(7) An electric motor meter constructed arranged and operated substantially as
herein before described and as illustrated by Figs. 1 and 2 of the accompanying
drawings.
(8) An electric motor meter constructed arranged and operated substantially as
hereinbefore described and as illustrated by Figs. 3 and 4 of the accompanying
drawings.
(9) An electric motor meter constructed arranged and operated substantially as
herein before described and as illustrated by Figs. 5 and 6 of the accompanying
drawings.
(10) An electric motor meter constructed arranged and operated substantially
as herein before described and as illustrated by Figs. 7 and 8 of the accompanying
drawings.
(11) An electric motor meter constructed arranged and operating substantially
as herein before described and as illustrated by Fig. 9 of the accompanying
drawings.
(12) An electric motor meter constructed arranged and operated substantially as
herein before described and as illustrated by Figs. 10 and 11 of the accompanying
drawings.
D
1000
WILLIAM E. HEYS,
Agent for the Applicant.