An Electric Supply Meter.
Year: 1890

page_text: Date of Application, 9th May, 1890
Complete Specification Left, 9th Feb., 1891-Accepted, 9th May,
1891
PROVISIONAL SPECIFICATION.
An Electric Supply Meter.
I, JOHN PERRY, Fellow of the Royal Society, of 31 Brunswick Square
London W.C. do hereby declare the nature of this invention to be as follows:-
If a mass of electrically conducting liquid such as mercury is in the neighbour-
hood of a magnet and if at a place A the liquid receives electric current, say by a
wire dipping in there & if at a place B the liquid gives off the electric current, say
by another wire; in almost any positions of the arrangement the liquid particles
will be set in motion among one another & will continue moving so long as the
current flows. A solid body free to move & touching the liquid will also usually
be set in motion. If the magnetic field is not allowed to alter & if the motion is
everywhere slow I find that the velocity of motion at any place is proportional to
the current. If such a solid body as I have mentioned be free to turn a spindle
driving a train of wheels the arrangement forms an electric supply meter whose
only defects are due to solid friction.
In all cases my magnet (by which I mean a magnet or system of magnets) is as
nearly constant in strength as I can get it, whether it is a permanent magnet of
steel or an electromagnet or a coil of wire with constant current circulating in it.
If it is an electromagnet or a coil, I prefer that it should be wound with a wire
which is a shunt to the constant potential supply leads. If the iron of the electro-
magnet is nearly saturated, small alterations of the exciting current do not affect
the accuracy of the instrument. The magnetism must not be produced by the
current which is to be measured or rather integrated.
I prefer the boundaries of the liquid in which the magnetic poles are usually
placed to be fixed co-axial surfaces of revolution, the magnetic induction directed
mainly in axial planes, the solid body being preferably of good conducting material
rotating about the axis of the surfaces of revolution & preferably shaped as a
surface of revolution itself. As it is mainly on Foucault currents that I rely for
retarding the motion, any point on the solid body should find itself in magnetic
fields of very different strengths as it rotated.
As an example of one form of my invention, the magnet is made a tubular
magnet whose poles are concentric cylindric surfaces. A concentric cylindric
vessel of copper rotates in the space between the poles being attached to the
spindle at its upper end. An insulated copper ring lying at the bottom of the
space which forms a circular trough is connected with the supply conductor.
Mercury fills the space lying both inside and outside the copper vessel which is
completely immersed, only the spindle passing out of the surface of the mercury.
A cover is provided confining all the outer parts of the upper surface of the
mercury so that its free surface is merely at a central opening where the spindle
passes. Care is taken to prevent the mercury getting into the winding of the
magnet at the bottom.
Current comes from the bottom copper ring through the mercury to the lower
edge of the copper cylindric vessel; it passes vertically along the vessel all
round & leaves the vessel at its upper cylindric edge or by a flat end & passes
through the mercury to some fixed circular conductor which the mercury touches,
such as another ring of copper or a bright part of the iron of the magnet. All
other parts of the magnet & indeed of the copper vessel except at the top &
bottom are covered with insulating material preventing the mercury from making
electric contact anywhere except at the bottom & top & none of the supply
current flows except through the mercury & the copper vessel. The copper vessel
rotates because it is conveying current is in a magnetic field, the direction of the

page_text: current not being the same as that of the magnetic induction. One or both of the
cylindric poles has a number of gaps in it filled up with plaster of paris or other
suitable material so that in the cylindric space the strength of the magnetic field
varies greatly & hence the resistance to motion is mainly due to Fouenult currents.
I sometimes supplement this Foucault enrrent resistance by the use of a conductor
like a dise of copper, on the spindle or driven from the spindle, rotating in the
fields of one or more magnets of constant strength such dise having only Foucault
currents flowing in it. "It is generally better to obtain all the Fourault current
resistance in the cylindric copper vessel. Hence 1 make this eylinder much thicker
than it would otherwise be & I reduce as much as possible supply currents in the
mercury which would tend to make the merenry rotate. This is why I coat with
insulating varnish all parts of the copper cylinder except the lip at the bottom which
receives the current & that part at the top which gives it off.
I sometimes shunt part of the main current past the meter by one or more con-
ductors of such materials that the change of résistance of the shunt with tempera-
ture is the same as that of the meter. E sometimes use resistance coils in the
magnet eircuit when the supply voltage is not the same as that for which the meter
was designed. When considerable alterations of voltage are probable in the
electric supply I do not have gaps in the cylindric pole piece & I produce my
retarding Foucault currents on the auxiliary dise or other conductor by magnets of
more constant strength than the motion-producing magnet.
The main distinction between this invention and the meters described by me in
two Specifications one of last January & the other just previously is this:-Only
the spindle which drives the recording dials is allowed to pass through the surface
of the merenry as I find that a mercury surface even when very clean exercises a
quasi-solid friction on any solid body which passes through it. This is a fact never
before published & it is of great importance here, because solid friction is pernicious
in supply meters. It is of great importance on all instruments in which we rely
upon the resistance to motion being less & less as the velocity is less & less. The
mercury moves, but the highest speed for good working is less than that which
causes motion of the superficial mercury. "To diminish friction at the pivots 1
have the weights of such dises or wheels or other objects attached to the spindle
outside the mercury, sufficiently great to nearly balance the lifting power of the
mercury on the copper vessel. I sometimes have inside the case an appliance for
keeping the air dry such as a vessel of strong sulphuric acid. Sometimes instead
of air I use in the case an atmosphere of nitrogen hydrogen or other inert gas
which will not be harmful if it creeps down the spindlo to renew the film at the
boundaries of the mercury. I also sometimes use a layer of oil or other preserva-
tive fluid on the surface of the mercury so that the state of the mercury may be
kept as nearly constant as possible.
Dated this Sixth day of May 1890.
JOHN PERRY.
COMPLETE SPECIFICATION.
An Electric Supply Meter.
1, Joux PERRY, of 31 Brunswick Square, London W.C. Fellow of the Royal 4
Society 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 :-
If a mass of electrically conducting liquid such as merenry is in the neighbour-
hood of a magnet, and if at a place A the liquid receives electric current, say by a 5
wire dipping in there, and if at a place B the liquid gives off the electric current,
say by another wire; in almost any positions of the arrangement the liquid particles
will be set in motion among one another and will continue moving so long as the
current flows. A solid body (free to move and touching the liquid will also

page_text: usually be set in motion. If the magnetic field is not allowed to alter with time
and if the motion is everywhere slow I find that the velocity of motion at any
place is proportional to the current. If such a solid body Cas I have mentioned
be free to turn a spindle driving a train of wheels the arrangement forms an electric
supply meter whose only defects are due to solid friction.
In all cases my muguet (by which I mean a magnet or system of magnets) is as
nearly constant in strength as I can get it, whether it be a permanent magnet of
steel or an electromagnet or a coil of wire with constant current circulating in it.
If it is an electromagnet or a coil, I prefer that it should be wound with a wire
that is a shunt to the constant potential supply leads. If the iron of the electro-
magnet is nearly saturated, small alterations of the exciting current do not affect
the accuracy of the instrument. The magnetism must not be produced by the
current which is to be measured or rather integrated. I sometimes, however, usc
in addition to the shunt winding a series coil to correct a defect in the instrument
in case the Foucault current resistance to motion is not sufficiently great in com-
parison with the fluid friction resistance.
I prefer the boundaries of the liquid in which or near which the magnetic poles
are usually placed to be fixed coaxial surfaces of revolution, the magnetic induction
being directed mainly in axial planes through the trough-like space between these
surfaces, the solid body being preferably of good conducting material rotating about
the axis of the surfaces of revolution and preferably shaped as a surface of revolu-
tion itself. As it is mainly on Foucault currents that I rely for retarding the
motion any point on the solid body should find itself in magnetic fields of very
different strengths as it rotates.
As an example of one form of my invention (Fig. 1) the magnet S M N¹ N is
made a tubular magnet whose poles S S & N N are concentric cylindric surfaces.
A concentric cylindric vessel of copper C rotates in the space between the
poles N, S, being attached to the spindle D at its upper end. An insulated copper
ring A lying at the bottom of the space which forms a circular trough is connected
with the supply conductor A. Mercury fills the space lying both inside and
outside the copper vessel which is completely immersed, only the spindle passing
out of the surface of the mercury. A cover P is provided confining all the outer
parts of the upper surface of the mercury so that its free surface is merely at the
central opening where the spindle passes. Care is taken to prevent the mercury
getting into the winding W of the electromagnet at the bottom.
Current enters the meter from the supply conductor A¹ passes through the
bottom copper ring A, then through the mercury, through the lower edge of the
copper cylindric vessel; it passes vertically along the vessel all round and leaves
the vessel at its upper cylindric edge or by a flat end and passes through the
mercury to some fixed circular conductor which the mercury touches, such as
another ring of copper, or a bright part of the iron of the magnet (at B in
the figure). It then leaves the meter at B¹ and passes to the lamps or other
appliances.
Except the bright part B all other parts of the magnet are covered with
insulating material preventing the mercury from making electric contact with the
iron anywhere except at B.
Sometimes too I cover the copper vessel with insulating material except at the
top & bottom, so that there is electric contact between the mercury and the copper
only at the top and bottom. None of the supply current flows except through the
mercury and the copper vessel.
The copper vessel rotates because it is conveying a current and is in a magnetic
field, the direction of the current not being the same as that of the magnetic
induction. The mercury also rotates and tends to make the copper rotate. One
or both of the cylindric poles has a number of gaps in it (Fig. 2) filled up with
plaster of paris or wood or brass or other suitable material so that in the cylindric
space the strength of the magnetic field varies greatly and hence a great resistance
to motion due to Foucault currents is produced. I sometimes supplement this

page_text: Foncault current resistance by the use of a conductor, such as a disc of copper, on
the spindle or driven from the spindle, rotating in the fields of one or more magnets
of constant strength, such disc having only Foucault currents flowing in it. It
is generally better to obtain all the Foucault current resistance in the cylindric
Copper vessel.
Hence make this cylinder much thicker than it would other-
wise be and I reduce as much as possible supply currents in the mercury which
would tend to make the mercury rotate. This is why sometimes coat with
insulating varnish all parts of the copper cylinder except the lip at the bottom
which receives the current and that part at the top which gives it oll.
times use a copper cylindric vessel of the form shewn in Figure 3: in this
case the vessel is fixed to the spindle by means of a piece of insulating material *.
the spindle is covered with insulating material, and the whole of the copper
vessel is also covered with insulating material except the lip at the bottom, and
the inner side of the upper cylindric part. Current leaves the meter by the
copper piece, the whole of the iron of the magnet being insulated. The
between the cover and the copper vessel is made as small as possible.
•
Some-
this arrangement very little current will flow through the mercury, nearly
all passing through the copper. Sometimes, however, I completely cover the
copper vessel with insulating material, so that the whole current passes through
the mercury.
It is easy to see how the two polar surfaces S and N instead of being the
poles of a tubular magnet, may be the two poles of any other kind of magnet,
or may be the poles of several magnets placed in juxtaposition. The important
thing is that magnetic induction should pass in the same sort of way through
the copper vessel and that there should be gaps or discontinuities in the polar
surfaces so arranged that a point on the copper vessel should find itself in places
of very different magnetic fields during its rotation.
I sometimes shunt part of the main current past the meter by one or more
conductors of such materials that the change of resistance of the shunt with
temperature is the same as that of the meter. I sometimes use resistance coils
in the magnet circuit when the supply voltage is not the same as that for which
the meter was designed. When considerable alterations of voltage are probable
in the electric supply I do not have gaps in the cylindric pole pieces and
produce my retarding Foucault currents in the auxiliary disc or other conductor
by magnets of more constant strength than the motion producing magnet.
The main distinction between this invention and the meters described by me
in two Specifications one No. 873 of the 17th January 1890, and the other
(No. 16839 of the 25th October 1889) just previously is this only the spindle
which drives the recording dials is allowed to pass through the surface of the
mercury as I find that a merenry surface even when very clean exercises a quasi
solid friction on any solid body which passes through it. This is a fact never
before published and it is of great importance here because solid friction is
pernicious in supply meters. It is of great importance in all instruments in which
we rely upon the resistance to motion being loss and less as the velocity is loss and
less. The mercury moves but the highest speed for good working is less than that
which causes motion of the superficial mercury.
I sometimes have inside the case an appliance for keeping the air dry such as a
vessel of strong sulphuric acid. Sometimes instead of air I use inside the case an
atmosphere of nitrogen hydrogen or other inert gas, which will not be harmful if
it creeps down the spindle to renew the film at the boundaries of the mercury.
also sometimes uso a layer of oil or other preservative fluid on the surface of the
mercury so that the state of the merenry may be kept as nearly constant as
possible.
Any supply meter actuated by electricity whether through the agency of heated
air driving a windmill or heated water driving a water wheel, or of electro-
deposition or electrolysis may he said to use or is itself truly an electro motor. But
in the following claims I use the term 'motor as in motor-supply-meter to mean
:

page_text: something like an electro-magnetic or dynamo-machine with a field magnet part and
an armature part, either of which may be looked upon as moveable the other being
fixed.
In my claims I use the word 'armature' to denote the solid conducting or non-
conducting moving body in a motor which causes the spindle to rotate whether
currents pass through it or not. It may be of copper iron or other metal or of a
non-conducting material. If of copper or some other metal easily amalgamated it
must be coated with nickel iron or some other material which is not easily amal-
gamated, or with a non-conducting material.
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. The use as the armature of a motor-supply-meter of material conducting or
not, shaped like a hollow cylinder or cone or other hollow surface of revolution,
immersed in mercury, the mercury receiving and giving out the electric current.
2. In any motor-supply-meter in which the armature is a hollow cylinder or cone
or any other hollow surface of revolution immersed in mercury, the use of magnetic
pole pieces on the field magnet, the polar surfaces being arranged in surfaces of
revolution.
3. In any motor-supply-meter in which the armature is a hollow cylinder or cone
or any other hollow surface of revolution immersed in mercury, the use of a tubular
field magnet.
4. In any motor supply meter in which the armature is a body completely
immersed in mercury the use of a field-magnet or field-magnets so arranged that
during its motion any point in the armature shall pass through parts of the
magnetic field of very different strengths, and therefore the Foucault current
resistance to motion in mercury or armature or both shall be considerable.
5. The use in a motor-supply-meter in which the armature is a body immersed in
mercury, of magnetic pole pieces on the field magnets, the polar surfaces shaped
as surfaces of revolution, but with gaps introducing discontinuities in the surfaces
so as to have a very variable magnetic field from point to point all round.
6. In a motor-supply-meter to produce a Foucault current resistance to motion,
the use of a tubular magnet of constant strength whose polar surfaces are surfaces
of revolution coaxial with the axis of a conducting body shaped also like a surface
of revolution and rotating between them, there being gaps or discontinuities in the
magnetic polar surfaces so that any point of the armature finds itself in fields of
very different strengths as it rotates.
7. In combination with any motor-supply-meter in which the armature is a disc
or hollow cylinder or any other hollow surface of revolution immersed in mercury,
the use of a field magnet or field-magnets whose polar surfaces are arranged in
surfaces of revolution, the field magnets being of as nearly constant strength as
possible.
8. The supply meters substantially as described and shewn in Figures 1, 2 & 3.