Year: 1887

page_text: Date of Application, 26th Apr., 1887
Complete Left, 24th Jan., 1888
Complete Accepted, 6th Apr., 1888
We ARTHUR LE NEVE FOSTER of 65 Cadogan Square, Chelsea, in the County.
of Middlesex, Engineer, and FREDERICK VILHELM ANDERSEN, of 4 Milford Terrace,
Catford Bridge, in the County of Kent, Electrician, do hereby declare the nature of
this invention to be as follows:-
Our invention for improvements in electrical measuring instruments relates to
instruments of the class known as electrometers, such as Sir William Thomson's, in
which a moveable disc or needle is mounted on an axis perpendicular to the plane of
the needle which when the instrument is in use receives an electrical charge in virtuo
of which it is acted upon by electrical charges simultaneously communicated to certain
stationary parts. The said moveable disc or needle thereby acquires a tendency to take
up a certain definite position relatively to the stationary parts, which tendency is
utilized in various well known ways for the purposes of electrical measurement.
Our improvements consist mainly in constructing the moveable part or needlo
bi-polar so that it receives simultaneously two electrical charges, one positive and the
other negative, and in arranging this bi-polar needle between two pairs of inductive
plates which are charged simultaneously with the needle by electric potentials of
opposite polarities.
Instruments constructed according to our invention possess greater sensitiveness,
and a much larger range of deflection than the ordinary form of electrometer which
has an unipolar needle and stationary quadrants for inductive plates.
In carrying our invention into practical effect, the needle is constructed of a circular
disc of mica or other suitable insulating material and is provided with two insulated
coatings of tin foil or other suitable conducting material symmetrically disposed on
the disc on opposite sides of its axis. The needle is pivotted or suspended from its
centre and electrical connections are made respectively from the two inetallic coatings
to two fixed points on the instrument from which these coatings are electrically
charged. The electrical connections are made through the two ends of the suspending
The instrument is constructed with
axis or spindle or in any other suitable manner.
either one or a number of such needles and with a corresponding number of sets of

page_text: inductive plates. Where more than one needle are used, they are fixed upon one axis
and the metallic coatings on the discs are electrically connected together in two sets
in such manner that one coating on every needle is positively charged whilst all the
other coatings are negatively charged. Two sets of inductive plates are arranged so
as to enclose and partly cover the needle or needles. These plates are fixed opposito
one another in symmetrical positions relatively to the axis of the needle, and are
constructed, either, of solid metal plates or of insulating material covered with some
suitable-conducting material..
Each set of plates is insulated from the other and so arranged-that-each-set-is-
charged simultaneously with electricity of opposite polarity.
The instrument is used to indicate and measure electric potential, either by the
deflection of the needle-against-any-suitable resistance such as a weight or a spring
attached to the said needle, or its axis, or measurements may be indicated by the
torsion produced on a spring in turning the needle to zero against the deflecting
tendency of the charged needle.
In a modification, instead of constructing the needles out of discs, the needle is
inade in cylindrical form with the metallic coatings symmetrically disposed around the
periphery, and the inductive plates aro constructed in a semicircular form to envelope
the needle.

page_text: Improvements in Electrical Measuring Instruments.
We, ARTHUR LE NEVE FOSTER of 65 Cadogan Square, Chelsea, in the County
of Middlesex, Engineer, and FREDERICK VILHELM ANDERSEN of 4 Milford Torrace,
Catford Bridge, in the county of Kent, Electrician 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 :-
Our invention for improvements in electrical measuring instruments relates to
instruments of the class known as electrometers, such as Sir William Thomson's in
which a moveable disc or needle is mounted on an axis perpendicular to the plane of
the needle, which, when the instrument is in use receives an electrical charge in virtue
of which it is acted upon by electrical charges simultaneously communicated to
certain stationary parts. The said moveable disc or needle thereby acquires a tendency
to take up a certain definite position relatively to the stationary parts, which tendency
is utilised in various well known ways for the purposes of electrical measurement.
Our improvements consist mainly in constructing the moveable part or needle
bi-polar, so that it receives simultaneously two electrical charges, one positive, and the
other negative, and in arranging this bi-polar needle between two pairs of inductive
plates which are charged simultaneously with the needle by electrical potentials of
opposite polarities.
Instruments constructed according to our invention possess greater sensitiveness,
and a much larger range of deflection than the ordinary form of electrometer which
has an unipolar needle and stationary quadrants for inductive plates.
In carrying our invention into practical effect the needle is constructed of a circular
disc of mica or other suitable insulating material, and is provided with two insulated
coatings of tin-foil or other suitable conducting material symmetrically disposed on
the disc on opposite sides of its axis. The needle is pivotted or suspended from its
centre, and electrical connections are made respectively from the two inetallic coatings
to two fixed points on the instrument from which these coatings are electrically
charged. The electrical connections are made through the two ends of the suspending
axis or spindle, or in any other suitable manner. The instrument is constructed with
either one or a number of such needles, and with a corresponding number of sets of
inductive plates. Where more than one needle are used they are fixed upon one axis,
and the metallic coatings on the discs are electrically connected together in two sets
in such manner that one coating on every needle is positively charged, whilst all the
other coatings are negatively charged. Two sets of inductive plates are arranged so
as to enclose and partly cover the needle or needles. These plates are fixed opposite
one another in symmetrical positions relatively to the axis of the needle, and are
constructed either of solid metal plates, or of insulating material covered with some
suitable conducting material.
Each set of plates is insulated from the other and so arranged that each set-is
charged simultaneously with electricity of opposite polarity..

page_text: The instrument is used to indicate and measure electric potential either, by the
deflection of the needle against any suitable resistance such as a weight or a spring
attached to the said needle, or its axis, or measurements may bo indicated by the torsion
produced on a spring in turning the needle to zero against the deflecting tendency of
the charged needle.
In a modification, instead of constructing the needles out of discs the needle is
made in cylindrical form with the metallic coatings symmetrically disposed around the
periphery, and the inductive plates are constructed in a semicircular form to envelop
the needle.
In the accompanying sheet of drawings Fig. 1 is a sectional side elevation of an
electrometer constructed according to our invention, and suitable for measuring
differences of electric potential moro especially with respect to electric light
circuits.
Fig. 2 is a front elevation of the same with the front glass plate and suspension
attacliment removed, and Fig. 3 is a front view of a bipolar needle constructed of
plates of aluminium or other suitable metal, and secured to a centre of ivory or other
insulating material.
The wooden case a of the instrument is provided with a circular glass plate 6 having
a circular opening in its centre. A small brass cylinder c is cemented in the central
opening of the glass plate b. Two sets of inductive plates de and fg are fixed
immediately behind the glass plate b. The two plates de are electrically connected
together as shewn, and are held at a sufficient distance apart to allow the bi-polar
needle to work freely between them. The two plates are also electrically connected
together and held apart in a similar manner to the plates de, the plates d f and eg
being in two parallel planes.
The bipolar needle consists of a circular disc of mica or other suitable insulating
material the face of which is covered with thin metal foil with the exception of a smalí
space across the diameter of the disc, so that, the two pieces of inetal foil on opposito
sides of the diameter are insulated from one another. Or the needle may be constructed.
of two metal plates (Fig. 3) insulated from one another and secured to a centre
of ivory or other insulating material. Two pointers p p project from the opposite
extremities of a diameter of the needle, and serve to indicate the position of the
needle by means of two scales oo attached to the inductive plates df, the front
inductive plates eg being cut away where they would otherwise hide the dials and
pointers. At one side the centre of the needle is attached to one end of a silk
fibre n, whose other end is attached to one end of a spiral spring m, whose other end
is in turn fixed to a small bracket supported on the plate g. The spring m and
bracket are surrounded and protected by the brass cylinder c. At the other side the
centre of the needle is attached to a wirej whose other end is connected to a small
bracket supported on the plate g. The spiral spring m maintains a regular tension
in the wire j
The right hand piece of foil on the bi-polar needle k is connected to the wire j, and
thus by means of the metal support h with the inductivo plates de; whilst the left
hand piece is connected to the inductive plates fg by a fine wire or other suitablo
means not shewn on the drawings.
The two sets of inductive plates are metallically connected respectively to the two
terminals 9 of the instrument. If now the two terminals of the instrument are
connected to any two points in an electric circuit between which there is a difference
of electric potential, one set of inductive plates will receive a positive charge of
electricity, whilst the other will receive a negative charge, and similarly, one coating
of the bi-polar needle will be charged positively and the other negatively. It will
thus be seen that when the inductive plates de become charged with a certain polarity,
the right hand piece of foil on the needle will also be charged with a similar polarity,
whilst the inductivo plates fg, and the left hand piece of foil on the needle will be
charged with an opposite polarity. The repulsion and attraction between the charges
on the bi-polar needle and the inductive plates will deflect the needle and impart a
certain torsion to the wire j, which in its turn balances, at a certain deflection, the

page_text: force exerted between the charges on the inductive plates and those on the needle.
The pointers thus take up a fresh position on the dial, which position, will depend upon
the electric potential.
In another form of the instrument where more delicate readings are required, the
bi-polar needle is suspended between its inductive plates in a horizontal position by a
fine wire, or other suitable means, the readings being taken by imparting such torsion
to the suspending wire, that the deflecting tendency of the charged needle and inductive
plates is balanced when the needle is brought to its zero position. The value of the
readings may then bo obtained by measuring by any of the well known methods the
amount of torsion that had to bo imparted to the suspending wire in order to bring
the needle into this position.
Where extremely low differences of potentials are required to be measured, instead
of connecting the two poles of the bi-polar needle to the two sets of of inductive
plates, either the needle or the plates may be separately charged with potentials having
a known fixed difference.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
In electrical measuring instruments :
1. The construction of a bi-polar moveable part or needle, arranged to oscillate
between bi-polar fixed parts or inductive plates, and charged with electric potentials
the difference between which it is desired to measure, or with electric potentials
between which is a fixed difference substantially as described.
2. Arranging a series of moveable parts or bi-polar needles substantially as described
upon a common axis between a corresponding number of sets of bi-polar fixed parts
or inductive plates.
3. The construction of instruments for measuring difference of electric potential
substantially as described with reference to the drawings.
Dated this 24th day of January 1888.
WHEATLEY & MACKENZIE,
156, Strand, Agents.