Improvements relating to Electric Measuring Instruments.
Year: 1894

page_text: Date of Application, 21st Apr., 1894.
Complete Specification Left 21st Jan. 1895-Accepted. 23rd Feb.. 1895
PROVISIONAL SPECIFICATION.
Improvements relating to Electric Measuring Instruments.
I, JOCELYN HOME THOMSON, Captain, Royal Artillery, of No. 18 Draycott
Place, in the County of London, do hereby declare the nature of this invention to
be as follows:--
My invention relates to the measuring of differences of electrostatic quantities
or potentials by a "zero or "balance" method.
"
"
It is well known that by means of an instrument such as is known as a
replenisher" it is possible to multiply a small quantity of electricity until it
reaches a considerable potential.
My invention has for its object to apply the principle of that instrument to
practical use in electrostatic measurement and to construct apparatus for that
purpose.
In carrying out my invention I make the electrical connections in such a way as,
by using a "replenisher," to balance the difference of potential which it is required
to measure against a known difference of potential thereby bringing two points in
the system to the same potential. I may connect one of these two points to earth
and the other point will then have a positive or negative potential unless the
balance is perfect. This latter point will be electrically connected to a part or
parts (which I will call the "inductors") of the instrument which I shall construct.
The inductor or inductors induce a charge in a conductor or conductors which will
be caused, either by hand or by a suitable electro or other motor, to revolve about
an axis. These conductors are arranged to give up to a suitable electrometer or
electroscope the successive charges which have been induced upon them.
In cases where it is required to compare a positive electromotive force with a
negative electromotive force of known amount, the inductors are arranged in two
sets in such a manner as to induce charges in the revolving conductors only when
the two electromotive forces are not equal.
The instrument may be used for detecting differences of potential between any
two points.
In a similar manner by the use of a suitable dynamo or other electric generator.
I may magnify a small current exciting the same and pass the current so magnified
through a galvanometer or other electro-magnetic apparatus.
Dated this 21st day of Anril 1894
A. F. SPOONER,
124, Chancery Lane, W.C., Agent for the Applicant.
Improvements relating to Electric Measuring Instruments.
I, JOCELYN HOME THомSON, Сaptain, Royal Artillery, of No. 18 Draycott
Place, in the County of. London, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and-ascertained in and by the following statement :—
My invention relates to the measuring of differences of electrostatic quantities
or potentials by a zero or "balance" method.
"
33

page_text: 66
It is well known that by means of an instrument such as is known as a
replenisher" it is possible to multiply a small quantity of electricity until it
reaches a considerable potential.
My invention has for its object to apply the principle of that instrument. to
practical use in electrostatic measurement and to construct apparatus for that
purpose.
In carrying out my invention I prefer to employ a special form of replenisher
which may be called a "multiplier" driven by an electro or other motor and in
combination with an electroscope of special construction or any suitable electrometer
which is capable of indicating positive or negative potentials.
The accompanying drawings show the form of instrument I prefer to employ,
Figure 1 being an elevation and
Figure 2 a plan at the line 1-2.
The
A cylinder of insulating material C is secured on an axle a which takes its
bearings on standards b. The cylinder is capable of being rotated by an electro-
motor A through a flexible coupling B. The cylinder C has strips of metal D or
"carriers" fixed to it in suitable positions. Located adjacent to the periphery of
the cylinder C are two metallic pieces E and F, preferably shaped to correspond to
the contour of such cylinder, carried by insulating supports e and respectively.
The part E I will term "the inductor" and the part F "the receiver." The
electrical connections are such that when the carriers D are adjacent to the
inductor E they are connected with the case of the instrument by means of a
contact-piece and when they are adjacent to the receiver F they are
momentarily connected thereto by means of a second contact-piece.
contact-pieces are not shown in the drawings. The receiver, F is in electrical
connection with an aluminium vane or needle G in the upper part of the
instrument or electroscope. This needle is suspended between four metallic
plates H connected alternately in pairs as in the well-known quadrant electro-
meter. One pair of these plates is kept at a potential above and the other
pair at a potential below the case of the instrument. This I prefer to effect by
means of a battery of small standard cells arranged in a frame in the upper part
of the instrument. The middle of the battery is connected to the case, the positive
pule to one pair of plates and the negative pole to the other pair. The needle G
is free to turn on a vertical axis between two stops which limit its motion so that
it cannot touch the plates. A suitable adjustment J is provided to enable the
needle to be brought to a zero position between the plates. Connection is made
with the needle by means of a metallic suspension. The needle carries a small
mirror K which enables its movement to be observed.
Upon a small difference of potential being established between the inductor E
and the case of the instrument and on the cylinder C being rotated, the carriers 1>
as they pass the inductor become charged with electricity of the opposite sign.
Leaving the inductor, the carriers pass the receiver F and give up to it the whole
or a large portion of their charge. These successive charges raise the potential of
the receiver and of the needle which is in connection with it until the latter is
deflected from its central position by the attraction of one pair of electrified plates
and the repulsion of the other pair.
The combination can be utilized for electrical testing by arranging the
connections in such a manner as to balance the difference of potential which is
required to be measured against a known difference of potential thereby bringing
two points of the system to the same potential; one of these points may be con-
nected to earth and the other point may be connected to the inductor E, the case
of the instrument being at the same time connected to earth. The electroscope or
its equivalent will then show whether there is a balance or not.
In cases where it is required to compare an unknown positive electro-
motive force with a negative electromotive force of known amount I substitute
for the inductor E two sets of metal plates arranged at equal distances on
either side of the carriers D. One of these sets is connected to the point whose

page_text: potential is known and the other to the point having potential of opposite sign.
The carriers as before make contact with the case of the instrument when between
the sets of plates and receive charges of electricity when the electromotive forces
of the two points are not identical. These charges are imparted by means of
receivers to a needle suspended between charged plates as herein before described
or to other electroscopic apparatus or electrometer.
When it is required to use the instrument for the purpose of detecting difference
of potential between any two points in an electrical system, the case of the instru-
ment may be connected to one of the said two points instead of to earth the other
point being connected to the inductor E.
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 measuring instrument a multiplier consisting of an insulated
part or parts with carriers secured thereto rotated in the neighbourhood of an
inductor and receiver or a system of inductors and receivers substantially as and
for the purposes set forth.
2. In an electric measuring instrument the combination, with an electroscope or
its equivalent, of a multiplier constructed substantially as hereinbefore claimed and
means for rotating such multiplier.
1005
A. F. SPOONER,
124, Chancery Lane, W.C., Agent for the Applicant.