MEASURING ELECTRICITY
Year: 1884

page_text: I LESLIE BRADLEY MILLER of 20 Bolan Street, Bridge Rd, Battersea in tho
County of Surrey Electrical Engineer do hereby declare the nature of my
Invention for MEASURING ELECTRICITY to be as follows:-
At the bottom of a vertical brass tube is wound a coil or coils of insulated wire,
with or without an outer casing of soft iron, and having its ends connected to
suitable binding screws. Within this brass tube (which has its sides cut away for
the greater part of its length) is a tube of glass closed up at both ends. Inside tho
glass tube at the bottom is, say, three or four inches of mercury. Floating in the
mercury and with about half its length under the surface is a hollow core of thin
soft iron, or other magnetic metal into the top of which is cemented a thin glass
Lube, such as a light thermometer tube, the internal diameter of which is small
compared to that of the iron core. The latter has a small hole bored in each side
just where it rises above the surface of the mercury On the top of the mercury
and around and within the iron core is sufficient spirit to cover the latter and
enter a short distance up the thin glass tube. By means of an adjusting screw
I can raise or lower the glass tube within the brass one and therefore accurately
place the iron core with any determined part of its length out of the solenoid.
As soon as the current is switched on the iron plunger is sucked down and the
mercury rises above the small hole shutting off the spirit inside the core from that
outside. As the core is further sucked down the mercury, acting like a piston,
drives the spirit before it up the narrow tube. The height of liquid in the latter
can therefore be made to measure the current and by properly proportioning the
diameter of the core, or that of the thin glass tube, or both, the rise of the liquid in
inches can be made proportional to the current in ampéres so that the latter can be
read off at once on a scale.
To prevent air bubbles interfering with the accuracy of the readings I may
exhaust the air, contract the inner glass tube very much in one place, or place a
fine thread within the tube.
By using a solenoid of very high resistance an instrument of this description
can be made to measure difference of potential in volts. If a fine wire shunt
solenoid is employed in the place of the soft iron core it will measure electric energy
in volt-amperes.
In conclusion I wish to point out that I do not confine myself to the above
mentioned hollow iron tube as the plunger of my instrument but may use any
combination of magnetic and non-magnetic materials in order to secure a rapid
rise of liquid in the fine glass tube for a small movement of the core of the
solenoid.

page_text: I, LESLIE BRADLEY MILLER, of 20 Bolan Street, Battersea, London Electrical
Engineer do hereby declare the nature of my invention for IMPROVEMENTS IN
APPARATUS FOR MEASURING ELECTRICITY 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 Improvements in Electric Meters. Instruments con-
structed according to my invention can be made to measure amperes, volts, or
volt-amperes.
The following is a description of one form of my ampero meter:-
At the lower end of a vertical brass tube a coil or coils of insulated wire is
wound, having the ends connected to suitable terminal screws fixed in a circular
wooden base. Inside the brass tube, (which has its sides cut away for the greater
part of its length) there is a closely fitting glass tube closed at its lower end by
fusion. At the bottom of the glass tube, where it is within the wire solenoid,
there is a small quantity of mercury, and over this some alcohol colored rod.
Floating in the mercury and alcohol is the plunger of the instrument, the con-
struction of which is as follows:-I take a small piece of sheet charcoal iron, thin
and extremely soft, and bend it into a tube. This forms the core of the solenoid.
I then take a piece of glass tube similar to a thermometer tube but not so thick
and fuse it to the top of a short length of glass tube of such an internal diameter
that the iron core will just fit into it and project a short distance underneath.
Into the bottom of the iron core I fix four small guides to keep the plunger central
(The core and the glass surrounding it will hereafter bo called "the plunger," and
the prolongation of the glass upward the "indicating tube"). I then lower the
whole into the mercury and spirit and find the level at which it will float and
there I make a small hole through the iron or through both iron and glass. In
order to increase the buoyancy of the plunger I sometimes surround the iron core
below the glass with a small ring of ebonite. Finally I close up the top of the
outer glass tube, either by fusion or with an indiarubber stopper, having previously
formed a small guide of twisted wire to keep the top of the indicating tube at the
centre of the outer glass tube. The spirit cannot therefore evaporate, and tho
instrument may be casily transported and even inverted without being damaged or
disarranged.
The action of the instrument is as follows:-
When the current passes round the solenoid the iron core of the plunger is
attracted towards the centre of the solenoid. Directly it commences to move
downward the small hole or valve at the junction line between the spirit and the
mercury is covered up by the latter, and the spirit inside the plunger, having no
exit, is forced up the bore of the indicating tube for a distance depending on the
power of the current to drag down the iron and glass against the buoyancy of the
mercury and spirit, a small movement of the plunger necessarily causing a large
rise of the spirit in the fine tube. I have found by experiment that if the core is
about two thirds of its length within the solenoid, and moves only through a small
distance, the rise of the spirit as shown on a conveniently placed scale is pro-
portional to the current strength when the glass and core are quite cylindrical
and the iron very soft and thin. If these conditions are not fulfilled the readings
will not be proportional but must each be marked separately on the instrument.
If, however, some other non-magnetic material, such as ebonite, is used instead of
the glass it may be turned till its shape is made such that the distance it will

page_text: be pulled down is strictly proportional to the current strength. Therefore by
constructing a core in the manner described, that floats in mercury or, preferably,
in mercury and a lighter fluid that will act as a lubricant, a vertical movement
that is strictly proportional to current strength may always be obtained and
this movement may be utilized in various forms of electrical measuring instruments.
When I intend the instrument to incasure amperes I wind the solenoid with a
few turns of thick wire placed in the main circuit; when volts are to be measured
I use thin wire offering a high resistance placed as a shunt to the main circuit;
and when volt-amperes are to be measured I either wind the solenoid with both
main and shunt wires or I wind the solenoid with the main wire and the core with
the shunt wire protecting the latter from the mercury by gutta percha and making
suitable flexible connections.
In the accompanying sheet of drawings Fig 1 is a side view of one form of my
electric meter, Fig 2 is a contral vertical section of the saune, Fig 3 is a section
plan or top view through the line x. x Fig 2, and Fig 4 is a detailed view drawn
to an enlarged scale.
Referring to the drawings a is the solenoid, b the protecting brass tube, c the
outer glass tube, & the mercury, e the alcohol, h the iron core, ¹ the iron guides
in the core, * the small hole in the core at the junction line between the mercury
and the spirit, i the glass portion of the plunger, j the indicating tube, ka screw
for regulating the position of the iron core, k¹ a piece of ebonite interposed between
the screw & and the bottom of the tube, a washer interposed between the nut m
and the base of the instrument n.
Having now particularly describod and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. In an electric meter the employment in combination with a solenoid of a
plunger constructed partly of iron and partly of non-magnetic material arranged to
Boat in mercury, or in mercury and a second lighter fluid, substantially as
liereinbefore described.
2. In an electric meter the employment in combination with a solenoid of a
plunger constructed partly of iron and partly of a non magnetic material floating
in mercury, or in mercury and a lighter fluid, so formed that its vertical movement
due to the action of an electric current circulating through the said solenoid shall
be proportional to the strength of the said current.
3. In an electric meter the method of indicating or measuring the strength of an
electric current by the rise or fall of a column of liquid substantially as herein-
before described.
4. In an electric meter the combination with the solenoid a of the outer glass
tube c, the plunger e, the indicating tube d, the mercury f, & the indicating
fluid g, substantially as herein before described and for the purpose set forth.
5. The electric meter constructed arranged and operating substantially as
described with reference to the drawings.
Deted this 10th day of October 1881