AN ELECTRIC AND MAGNETIC METER
Year: 1884

page_text: I, CHARLES DENTON ABEL of No 28 Southampton Buildings, Chancery Lane
in the county of Middlesex, Consulting Engineer and Patent Agent, do hereby
declare the nature of the said invention for "AN ELECTRIC AND MAGNETIC
METER" to be as follows:-
"
It is known that when a moveable conductor of electricity is placed in a magnetic
field so that the direction of the electric current is at right angles to the line of
force, the conductor tends to move with a force proportionate to the intensity of
the current and that, of the magnetic field.
.
This invention relates to means of applying this principle for the purpose of
measuring eléctric or magnetic force. For this purpose, an insulated tube containing
mercury is placed in the magnetic field, which may consist of a horse-shoe magnet,
between the poles of which is a block of ebonite or other suitable insulating
material formed of two longitudinal halves fixed together and having a horizontal
channel formed therein, in the ends of which are fixed the ends of two graduated
vertical glass gauge tubes, which together with the insulated channel form the
receptacle or gauge containing the mercury. Two platinum plates are fixed to
contact posts secured to the upper and underside of the ebonite block and have
their inner ends in contact with the mecury in the channel, such platinum plates
being at right angles to the channel and to the lines of force. An electric current
of the intensity i being passed through the two contact posts, platinum strips, and
mercury, will produce a force at right angles to the direction of the current and to
that of the lines of magnetic force, thereby causing the mercury to move so as to
establish a difference of level thereof in the two vertical tubes which difference of
level will be proportional to the intensity of the magnetic field.
If m be this intensity and the height of the mercury between the platinum
electrodes the force produced will be--
T = im I

page_text: by altering the form of the gauge tubes and the liquid contained in the upper part
of the one or the other of these.
The one tube may be of large diameter so that the level of the mercury does
not materially vary therein, while the other may be of small diameter and may
contain water above the mercury.
The variations of level of the mercury may either be read off directly on the
glass gauge, or this may contain a float imparting motion to an index moving either
along a graduated scale, or round a dial.
The mercury channel may be made of a tortuous form in order still further to
increase the sensitiveness of the apparatus.
The magnetic field may either be formed by a permanent magnet or by an
electromagnet or a solenoid, the exciting electric current in the two last cases being
either the total current to be measured or a branch thereof or an independent
constant current.
When using a solenoid, or an electromagnet, the sensitiveness increases with the
intensity of the current, while with the electromagnet, it becomes constant when
the soft iron core is saturated.
When using a solenoid, the instrument will constitute an electro-dynamometer,
the constant of which can be determined accurately from its form and dimensions.
Alternating currents can also be measured by this apparatus by employing an
electromagnet, the exciting current of which is either a branch of the main current,
or the main current itself. For determining magnetic intensities by means of
this instrument an electric current of known intensity is passed through the
mercury, the variations of the level of which will indicate the magnetic intensity.
If the magnetic field is of an alternating nature there is substituted for the before
mentioned constant current, the alternating current that produces the magnetic
field, the intensity of which will be measured by the above described electro-
dynamometer.
ABEL & IMRAY,
Agents for the Applicant,
28, Southampton Buildings,
London, W.C.
3

page_text: COMPLETE
"
I, CHARLES DENTON ABEL of N° 28 Southampton Buildings, Chancery Lane,
in the county of Middlesex, Consulting Engineer and Patent Agent do hereby
declare the nature of my said invention for "AN ELECTRIC AND MAGNETIC METER
and in what manner the same is to be performed to be particularly described
and, ascertained in and by the following statement:—
It is known that when a moveable conductor of electricity is placed in a magnetic
field so that the direction of the electric current is at right angles to the lines
of force, the conductor tends to move with a force proportional to the intensity of
the current and that of the magnetic field. This invention relates to means of
applying this principle for the purpose of measuring, electric or magnetic force.
The accompanying drawing shews the construction of apparatus employed for
this purpose.
Fig. 1 shews a front view, fig. 2 an end view and fig. 3 a plan of the same;
figs. 4 and 5 shew details of the connection of the two branches of the gauge.
The moveable conductor employed is a thin column of mercury situated between
the poles of a magnet A and forming the horizontal connection between the two
vertical branches ab of a gauge; it is insulated from the polar extremities by
means of paper or other insulating material, and is enclosed between two pieces of
ebonite forming a liquid tight channel to the ends of which are connected glass
gauge tubes a b, which, together with the insulated channel form the mercury gauge.
Two platinum plates are fixed to contact posts B and C secured to the upper and
underside of the ebonite block, and have their inner ends in contact with the
mercury in the channel, such platinum plates being at right angles to the mercury
channel and to the lines of force. An electric current of the intensity i being
passed through the two contact posts from B to C and through the platinum strips
and mercury will produce a force at right angles to the direction of the current
and to that of the lines of magnetic force, thereby causing the mercury to move
so as to establish a difference of level thereof in the two vertical tubes, which
difference of level will be proportional to the intensity of the magnetic field.
If m be this intensity and the height of the mercury between the platinum
electrodes the force produced will be-
F = iml
If d be the amount of displacement, S the thickness of the thread of mercury

page_text: The variations of level of the mercury may either be read off directly on the
glass gauge or this may contain a float imparting motion to an index moving
either along a graduated scale, or round a dial.
The mercury channel may be made of a tortuous form in order still further to
increase the sensitiveness of the apparatus; it may be of any desired transverse
sectional form, and be made of glass, ebonite, or any other insulating material that
is not acted upon by mercury.
The magnetic field may either be formed by a permanent magnet or by an
electro-magnet or a solenoid, the exciting electric current in the last two cases
being either the total current to be measured, or a branch thereof or an independent
constant current.
When using a solenoid or an electromagnet the sensitiveness increases with the
intensity of the current, while with the electromagnet it becomes constant when
the soft iron core is saturated, whereby the apparatus is rendered particularly
applicable for measuring very great intensities, inasmuch as the resistance of the
apparatus can be made as small as desired.
When using a solenoid, the instrument will constitute an electrodynamometer, the
constant of which can be determined accurately from its form and dimensions.
Alternating currents can also be measured by this apparatus by employing an
electromagnet, the exciting current of which is either a branch of the main current
or the main current itself.
Lastly, this apparatus is applicable for determining magnetic instensities; for
this purpose it is sufficient to place it in the magnetic field to be measured, using
it as an Ampère-meter the thickness of the thread of mercury of which is known
and passing through the posts B and C a current, the intensity of which is known.
The variations read off from the gauge tubes will enable the intensity to be readily
determined. If the magnetic field is of an alternating nature there is substituted
for the before-mentioned constant current the alternating current that produces the
magnetic field, the intensity of which current will then be measured by the above
described electro-dynamometer.
Having now particularly described 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, The use for measuring an electric current of apparatus wherein a liquid
conductor is caused to move in a magnetic field to an extent proportionate to the
product of the intensity of the magnetic field with the intensity of the current,
substantially as herein described.
2, The use of apparatus such as is referred to in the preceding claim for
measuring the force of a magnetic field; substantially as herein described.
Dated this 14th day of April 1885:
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