Improvements in Apparatus for Electrical and Magnetic Measurements.
Year: 1892

page_text: Date of Application, 2nd June, 1892
Complete Specification Left, 15th Feb., 1893-Accepted, 29th Apr., 1893
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Electrical and Magnetic
Measurements.
I, JAMES ALFRED EWING, of Langdale Lodge, Cambridge, Professor of
Mechanism and Applied Mechanics in the University of Cambridge, do hereby
declare the nature of this invention to be as follows:-
My improved apparatus for electrical and magnetic measurements consists of a
conducting wire or wires tightly stretched between supports in a magnetic field, a
magnet or other appliance for producing the field, which is arranged in such
a manner that the lines of force of the field lie across the stretched wire, and an
indicating apparatus by, which any deflection of the central portions of the wire
across the lines of force of the field is magnified for observation. When the
magnetic field is in action and the wire is caused to convey an electric current, the
central portions of the wire are deflected to an extent which is proportional to
the current in the wire and to the strength of the field. I use this deflection to
measure variations in either of these quantities provided the other be kept constant,
or to measure their product when both vary. By using a short and very tightly
stretched wire together with an indicator possessing little inertia the apparatus may
be made specially well fitted on account of its "dead-beat" character to exhibit
rapid changes in the quantities it is applied to measure. Several conducting wires
may be used in place of one: and in some cases I employ two distinct wires each
stretched in a distinct magnetic field and connected either to separate indicators or
to a single indicator so constructed that it exhibits simultaneously the deflections of
both the wires. For many purposes, especially in dealing with rapidly varying
quantities, the most convenient indicator is a light mirror attached to the wire in
such a way that when the wire deflects the mirror turns through a corresponding
angle. When it is desired to combine the indications given by two distinct
stretched wires, two such mirrors may be used, arranged in a well-known manner
so that light is successively reflected from both: I also employ a single mirror
connected with both wires and so pivotted that it is free to respond to the deflection
of each by motions which take place at an angle, such as a right angle, with each
other. The magnetic field may be formed by a permanent magnet or group of
magnets or by an electromagnet with or without an iron core. A convenient form
of core for an electromagnet for this purpose is obtained by slitting up one side of
a piece of iron pipe so that a narrow gap is formed in which the wire may be
stretched the pipe is wound as an electromagnet so that the sides of the
opposed poles.
:
gap
form
When the apparatus is to be used simply as a galvanometer, either as an ampère-
meter or as a volt meter, the strength of the magnetic field is kept constant, and
the current to be measured or a known fraction of it is passed through the stretched
wire. When, on the other hand, the stretched wire has a constant current
maintained in it, its deflection serves to measure any change in the strength of the
magnetic field: the apparatus is therefore applicable as a magnetometer. Further,
if the field be produced by means of an electromagnet without an iron core, or with
a core such that the field is sensibly proportional to the exciting current, the
deflection of the stretched wire will be proportional to the product of two currents,
namely the current in the wire itself and the current which is used to excite the
field. Hence the apparatus may be arranged to serve as a Watt-meter.
Rapid variations of the deflection may be exhibited and recorded by means of
several known devices such as projecting a beam of light from the indicating

page_text: mirror or mirrors on a moving sheet of sensitized paper. The sensibility of the
wire to deflection may be adjusted by altering its length or its tightness, as well as
by using currents or fields of various strengths.
By having two distinct conducting wires each stretched in a distinct magnetic
field, the apparatus serves further to exhibit the relation of the current in one wire
to the current in the other, or to the magnetic field in which the other is stretched.
Thus if an alternate current be passed through each of the two wires, while the
magnetic fields are both kept constant, the compound motion which the indicator
receives will show whether the currents have the same frequency. It will also
allow any difference in form and difference in phase between alternate currents of
the same frequency to be examined. If one of the two component motions of the
indicator be caused to have an assigned character the character of the current
which produces the other component of motion can be determined. Thus the
apparatus may be applied to a number of useful purposes in connection with the
observation and analysis of alternate currents as well as to the measurement of
the power spent upon an alternate current circuit.
I further employ the apparatus to exhibit and examine the magnetic properties
of iron or other metals. In this case the metal to be examined is arranged to
form a magnetic circuit in which there is a narrow gap between suitable pole-
pieces, and in this gap one of the two conducting wires is stretched. In this wire
a constant current is maintained: its deflection therefore measures variations in the
magnetism of the magnetic circuit. The magnetism of the magnetic circuit is
produced and varied by means of a magnetising current in a suitable coil; this
inagnetising current passes through the other conducting wire which is stretched
in a constant field. The deflection of this second stretched wire is therefore
proportional to the magnetising force which is applied to the magnetic circuit.
The magnetising current varied in a continuous manner and a mirror or other
indicator which compounds the deflections of the two stretched wires traces out
curves which exhibit the relation of magnetism to magnetising force.
Dated this First day of June 1909
COMPLETE SPECIFICATION.
Improvements in Apparatus for Electrical and Magnetic
Measurements.
I, JAMES ALFRED EWING, of Langdale Lodge, Cambridge, Professor of
Mechanism and Applied Mechanics in the University of Cambridge, 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 improved apparatus for electrical and magnetic measurements consists of a
conducting wire or wires tightly stretched between supports in a magnetic field, a
magnet or other appliance for producing the magnetic field, which is arranged in
such a manner that the lines of force of the field lie across the stretched wire, and
an indicating apparatus by which any deflection of the central portions of the wire
across the lines of force of the field is magnified for observation. When the
magnetic field is in action and the wire is caused to convey an electric current the
central portions of the wire are deflected to an extent which is proportional to
the current in the wire and to the strength of the field. I use this deflection to
measure variations in either of these quantities provided the other be kept constant,
or to measure their product when both vary.
By using a short and very tightly stretched wire, together with an indicator
possessing little inertia, the apparatus may be made specially well fitted on account
of its "dead-beat" character to exhibit rapid changes in the quantities it is applied
to measure. Several conducting wires may be used in place of one, and in some
cases I employ two distinct wires each stretched in a distinct magnetic field and

page_text: connected either to separate indicators or to a single indicator so that it exhibits
simultaneously the deflections of both the wires. For many purposes, especially
in dealing with rapidly varying quantities, the most convenient indicator is a light
mirror attached to the wire in such a way that when the wire deflects the mirror
turns through a corresponding angle. When it is desired to combine the indica-
tions given by two distinct stretched wires two such mirrors may be used, arranged
in a well-known manner so that light is successively reflected from both. I also
employ a single mirror connected with both wires and so pivotted that it is free to
respond to the deflection of each, by motions which take place at an angle (such
as a right angle) to each other. The magnetic field may be formed by a per-
manent magnet or group of magnets, or by an electro-magnet with or without an
iron core.
A convenient form of core for an electromagnet for this purpose is
obtained by slitting up one side of a piece of iron or steel pipe so that a narrow
gap is formed in which the wire may be stretched. The pipe is wound as an
electromagnet, or is permanently magnetised, in such a way that the sides of the
gap form opposed poles.
When the apparatus is to be used simply as a galvanometer, whether as an
ampère-meter or as a volt meter, the strength of the magnetic field is kept constant,
and the current to be measured, or a known fraction of it, is passed through the
stretched wire. When, on the other hand, the stretched wire has a constant
current maintained in it, its deflection serves to measure any change in the strength
of the magnetic field: the apparatus is therefore applicable as a magnetometer.
Further, if the field be produced by using an electromagnet without an iron core,
or with a core such that the field is sensibly proportional to the exciting current,
the deflection of the stretched wire will be proportional to the product of the two
currents, namely the current in the stretched wire itself and the current which is
used to excite the field. Hence the apparatus may be arranged to serve as a
Watt meter and also as an electrodynamometer. Rapid variations of the deflection
may be exhibited and recorded by means of several known devices such as pro-
jecting a beam of light from the indicating mirror or mirrors upon a screen, which
may be photographically sensitive and may be caused to move.
the stretched wire to deflection may be adjusted by altering its length or its
The sensibility of
tightness as well as by using currents of various strengths.
By having two distinct conducting wires, each stretched in a distinct magnetic
field, the apparatus serves further to exhibit the relation of the current in one
wire to the current in the other wire, or to the magnetic field in which the other
is stretched. Thus if an alternate current be passed through each of the two
wires while the magnetic fields are both kept constant, the compound motion which
the indicator receives will show whether the currents have the same frequency.
It will also allow any difference in form and difference in phase between alternate
currents of the same frequency to be examined. If one of the two component
motions of the indicator have an assigned character the character of the current
which produces the other component of motion can be determined. Thus the
apparatus may be applied to a number of useful purposes in connection with the
observation and analysis of alternate currents as well as to the measurement of
the power spent upon an alternate current circuit.
I further employ the apparatus to exhibit and examine the magnetic properties
of iron or other metals. In this case the metal to be examined is arranged to form
a magnetic circuit in which there is a narrow gap between suitable pole-pieces, and
in this gap one of the two conducting wires is stretched. In this wire a constant
current is maintained; its deflection therefore measures variations in the magnetism
of the magnetic circuit. The magnetism of the magnetic circuit is produced and
varied by means of a magnetising current in a suitable coil or coils surrounding
the metal under test. This magnetising current passes through the other con-
ducting wire, which is stretched in a constant magnetic field. The deflection of this
second stretched wire is therefore proportional to the magnetising current which is
applied to the magnetic circuit of the metal under test. The magnetising current

page_text: being varied in a continuous manner, a mirror or other indicator which compounds
the deflections of the two stretched wires traces out curves which exhibit the
relation of the magnetisation of the metal under test to the magnetising force
which acts upon it. I call the apparatus arranged in this way a magnetic curve
tracer.
In order that my said invention may be most fully understood and readily carried
into effect I will proceed to describe the drawings hereunto annexed.
Figures 1 and 2, Sheet I, show the apparatus in a form suitable for the measure-
ment of electric currents. Figure 1 is a front elevation and Figure 2 is a sectional
side elevation. The conductor a b is supported by a fixed bridge at a and a hinged
bridge at b, and is kept tightly stretched by the weight W. It stands in a narrow
slot in the tubular magnet c c. When a current passes through the conductor a b
:
it bends out or in and deflects the mirror & which is held in such a manner that the
bending of a 6 causes the mirror to turn through a small angle. Figure 3 shows a
method of supporting the mirror d e is a wire capable of torsion, to which the,
mirror is attached by turning the pin f the torsion of this wire can be adjusted to
cause a point at one side of the mirror to press against the stretched conductor a b.
Figures 4 and 5 show another form of the apparatus, in which two conducting
wires ab and a¹¹ are stretched side by side in the same magnetic field: the current
passes down one and up the other causing the middle portion of one to bend out and
that of the other to bend in. Both motions contribute to turn the mirror d. The
motion of the mirror is due to the bending of the two conductors individually and
not to a rotation of the conducting system as a whole, as in the well-known
galvanometer of D'Arsonval. By substituting a coil for the magnet of Figures 1
and 2, or of Figures 4 and 5, the apparatus may be modified to serve as a Watt
meter or as an electro dynamometer.
The
Figures 6, 7, and 8, Sheet II, show one form of the magnetic curve tracer.
metal whose magnetic qualities are to be examined is made to form the limbs g g of
an electromagnet, which is completed by a soft iron yoke and pole-picces i i
between which there is a narrow gap forming the field in which one conductor ab
is stretched. Another conductor a¹ is stretched within a slot in the tubular
electromagnet c. The conductors are connected by threads kk with a small cradle
which carries the mirror d, and the mirror cradle is pivotted upon a single fixed
point in such a manner that it is deflected by either thread, the threads being kept
taut by a pair of light springs. The suspension of the mirror is shown separately
in Figure 9. The fixed point which supports the mirror cradle may have its
position adjusted both horizontally and vertically by screws, as is shown in Figure 8.
The conductor a¹ is electrically connected with the coils of the magnet limbs
so that the magnetising current passes through a¹¹ and is measured by the bending
of a¹ b¹. A constant current is maintained in a band the bending of a b
consequently measures the magnetisation of gg. Thus the mirror receives two
component motions one proportional to the magnetising current and the other to
the magnetisation of the metal under examination. The constant current which
passes through a b may also be used to excite the tubular magnet c. The magnetic
circuit of which gg form part is arranged to admit of the substitution of one sample
of metal for another in the limbs g g, the yoke and pole-pieces being attached to
the limbs by clamps which allow the limbs to be readily removed and replaced.
99
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, in apparatus for electrical or magnetic measurement, of a conducting
wire or wires tightly stretched between supports in a magnetic field, together with
a magnet or other appliance for producing the field arranged so that the lines of
force of the field lie across the stretched wire or wires, and an indicating apparatus
by which the bending of the central portions of the wire or wires across the lines of
force of the field is magnified for observation.

page_text: 2. A galvanometer in which the current to be measured passes through a
conductor tightly stretched between supports in a magnetic field, causing the central
portions of the conductor to bend in consequence of electromagnetic force, with an
indicator which exhibits the amount of bending of the conductor.
3. A galvanometer with two stretched conductors substantially as described and
shown in Figures 4 and 5.
1. Apparatus for measuring electric currents or electric work, in which the
product of two currents is determined by making one of them traverse a conductor
tightly stretched in a field due to the other current, the bending of the stretched
conductor operating an indicator.
5. The magnetic curve tracer substantially as described.