Year: 1886

page_text: Circuit.
I, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain do hereby declare the nature of this invention to be
as follows:-
:-
This apparatus consists of an inspectional magneto-static current meter used in
connection with adjustable resistance coils, and an electrodynamic balance, with
electrolytic apparatus for determining its constant, by which the co-efficient of the
current meter, varying as it does from time to time, is at any time determined in
terms of constant units.
The magneto-static current meter consists of a suspended magnet, preferably a thin
circular disc of steel, suspended by a silk fibre so as to be in the centre of the field of
a double electro-magnetic coil so arranged as to give, as nearly as may be, an uniform
magnetic field in its centre. The controlling magnets are adjustably fixed in an iron
sheath enclosing the electro-magnetic coil, and their distances from the centre of the
field are adjusted, and varied, if need be, from time to time, to give any convenient
value to the co-efficient, according to comparison with the electro-dynamic
balance. The indicator of deflections of the suspended magnet may be either a non-
magnetic needle pointing to divisions on an adjustable tangent scale, or a ray of light
reflected from a mirror, and it may be either wholly outside the iron sheath, or it may
project from the inside to the outside transversing a horizontal slot in the sheath.
The upper end of the fibre is attached to a spring yielding so freely to a downward
pull that before the fibre can be broken, the suspended magnet and attached needle or
mirror reaches the bottom of its range. The electro-dynamic balance consists of a
piece of soft iron, or a moveable coil made temporarily magnetic in virtue of the
current to be measured, and actuated by the electro-magnetic force of a fixed coil or
coils through which the current passes. The piece of soft iron may be suspended on
a gravity balance and actuated in the manner described in the specification of the said

page_text: Sir William Thomson Number 11,106 A.D. 1884, but for sea use, I prefer to make it
in the shape of an oblate spheroid and to suspend it on a stretched elastic wire. Its
tendency to turn its equatorial plane to .parallelism with the lines of force of the
fixed coil or coils, balanced by the torsion of the wire after the manner of a Coulomb's
torsion balance, shews the strength of the current to be measured. For land use I
prefer a moveable coil and a gravity balance with a trunnion to prevent horizontal
motion of the axis of the balance, and with decimal arrangements for putting on and
taking off the weights. The resistance coils are of wire, preferably platinoid, wound
on metal drums or cores, preferably copper coated with thin insulating material such
as varnished paper, so that the heat generated by the current may be carried away
whether by emission to air, or by aid of a stream of water across the uncoated parts
of the surface of the core. The coils are either each separately moveable and are
placed in combination, in series or in multiple arc, by stout metal terminals dipping
into cups of mercury, or they are connected by means of copper spring wedges
between fixed terminals of the coils and fixed studs of copper. To adjust the
resistance continuously to any desired amount, I use an improved form of
Wheatstone's rheostat in which the wire is guided from one cylinder to the other by a
fork carried along through the requisite range by a nut travelling on a long screw shaft.
This screw shaft carries a toothed wheel which turns the two cylinders by means of
toothed wheels attached to their shafts a watch-spring as in Joulin's improvement of
Wheatstone's rheostat keeps the wire always tightened to the proper degree. A
leather buffer at each end of the range of the nut acts as a guard against overwinding
in either direction.
The current of the circuit is divided into two branches, one of them a known high
resistance in circuit with the magneto-static current meter, and the other through the
electrolytic vessel, the electro-dynamic balance, and a resistance continuously
regulated by the rheostat. The rheostat is worked by hand so as to keep the current
as indicated by the electro-dynamic balance very accurately constant during a certain
time an hour for example and the quantity of copper deposited or dissolved during
that time in the electrolytic vessel is determined by accurate weighing. Thus,
according to the known electro-chemical equivalent of copper, the strength of the
current is calculated in absolute units; and from it, the co-efficient of the magneto-
static current meter, and the constant of the electro-dynamic balance are determined.
In continued use of the apparatus on an electric lighting circuit, the working circuit
of the lights takes the place of the regulating by rheostat. The electro-dynamic
balance shews the strength of the current at any time by the proper adjustment of its
weights; the electrolytic appliance shews the whole quantity of current that has
passed in any time and the magneto-static current meter shews the potential of the
circuit.

page_text: COMPLETE SPECIFICATION (AMENDED).
Improved Apparatus for Measuring the Efficiency of an Electric
Circuit.
I, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain 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:-
This apparatus consists of an inspectional magneto-static current meter used in
connection with adjustable resistance coils, and an electro-dynamic balance, with
electrolytic apparatus for determining its constant, by which the co-efficient of the
current meter, varying as it does from time to time, is at any time determined in
terms of constant units.
The magneto-static current meter consists of a suspended magnet, preferably a thin
circular disc of steel, suspended by a silk fibre so as to be in the centre of the field of
a double electric-magnetic coil so arranged as to give, as nearly as may be, a uniform
magnetic field in its centre. The controlling magnets are adjustably fixed in an iron
sheath enclosing the electro-magnetic coil, and their distances from the centre of the
field are adjusted, and varied, if need be, from time to time, to give any convenient
value to the co-efficient, according to comparison with the electro-dynamic balance.
The indicator of deflections of the suspended magnet may be either a non-magnetic
needle pointing to divisions on an adjustable tangent scale, or a ray of light reflected
from a mirror, and it may be either wholly outside the iron sheath, or it may project
from the inside to the outside traversing a horizontal slot in the sheath. The upper
end of the fibre is attached to a spring yielding so freely to a downward pull that
before the fibre can be broken, the suspended magnet and attached needle or mirror
reaches the bottom of its range.
The electro-dynamic balance consists of a piece of soft iron, or a moveable coil
made temporarily magnetic in virtue of the current to be measured, and actuated by
the electro-magnetic force of a fixed coil or coils through which the current passes.
The piece of soft iron may be suspended on a gravity balance and actuated in the
manner described in the specification of the said Sir William Thomson, Number
11,106 A.D. 1884, but for sea use, I prefer to make it in the shape of an oblate
spheroid and to suspend it on a stretched elastic wire. Its tendency to turn its
equatorial plane to parallelism with the lines of force of the fixed coil or coils, balanced
by the torsion of the wire after the manner of a Coulomb's torsion balance, shows the
strength of the current to be measured.
For land use I prefer a moveable coil and a gravity balance with a trunnion to
prevent horizontal inotion of the axis of the balance, and with decimal arrangements
for putting on and taking off the weights.
The resistance coils are of wire preferably platinoid, wound on metal drums or
cores, preferably copper coated with thin insulating material such as varnished paper,

page_text: so that the heat generated by the current may be carried away whether by emission
to air, or by aid of a stream of water across the uncoated parts of the surface of the
core. The coils are either each separately moveable and are placed in combination,
in series or in multiple arc, by stout metal terminals dipping into cups of mercury,
or they are connected by means of copper spring wedges or copper cams between
fixed terminals of the coils and fixed studs of copper.
To adjust the resistance continuously to any desired amount, I use an improved
form of Wheatstone's Rheostat in which the wire is guided from one cylinder to the
other by a fork carried along through the requisite range by a nut travelling on a
long screw shaft. The screw shaft carries a toothed wheel which turns the two
cylinders by means of toothed wheels attached to their shafts a watchspring as in
Jolin's improvements of Wheatstone's Rheostat keeps the wire always tightened to
the proper degree. A leather buffer at each end of the range of the nut acts as a
guard against over winding in either direction.
The current of the circuit is divided into two branches, one of them a known high
resistance in circuit with the magneto-static current meter, and the other through
the electrolytic vessel, the electro-dynamic balance, and a resistance continuously
regulated by the rheostat. The rheostat is worked by hand so as to keep the current
as indicated by the electro-dynamic balance very accurately constant during a certain
time an hour for example-and the quantity of copper deposited or dissolved during
that time in the electrolytic vessel is determined by accurate weighing. Thus,
according to the known electro chemical equivalent of copper, the strength of the
current is calculated in absolute units; and from it, the co-efficient of the magneto-
static current meter, and the constant of the electro-dynamic balance are determined.
In continued use of the apparatus on an electric lighting circuit, the working circuit
of the lights takes the place of the regulating by rheostat. The electro-dynamic
balance shews the strength of the current at any time by the proper adjustment of its
weights; the electrolytic appliance shews the whole quantity of current that has
passed in any time and the magneto-static current meter shews the potential of the
circuit.
In order that my Invention may be properly understood and readily carried into
effect, I will now proceed to describe the drawings hereunto annexed.
The magneto-static current meter is shewn at Figures 1 to 7 inclusive in the
annexed sheets of drawings. It consists of a suspended magnetic needle preferably
a thin circular disc, plate, or bar, of steel suspended by a silk fibre so as to be in the
centre of the field of a double electro-magnetic coil so arranged as to give as nearly
as may be an uniform magnetic field in the centre. The double electro-magnetic coil
may be two circular coils A, Figures 1, 2 and 3 of sheets 1, 2 and 3, placed according
to the well-known Helmholtz principle, or when only one turn of the conductor is
used in each coil, they may for convenience of manufacture be D-shaped as shewn at
A, in Figures 4 and 5 of sheet 4, but for some purposes and especially for marine
use I prefer to make the coil of one turn of broad copper ribbon of some such shape
as that shewn at A, in Figures 6 and 7 of sheet 5 (which shews a sectional plan and
an elevation of the central portion of the instrument) and to support the magnetic
needle in its centre by means of a rigid axis B, passing through the centre of inertia
of the magnetic needle and its attachments and resting on knife edges or fine pivots
on the supports C. D. For marine use in this way the instrument is turned on its
side and supported by fixing the levelling screws E, to the wall of the room or to a
vertical support in such a way that the index turns round in a vertical plane.
The controlling magnets are adjustably fixed in an iron sheath enclosing the
electro-magnetic coils and their distances from the centre of the field are adjusted and
varied, if need be, from time to time to give any convenient value o the co-efficient
according to comparison with the electro-dynamic balance. In some cases the iron
sheath may be dispensed with and I then fix the magnets to the framework of the
instrument in the manner shewn at F, in Figures 1 to 5 or in an equivalent manner,
and their distances from the centre of the field are adjusted and varied, if need be, as
herein before described. The magnet system rests on a table G, G, which can be

page_text: screwed nearer to or further from the centre of the coils along a screwed rod H, and
can be clamped in any desired position by means of a clamping nut I. When the
table is clamped in any position the controlling magnet system can be turned in its
own plane so as to bring the index which shews the deflections of the suspended
magnetic needle to zero without turning the table and hence without altering the
intensity of the field at the centre of the coils. The magnet is held firmly against the
top of the table G by means of a flexible bar N, in the manner clearly shewn in the
accompanying drawings. The indicator of deflections of the suspended magnet may
be either a non-magnetic needle L, pointing to divisions as an adjustable tangent
scale M or a ray of light reflected from a mirror and it may be either wholly outside
the iron sheath or, as shown at d, in Figures 11 and 13 of sheet 9 (being drawings of
my electro-dynamic balance) it may project from the inside to the outside transversing
a horizontal slot in the sheath. The upper end of the fibre is attached to a spring O,
Figures, 1, 3, 4 and 5, yielding so freely to a downward pull that before the fibre can
be broken the suspended magnet and attached index or mirror reaches the bottom of
its range. The height of the point of suspension can be varied by the screw P, on
the end of which the spring O, rests. Side motion of the suspended system is
prevented by guard rings 64, Figures 1, 2 and 3 which are made large enough not to
touch the vertical rod which carries the disk but small enough to prevent risk of
damage to the suspending fibre by side motion. The instrument is supported on three
levelling screws of the form shewn at E in Figures 1, 2 and 4, of sheets 1, 2 and 4.
It consists of a screwed rod fixed at the centre, and with its length at right angles to
the plane, of a circular plate provided with holes through which it can be screwed to
the table or other support. The instrument rests on the nuts Q, which can be screwed
up or down along these rods and fixed in any desired position by means of clamping
nuts R, in the manner shewn in the drawings Figures 1, 2 and 4.
The electrodes S, which convey the current into and out from the coils are preferably
made of several strands of copper cord made up of thin copper wires. The two
electrodes are when necessary twisted together so as to practically annul the action of
the incoming and outgoing currents on the needle.
The electro-dynamic balance consists of a piece of soft iron or a movable coil made
temporarily magnetic in virtue of the current to be measured, and actuated by the
electro-magnetic force of a fixed coil or coils through which the current passes. The
piece of soft iron may be suspended on a gravity balance and actuated in the manner
described in the specification of the said Sir William Thomson Number 11,106 A.D.
1884, but for use on board ship, I prefer to make it in the shape of an oblate spheroid
and to suspend it on a stretched elastic wire. Its tendency to turn its equatorial plane
to parallelism with the lines of force of the fixed coil or coils, balanced by the torsion
of the wire after the manner of a Coulomb's torsion balance, shews the strength of the
current to be measured.
The manner in which this is carried out is shewn in the drawings Figures 8, 9, 10,
11, 12 and 13, sheets 6, 7, 8 and 9 of which Figure 8, is a side elevation, Figure 9, a
front elevation, Figure 10, a vertical section, Figure 11, a plan of the top, Figure 12,
a plan of the bottom and Figure 13, a horizontal section through the scale box above
the index of the instrument. A brass tube T, has fixed near the middle of its length a
coil of insulated wire U, which may be a coil of copper wire insulated with silk
or any other equivalent form. Near the centre of the axis of this coil the oblate
spheroid of soft iron V-Figure 13 is suspended by an elastic wire W, from
two springs X, fixed to adjusting screws Y, in the manner shewn in Figures 10
and 13, sheets 8 and 9 with its equatorial section vertical but inclined at such an
angle to the axis of the coil, that when the lowest current the instrument is required
to measure is passed through the coil the spheroid assumes a position in which
under the electrical forces and the torsional force of the suspension, it has just a
sensible amount of stability. The middle portion of the tube T, is surrounded
by an iron sheath Z, on the side of which a scale box a, is fixed. This scale box
is provided with a glass or other transparent cover through which the scale b, Figures 11

page_text: and 13, and the position relatively to it of the end of a light index C, attached to
the spheroid of soft iron can be observed. The index passes from the inside to the
outside of the iron sheath through a horizontal slot d, Figure 13, which is made long
enough to allow the index to transverse the whole of the scale b. In order to allow
the instrument to be so adjusted that its indications are nearly enough the same
whether the current flows in one direction or the other through the coil U, I use two
or more magnets e, adjustably fixed in the upper part of the iron sheath in such a way
that they can be screwed further into or out of the sheath and that part of the sheath
turned in azimuth until the necessary adjustment is obtained after which the magnets
are clamped by the lock nuts f, and the sheath by the screws g. Should this adjust-
ment not be perfectly made the necessary correction can be nearly enough obtained
by taking the mean of the indications of the instrument when the current is caused to
flow first in one direction and then in the other through the coil U. In order to
facilitate the reversal of the current a commutator or reversing key h, is added to the
instrument.
For land use and for a standard instrument not liable to change with time, I prefer
a movable coil and a gravity balance with a trunnion or other equivalent arrangement
to prevent horizontal motion of the axis of the balance.
One method of carrying out this part of my Invention is shewn in Figures 14 to 26
of sheets 10 to 16 inclusive of the accompanying drawings referring to which tho part
marked i, represents the beam of the balance which is either supported on knife edges
or suspended in the manner to be hereinafter described near one end and made to
carry a coil, at the other end the weight of the coil and beam being counterpoised
by weight added to the beam on the side of the suspension remote from the coil.
In this form I sometimes use a set of weights and lifters of the form shewn in
Figures 19 to 26 of sheets 15 and 16. The lifter is shewn separately in Figures 22
and 23. It consists of a straight piece k, pivoted at one end 1, and having attached
to it near the other end, a knee piece m, in such a way as to form a fork. When the
lever k, is raised the fork lifts the weights by the cross bars n, n, which are fixed to
them in the manner shewn in Figures 25 and 26 of sheet 16.
I arrange the weights in three groups as shewn at o, o, o, Figures 20 and 21 of
sheet 15 and make the weights in the different groups preferably in the ratio of
10, 100, 1000 and the weights in each group equal. I prefer as shewn to make each
group of weights in the form of a chain (the several links of which each constitute a
weight) and to hang the three chains from a stirrup p, which in its turn hangs from
two knife edges q, (Figures 14, 15 and 16) one of which is fixed at each end of the
transverse diameter of the coil so that the gravitation force of the weights acts directly
against the electro-dynamic force of the coils when the current is flowing through
them. A hook of the form shown in Figure 24, is passed over the lower link of each
chain as shewn in Figure 20, and is convenient for holding the chains in position
when the instrument is being transported from place to place. Forces smaller than
can be measured by the smallest weights in the chains are estimated from the extension
of a fine spiral spring, enclosed in the tube s, and acting on the same stirrup p.
The extension of the spring can be read on the scale t, Figure 15, which is opposite
the lower end of the spring and the position to be taken as that of zero extension may
be adjusted by sliding the scale t, along a second scale u, Figure 15. The spring can
thus be used for the purpose of bringing the beam of the balance to a horizontal
position as indicated by the index v, which is attached to the front of the movable coil,
pointing to zero on the scale w, Figure 15. The arrangement of weights and lifters
hereinbefore referred to with reference to Figures 10 to 20 is also applicable to
ordinary weighing balances. The suspended coil j, is acted upon by one or more but
preferably by two fixed coils x, Figures 15, 16 and 18, which may be either flat coils
of approximately the same mean diameter as the suspended coil and arranged with
their planes nearly horizontal one above and the other below the movable coil as
shewn in another form of this instrument at Figures 27 and 28, sheets 17 and 18 of
the accompanying drawings or coils of comparatively small depth in the direction of

page_text: the diameter and of external diameter somewhat less than the internal diameter of the
suspended coil and fixed coaxially with it. their planes being parallel and nearly
horizontal and at such a distance apart as gives convenient electro-dynamic stability.
The latter form of fixed coils is preferably adopted when the instrument is intended to
be used to measure powerful currents and in such cases the coils are for direct current
measurements, made of copper ribbon of such breadth and thickness as is sufficient to
carry without inconvenient heating the maximum current to be measured. For
alternating-current measurements the coils, both movable and fixed, are constructed
of twisted copper rope made up of sufficiently thin insulated wire to prevent
disturbance from unequal distribution of the current over the cross section of the
conductor. The twist in the rope is to be such that there is nearly enough an integral
number of twists in the rope for each turn round the coil. The section of the rope is
either round or flattened to a ribbon shape as is found most suitable in different cases.
The coils are preferably wound on massive copper bobbins fixed in massive copper or
other metallic plates y, forming the sole plate and framework of the instrument and when
the instrument is intended for the measurement of alternating currents these bobbins
and plates are cut in such a way as to prevent the circulation of induced currents
round them and are supported when necessary on insulating material. These plates
in consequence of their large surface and high thermal conductivity greatly facilitates
the carrying away of the heat generated in the coils by the passage of the current,
and hence to a great extent prevent error from this cause due to change of dimensions
of the beam or upward currents of air. The mode of suspending the beam of the
balance which prefer is shewn in Figures 14 to 17, sheets 10 to 13. It consists of
two flat ligaments z, formed of a sufficient number of very fine wires laid side by side
in one plane. The two ends of this ligament are securely soldered to semi-cylindrical
pieces a, b, the upper pair a¹, of these pieces being fixed to the framework through
the pillars c', and the cross pieces d', and the lower pair 61, to the beam of the balance.
The beam of the balance is prevented from taking such an amount of horizontal
motion in the direction of its length as would bend the ligament so much as to
change the zero reading of the instrument by means of the fork e¹, and the steady
pins. The pins 1, are arranged so as to be out of contact with the sides of the
forks e', when the instrument is in use. The ligamental suspension here referred to is
also applicable to ordinary weighing balunees.
For the highest accuracy, I prefer another form in which the beam of the balance is
suspended from a point near the centre of its length as shewn in Figures 27 to 30 of
sheets 17 to 20 of the accompanying drawings. In this form a coil j, is fixed to both
ends of the beam of the balance and each of these coils is acted on by one or more fixed
coils a, in the manner hereinbefore described with reference to Figures, 15, 16 and 18.
For the weights and lifters, I substitute in this case either scale pans and weights or a
slide 9, fixed to the side of the beam along which weights 7, of the proper magnitude
to give the requisite sensibility, may be moved by means of sliders i, so as to balance
the electro-dynamic forces produced by the current in the coils. The sliders i, may be
of the form shewn in Figures 27 and 28 or as a modification of the form shewn in
Figures 29 and 30. In the form shewn in Figures 27 and 28, a rigid frame furnished
with three feet j, slides along a horizontal platform fixed in front of the instrument and
along the length of which a V-groove is cut forming a guide for two of the feet j.
The slider ¹, carries on it a pivoted frame k¹, held in an upright position by light
springs. An upright piece m³, forming part of the frame k¹, passes through a recess
in the weight and when the weight is to be moved along the slide 9, the frame k¹, is
tilted over in the direction of motion by the finger and then the whole frame is moved
so as to push the weight to the desired position after which when the finger is removed
the upright bar m², assumes a position in the middle of the recess as shewn in Figure 28,
thus leaving the weight clear and the balance free to move.
In the arrangement
shewn in Figures 29 and 30, a pendant n', is substituted for the pivoted frame k', and
the slider is pulled to one side or other by means of threads o', attached to the bottom
of the pendant. When the weight has been moved to the desired position the thread

page_text: is left slack and the pendant by assuming a vertical position under the action of gravity
falls to the centre of the recess in the weight and hence leaves the beam free. The
weight on the right hand end of the slide is intended to be used as a counterpois for
the sliding weight when it is at its zero position and also to give a convenient means
of adjusting the beam of the balance to its zero position. For this purpose it is not
necessary that the frame which carries the pendant should be movable as the
range of motion of the pendant can be made sufficient to give the required
adjustment.
On the slide g', a scale of equal divisions is engraved and also a series of fine notches
corresponding in position to the lines of a second scale p', fixed to the framework of
the instrument in a position above the beam and at the back of the slide. These scales
allow the position of weights on the slide to be at any time read off. The numbers on
the fixed scale p', are proportional to the square roots of the numbers on the scale of
equal divisions g', and hence are such that when the weight is brought to different
positions so as to balance the electro-dynamic force due to different currents, equal
differences of reading indicate equal differences of current.
The instrument is thus
arranged to give direct readings of differences of current. Side motion of the beam
is, in this form of the instrument, prevented by the screws 9, between the points of
which, but not touching them, the slide rests. End motion is prevented in the form
shewn in Figures 29 and 30 by a similar pair of screws fixed to the framework and
adjusted near to but not touching the semi-cylindrical pieces b, and in the form shewn
in Figures 27 and 28, which is intended for small currents and has in consequence
lighter and longer suspension ligaments attached to beam of the balance through a
round central axis or trunnion, by passing this trunnion through a square hole in an
upright piece, adjustably fixed to the sole plate of the instrument, or alternatively by
two screws adjustably fixed on the two sides of the trunnion and guard pieces fixed to
the framework above the trunnion to prevent the ligament being so much slackened as
to damage it should the instrument be turned upside down. The arrangement of
graduated slide with self relieving pendants to move the sliders here described with
reference to Figures 27 to 30 is also applicable to ordinary weighing balances.
When scale pans are employed I prefer for convenience to use two scale pans at each
end of the beam each hung from one of four knife edges forming a prolongation at the
end of the transverse diameter of the coils. When no current is flowing through the
coils the whole or the greater part of the weights to be used in the measurements should
be placed on the scale pan nearest the observer at one end of the beam and balance
restored by weight placed in the most distant pan at the other end. The strength of
current flowing at any time through the coils is then to be estimated from the amount
of weight which has to be transferred from one end of the bean to the other in order
to restore equilibrium.
Another modification of the balance which I used for measuring by the motion
of an index lever over a vertical scale, moderate changes of current and which is
suitable for a volt-meter is illustrated in elevation in Figure 31, sheet 21 and in
plan with the cover on in Figure 32, sheet 22 of the accompanying drawings. This
form differs from those already described in having only one movable coil j, and a
single fixed coil x, and in the addition of a light index s¹, resting on a knife edge
at , and connected to the moveable coil by a hook u¹. A motion up or down of the
movable coil causes this index to turn round its knife edge by an amount which can
be read on the scale ¹, suitably divided to indicate directly percentage changes of
current. The requisite stability to allow the instrument to have a sufficient range is
furnished by the variation of the electrical forces between the two coils as their
distance apart varies. The gravitational force against which the electro-dynamic
force produced by the current acts is obtained by adding the necessary weight, the
amount of which depends on the strength of the current to be measured, to the
movable coil, preferably as nearly as possible at the transverse diameter of the coil,
but in practice it is found more convenient to place the weight, in the form of a round
rod, in a V-trough fixed to the outer end of the coil with its length at right angles to

page_text: that of the beam of the balance. This form of balance is specially suitable in con-
junction with resistance coils for a volt meter to indicate changes in the potential
which is being maintained on an electric circuit. In Figure 31 a resistance coil is
shewn at w', fixed to the underside of the sole plate of the instrument but for more
general use, I prefer to join the instrument in circuit with a set of resistance coils
and with the magneto-static current meter in the manner indicated in Figures 32 to 34
of sheet 22. In this arrangement the resistances may be varied to suit any required
potential within certain limits depending on the magnitude of the resistances, and the
range of variation through which readings can be obtained is continued down to zero
by means of the magneto-static instrument, the constant of which can be at any time
obtained by so varying the resistance that simultaneous readings can be obtained both
on it and on the balance.
The resistance coils show in plan in Figure 34 sheet 22 and in vertical section in
Figure 35, sheet 23, consist of coils a¹, of insulated wire, preferably platinoid wire
covered with silk and soaked in purified paraffin wax wound on a heavy metallic
cylinder y, and covered with a copper sheath z', for the purpose of minimising as
much as possible the changes of temperature caused by the passage of the electric
current. The ends of the coils are connected to vertical rods of copper a², in such a
way that the inside end of the top coil is connected to a rod 1, the outside end to
rod 2; the inside end of coil 2 to rod 2 and the outside end to rod 3; the inside end
of coil to rod 3 and the outside end to rod 4 and so on.
These rods are held in position by a ring 62, and binding screws c², but are insulated
by suitable insulating collars at, from the metal cylinder y', on the upper ends of the
rods a², cams d², fixed to short tubes e³, each having on its upper end a cross head or
handle 2, are fitted. Through the tubes e², pins 92, are passed and when the cam is
pulled up to the level of the top of the ring h², can be pushed in over the end of the
rod a², and serves to keep the cam at that level. The cams can be turned between
two metallic rings h2, and 12, and into contact with the blocks c, which are in metallic
connection with the rods a², and they are so adjusted that when the tube carrying the
cam is at its lower position the cam may be turned into contact with the block c*,
and when the cam is raised to the level of the top of the ring h², and 2, it can be
turned into contact with either of these rings. By putting these cams in the proper
order into contact with these two rings any number of the resistances can be put in
parallel circuit or alternatively by putting any one cam in contact with one of the rings
and any other cam in contact with the other ring the intermediate resistances are
interposed in series between the two rings. Any one or more of the intermediate
resistances may be short circuited by means of the proper cams and blocks c¹.
The rings form the terminal plates of the box.
As an alternative I sometimes fix the cams to the rods a², and make the rods
movable so that they can be turned round their axis, or moved in the direction
of their length so as to perform the same function as the tubes and cams herein-
before described. In this case the block c, or equivalent springy contact pieces
are in metallic connection with the rods a², through flexible wire connecting
pieces and are rigidly fixed to the framework. The rings h², 2, are sometimes
cut through a part of their breadth into as many sections as there are cams for
the purpose of giving flexibility to the ring at the points of contact with the cams.
As another alternative, I sometimes substitute for the rods a², a series of
insulated metal blocks fixed between the rings h², 2, and I then make the con-
nections between the blocks and the rings by suitable contact plugs preferably
split plugs or springs so constructed as to maintain elastic pressure on the sides
of the blocks and rings.
To adjust the resistance continuously to any desired amount, I use an improved
form of Wheatstone's Rheostat one form of which is shewn in Figures 36 to 38 of
sheets 24 to 26 of the accompanying drawings. Referring to these drawings a screw
shaft, provided at one end with a convenient handle 2, has a toothed wheel 12, fixed
to it and in gear with two toothed wheels m², n², fixed respectively to the shafts of
B

page_text: two cylinders o², p². One of these cylinders is fast on its shaft and the other is
connected with its shaft through a coiled spring which by its pull on the cylinder
serves as in Jolin's improvement of Wheatstone's Rheostat to keep the wire q²,
tightened round the cylinder. One of the cylinders presents a smooth metallic
surface to the wire while the other is covered with a sinooth insulating covering.
When the screwed shaft is turned the wire is guided from one cylinder to the other
by means of a fork or a small wheel 72, carried by the nut s². The nut is prevented
from turning when the shaft is turned by a guide fork t², which slides along the edges
of a scale 2, and carries a vernier for indicating the position of the nut on the screw.
The current circuit through the wire passes from a terminal 2, through a flexible
spring w², pressing against the end of a stud 2, in contact with one end of the wire
and from the wire it passes to a stud y2, to another flexible spring 22, and through it
to the other terminal a³. A guard washer 63, of leather or suitable substance (placed
at each end of the screw 3) prevents over winding in either direction by limiting the
travel of the nut s².
In order to standardise the instruments in the circuit at any time the current of the
circuit is divided into two branches, one of them a known high resistance in circuit
with the magneto-static current meter, and the other through the electrolytic vessel,
the electro-dynamic balance, and a resistance continuously regulated by the Rheostat.
The Rheostat is worked by hand so as to keep the current as indicated by the electro-
dynamic balance very accurately constant during a certain time-an hour for example
-and the quantity of copper deposited or dissolved during that time in the electrolytic
vessel is determined by accurate weighing. Thus, according to the known electro-
chemical equivalent of copper, the strength of the current is calculated in absolute
units; and from it by substituting a known resistance in place of the electrolytic vessel,
and the rheostat and the reproduction of the same current in the balance, the co-
efficient of the magneto-static current meter, and the constant of the electro-dynamic
balance are determined. In continued use of the apparatus on an electric lighting
circuit, the working circuit of the lights takes the place of the regulating by rheostat.
The electro-dynamic balance shews the strength of the current at any time by the proper
adjustment of its weights; the electrolyte appliance shews the whole quantity of
electricity that has passed in any time and the imagneto-static current meter shows the
potential of the circuit.
For the electrolytic appliance, I prefer to use copper plates in solution of copper
sulphate and to suspend the set of plates which gain in weight, by a ligamental
suspension of a similar kind to that hereinbefore described with reference to
Figures 14 to 26 and 27 to 30. The beam of the balance for this purpose is sus-
pended in a similar manner to that hereinbefore described with reference to Figures 14
to 26 and 27 to 30 and is provided with a graduated slide and weights for the purpose
of measuring the gain in weight of the copper plates. Thus the plate is hung by a
ligament from end of the beam, and the beam is suspended by ligament from a
fixed support the current passing from the plate through the ligaments and beam to
the support, and from this support to the lighting circuit. The mode of using
this balance is precisely similar to that herein before described with reference to
Figures 14 to 26 and 27 to 30.
The electrolytic appliance may in continued use of the apparatus, be omitted, and
the whole quantity of electricity that has passed in any time may be found by adding
to the balance a projecting pin c³, figures 39 and 40, sheets 27 and 28 to actuate a
bent lever d³, resting on knife edges at e³. The lever d³, is kept in continuous rotation
by a train of clockwork mechanism driven by a spring or weight and in consequence
of this rotation the mass g³, tends to turn the lever d³, round its knife edge at e³,
hence to lower the beam i, and the coil j, of the electro-dynamic balance. In conse-
quence of this lowering of the beam i, of the balance, a projecting pin h³, prevents the
rotation of a light arm 3, which is carried by a friction collar on the axis of the disk j³
The friction of a foot k³, fixed to 3, on the surface of the disk j³, then slows the motion
of the mechanism and allows the mass g³, to fall towards the axis of rotation by such
and

page_text: an amount that the electro-dynamic force of the current in the coils of the balance is
just able to lift the pin ³, out of contact with the arm 3. Supposing the current to
remain constant the speed is maintained uniform by the regulating action of the pin h³,
and the friction of the pin k³, on the disk 3. When the current in the circuit is
increased or diminished the speed is correspondingly increased or diminished by the
action of the electro-dynamic forces in raising or lowering the beam i, and hence
causing the mass g³, to approach towards or recede from its centre of rotation. The
electro-dynamic forces are thus balanced at all times by the centrifugal force of the
mass g³, and since the electro-dynamic force is proportioned to the square of
the current through the coils, and the centrifugal force to the square of the velocity of
rotation of the mass g³, the velocity of rotation will be always proportional to the
current flowing in the circuit. Hence by the use of any suitable counter to shew the
number of turns the mass g³, makes round its axis of rotation in any time the quantity
of electricity which has flowed through the circuit in that time may be measured.
When no current flows through the circuit the pin h³, catches the arm 3, and in the
course of a few minutes the mechanism comes to rest. When a current of sufficient
strength is again set up in the circuit the pin h³, is lifted out of contact with the
arm, and the mechanism immediately starts into motion. In order to allow one
instrument to measure currents through a sufficient range of strength the coils at the
opposite ends of the beam of the balance, and the fixed coils acting on them, have
different numbers of turns. The one set of coils being adapted to raise the beam and
start the mechanism with a current which is 10 or any other convenient number of
times greater than the current which, when flowing through the other set of coils, will
do so.
When the current is so great that the less powerful set of coils is able to keep
the mechanism in motion the other set of coils is automatically short circuited or
otherwise prevented from acting but when the current becomes too weak for this to be
the case the short circuit is automatically broken. The same automatic contrivance
which short circuits the coils is arranged to produce such a change in the counter
mechanism that the counter continues to indicate in accordance with the same
co-efficient the quantity of electricity which has flowed through the circuit. In order
to avoid the possibility of using the instrument after the driving mechanism has run
down this mechanism is made to break the electric circuit after it has run for a certain
number of turns and must then be rewound before a current can pass through
the circuit. To avoid the use of stronger currents than the meter is capable of
measuring, a safety fuse of any convenient form is introduced into the circuit and
convenient arrangements are made for replacing a broken fuse by a sound one should
by any accident an excessive current be passed through the circuit.
Having now particularly described and ascertained the nature of my said Invention
and in what manner the same is to be performed, 1 declare that what I claim is :---
1. In the magneto-static currents or volt-meter such as is shewn at Figures 1 to 5
of the annexed drawings the springy support for the silk fibre suspension of the
magnetic needle having safety guards not requiring adjustment for carriage as
herein before described.
2. The combination in the instrument claimed in the preceding clause Number 1 of
an adjustable scale and the arrangement of field magnets which permits the intensity
of the field to be varied and the direction thereof to be changed without changing
the fields intensity as hercinbefore described.
3. In a magneto-static current meter such as is shewn at Figures 6 and 7, the
magnetic needle supported in neutral equilibrium on knife edges or pivots near the
centre of a narrow tubular coil in such a way that an index attached to the needle
indicates deflections on a vertical scale, the needle being controlled by an adjustable
field magnet; and the whole instrument being suitable for marine use as hereinbefore
described.

page_text: 4. In an electro-dynamic balance, such as is shewn at Figures 8 to 13 of the
accompanying drawings and adapted for marine use as a volt meter the oblate spheroid
of soft iron suspended in the centre of a coil of insulated wire by means of fine
stretched wires and used in combination with resistance coils for indicating by the
tendency of the oblate to turn, in consequence of the electro-magnetic force acting
upon it, when a current is passed through the coil the difference of the potential
between two points of an electric circuit; the coil and oblate being enclosed in an
iron sheath as hereinbefore described.
5. The combination of the instrument claimed in the preceding claiming clause
number 4 with a current reverser to test and to shake out effects of retained magnetism
as hereinbefore described.
6. In an electro-dynamic balance such as is shewn in Figures 14 to 31 of the
accompanying drawings the ligamental suspension for the beam of the balance
through which the current is led into and out from the circuit of the movable coils as
hereinbefore described.
7. In the balance claimed in the preceding claiming clause Number 6 the graduatel
slide attached to the beam and along which a weight can be moved so as to balance
the electrical forces as hereinbefore described.
8. In the balance claimed in the preceding claiming clauses 6 and 7 the combination
of a scale of equal divisions and of a square root scale on the same slide by means of
which a direct reading of the strength of the current in the circuit can be obtained as
hereinbefore described.
9. In the balance claimed in the preceding claiming clauses 6, 7 and 8 the two
slides, one of which is used to adjust the zero of the balance while the other is used to
measure the current as herein before described.
10. In instruments of the form shewn at Figures 27 to 30 of the accompanying
drawings the self-relieving pendants for moving the weights along the slide as
herein before described.
11. In instruments such as are shewn at Figures 14 to 26 the sets or chains of
weights hung from the movable coil with sets of lifters for putting on or removing the
weights and in combination with these the fine spring used for adjusting the zero and
giving continuous variation of force from zero to the smallest weight as hereinbefore
described.
12. In an electro-dynamic balance such as is shewn at Figures 14 to 31 of the
accompanying drawings the divided conductors and supporting bobbins for the
purpose of practically annulling the effects of induction when alternating currents are
to be measured as herein before described.
13. In a rheostat of the form such as that shewn at Figures 36 to 38 of the
accompanying drawings constructing both cylinders with smooth surfaces and the fork
or wheel attached to a nut working on a screwed shaft geared to the cylinders, for
the purpose of guiding the wire from one cylinder to the other as hereinbefore
described.
14. In a set of resistance coils the sets of cams working between two concentric
rings for the purpose of allowing the resistances to be put in parallel circuit and in
the same combination working between fixed blocks or elastic contact pieces for the
purpose of allowing any number of the coils to be joined in series also the same
arrangements but without working in combination as hereinbefore described.
15. In sets of resistance coils such as these claimed in the preceding claiming
clause No. 14 the massive copper cylinder and the separating partitions between the
several coils for the purpose of allowing the heat generated by the current to be
rapidly carried away from the coils as hereinbefore described.

page_text: 16. In all such instruments as those hereinbefore described the massive copper or
other metallic sole plates and supporting bobbins for the purpose of facilitating the
cooling of the coils as hereinbefore described.
17. In an instrument such as is shewn in Figures 39 and 40 the combination of an
electrodynamic balance with a centrifugal governor and proper counting mechanism
for measuring the total quantity of electricity which has flowed through the circuit in
any time as herein before described.
18. In an electrolytic appliance, the balance with ligamental suspension together
with a graduated slide and movable weights for measurement of the total quantity
of electricity which has flowed through the circuit in any time as hereinbefore
⚫described.

page_text: Date of Application, 10th July, 1886.
Complete Left, 9th Apr., 1887.
Complete Accepted, 24th June, 1887.
PROVISIONAL SPECIFICATION.
Improved Apparatus for Measuring the Efficiency of an Electric
Circuit.
I, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain do hereby declare the nature of this invention to be
as follows:-
This apparatus consists of an inspectional magneto-static current meter used in
connection with adjustable resistance coils, and an electrodynamic balance, with
electrolytic apparatus for determining its constant, by which the co-efficient of the
current meter, varying as it does from time to time, is at any time determined in
terms of constant units.
The magneto-static current meter consists of a suspended magnet, preferably a thin
circular disc of steel, suspended by a silk fibre so as to be in the centre of the field of
a double electro-magnetic coil so arranged as to give, as nearly as may be, an uniform
magnetic field in its centre. The controlling magnets are adjustably fixed in an iron
sheath enclosing the electro-magnetic coil, and their distances from the centre of the
field are adjusted, and varied, if need be, from time to time, to give any convenient
value to the CO- - efficient, according to comparison with the electro-dynamic
balance. The indicator of deflections of the suspended magnet may be either a non-
magnetic needle pointing to divisions on an adjustable tangent scale, or a ray of light
reflected from a mirror, and it may be either wholly outside the iron sheath, or it may
project from the inside to the outside transversing a horizontal slot in the sheath.
The upper end of the fibre is attached to a spring yielding so freely to a downward
pull that before the fibre can be broken, the suspended magnet and attached needle or
mirror reaches the bottom of its range. The electro-dynamic balance consists of a
piece of soft iron, or a moveable coil made temporarily magnetic in virtue of the
current to be measured, and actuated by the electro-magnetic force of a fixed coil or
coils through which the current passes. The piece of soft iron may be suspended on
a gravity balance and actuated in the manner described in the specification of the said

page_text: Sir William Thomson Number 11,106 A.D. 1884, but for sea use, I prefer to make it
in the shape of an oblate spheroid and to suspend it on a stretched clastic wire. Its
tendency to turn its equatorial plane to parallelism with the lines of force of the
fixed coil or coils, balanced by the torsion of the wire after the manner of a Coulomb's
torsion balance, shews the strength of the current to be measured. For land use I
prefer a moveable coil and a gravity balance with a trunnion to prevent horizontal
motion of the axis of the balance, and with decimal arrangements for putting on and
taking off the weights. The resistance coils are of wire, preferably platinoid, wound
on metal drums or cores, preferably copper coated with thin insulating material such
as varnished paper, so that the heat generated by the current may be carried away
whether by emission to air, or by aid of a stream of water across the uncoated parts
of the surface of the core. The coils are either each separately moveable and are
placed in combination, in series or in multiple arc, by stout metal terminals dipping
into cups of mercury, or they are connected by means of copper spring wedges
between fixed terminals of the coils and fixed studs of copper. To adjust the
resistance continuously to any desired amount, I use an improved form of
Wheatstone's rheostat in which the wire is guided from one cylinder to the other by a
fork carried along through the requisite range by a nut travelling on a long screw shaft.
This screw shaft carries a toothed wheel which turns the two cylinders by means of
toothed wheels attached to their shafts a watch-spring as in Joulin's improvement of
Wheatstone's rheostat keeps the wire always tightened to the proper degree. A
leather buffer at each end of the range of the nut acts as a guard against overwinding
in either direction.
The current of the circuit is divided into two branches, one of them a known high
resistance in circuit with the magneto-static current meter, and the other through the
electrolytic vessel, the electro-dynamic balance, and a resistance continuously
regulated by the rheostat. The rheostat is worked by hand so as to keep the current
as indicated by the electro-dynamic balance very accurately constant during a certain
time an hour for example and the quantity of copper deposited or dissolved during
that time in the electrolytic vessel is determined by accurate weighing. Thus,
according to the known electro-chemical equivalent of copper, the strength of the
current is calculated in absolute units; and from it, the co-efficient of the magneto-
static current meter, and the constant of the electro-dynamic balance are determined.
In continued use of the apparatus on an electric lighting circuit, the working circuit
of the lights takes the place of the regulating by rheostat. The electro-dynamie
balance shews the strength of the current at any time by the proper adjustment of its
weights; the electrolytic appliance shews the whole quantity of current that has
passed in any time and the magneto-static current meter shews the potential of the
circuit.

page_text: Improved Apparatus for Measuring the Efficiency of an Electric
Circuit.
I, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain 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 :-
This apparatus consists of an inspectional magneto-static current meter used in
connection with adjustable resistance coils, and an electro-dynamic balance, with
electrolytic apparatus for determining its constant, by which the co-efficient of the
current meter, varying as it does from time to time, is at any time determined in
terms of constant units.
The magneto-static current meter consists of a suspended magnet, preferably a thin
circular disc of steel, suspended by a silk fibre so as to be in the centre of the field of
a double electro-magnetic coil so arranged as to give, as nearly as may be, a uniform
magnetic field in its centre. The controlling magnets are adjustably fixed in an iron
sheath enclosing the electro-magnetic coil, and their distances from the centre of the
field are adjusted, and varied, if need be, from time to time, to give any convenient
value to the co-efficient, according to comparison with the electro-dynamic balance.
The indicator of deflections of the suspended magnet may be either a non-magnetic
needle pointing to divisions on an adjustable tangent scale, or a ray of light reflected
from a mirror, and it may be either wholly outside the iron sheath, or it may project.
from the inside to the outside traversing a horizontal slot in the sheath. The upper
end of the fibre is attached to a spring yielding so freely to a downward piece that
before the fibre can be broken, the suspended magnet and attached needle or mirror
reaches the bottom of its range.
The electro-dynamic balance consists of a piece of soft iron, or a moveable coil
made temporarily magnetic in virtue of the current to be measured, and actuated by
the electro-magnetic force of a fixed coil or coils through which the current passes.
The piece of soft iron may be suspended on a gravity balance and actuated in the
manner described in the specification of the said Sir William Thomson, Number
11,106 A.D. 1884, but for sea use, I prefer to make it in the shape of an oblate
spheroid and to suspend it on a stretched elastic wire. Its tendency to turn its
equatorial plane to parallelism with the lines of force of the fixed coil or coils, balanced
by the torsion of the wire after the manner of a Coulomb's torsion balance, shows the
strength of the current to be measured.
For land use I prefer a moveable coil and a gravity balance with a trunnion to
prevent horizontal motion of the axis of the balance, and with decimal arrangements
for putting on and taking off the weights.
The resistance coils are of wire preferably platinoid, wound on metal drums or
cores, preferably copper coated with thin insulating material such as varnished paper,

page_text: so that the heat generated by the current may be carried away whether by emission
to air, or by aid of a stream of water across the uncoated parts of the surface of the
core. The coils are either each separately moveable and are placed in combination,
in series or in multiple arc, by stout metal terminals dipping into cups of mercury,
or they are connected by means of copper spring wedges or copper cams between
fixed terminals of the coils and fixed studs of copper.
To adjust the resistance continuously to any desired amount, I use an improved
form of Wheatstone's Rheostat in which the wire is guided from one cylinder to the
other by a fork carried along through the requisite range by a nut travelling on a
long screw shaft. The screw shaft carries a toothed wheel which turns the two
cylinders by means of toothed wheels attached to their shafts a watchspring as in
Jolin's improvements of Wheatstone's Rheostat keeps the wire always tightened to
the proper degree. A leather buffer at each end of the range of the nut acts as a
guard against over winding in either direction.
The current of the circuit is divided into two branches, one of them a known high
resistance in circuit with the magneto-static current meter, and the other through
the electrolytic vessel, the electro-dynamic balance, and a resistance continuously
regulated by the rheostat. The rheostat is worked by hand so as to keep the current
as indicated by the electro-dynamic balance very accurately constant during a certain
time an hour for example and the quantity of copper deposited or dissolved during
that time in the electrolytic vessel is determined by accurate weighing. Thus,
according to the known electro chemical equivalent of copper, the strength of the
current is calculated in absolute units; and from it, the co-efficient of the magneto-
static current meter, and the constant of the electro-dynamic balance are determined.
In continued use of the apparatus on an electric lighting circuit, the working circuit
of the lights takes the place of the regulating by rheostat. The electro-dynamic
balance shews the strength of the current at any time by the proper adjustment of its
weights; the eloctrolytic appliance shews the whole quantity of current that has
passed in any time and the magneto-static current meter shews the potential of the
circuit.
In order that my Invention may be properly understood and readily carried into
effect, I will now proceed to describe the drawings hereunto annexed.
The magneto-static current meter is shewn at Figures 1 to 7 inclusive in the
annexed sheets of drawings. It consists of a suspended magnetic needle preferably
a thin circular disc, plate, or bar, of steel suspended by a silk fibre so as to be in the
centre of the field of a double electro-magnetic coil so arranged as to give as nearly
as may be an uniform magnetic field in the centre. The double electro-magnetic coil
may be two circular coils A, Figures 1, 2 and 3 of sheets 1, 2 and 3, placed according
to the well-known Helmholtz principle, or when only one turn of the conductor is
used in each coil, they may for convenience of manufacture be D-shaped as shewn at
A, in Figures 4 and 5 of sheet 4, but for some purposes and especially for marine
use I prefer to make the coil of one turn of broad copper ribbon of some such shape
as that shewn at A, in Figures 6 and 7 of sheet 5 (which shews a sectional plan and
an elevation of the central portion of the instrument) and to support the magnetic
needle in its centre by means of a rigid axis B, passing through the centre of inertia
of the magnetic needle and its attachments and resting on knife edges or fine pivots
on the supports C. D. For marine use in this way the instrument is turned on its
side and supported by fixing the levelling screws E, to the wall of the room or to a
vertical support in such a way that the index turns round in a vertical plane.
The controlling magnets are adjustably fixed in an iron sheath enclosing the
electro-magnetic coils and their distances from the centre of the field are adjusted and
varied, if need be, from time to time to give any convenient value to the co-efficien
according to comparison with the electro-dynamic balance. In some cases the iro
sheath may be dispensed with and I then fix the magnets to the framework of th
instrument in the manner shewn at F, in Figures 1 to 5 or in an equivalent manner
and their distances from the centre of the field are adjusted and varied, if need be, a
hereinbefore described. The magnet system rests on a table G, G, which can b

page_text: screwed nearer to or further from the centre of the coils along a screwed rod H, and
can be clamped in any desired position by means of a clamping nut I. When the
table is clamped in any position the controlling magnet system can be turned in its
own plane so as to bring the index which shews the deflections of the suspended
magnetic needle to zero without turning the table and hence without altering the
intensity of the field at the centre of the coils. The magnet is held firmly against the
top of the table G by means of a flexible bar N, in the manner clearly shewn in the
accompanying drawings. The indicator of deflections of the suspended magnet may
be either a non-magnetic needle L, pointing to divisions as an adjustable tangent
scale M or a ray of light reflected from a mirror and it may be either wholly outside
the iron sheath or, as shewn at d, in Figures 11 and 13 of sheet 9 (being drawings of
my electro-dynamic balance) it may project from the inside to the outside transversing
a horizontal slot in the sheath. The upper end of the fibre is attached to a spring O,
Figures, 1, 3, 4 and 5, yielding so freely to a downward pull that before the fibre can
be broken the suspended magnet and attached index or mirror reaches the bottom of
its range. The height of the point of suspension can be varied by the screw P, on
the end of which the spring O, rests. Side motion of the suspended system is
prevented by guard rings 4, Figures 1, 2 and 3 which are made large enough not to
touch the vertical rod which carries the disk but small enough to prevent risk of
damage to the suspending fibre by side motion. The instrument is supported on three
levelling screws of the form shewn at E in Figures 1, 2 and 4, of sheets 1, 2 and 4.
It consists of a screwed rod fixed at the centre, and with its length at right angles to
the plane, of a circular plate provided with holes through which it can be screwed to
the table or other support. The instrument rests on the nuts Q, which can be screwed
up or down along these rods and fixed in any desired position by means of clamping
nuts R, in the manner shewn in the drawings Figures 1, 2 and 4.
The electrodes S, which convey the current into and out from the coils are preferably
made of several strands of copper cord made up of thin copper wires. The two
electrodes are when necessary twisted together so as to practically annul the action of
the incoming and outgoing currents on the needle.
The electro-dynamic balance consists of a piece of soft iron or a movable coil made
temporarily magnetic in virtue of the current to be measured, and actuated by the
electro-magnetic force of a fixed coil or coils through which the current passes. The
piece of soft iron may be suspended on a gravity balance and actuated in the manner
described in the specification of the said Sir William Thomson Number 11,106 A.D.
1884, but for use on board ship, I prefer to make it in the shape of an oblate spheroid
and to suspend it on a stretched elastic wire. Its tendency to turn its equatorial plane
to parallelism with the lines of force of the fixed coil or coils, balanced by the torsion
of the wire after the manner of a Coulomb's torsion balance, shews the strength of the
current to be measured.
The manner in which this is carried out is shewn in the drawings Figures 8, 9, 10,
11, 12 and 13, sheets 6, 7, 8 and 9 of which Figure 8, is a side elevation, Figure 9, a
front elevation, Figure 10, a vertical section, Figure 11, a plan of the top, Figure 12,
a plan of the bottom and Figure 13, a horizontal section through the scale box above
the index of the instrument. A brass tube T, has fixed near the middle of its length a
coil of insulated wire U, which may be a coil of copper wire insulated with silk
or any other equivalent form. Near the centre of the axis of this coil the oblate
spheroid of soft iron V-Figure 13 is suspended by an elastic wire W, from
two springs X, fixed to adjusting screws Y, in the manner shewn in Figures 10
and 13, sheets 8 and 9 with its equatorial section vertical but inclined at such an
angle to the axis of the coil, that when the lowest current the instrument is required
to measure is passed through the coil the spheroid assumes a position in which
under the electrical forces and the torsional force of the suspension, it has just a
sensible amount of stability. The middle portion of the tube T, is surrounded
by an iron sheath Z, on the side of which a scale box a, is fixed. This scale box
is provided with a glass or other transparent cover through which the scale b, Figures 11

page_text: and 13, and the position relatively to it of the end of a light index (, attached to
the spheroid of soft iron can be observed. The index passes from the inside to the
outside of the iron sheath through a horizontal slot d, Figure 13, which is made long
enough to allow the index to transverse the whole of the scale b. In order to allow
the instrument to be so adjusted that its indications are nearly enough the same
whether the current flows in one direction or the other through the coil U, I use two
or more magnets e, adjustably fixed in the upper part of the iron sheath in such a way
that they can be screwed further into or out of the sheath and that part of the sheath
turned in azimuth until the necessary adjustment is obtained after which the magnets
are clamped by the lock nuts f, and the sheath by the screws g. Should this adjust-
ment not be perfectly made the necessary correction can be nearly enough obtained
by taking the mean of the indications of the instrument when the current is caused to
flow first in one direction and then in the other through the coil U. In order to
facilitate the reversal of the current a commutator or reversing key h, is added to the
instrument.
For land use and for a standard instrument not liable to change with time, I prefer
a movable coil and a gravity balance with a trunnion or other equivalent arrangement
to prevent horizontal motion of the axis of the balance.
One method of carrying out this part of my Invention is shewn in Figures 14 to 26
of sheets 10 to 16 inclusive of the accompanying drawings referring to which the part
marked i, represents the beam of the balance which is either supported on knife edges
or suspended in the manner to be hereinafter described near one end and made to
carry a coil j, at the other end the weight of the coil and beam being counterpoised
by weight added to the beam on the side of the suspension remote from the coil.
In this form I sometimes use a set of weights and lifters of the form shewn in
Figures 19 to 26 of sheets 15 and 16. The lifter is shewn separately in Figures 22
and 23. It consists of a straight piece k, pivoted at one end 1, and having attached
to it near the other end, a knee piece m, in such a way as to form a fork. When the
lever k, is raised the fork lifts the weights by the cross bars n, n, which are fixed to
them in the manner shewn in Figures 25 and 26 of sheet 16.
I arrange the weights in three groups as shewn at 0, 0, 0, Figures 20 and 21 of
sheet 15 and make the weights in the different groups preferably in the ratio of
10, 100, 1000 and the weights in each group equal. I prefer as shewn to make each
group of weights in the form of a chain (the several links of which each constitute a
weight) and to hang the three chains from a stirrup p, which in its turn hangs from
two knife edges y, (Figures 14, 15 and 16) one of which is fixed at each end of the
transverse diameter of the coil so that the gravitation force of the weights acts directly
against the electro-dynamic force of the coils when the current is flowing through
them. A hook of the form shown in Figure 24, is passed over the lower link of each
chain as shewn in Figure 20, and is convenient for holding the chains in position
when the instrument is being transported from place to place. Forces smaller than
can be measured by the smallest weights in the chains are estimated from the extension
of a fine spiral spring r, enclosed in the tube s, and acting on the same stirrup p.
The extension of the spring can be read on the scale t, Figure 15, which is opposite
the lower end of the spring and the position to be taken as that of zero extension may
be adjusted by sliding the scale t, along a second scale u, Figure 15. The spring can
thus be used for the purpose of bringing the beam of the balance to a horizontal
position as indicated by the index v, which is attached to the front of the movable coil,
pointing to zero on the scale w, Figure 15. The arrangement of weights and lifters
hereinbefore referred to with reference to Figures 19 to 26 is also applicable to
ordinary weighing balances. The suspended coil j, is acted upon by one or more but
preferably by two fixed coils a, Figures 15, 16 and 18, which may be either flat coils
of approximately the same mean diameter as the suspended coil and arranged with
their planes nearly horizontal one above and the other below the movable coil as
shewn in another form of this instrument at Figures 27 and 28, sheets 17 and 18 of
the accompanying drawings or coils of comparatively small depth in the direction of

page_text: the diameter and of external diameter somewhat less than the internal diameter of the
suspended coil and fixed coaxially with it, their planes being parallel and nearly
horizontal and at such a distance apart as gives convenient electro-dynamic stability.
The latter form of fixed coils is preferably adopted when the instrument is intended to
be used to measure powerful currents and in such cases the coils are for direct current
measurements, made of copper ribbon of such breadth and thickness as is sufficient to
carry without inconvenient heating the maximum current to be measured. For
alternating-current measurements the coils, both movable and fixed, are constructed
of twisted copper rope made up of sufficiently thin insulated wire to prevent
disturbance from unequal distribution of the current over the cross section of the
conductor. The twist in the rope is to be such that there is nearly enough an integral
number of twists in the rope for each turn round the coil. The section of the rope
either round or flattened to a ribbon shape as is found most suitable in different cases.
The coils are preferably wound on massive copper bobbins fixed in massive copper or
other metallic plates y, forming the sole plate and framework of the instrument and when
the instrument is intended for the measurement of alternating currents these bobbins
and plates are cut in such a way as to prevent the circulation of induced currents
round them and are supported when necessary on insulating material. These plates
in consequence of their large surface and high thermal conductivity greatly facilitates
the carrying away of the heat generated in the coils by the passage of the current,
and hence to a great extent prevent error from this cause due to change of dimensions
of the beam or upward currents of air. The mode of suspending the beam of the
balance which I prefer is shewn in Figures 14 to 17, sheets 10 to 13. It consists of
two flat ligaments z, formed of a sufficient number of very fine wires laid side by side
in one plane. The two ends of this ligament are securely soldered to semi-cylindrical
pieces a, b, the upper pair a', of these pieces being fixed to the framework through
the pillars c, and the cross pieces d', and the lower pair 6, to the beam of the balance.
The beam of the balance is prevented from taking such an amount of horizontal
motion in the direction of its length as would bend the ligament z, so much as to
change the zero reading of the instrument by means of the fork e', and the steady
pins . The pins f1, are arranged so as to be out of contact with the sides of the
forks e', when the instrument is in use. The ligamental suspension here referred to is
also applicable to ordinary weighing balances.
9,
For the highest accuracy, I prefer another form in which the beam of the balance is"
suspended from a point near the centre of its length as shewn in Figures 27 to 30 of
sheets 17 to 20 of the accompanying drawings. In this form a coil 3, is fixed to both
ends of the beam of the balance and each of these coils is acted on by one or more fixed
coils x, in the manner hereinbefore described with reference to Figures, 15, 16 and 18.
For the weights and lifters, I substitute in this case either scale pans and weights or a
slide fixed to the side of the beam along which weights h, of the proper magnitude
to give the requisite sensibility, may be moved by means of sliders i, so as to balance
the electro-dynamic forces produced by the current in the coils. The sliders i, may be
of the form shewn in Figures 27 and 28 or as a modification of the form shewn in
Figures 29 and 30. In the form shewn in Figures 27 and 28, a rigid frame furnished
with three feet j, slides along a horizontal platform fixed in front of the instrument and
along the length of which a V-groove is cut forming a guide for two of the feet j.
The slider, carries on it a pivoted frame k¹, held in an upright position by light
springs. An upright piece m', forming part of the frame k¹, passes through a recess
in the weight and when the weight is to be moved along the slide gl, the frame k¹, is
tilted over in the direction of motion by the finger and then the whole frame is moved
so as to push the weight to the desired position after which when the finger is removed
the upright bar m', assumes a position in the middle of the recess as shewn in Figure 28,
thus leaving the weight clear and the balance free to move. In the arrangement
shewn in Figures 29 and 30, a pendant n', is substituted for the pivoted frame k', and
the slider is pulled to one side or other by means of threads o¹, attached to the bottom
of the pendant. When the weight has been moved to the desired position the thread

page_text: °
is left slack and the pendant by assuming a vertical position under the action of gravity
falls to the centre of the recess in the weight and hence leaves the beam free. The
weight on the right hand end of the slide is intended to be used as a counterpois for
the sliding weight when it is at its zero position and also to give a convenient means
of adjusting the beam of the balance to its zero position. For this purpose it is not
necessary that the frame which carries the pendant should be movable as the
range of motion of the pendant can be made sufficient to give the required
adjustment.
On the slide g¹, a scale of equal divisions is engraved and also a series of fine notches
corresponding in position to the lines of a second scale p¹, fixed to the framework of
the instrument in a position above the beam and at the back of the slide. These scales
allow the position of weights on the slide to be at any time read off. The numbers on
the fixed scale p³, are proportional to the square roots of the numbers on the scale of
equal divisions g', and hence are such that when the weight is brought to different
positions so as to balance the electro-dynamic force due to different currents, equal
differences of reading indicate equal differences of current. The instrument is thus
arranged to give direct readings of differences of current. Side motion of the beam
is, in this form of the instrument, prevented by the screws q, between the points of
which, but not touching them, the slide rests. End motion is prevented in the form
shewn in Figures 29 and 30 by a similar pair of screws fixed to the framework and
adjusted near to but not touching the semi-cylindrical pieces b, and in the form shewn
in Figures 27 and 28, which is intended for small currents and has in consequence
lighter and longer suspension ligaments attached to beam of the balance through a
round central axis or trunnion, by passing this trunnion through a square hole in an
upright piece 7, adjustably fixed to the sole plate of the instrument, or alternatively by
two screws adjustably fixed on the two sides of the trunnion and guard pieces fixed to
the framework above the trunnion to prevent the ligament being so much slackened as
to damage it should the instrument be turned upside down. The arrangement of
graduated slide with self relieving pendants to move the sliders here described with
reference to Figures 27 to 30 is also applicable to ordinary weighing balances.
When scale pans are employed I prefer for convenience to use two scale pans at each
end of the beam each hung from one of four knife edges forming a prolongation at the
end of the transverse diameter of the coils. When no current is flowing through the
coils the whole or the greater part of the weights to be used in the measurements should
be placed on the scale pan nearest the observer at one end of the beam and balance
restored by weight placed in the most distant pan at the other end. The strength of
current flowing at any time through the coils is then to be estimated from the amount
of weight which has to be transferred from one end of the beam to the other in order
to restore equilibrium.
and a
Another modification of the balance which I used for measuring by the motion
of an index lever over a vertical scale, moderate changes of current and which is
suitable for a volt-meter is illustrated in elevation in Figure 31, sheet 21 and in
plan with the cover on in Figure 32, sheet 22 of the accompanying drawings. This
form differs from those already described in having only one movable coil
single fixed coil, and in the addition of a light index s¹, resting on a knife edge
at, and connected to the moveable coil by a hook u¹. A motion up or down of the
movable coil causes this index to turn round its knife edge by an amount which can
be read on the scale r', suitably divided to indicate directly percentage changes of
current. The requisite stability to allow the instrument to have a sufficient range is
furnished by the variation of the electrical forces between the two coils as their
distance apart varies. The gravitational force against which the electro-dynamic
force produced by the current acts is obtained by adding the necessary weight, the
amount of which depends on the strength of the current to be measured, to the
movable coil, preferably as nearly as possible at the transverse diameter of the coil,
but in practice it is found more convenient to place the weight, in the form of a round
rod, in a V-trough fixed to the outer end of the coil with its length at right angles to

page_text: that of the beam of the balance. This form of balance is specially suitable in con-
junction with resistance coils for a volt meter to indicate changes in the potential
which is being maintained on an electric circuit. In Figure 31 a resistance coil is
shewn at w¹, fixed to the underside of the sole plate of the instrument but for more
general use, I prefer to join the instrument in circuit with a set of resistance coils
and with the magneto-static current meter in the manner indicated in Figures 32 to 34
of sheet 22. In this arrangement the resistances may be varied to suit any required
potential within certain limits depending on the magnitude of the resistances, and the
range of variation through which readings can be obtained is continued down to zero
by means of the magneto-static instrument, the constant of which can be at any time
obtained by so varying the resistance that simultaneous readings can be obtained both
on it and on the balance.
The resistance coils show in plan in Figure 34 sheet 22 and in vertical section in
Figure 35, sheet 23, consist of coils a¹, of insulated wire, preferably platinoid wire
covered with silk and soaked in purified paraffin wax wound on a heavy metallic
cylinder y¹, and covered with a copper sheath ¹, for the purpose of minimising as
much as possible the changes of temperature caused by the passage of the electric
current. The ends of the coils are connected to vertical rods of copper a², in such a
way that the inside end of the top coil is connected to a rod 1, the outside end to
rod 2; the inside end of coil 2 to rod 2 and the outside end to rod 3; the inside end
of coil 3 to rod 3 and the outside end to rod 4 and so on.
These rods are held in position by a ring 62, and binding screws c², but are insulated
by suitable insulating collars at, from the metal cylinder y', on the upper ends of the
rods a², cams d², fixed to short tubes e², each having on its upper end a cross head or
handle, are fitted. Through the tubes e², pins g², are passed and when the cam is
pulled up to the level of the top of the ring h², can be pushed in over the end of the
rod a², and serves to keep the cam at that level. The cams can be turned between
two metallic rings h², and 2, and into contact with the blocks c, which are in metallic
connection with the rods a², and they are so adjusted that when the tube carrying the
cam is at its lower position the cam may be turned into contact with the block c²,
and when the cam is raised to the level of the top of the ring h², and 2, it can be
turned into contact with either of these rings. By putting these cams in the proper
order into contact with these two rings any number of the resistances can be put in
parallel circuit or alternatively by putting any one cam in contact with one of the rings
and any other cam in contact with the other ring the intermediate resistances are
interposed in series between the two rings. Any one or more of the intermediate
resistances may be short circuited by means of the proper cams and blocks c¹.
The rings form the terminal plates of the box.
As an alternative I sometimes fix the cams to the rods a², and make the rods
movable so that they can be turned round their axis, or moved in the direction
of their length so as to perform the same function as the tubes and cams herein-
before described. In this case the block c, or equivalent springy contact pieces
are in metallic connection with the rods a², through flexible wire connecting
pieces and are rigidly fixed to the framework. The rings h², 2, are sometimes
cut through a part of their breadth into as many sections as there are cams for
the purpose of giving flexibility to the ring at the points of contact with the cams.
As another alternative, I sometimes substitute for the rods a³, a series of
insulated metal blocks fixed between the rings h², 2, and I then make the con-
nections between the blocks and the rings by suitable contact plugs preferably
split plugs or springs so constructed as to maintain elastic pressure on the sides
of the blocks and rings.
To adjust the resistance continuously to any desired amount, I use an improved
form of Wheatstone's Rheostat one form of which is shewn in Figures 36 to 38 of
sheets 24 to 26 of the accompanying drawings. Referring to these drawings a screw
shaft j, provided at one end with a convenient handle 2, has a toothed wheel 12, fixed
to it and in gear with two toothed wheels m², n², fixed respectively to the shafts of
B

page_text: two cylinders o², p². One of these cylinders is fast on its shaft and the other is
connected with its shaft through a coiled spring which by its pull on the cylinder
serves as in Jolin's improvement of Wheatstone's Rheostat to keep the wire q²,
tightened round the cylinder. One of the cylinders presents a smooth metallic
surface to the wire while the other is covered with a smooth insulating covering.
When the screwed shaft is turned the wire is guided from one cylinder to the other
by means of a fork or a small wheel 2, carried by the nut s². The nut is prevented
from turning when the shaft is turned by a guide fork t², which slides along the edges
of a scale u², and carries a vernier for indicating the position of the nut on the screw.
The current circuit through the wire passes from a terminal v², through a flexible
spring w², pressing against the end of a stud 2, in contact with one end of the wire
and from the wire it passes to a stud y², to another flexible spring 2, and through it
to the other terminal a³. A guard washer 63, of leather or suitable substance (placed
at each end of the screw 2) prevents over winding in either direction by limiting the
travel of the nut s².
In order to standardise the instruments in the circuit at any time the current of the
circuit is divided into two branches, one of them a known high resistance in circuit
with the magneto-static current meter, and the other through the electrolytic vessel,
the electro-dynamic balance, and a resistance continuously regulated by the Rheostat.
The Rheostat is worked by hand so as to keep the current as indicated by the electro-
dynamic balance very accurately constant during a certain time an hour for example
-and the quantity of copper deposited or dissolved during that time in the electrolytic
vessel is determined by accurate weighing. Thus, according to the known electro-
chemical equivalent of copper, the strength of the current is calculated in absolute
units; and from it by substituting a known resistance in place of the electrolyte vessel,
and the rheostat and the reproduction of the same current in the balance, the co-
efficient of the magneto-static current meter, and the constant of the electro-dynamic
balance are determined. In continued use of the apparatus on an electric lighting
circuit, the working circuit of the lights takes the place of the regulating by rheostat.
The electro-dynamic balance shews the strength of the current at any time by the proper
adjustment of its weights; the electrolyte appliance shews the whole quantity of
electricity that has passed in any time and the magneto-static current meter shews the
potential of the circuit.
For the electrolytic appliance, I prefer to use copper plates in solution of copper
sulphate and to suspend the set of plates which gain in weight, by a ligamental
suspension of a similar kind to that herein before described with reference to
Figures 14 to 26 and 27 to 30. The beam of the balance for this purpose is sus-
pended in a similar manner to that hereinbefore described with reference to Figures 14
to 26 and 27 to 30 and is provided with a graduated slide and weights for the purpose
of measuring the gain in weight of the copper plates. Thus the plate is hung by a
ligament from end of the beam, and the beam is suspended by ligament from a
fixed support the current passing from the plate through the ligaments and beam to
the support, and from this support to the lighting circuit. The mode of using
this balance is precisely similar to that hereinbefore described with reference to
Figures 14 to 26 and 27 to 30.
The electrolytic appliance may in continued use of the apparatus, be omitted, and
the whole quantity of electricity that has passed in any time may be found by adding
to the balance a projecting pin c³, figures 39 and 40, sheets 27 and 28 to actuate a
bent lever d³, resting on knife edges at e³. The lever d³, is kept in continuous rotation
by a train of clockwork mechanism driven by a spring or weight and in consequence
of this rotation the mass 9³, tends to turn the lever d³, round its knife edge at e³, and
hence to lower the beam and the coil, of the electro-dynamic balance. In conse-
quence of this lowering of the beam i, of the balance, a projecting pin h³, prevents the
rotation of a light arm³, which is carried by a friction collar on the axis of the disk j³.
The friction of a foot k³, fixed to ³, on the surface of the disk 3, then slows the motion
of the mechanism and allows the mass g³, to fall towards the axis of rotation by such

page_text: an amount that the electro-dynamic force of the current in the coils of the balance is
just able to lift the pin ³, out of contact with the arm 3. Supposing the current to
remain constant the speed is maintained uniform by the regulating action of the pin h³,
and the friction of the pin k³, on the disk 3. When the current in the circuit is
increased or diminished the speed is correspondingly increased or diminished by the
action of the electro-dynamic forces in raising or lowering the beam i, and hence
causing the mass g³, to approach towards or recede from its centre of rotation. The
electro-dynamic forces are thus balanced at all times by the centrifugal force of the
mass 93, and since the electro-dynamic force is proportioned to the square of
the current through the coils, and the centrifugal force to the square of the velocity of
rotation of the mass 93, the velocity of rotation will be always proportional to the
current flowing in the circuit. Hence by the use of any suitable counter to shew the
number of turns the mass 93, makes round its axis of rotation in any time the quantity
of electricity which has flowed through the circuit in that time may be measured.
When no current flows through the circuit the pin h³, catches the arm 3, and in the
course of a few minutes the mechanism comes to rest. When a current of sufficient
strength is again set up in the circuit the pin h³, is lifted out of contact with the
arm, and the mechanism immediately starts into motion. In order to allow one
instrument to measure currents through a sufficient range of strength the coils at the
opposite ends of the beam of the balance, and the fixed coils acting on them, have
different numbers of turns. The one set of coils being adapted to raise the beam and
start the mechanism with a current which is 10 or any other convenient number of
times greater than the current which, when flowing through the other set of coils, will
do so.
When the current is so great that the less powerful set of coils is able to keep
the mechanism in motion the other set of coils is automatically short circuited or
otherwise prevented from acting but when the current becomes too weak for this to be
the case the short circuit is automatically broken. The same automatic contrivance
which short circuits the coils is arranged to produce such a change in the counter
mechanism that the counter continues to indicate in accordance with the same
co-efficient the quantity of electricity which has flowed through the circuit. In order
to avoid the possibility of using the instrument after the driving mechanism has run
down this mechanism is made to break the electric circuit after it has run for a certain
number of turns and must then be rewound before a current can pass through
the circuit. To avoid the use of stronger currents than the meter is capable of
measuring, a safety fuse of any convenient form is introduced into the circuit and
convenient arrangements are made for replacing a broken fuse by a sound one should
by any accident an excessive current be passed through the circuit.
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. In the magneto-static currents or volt-meter such as is shewn at Figures 1 to 5
of the annexed drawings the springy support for the silk fibre suspension of the
magnetic needle having safety guards not requiring adjustment for carriage as
herein before described.
2. The combination in the instrument claimed in the preceding clause Number 1 of
an adjustable scale and the arrangement of field magnets which permits the intensity
of the field to be varied and the direction thereof to be changed without changing
the fields intensity as hereinbefore described.
3. In a magneto-static current meter such as is shewn at Figures 6 and 7, the
magnetic needle supported in neutral equilibrium on knife edges or pivots near the
centre of a narrow tubular coil in such a way that an index attached to the needle
indicates deflections on a vertical scale, the needle being controlled by an adjustable
field magnet; and the whole instrument being suitable for marine use as herein before
described.

page_text: 4. In an electro-dynamic balance, such as is shewn at Figures 8 to 13 of the
accompanying drawings and adapted for marine use as a volt meter the oblate spheroid
of soft iron suspended in the centre of a coil of insulated wire by means of fine
stretched wires and used in combination with resistance coils for indicating by the
tendency of the oblate to turn, in consequence of the electro-magnetic force acting
upon it, when a current is passed through the coil the difference of the potential
between two points of an electric circuit; the coil and oblate being enclosed in an
iron sheath as hereinbefore described.
5. The combination of the instrument claimed in the preceding claiming clause
number 4 with a current reverser to test and to shake out effects of retained magnetism
as hereinbefore described.
6. In an electro-dynamic balance such as is shewn in Figures 14 to 31 of the
accompanying drawings the ligamental suspension for the beam of the balance
through which the current is led into and out from the circuit of the movable coils as
hereinbefore described.
7. In the balance claimed in the preceding claiming clause Number 6 the graduated
slide attached to the beam and along which a weight can be moved so, as to balance
the electrical forces as hereinbefore described.
8. In the balance claimed in the preceding claiming clauses 6 and 7 the combination
of a scale of equal divisions and of a square root scale on the same slide by means of
which a direct reading of the strength of the current in the circuit can be obtained as
hereinbefore described.
9. In the balance claimed in the preceding claiming clauses 6, 7 and 8 the two
slides, one of which is used to adjust the zero of the balance while the other is used to
measure the current as hereinbefore described.
10. In instruments of the form shewn at Figures 27 to 30 of the accompanying
drawings the self-relieving pendants for moving the weights along the slide as
hereinbefore described.
11. In instruments such as are shewn at Figures 14 to 26 the sets or chains of
weights hung from the movable coil with sets of lifters for putting on or removing the
weights and in combination with these the fine spring used for adjusting the zero and
giving continuous variation of force from zero to the smallest weight as hereinbefore
described.
12. In an electro-dynamic balance such as is shewn at Figures 14 to 31 of the
accompanying drawings the divided conductors and supporting bobbins for the
purpose of practically annulling the effects of induction when alternating currents are
to be measured as hereinbefore described.
13. In a rheostat of the form such as that shewn at Figures 36 to 38 of the
accompanying drawings constructing both cylinders with smooth surfaces and the fork
or wheel attached to a nut working on a screwed shaft geared to the cylinders, for
the purpose of guiding the wire from one cylinder to the other as hereinbefore
described.
14. In a set of resistance coils the sets of cams working between two concentric
rings for the purpose of allowing the resistances to be put in parallel circuit and in
the same combination working between fixed blocks or elastic contact pieces for the
purpose of allowing any number of the coils to be joined in series also the same
arrangements but without working in combination as hereinbefore described.
15. In sets of resistance coils such as these claimed in the preceding claiming
clause No. 14 the massive copper cylinder and the separating partitions between the
several coils for the purpose of allowing the heat generated by the current to be
rapidly carried away from the coils as hereinbefore described.

page_text: 16. In all such instruments as those hereinbefore described the massive copper or
other metallic sole plates and supporting bobbins for the purpose of facilitating the
cooling of the coils as herein before described.
17. In an instrument such as is shewn in Figures 39 and 40 the combination of an
electrodynamic balance with a centrifugal governor and proper counting mechanism
for measuring the total quantity of electricity which has flowed through the circuit in
any time as hereinbefore described.
18. In an electrolytic appliance, the balance with ligamental suspension together
with a graduated slide and movable weights for measurement of the total quantity
of electricity which has flowed through the circuit in any time as hereinbefore
described.
ST. JOHN V. DAY,
Applicant's Agent.