Year: 1896

page_text: Date claimed for Patent under Sect. 103 of Act,
being date of first Foreign Application (in 2nd Oct., 1895
United States of America),
Date of Application (in United Kingdom), 2nd May, 1896
Complete Specification Left, 18th Dec., 1896-Accepted, 27th Feb., 1897
United States of America),
Date of Application (in United Kingdom), 2nd May, 1896
Complete Specification Left, 18th Dec., 1896-Accepted, 27th Feb., 1897
PROVISIONAL SPECIFICATION.
I, HENRY AUGUSTUS ROWLAND, of 913 Cathedral Street, in the City of
Baltimore, State of Maryland, United States of America, Professor of Physics, a
citizen of the United States, do hereby declare the nature of this invention to be
as follows:-
My present invention relates to improvements in instruments for making various
electrical measurements, and the object of this invention is to provide an improved
instrument for the measurement of various electrical quantities, such as current,
potential, self induction electrical energy, and other quantities hereinafter
referred to.
The invention is especially applicable to galvanometers of the D'Arsonval type
and dynamometers, where the instrument is intended for use as a wall instrument to
be suspended on the wall.
One of the principal features of the invention is the providing of a wall
instrument furnished with a telescope and scale or lamp and scale which hang
on the instrument so as to be capable of being folded against the wall when not
in use.
The galvanometer will first be described, and then the dynamometer.
The galvanometer is provided with a base with holes therein, by means of which
it may be readily screwed or otherwise attached to a wall. The frame of the
galvanometer forms a magnetic field, between the poles of which a coil is suspended.
The frame may have a continuous periphery, or the top of the frame may be closed
by means of a cap of brass or other non-magnetic material.
Besides forming a magnetic field, the frame also constitutes a box and support
for other parts of the instrument. A coil of fine wire is suspended from a screw
and the said screw affords a means for adjusting the position of the said coil. The
suspended wire connecting this screw and the said coil carries a mirror and a vane
of mica or other suitable material whereby. the instrument is damped. The
telescope is mounted upon arms pivoted to the side of the base of the instrument,
which arms converge so as to bind against the sides of the base, and through the
friction therewith tend to deaden the vibrations transmitted from the wall to the
telescope.
Instead of having the instrument suspended from the wall, the same may be
mounted upon a tripod to stand upon a table or other horizontal plane.
The angle of deflection which the mirror makes is, of course, proportional to the
intensity of the current. The graduations on the scale are reflected by the mirror
into the telescope where the amplitude of deflection is read. The current to be

page_text: measured enters at the binding post, passes into the small wire above the coil,
traverses the coil deflecting the same and passes out in the ordinary way.
In connection with the said instrument, I use an arrangement of shunts for
reducing the current in a given series of ratios, which consists of three series of
résistances. If we call these series of resistances R, R1 and R2 in which the
series R equals the series R2 and they are so connected that R and R' are in
the sbunt circuit and R' is in the main circuit, and so arranged that when the
resistance R is increased by r the shunt resistance is decreased by r, the shunt
values become―
The special value of this arrangement is, that if the series of resistances and R
both change according to a geometrical progression, the shunt values will also form
a geometrical progression which makes the range of such shunt values immense, and
the range of currents to be measured correspondingly great.
For potential a separate set of resistance coils are added. A box hinged to one
side of the base of the galvanometer, or a glass cover should preferably be provided
to exclude all draughts from the moving parts of the instrument.
The arm supporting the telescope is pivoted on screws, and the arm grasping the
base when it falls in position, the friction between the base and the said arms
soon dissipates the energy of vibration, and causes the telescope to come to rest.
Referring now to the dynamometer, when used as a wall instrument, the
dynamometer is usually provided with a base which can be easily screwed or
otherwise attached to the wall. Upon this base is held the dynamometer proper,
which is made up of a split metal frame, the parts being hinged together, sustaining
on each side of the said frame two vulcanite or other insulating plates, which
together with the frame form a box in which is enclosed the suspended system.
This system is thus protected from draughts or other exterior damaging effects.
In this instrument I use two pairs of fixed coils and one movable coil. One of
the pairs of fixed coils is made of fine wire for use with small currents, while
the other is made of coarse wire for the measurement of currents of greater
magnitude. These coarse wire coils preferably consist of copper ribbon wound
upon a core held very securely in position by a vulcanite button or other like
device, and the core is composed of any suitable insulating material. These coils
preferably occupy similar positions on the front and back respectively of the
instrument. Being outside they are open to a free circulation of air, which
prevents to a great extent heating effects which would otherwise occur were the
coils closely confined when large currents are passed through them. The coils are
connected in series with suitable terminals.
The other pair of fixed or stationary coils consist of fine wire which coils are also
in series.
A ring made of fibre or other insulating material and fastened to the inside of
vulcanite faces front and back form cavities or receptacles in which the coils of
fine wire are held, and when the front of the instrument is closed, these fine wire
coils completely enclose the movable coils.
A movable coil is suspended by a fine wire from a rod held in position by
Just above the coil and suspended on the same wire is a mirror, which
mirror reflects into the telescope the graduations on the scale by which the
amplitude of the deflection may be noted. The mirror carries upon its back a mica
vane to facilitate damping, and this may be further aided by being enclosed in the
chamber. When the front of the instrument is closed the mirror reflects the light
through a suitable aperture therein. The dynamometer is provided with a
swinging stand upon which is held a telescope and scale similar to that already
described with relation to the galvanometer.
This instrument when not used as a wall instrument, may also be mounted on a

page_text: tripod and used upon a table or other horizontal plane, and the box containing the
resistance coils may be either stood on the floor under the instrument or attached
to the wall, as desired.
I provide contact makers in the shunt box, by which the resistances may be
controlled. For this purpose I provide a device consisting of metallic segments
and contact arms for reversing the direction of the current when desired, and contact
blocks used for making contact with said arms. The shunts are similar to those
already described.
PHILIP M. JUSTICE,
London, Chartered Patent Agent.
Improvements in Electrical Measuring Instruments.
HENRY AUGUSTUS ROWLAND of 913 Cathedral Street in the City of
Baltimore State of Maryland United States of America Professor of Physics,
a citizen of the United States do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
My present invention relates to improvements in methods of and instruments
for making various electrical measurements; and the object of this invention
is to make a more convenient and accurate system of instruments for the
measurement of electrical currents of various strengths as well as various
potentials.
One of the principal features of the invention is the providing of a wall
instrument furnished with a telescope and scale or lamp and scale hinged to it
and capable of being folded against the wall when not in use.
I attain the objects above stated by the arrangement illustrated in the accom-
panying drawings, in which-
Fig. 1 is a front elevation of my improved form of D'Arsonval galvanometer
with telescope and scale mounted thereon, said telescope and scale being raised as
in position when not in use.
Fig. 2 is a side elevation of the same galvanometer, the frame carrying the
telescope and scale being down as in position for reading the deflections on the
scale, and in addition thereto is shown in dotted lines the support, telescope, and
scale raised and hooked against the wall, to which wall the base of the galvano-
meter is also attached.
Fig. 3 represents in frout elevation a modified form of the D'Arsonval galvano-
meter shown in Figs. 1 and 2, this form being more especially adapted to rest upon
a table or other horizontal plane.
Fig. 4 is a diagram of the circuits of the currents to be measured, showing the
arrangement of resistances for obtaining various shunt-values.
Fig. 5 represents an instrument differing in form from that shown in the
preceding figures, shown in front elevation with telescope stand attached.
Fig. 6 represents the same in side elevation showing the telescope and stand
down as in position for reading, while in the same fig. the telescope is shown in
dotted lines lilted and hooked to the wall, as when not in use.
Fig. 7 represents the instrument shown in Figs. 5 and 6 in front elevation with
the telescope and stand detached.
Fig. 8 represents the same with the front open to show the interior.
Fig. 9 represents the same instrument in side elevation.

page_text: broken away.
Fig. 11 represents the lower portion of the instrument shown in Figs. 5 to 10
with a shunt box situated directly thereunder, all of which shunt box is broken
away except that portion holding the contact makers, by means of which such
amounts of resistance contained in the shunt box may be thrown in or out of the
circuit as is deemed necessary for the particular measurement.
Fig. 12 is a detail view in section along the line 12-12 of Fig. 11.
Fig. 13 is a diagram of the circuits, showing the paths of the currents,
arrangement of resistances, and connections for the instrument shown in Figs. 5
to 12.
Similar letters refer to similar parts throughout the several views.
A is a galvanometer of the D'Arsonval type constructed in a manner to render
it particularly free from all vibrations, which is in a large degree accomplished by
making the instrument readily attachable to the wall of a room or other object in
a vertical plane.
The galvanometer A. consists of a base a, to which is attached the other parts of
the instrument, said base being provided with holes a°, by means of which the same
may be readily screwed or otherwise attached to a wall.
A° is an iron frame attached to the base a, which frame forms a magnetic field,
and between the poles N. S of which is suspended the coil E. In the form of
frame shown in Fig. 1 the frame A° is shown as having a continuous periphery,
while the frame shown in Fig. 3 has a cap A², secured to the top of the frame by
screws a². This cap is of brass or other non-magnetic material. The upper or
lower portion of the frame A° (shown in Fig. 1) may also be completed by a
cap similar to that shown in Fig. 3, if desired. Besides forming a magnetic
field the frame A° constitutes a box and support for other parts of the
instrument.
The coil of fine wire E is suspended from the screw f, said screw affording a
means for adjusting the position of the coil E.
F is a metallic tube through which passes the wire e. Just above the coil E
and attached to the wire e is the mirror M, directly behind which mirror and also
attached to the wire e is a mica vane m, the effect of which vane is to greatly
facilitate damping, thereby rendering the instrument practically dead-beat. The
arms C, upon which are carried the telescope and scale are pivotally connected, as
at c, to the sides of the base a of the instrument. The arms C of the support
converge and become parallel, as at b, thereby forming a slot through which pass
the thumb-screws 61 of the telescope. By this arrangement the telescope may be
readily detached from the frame.
Instead of having the arms C pivotally connected to the base of the instrument,
as shown in the figures, one side may be hinged and the other provided with a
catch, thus allowing the telescope and scale to be moved around to the right or
left in a horizontal plane.
B is a reading-telescope attached to the support C by means of the thumb-
screws b, as above described. A slotted frame d forms a convenient means of
support for the scale D, which scale is adjustable either to right or left. As
the small block 6 forms a bearing under the center of the telescope-frame, it
is readily seen that the eyepiece may be raised or lowered by adjusting the
.screws bl
An eyelet d', attached to the back of the frame d, engages a small hook d³, by
means of which arrangement the telescope frame and support are held vertically
against the wall.
The essential difference between the galvanometers shown in Figs. 1 and 2 and
that shown in Fig. 3 lies in the fact that the latter is provided with a tripod T
intended to stand upon a table or other horizontal plane, while the former is
.essentially a wall instrument.
The frame A', Fig. 3, is provided with a socket a

page_text: By virtue of the socket-joint at a' the galvanometer is capable of being revolved.
in any desired direction.
The tripod T is provided with the leveling-screws t.
The current to be measured, entering at the binding-post n, passes into the small
wire e above the coil, traverses the coil, and passes out at n¹.
The angle of deflection which the mirror makes is of course proportional to the
intensity of the current. The gradations on the scale D are reflected by the
mirror into the telese-pe, where the amplitude of the angle of deflection is
read.
While in this special case I have chosen the D'Arsonval type of galvanometers
it can readily be seen that almost any form of reflecting-gulvanometer could be used.
For measuring current of various degrees of intensity I use in connection with the
above described galvanometer a system of shunts. This arrangement of shunts for
reducing the current in a given series of ratios consists of three series of resistances,
as seen at W, W', and R, Fig. 4.
For measuring current, suppose the current enters at X, Fig. 4, passes through
the series of resistances W and out at Y. The current divides, a portion being
shunted through the circuit W', O, R, E, O' and O2, which circuit includes the
set of resistances R and the set W₁, equal to W. The arm I, moving over the
resistance W, also moves over W₁, so that when the resistance W is increased
by a certain increment-say the shunt-circuit resistance is decreased by the
same amount. From this arrangement the shunt value becomes
до
== RE
The practical value of this idea is in the fact that if the series of resistances
and R both change according to a geometrical progression, the shunt values will
also form a geometrical progression which by the combination may be of immense
Thus if R have values 1, 2, 4, 8, 16, and the series 1,
extent.
1
32768'
1 1
32 1024'
the inverse shunt ratios will be 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024,
2048, 4096, 8192, 16384, 32768, 65,536, 131072, 262144, 524,288. Thus out of
mine resistances and four compensating coils I have obtained twenty shunt ratios.
The special value of this arrangement is when, heavy currents are to be measured,
as, in this case, only the four resistances r need be adapted to heavy currents,
the other series r and R being of fine wire. The range of shunt values is also
immense.
The practical arrangement by which the main current is allowed to pass through
only low resistance while a portion thereof is shunted through higher resistance
and through the coil E, and by which arrangement the resistance in the main
current-circuit is increased by a certain increment-say r-and the shunt resistance
decreased by the same amount is shown in Fig. 12, which represents a section of
the contact maker I. The main current entering at K passes up the same rod
through the contact-arm 1' into the block G. G being a section through one of
the segments shown at W in Figs. 4 and 13, has interposed between it and the
other segments suitable resistance through which the current passes, making its exit
at Y. Now also upon the rod K, Fig. 12, is another contact arm I, which is insulated
from the rod K and makes contact with both the segments G and U. The current
entering a portion thereof is shunted through the arm I into the shunt-resistances
interposed between the contact pieces, of which U is a section. Now it is clear
that if the contact-arms I and I are revolved in the same direction by equal
amounts, as the resistance is increased in one circuit it will be decreased by the
same amount in the other. This arrangement does not allow the resistance at the
contact of the main current to cause any error.
The current which passes through thhe coil E is reduced to the shunt ratio,
and by obtaining a very large number of shunt ratios from only nine resistances

page_text: the great range of currents, from the strongest to the weakest, which can be
measured by this method is at once evident.
For measuring potential the set of resistance-coils R are added by closing the
switch P, and thus the potential is gotten between Z and Y.
Although the instruments, shown in Figs 1 to 4 have been shown for the sake of
clearness, without a covering of glass, wond, or other material, it is readily seen
that a box hinged to one side of the base of the galvanometer or glass cover
provided with catches would exclude all drafts from the moving parts of the
instrument.
An instrument differing somewhat from that above described and which in addition
to measuring current and potential may be used to measure directly watts or
electrical energy, self induction, mutual induction, and, indeed, a great many
electrical quantities, is chown in Figs. 5 to 11 inclusive, and like that illustrated in
the preceding figures, is, in its most complete form, a wall instrument and also like
the above described instrument is provided with a similar telescope, reading scale
-and frame.
For the sake of clearness as well as brevity, this last form of instrument will be
designated a "dynamometer." The instrument proper H, Figs, 5 to 11 is mounted
upon a base a and is made up of the split metal frame h, hinged as at h³, and
sustaining upon each side of the frame two vulcanite or other insulating plates h
forming thereby a box in which is inclosed the suspended system, which is thus
protected from drafts or other exterior damaging effects. In this instrument I use
two pairs of fixed coils and one movable coil. One of the pairs of fixed coils is
made of fine wire for use with small currents, while the other is of coarse wire for
the measurement of currents of greater magnitude.
L represents the coils of coarse wire, which wire consists, preferably of copper
ribbon wound upon the core and held more securely in position by the vulcanite
button . The core is composed of any suitable insulating material. These
coils L occupy similar positions on the front and back, respectively, of the
instrument. Being outside, they are open to the free circulation of the air, which
prevents, to a great extent, heating effects which would otherwise occur were. the
coils closely confined when large currents are passed through them. The coils are
connected in series, the terminals being the binding-posts N. The other pair of
fixed or stationary coils consist of fine wire, as shown at L', and are also in series
with each other.
A ring, made of fiber or other insulating material and fastened to the inside of
the vulcanite faces ', front and back, form cavities or receptacles in which are
held the coils of wire L'. When the front of the instrument is closed, the coils L
completely inclose the movable coil E¹.
The movable coil E¹ is suspended by the fine wire e' from the rod f¹, which rod
slides within the tube F¹ and is held in position by the screw f³. Just above the
coil E and suspended on the same wire is the mirror M¹. This mirror reflects
into the telescope the graduations on the scale by which the amplitude of the
deflection may be noted. The mirror M' carries upon its back a mica vane m², the
office of this vane being to facilitate damping, which is further aided in this by
being inclosed in a chamber V. When the front of the instrument is closed, the
mirror reflects the light through the aperture h².
To greatly facilitate the use of the above described dynamometer in the
measurement of current and potential, as well as to make the instrument especially
adapted to the measurement of various alternating current quantities such as
self-induction, mutual induction, electrical energy, and other quantities, the
measurement of which has always hitherto been accompanied with great com-
plexity I have by virtue of the present arrangement greatly simplified such
measurements. I achieve this end by the arrangement shown in Fig. 13, in which
I so group and arrange the resistances in the shunt-circuits as to secure a large
number of shunt ratios from a comparatively small number of resistance-coils.
This grouping and arrangement of shunt circuits to obtain a large number of

page_text: ratios from a small number of resistances is substantially the same as that shown
in Fig. 4 and fully described above, but while the arrangement of the resistances
for obtaining these shunt values is the same, the connections from the resistances
to the dynamometer differ from those shown in Fig. 4. The box which contains
the resistance coils may be either stood on the floor under the instrument or
attached to the wall as shown in Fig. 11, in which R and R³ are the contact-
makers by which the resistances R and R', respectively, are controlled; Q, a
device, consisting of the metallic quadrants q and the contact-arms q, for reversing
the direction of the current wben desired, and P1, P2, P and P the contact-
blocks.
Referring now particularly to Fig. 13, P, PP, P and P represent a series of
metallic contact-blocks provided with plugging-holes, 1, 2, 3, 4, 5, 6 and 7, by
which arrangement any desired combination of connections within the scope of the
instrument may be made.
As was stated above, the dynamometer as herein described is adapted to the
measurement of both large and very small currents. For the former a fixed coil
of coarse wire is provided and for the latter one of very fine wire; so in describing
the operation of measuring currents with the instrument it is immaterial which
pair of coils 1 use-that is, the same explanation will be sufficient for measuring
both large and small currents.
For the measurement of current I assume that the current enters at X and
insert plugs in 7 and 2 for large currents and 7 and 4 for small ones. The current
then passes through 7 into P4, from thence into the contact-maker 1 (shown in
detail in Fig. 12), through suitable low resistance, then into the block P, through
the plug 2, around through the large pair of fixed coils L of the dynamometer, and
out at Y.
A portion of the main current is shunted through the resistance W, around.
through R, then into the movable coil of the dynamometer E', back into the
circuit.
The practical arrangement by which the main current is allowed to pass through
only low resistance, while a portion thereof is shunted through higher resistance
and through the coil E', and by which arrangement, when the resistance in the
main circuit is increased hy a certain increment-say the shunt resistance is
decreased by the same amount, is shown in Fig. 12 and fully described above..
The arrangement of the resistances being the same, the number of shunt values
are correspondingly the same.
For measuring differences of potential the posts Y and Z are used and same
plugs inserted as for measuring current. In this instance the extra resistance R¹
is added.
For measuring watts a plug is inserted either at 1 and 2 or 4 and 5. The main
current then passes through one of the pairs of coils L or L, while the potential
current enters at Z, and after passing through the resistance R' is shunted through
the movable coil E. By this arrangement the same shunt system is used for the
measurement of all three quantities-current, potential, and watts or energy.
In the measurement of alternating currents by means of a shunt arrangement of
coils, the currents divide according to the impedance and not according to the
resistance of the circuits. The angle of phase is also dependent on the frequency
and the ratio of the resistance to the self-induction. The impedauce can be put
in the form R +
R*
where L is the self induction and R the true
resistance. From this we see that a great simplification in electrical measurements
and instruments can be made by making the ratio a constant quantity. I so
R
L
proportion the circuits as to keep the ratio of the resistance to the self induction a
When this is the case, all alternating currents of any frequency divide

page_text: in a shunt in the same ratio as do constant currents, and I propose to utilize
this fact in making alternating-current instruments. The phase-angle is also
unaltered.
While I have shown the frame carrying the telescope and scale as capable of
being lifted upward and fastened to the wall above the instrument, it is clear that
one arm might be hinged and the other provided with a catch, whereby the
telescope, and scale could be turned in a horizontal plane.
The dynamometer may, when not used as a wall instrument, be mounted
on a tripod or other suitable mounting and placed on a table or other horizontal
plane.
One of the advantages claimed for the berein describel instrument is absolute
freedom from shocks and vibrations. I have devised a method of support which
will accomplish this object by making the support a combination of rigidity and
friction. Thus in Figs. 1 and 5 for example the arm is supported by pivoting-
screws, to which is added the friction of the arms grasping the base-board when it
falls into position. The friction quickly dissipates the energy of vibration and
brings the arm to rest. This arrangement of telescope and scale has the following
advantages The telescope and scale cau be turned back on the wall and fixed
by a hook whenever not needed, and can be lowered into position and perfect
adjustment in a moment. Then again, the wall is free from the vibrations of the
floor and the floor-space is free to allow a table to be placed under the instrument
for taking notes or supporting other instruments. The table may be hinged to
the wall, if desired. Again, by the arrangement of shunts which I have described
the values are almost without limit which may be gotten therefrom.
There are various other advantages of the herein-described invention which
would readily suggest themselves to any one skilled in the art.
It will be obvious that various other modifications might be made which could
be used without departing from the spirit of my invention.
Where a lamp and scale are employed the lamp (which may be an incandescence
electric lamp or a lamp of any other suitable kind) is placed at the side of the
scale so that the light is reflected onto an angle mirror carried by the latter
said mirror casting the light onto the mirror of the galvanometer or like
instrument.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is.-
1. The combination of an electrical measuring instrument, means for attaching
the same to the wall, and a pivoted arm capable of folding against the wall, with
a reading-scale carried by said arm, substantially as described.
2. The combination of an electrical measuring instrument, means for attaching
the same to the wall, and a pivoted arm capable of folding against the wall, and a
telescope and reading-scale attached to said arm, substantially as described.
3. The combination with, a base suitable for attaching to the wall, of a pivoted
arm with scale and telescope attached, and an electric measuring instrument
mounted on said base, substantially as described.
4. The combination with an electrical measuring instrument, of a pivoted arm
carrying a reading-scale, and a shunt-box connected to the terminals of the
instrument, substantially as described.
5. The combination of an electrical measuring instrument, means for attaching
the same to the wall, a pivoted arm capable of folding against the wall, and
having frictional contact with the base of the instrument when in the operative
position and a reading-scale carried by same, substantially as described.
6. The combination of an electrical measuring instrument, means for attaching
the same to the wall, a pivoted arm capable of folding against the wall, and having
frictional contact with the base of the instrument when in the operative position,
and a telescope and reading scale attached to said arm substantially as described.

page_text: 7. The combination with a base suitable for attaching to the wall, of a pivoted
arm with scale and telescope attached, the said arm having frictional contact with
the base of the instrument, when in the operative position, and an electrical
measuring instrument mounted on said base, substantially as described.
8. The combination of an electrical measuring instrument, and means for
attaching the same to the wall, of a pivoted arm capable of folding against the
wall, with an adjustable reading scale carried by said arm, substantially as
described.
9. The combination of an electrical measuring instrument, and means for
attaching the same to the wall, of a pivoted arm capable of folding against the
wall, and a telescope and an adjustable reading-scale attached to said arm, substan-
tially as described.
10. The combination with a dynamometer, of a shunt-box connected to the
terminals of the dynamometer, and a pivoted arm making frictional contact with
the base of the instrument and carrying a reading scale substantially as and for the
purposes described.
11. The combination with an electric measuring instrument of a shunt-box
having a series of coils arranged for the main current, and two other series in the
shunt-circuit, the second series being equal to the first series, and serving to keep
the shunt ratios of the proper value, while the third series is in geometrical
progression, the whole arrangement being such as to make the series of shunt
ratios form a geometrical series of any required extent, substantially as described.
12. The combination with an electric measuring instrument of a shunt-box
having a series of coils arranged for the main current, and two other series in the
shunt-circuit, the second series being equal to the first series, and serving to keep
the shunt ratios of the proper value, while the third series is in geometrical
progression, the whole arrangement being such as to make the series of shunt
ratios form a geometrical series of any required extent, and a fourth resistance-
coil for measuring potential, substantially as described.
13. The combination with an electrodynamometer, of a shunt-box having a
series of coils arranged for the main current, and two other series in the shunt-
circuit, the second series being equal to the first series, and serving to keep the
shunt ratios of the proper value, while the third series is in geometrical
progression, the whole arrangement being such as to make the series of shunt
ratios form a geometrical series of the desired extent, substantially as described.
14. The combination with an electrodynamometer, of a shunt-box having a
series of coils arranged for the main current, and two other series in the shunt-
circuit, the second series being equal to the first series, and serving to keep
the shunt ratios of the proper value, while the third series is in geometrical
progression, the whole arrangement being such as to make the series of shunt ratios
form a geometrical series of the desired extent, and a fourth-resistance coil for
measuring potential, substantially as described.
15. An electrodynamometer containing a coarse fixed coil and a fine fixed coil
with means for passing the current through either coil as may be desired, and a
movable coil with means for passing the shunt-current therethrough, substantially
as described.
16. An electrodynamometer having its fixed coils supported by two nou-
conducting pieces forming when closed portions of a box to contain and protect
the moving system, substantially as described.
17. An electrodynamometer in which the coils are supported by non-conducting
material attached to metal frames hinged together so as to shut and form a box
for the protection of the moving system, substantially as described.
18. In an electrodynamometer, the combination with a frame bearing the fixed
coils and provided with a chamber, of a reflecting-mirror suspended in said chamber
and a vane attached to the back of the reflecting-mirror and free to oscillate in
said chamber, substantially as described.
19. In an apparatus of the character described, the combination with a pivot K

page_text: and an arm I and connections for carrying the main current, of an insulated arm I
also carried by said pivot with connections for carrying the shunt-circuit through
said arm, substantially as described.
20. An electrical measuring instrument, containing two fixed coils with con-
nections for passing the electric current through either one of said coils, and one
movable coil, with means for passing the shunt-current therethrough, substantially
as and for the purposes described.
21. The combination and arrangement of parts substantially as berein described
and shewn in Fig. 1 and 2 of the drawings hereunto annexed.
22. The combination and arrangement of parts substantially as herein described
and shewn in Figs. 5 and 6 of the drawings hereunto annexed.
23. The combination and arrangement of parts substantially as herein described
and shewn in Figs. 7 to 10 of the drawings hereunto annexed.
24. The arrangement of shunts substantially as herein described and shewn in
Figs. 4 and 13 of the drawings hereunto annexed.
Dated this 18th day of December 1896.
PHILIP M. JUSTICE,
55 & 56 Chancery Lane, London, Chartered Patent Agent,
For the Applicant.