Year: 1890

page_text: of the bar C and has its polar extremities exactly opposite the polar extremities of
the magnet, a, and in close proximity to the thin portion H. The purpose of the
two countersinks in the bar producing the thin intermediate part H, will now be
apparent, the object being to allow the poles of the magnets to be brought into very
close proximity to one another.
The circuit in the instrument proceeds from the binding post 1 through the bar C
to the binding post 2 or vice versa.
The operation of the instrument is as follows:-
-:
When the current passes through the bar C the magnets a and b in accordance
with well-known laws, tend to place themselves at an angle to the longitudinal axis
of the bar, which angle is determined by the strength of the current and by the
opposition offered by the springs Q and R. The opposing force of the springs by
reason of their form is practically constant. The position of the magnets is shown
by the index needle U. It remains simply to calibrate the instrument and to lay off
a suitable scale on the plate V, which scale may be graduated in amperes or fractions
thereof.
It will be apparent that the strength of the current passing through the thin
portion H of the bar C will depend, other things being equal, upon the thickness of
said thin portion. And therefore, the sensitiveness of the instrument may be governed
by increasing or diminishing said thickness in constructing the bar C.
A more
convenient way, however, of regulating the sensitiveness of the instrument, is by
controlling the proportion of current which passes through the thin plate H, as
compared with the remaining and thicker portion of the bar C. And for this purpose,
it is preferable to use the device shown in Figs. 4 and 5. In the edges of the bar C
are tapped two holes in which are inserted the screws c, d. It will be clear that
when these screws are inserted to their full extent, then the maximum proportion of
current will pass through the thicker portion of the bar on each side of the thin
portion H. But when the screws are drawn out, then less current will pass through
said thick portions of bar C, and more current will pass through the thin portion H.
In this way, a nice adjustment of the proportion of current allowed to pass through
the thin portion H may be made.
The construction and arrangement of the voltmeter, Figs. 6 to 8, inclusive, is as
follows:
A is the base provided with a chamber or recess B¹ for the reception of the coil.
At C are two cylindrical standards upon which rests a flange D¹ of the reel, spool, or
bobbin, E¹. Screws F pass through said flange and said standards and into the
base A¹, thus securing said parts together. The reel E' is of non-conducting material
and is box-shaped. In its upper side it has a circular aperture Q' across which
extends a supporting bar H¹. In said bar is a short tube or sleeve I'. In the lower
side of said reel there is a bushing J¹ which receives a screw step K¹. Said step may
be jewelled to receive the extremity of the vertical arbor L' which extends up through
the sleeve I¹ in bar H¹.
On the upper side of reel E¹ and opposite flange D' is a flange M' to which is
bolted a bracket N'. This bracket extends upwards and over the reel E¹ and is pro-
vided with a threaded nut which receives the screw O¹. The lower extremity of said
screw may be jewelled and forms a bearing for the upper end of the arbor L.
Extending from the bracket N' is an arm P', having its extremity bent downwardly.
To said extremity is attached one end of a coiled spring Q, the other end of said
spring being fastened to a fixed collar R¹ on the arbor L. Secured to the arbor L
below the collar Ris_a_light_disk_S_to_which is attached-an-index-needle-T,-which-
extends over the scale plate U¹. Said scale plate U is supported upon a bracket V₁
which is bolted to the flange D₁ of reel E¹. The disk S is omitted in Fig. 6, the
needle being there shown directly secured to the arbor.
The coil W¹ of the instrument is of insulated wire wound around the reel E
longitudinally and having its terminals connected to the binding posts 1 and 2, as
indicated by dotted lines Fig. 6.
The arbor L' carries two magnets, a and b, semi-circular in form and having their

page_text: oppositely named poles facing. The upper magnet, a, has its polar extremities in
close proximity to the upper side of the thin flat coil W. The lower magnet, b, has
its polar extremities exactly opposite the poles of magnet a and in close proximity to
the under side of said coil. The object of the circular aperture G¹ in the reel E¹ will
now be apparent. Its purpose is to allow the poles of the magnet 6 to be brought
very near to the coil W₁, the magnet rotating within the aperture.
The operation of the instrument is as follows: The current to be measured enters
at either binding post 1 or 2, passes through the coil W₁ and out at the other
binding post. In accordance with well-known laws, the magnets a and b then ten.
to place themselves at an angle to the longitudinal direction of the coil, which
angle is proportional to the strength of the current. But as a coil of fine wire of
high resistance is employed, the angle assumed becomes proportional to the difference
of potential between the terininals of the coil, and is also modified by the opposition
which the spring offers to the rotary movement of the arbor L'. By reason of the
form of the spring, this opposition is practically constant in all angular positions
assumed by the arbor L'. It remains simply to calibrate the instrument and to lay
off a suitable scale on the plate U₁ which scale may be graduated to volts. or
fractions thereof.
The following advantages result from the above-described construction:
1. In both forms of apparatus the magnets a and b may be mide in the form of
a ring of suitable steel which may be cut in two diametrically after tempering and
before magnetization. In this way, magnets may be produced closely alike in
strength, and the astatic quality of the apparatus may thus he more nicely determined.
2. By reason of the semicircular form of said magnets, their respective polar
extremities of opposite names can be brought into close juxtaposition, allowing, in
fact, between them, only just enough space to permit the upper layer of wires of
the coil to pass through without touching the polar faces. An intense magnetic
field is thus produced between said poles, which field is intersected by the field due
to the current traversing the bar or the coil wires. Thus the sensitiveness of the
instrument is augmented.
3. By making the magnets of comparatively heavy steel bars, the magnetic effect
is increased and the same rendered more permanent than is the case with the
ordinary thin and light parallel needles of an astatic galvanometer.
4. The mode of suspension of the magnets is exceedingly delicate and prevents
any possible displacement of said magnets laterally. By means of the screw pivot
bearings, the arbor may be raised or lowered so as to adjust the magnets with
reference to the coil or bar.
5. The working parts are simple, few and easily separated or assembled.
6. In the ammeter no wire coil is used, but in place thereof is substituted the
easily made bar C.
By the term "polar extremity" of the magnet as herein used, is meant the end
face of the magnet in contradistinction to the surface on either side; or in other
words, that face of the magnet which is at an angle to the longitudinal axis thereof,
if the magnet be regarded as straightened out, and not parallel to said axis. The
advantage of placing the polar extremities of the magnet in proximity to the surface
of the conductor is, that a very much more intense field of force is produced by the
magnet directly at its polar extremities than at points along its length on either
side thereof. And hence, through the re-action of this field of force upon the field
of force produced around the conductor by the current, a greater sensitiveness of
the needle is attained than would be possible if the needle were arranged with its
polar extremity practically at right angles to the surface of the conductor, instead
of parallel thereto.
Having now fully ascertained and described the nature of the said invention and in
what manner the same is to be performed, as communicated to me by my foreign
correspondent; I declare that what I claim is :-
1. In an electrical measuring instrument, a conducting body and a magnet rotary

page_text: on an axis perpendicular to the surface of said body, the said magnet having its polar
extremities in proximity to and facing said surface.
2. In an electrical measuring instrument, a conducting body, an arbor passing
through said body perpendicular to the surface thereof; and free to turn therein, a
magnet secured to said arbor and having its polar extremities in proximity to and
facing said surface, and means for adjusting said magnet nearer to or further from
said surface.
3. In an electrical measuring instrument, a conducting body having parallel
opposite faces and in each face a recess or countersink, said recesses being opposite
one another, and two magnets rotary on a common axis perpendicular to said faces:
the said magnets having their unlike poles opposed and respectively having their
polar extremities in proximity to and facing the bottom of said countersink.
4. In an electrical measuring instrument, a flat conducting body and a magnet free
to turn on an axis perpendicular to the surface of said body, and disposed in inductive
proximity thereto, and means for varying the relative proportion of current passing
through the mass of said body included within the area swept over by said magnet in
turning and through the mass of said body without said area.
5. In an electrical measuring instrument, a conducting body having parallel
opposite faces, and two magnets rotary on a common axis perpendicular to said faces,
said magnets having their unlike poles opposed and their polar extremities in proximity
to and facing said opposite faces: the said body being of less thickness within the
area swept over by said magnets than elsewhere.
6. The combination in an electrical measuring instrument of a bar or plate C of
conducting material, an arbor 1 passing transversely through said bar, two magnets
respectively supported on said arbor and having their unlike poles opposed and their
polar faces parallel and in inductive proximity to opposite surfaces of said bar, a
spring connected to said arbor and opposing its rotation, an index needle secured to
said arbor, and a scale for showing the deflections of said needle.
7. The combination in an electrical measuring instrument of the conducting bar C
having the thin portion H, a magnet, a, having its polar faces in inductive proximity
to said portion H and supported so as to be free to turn on an axis perpendicular to
said bar, and screws or plugs c, d entering and adjustable in said bar on opposite sides
of said thin portion H.
8. In an electrical measuring instrument a coil of wire, an arbor free to turn
passing through one side of said coil and free to rotate therein, and two magnets
secured to said arbor: said magnets being respectively located within and without
said coil and having their unlike poles opposed and their respective polar extremities
in proximity to and facing the inner and outer peripheries of said coil.
9. In an electrical measuring instrument, a hollow spool or bobbin having in one
side an opening, an arbor free to turn passing through said opening, two magnets
supported on said arbor having their unlike polar faces opposed and parallel and one
of said magnets being located within said spool and having its poles entering said
opening, and a coil of wire surrounding said spool and extending across said opening
and between said magnets.
10. In an electrical measuring instrument, a hollow spool or bobbin E¹ having in
one side an opening G¹, a bracket N¹ supported on said spool, arbor L' free to turn
passing through said opening and having a bearing at one end in the opposite side of
said spool and at the other end in said bracket N₁ an index needle secured to said
arbor and two magnets supported on said arbor having their unlike polar faces
opposed and parallel, one of said magnets being located within said spool and having
its poles entering said opening and a coil of wire surrounding said spool and extending
across said opening and between said magnets.
1 1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.