IMPROVE- MENTS IN MEANS FOR PROTECTING MAGNETIC NEEDLES FROM LOCAL ATTRACTION
Year: 1881

page_text: LETTERS PATENT to John Sacheverell Gisborne, Civil Engineer, of the City
of Manchester, in the County of Lancaster, for an Invention of "IMPROVE-
MENTS IN MEANS FOR PROTECTING MAGNETIC NEEDLES FROM LOCAL
ATTRACTION."
PROVISIONAL SPECIFICATION left by the said John Sacheverell Gisborne
at the Office of the Commissioners of Patents on the 9th April 1881.
JOHN SACHEVERELL GISBORNE, Civil Engineer, of the City of Manchester, in
the County of Lancaster. "IMPROVEMENTS IN MEANS FOR PROTECTING MAGNETIC
NEEDLES FROM LOCAL ATTRACTION."
I surround the magnetic needle with several series of concentric segments, or
other suitably shaped pieces of iron, which also extend underneath the needle
and meet in the centre as close as possible to the pivot upon which the needle is
mounted; these iron segments or other shaped pieces are not in touching contact
but are isolated from each other by intervening pieces of ebonite or other suitable
insulating material. By thus surrounding the needle I ensure that any polarisation
of the iron, even should it occur, shall not affect the magnetic needle, and yet
that the needle shall itself be effectually protected from the influence of any local
attraction.
Or I surround the magnetic needle with several series of concentric segmental
chambers filled with iron filings, and which chambers also extend underneath the
needle and meet in the centre and are isolated from each other as in the case of the
iron segments before mentioned.
Or I surround the magnetic needle by a coil of iron wire covered with
insulating material, and which insulated iron wire is extended underneath the
needle, and I cause a current of electricity to constantly pass through this iron
wire coil for the purpose of protecting the needle from the influences of local
attraction.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, and
of an Order of the Lord Chancellor, filed by the said John Sacheverell
Gisborne in the Great Seal Patent Office on the 18th October 1881.
JOHN SACHEVERELL GISBORNE, Civil Engineer, of the City of Manchester, in
the County of Lancaster. "IMPROVEMENTS IN MEANS FOR PROTECTING MAGNETIC
NEEDLES FROM LOCAL ATTRACTION."
I surround the magnetic needle with several series of concentric segments, or
other suitably shaped pieces of iron or steel, which also extend underneath the
needle and meet as near as possible in the centre; these iron segments or other
shaped pieces are not in touching contact, but are isolated from each other by
intervening pieces of ebonite or other suitable non-magnetic material.
By thus surrounding the needle I ensure that any polarisation of the iron or
steel, even should it occur, shall not effect the magnetic needle, and yet that the
needle shall itself be effectually protected from the influences of any local
attraction.
Or I surround the magnetic needle with several series of concentric segmental
chambers filled with iron or steel filings, and which chambers also extend
underneath the needle and meet in the centre, and are isolated from each other, as
in the case of the iron segments before mentioned; or I surround the magnetic
needle by a coil of iron or steel wire covered with silk or other insulating material,
and which insulated iron or steel wire is extended underneath the needle, and I
cause a current of electricity to pass through this iron or steel wire coil either
constantly or intermittently, the iron or steel wire coil effectually protecting the
magnetic needle from the influences of local attraction and the current controlling
the polarity of the coil. And in order that this my said Invention may be the
more readily understood and carried into practical effect I have hereunto annexed
a Drawing illustrative of my Invention, and will now proceed to describe the
same with the assistance of the Figures and letters of reference marked thereon.
Fig. 1 is a transverse section of a series of concentric segmental chambers
surrounding a magnetic needle in accordance with my Invention, and Fig. 2 is a
sectional plan of Fig. 1 upon the line A, B, and looking upward or in the direction
of the arrow,
and Fig. 3 is a similar section of Fig. I taken on the line C, D. In
Figs. 1, 2, and 3, A. is a central cylindrical compartment open at the top and
surrounded by the concentric chambers B, C, D, and E. These chambers not only
surround the central compartment A but extend underneath it, as seen more clearly
in Fig. 1, and such concentric chambers B, C, D, and E, are again divided into
segmental chambers by the radial partitions B¹, C¹, D¹, and E'.
These partitions, it will be noticed, are not opposite each other, but are placed
alternately midway between each other; for instance, the partitions C¹ and È¹ are
opposite each other, and again B' and D' are opposite each other, as seen more
clearly in the plan views. The walls of these compartments, as also the partitions,
are constructed of ebonite, brass, or other non-magnetic material, and the concentric
segmental chambers so formed are all filled with iron or steel filings. At the top
of this cylindrical compartment A I arrange the magnetic needle, either mounted
in the usual compass bowl and gimballed in the usual manner, or such magnetic
needle or needles may be mounted upon a pivot rising from the bottom of the
central compartment A, and the whole series of compartments will this form the
compass bowl and be gimballed in the binacle as compass bowls usually are.
In Fig. 4 I illustrate a similar series and arrangement of concentric segmental
chambers filled with iron or steel filings, and surrounding a central compartment F
for protecting a magnetic needle, which only differs from those illustrated in

page_text: Figs. 1, 2, and 3, in such chambers being conical instead of cylindrical in form,
Fig. 5 being a sectional plan of Fig. 4 on the line e-f.
A further modification of my Invention, illustrated in transverse section by
Fig. 6, consists of a central open topped compartment G for containing the
magnetic needle. This compartment is surrounded by segmental chambers H
filled with iron or steel filings, as in Figs. 1, 2, and 3, except that these chambers
are again divided by the horizontal or annular partitions I constructed of similar
non-magnetic material to the other partitions. Instead of segmental compartments
filled with iron or steel filings, as aforesaid, and as illustrated in the accompanying
Drawing, I also employ similar shaped segments or other shaped pieces of iron or
steel for surrounding and thus protecting the magnetic needle from the influence
of local attraction, but it must be understood that I do not confine myself to the
segmental forms, either for the chambers filled as aforesaid, or for the iron or steel
surrounding pieces, as other forms may be substituted, although I prefer the
segmental form; and in case of pieces of iron or steel being used it must be
understood that they are not in touching contact, but are insulated from each other
by intervening pieces of ebonite or other suitable non-magnetic material, and
extend underneath the needle, as in the case of the chamber herein before described.
By thus surrounding the needle I ensure that any polarisation of the iron or steel,
even should it occur, shall not effect the magnetic needle, and yet that the needle
shall itself be effectually protected from the influences of any local attraction.
In Figs. 7 and 8 I illustrate a transverse section and sectional plan respectively,
shewing how the central compartment K containing the magnetic needle may be
surrounded by a coil of iron wire L or steel covered with silk or other insulating
material. This insulated iron or steel coil L not only surrounds, but is extended
underneath the needle, and I cause a current of electricity to pass through this
iron or steel wire coil, either constantly or intermittently, the iron or steel wire
coil effectually protecting the magnetic needle from the influences of local
attraction and the electric current controlling the polarity of the coil. The section
of Fig. 8 is taken across the line E, F, in Fig. 7.
Having thus particularly described and ascertained the nature of this my said
Invention, together with the best methods with which I am acquainted for carrying
the same into practical effect, I wish it to be particularly understood that I do
not confine myself to the precise details, relative proportions, or dimensions of the
various parts of the magnetic needle protecting apparatus, hereinbefore described
and illustrated on the accompanying Drawing, as the same may be considerably
varied without departing from the Invention, but what I claim is,―
1st. Surrounding a magnetic needle with iron or steel, such iron or steel being
insulated to prevent polarisation, substantially as and for the purposes hereinbefore
described.
2nd. Surrounding a magnetic needle by a coil of insulated iron or steel wire
charged permanently or intermittently with a current of electricity, substantially
as and for the purposes herein before described.
3rd. The various constructions of apparatus for protecting magnetic needles
from the the influence of local attraction, substantially as herein before described
and illustrated on the accompanying Drawing.
In witness whereof, I, the said John Sacheverell Gisborne, have hereunto set
my hand and seal, this Fifth day of October, in the year of our Lord
One thousand eight hundred and eighty one.
JOHN S. GISBORNE. (L.S.)