Method of and Means for Increasing the Directive Force of Magnetic Needles.
Year: 1895

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 18 of the "Patents, &c., Act, 1883), as 'allowed by
the decision of the Chief Examiner of the 27th day of August 1896.
Date of Application, 25th Apr., 1895
Complete Specification Left, 12th Dec., 1895-Accepted, 18th Jan.. 1896
PROVISIONAL SPECIFICATION.
A Method of and Means for Increasing the Directive Force of
Magnetic Needles.
I, JOHN SACHEVERELL GISBORNE, of 13 Belitha Villas, Barnsbury,
London, N., Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to a method of and means 'for increasing the directive
force of magnetic needles.
According to my invention, I propose to surround a magnetic needle with, or to
dispose the same between, two electrical coils or circuits through which electric
currents are passed in reverse directions, i.e., the current passes through one coil or
circuit in the reverse direction to the current through' the other coil or circuit.
Dated this 25 day of April 1895.`
E. P. ALEXANDER & SON,
"Chartered Patent Agents,
19 Southampton Buildings, Chancery Lane, London, WC.,
Agents for the 'Applicant.
A Method of and Means for Increasing the Directive Force of:
Magnetic Needles.
I, JOHN SACHEVERELL GISBORNE, of 13 Belitha Villas, Barusbury,
London, N., Engineer, 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 invention relates to a method of and means for increasing the directive
force of magnetic needles. By directive force will of course be understood that
inherent force which causes one pole of a magnetic needle to point to the north.
According to my invention, I cause an electric current or currents to pass
simultaneously in reverse directions around a magnetic needle or needles, the effect
being to so increase the directive force of the needle, without deflecting the same,
as to prevent any deviation thereof from its position.

page_text: '
In carrying out my invention, I surround the magnetic needle with two electrical
coils of equal resistance through which an electric current or currents is or are
passed in reverse directions, i.e. the current passes through one coil in the reverse
direction to the current through the other coil. Whilst increasing the directive
force of the magnetic needle as above set forth, the excited coils will not cause any
deflection of the same, since the reverse directions of the current or currents
through the coils causes the latter to counteract one another so far as their tendency
to deflect the needle is concerned.
The two electrical coils may be arranged so as to form two separate circuits, or,
as will be obvious to any electrician, they may be so connected up and arranged as
to form a single circuit through which an electric current is passed simultaneously
in reverse directions around the needle and this last mentioned arrangement would
preferably be employed. If the coils are arranged to form two circuits, the current
through each circuit should be generated by the same battery, as the currents must
be of equal force.
My invention may be applied with especial advantage to the magnetic needle or
needles of the mariner's compass, in order to prevent any deviation of the said
needle or needles.
I will now proceed to more particularly describe my invention and the manner of
performing the same having reference to the accompanying drawings in which:
Figs. 1 and 2 are diagrams illustrating the principle of the invention as above
set forth.
Fig. 3 is a vertical section, Fig. 4 is an elevation, and Fig. 5 is a plan, shewing
the application of the invention to the magnetic needle or needles of the mariner's
compass.
Similar letters refer to like parts in all the figures.
Referring to Fig. 1, a indicates a magnetic needle swinging about a pivot 6 and
disposed within a cylindrical casing or bowl c. The cylindrical casing c and the
pivot b must both be of non-magnetic material, such as brass. d and e are the
wires (preferably copper) of two electrical coils of equal resistance which are
wound in parallel around the casing c and are connected up with the battery s0
as to form two circuits through which electric currents of equal strength are passed
simultaneously in reverse directions around the needle a, the reverse directions of
the currents being indicated by the arrows.
In the diagram Fig. 2 is shewn how by simply connecting the two parallel
wound coils d and e at one end, as indicated by the dotted line, the said coils are
caused to form a single circuit through which an electric current may be passed
simultaneously in reverse directions around the needle a, the arrows indicating the
course of the current.
Referring to Figs. 3, 4, and 5, which illustrate the application of my invention
to the magnetic needle or needles of the mariner's compass, a is the compass needle
which is suspended beneath and connected with the compass card g by means of a
suitable light framework h. c is a cylindrical casing or bowl of non-magnetic
material such as brass within which the needle a is suspended. In the centre of
the needle a an aperture is formed through which the pivot b, about which the
compass card
g swings, passes freely, said aperture being of sufficient size to permit
of the unavoidable oscillations of the needle a due to the movements of the vessel.
i is a disc of non-magnetic material secured to the lower extremity of the pivot bat
a little distance beneath the bottom of the casing c. d and e are the wires
(preferably copper) of two electrical coils of equal resistance which are wound in
parallel as hereinafter described so as to surround the casing c and are here
represented as being connected up at one end so as to form a single circuit through
which an electric current is simultaneously passed in reverse directions around the
needle a in the manner before described with reference to, and illustrated in, the
diagram Fig. 2.
The two wires d and e being placed side by side, the winding in parallel is
commenced round the lower end of the pivot b and is continued until the space

page_text: between the disc and the bottom of the casing c is filled, my object in thus
covering the bottom of the casing c with the coils being to prevent heeling error.
The winding is then continued up the side of the casing c to the top thereof and
then down again to the disc i (which is employed merely for retaining the coils in
position) and so on, up and down, until a sufficient thickness of coils, (preferably
about half an inch when 20 gauge wire having two or three coverings of silk is
employed) surrounds the casing c. The ends of both wires d and e may now be
connected up with the battery when the directive force of the needle a will be so
increased as herein before set forth as to prevent any deviation of the said needle
from its position.
Although in the drawings I have represented my invention as applied to a single
magnetic needle a only, it may obviously be applied in the same manner to a group
or cluster of magnetic needles, such as are commonly employed in the mariner's
compass for example. I find however that a more satisfactory result is obtained
by the use of a single needle.
As regards strength of current, this may vary considerably. The directive force
of the needle being proportionate to the force of the current it is only necessary to
see that the latter is not too weak in which case the said directive force might not
be sufficiently increased to ensure non-deviation of the needle. With coils having
about the resistance of those above mentioned, i.e. coils composed of 20 gauge wire
wound to a thickness of about half an inch, I consider that a current of about
10 volts would amply suffice. In conclusion I would observe that I am aware that
a testing instrument known as a "differential galvanometer " and consisting of &
galvanometer having two perfectly similar coils wound upon the same frame
through which coils a current is passed in opposite directions has been employed
for determining the relative force of two currents.
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 I
claim is :-
The herein described method of increasing the directive force of the magnetic
needle or needles of the mariner's compass consisting in causing an electric current
or currents to pass simultaneously in reverse directions around the said magnetic
needle or needles, substantially as set forth.
Dated this 11th day of December 1895.
E. P. ALEXANDER & SON,
Chartered Patent Agents,
19 Southampton Buildings, Chancery Lane, London, W.C., Agents.