Improvements in or relating to the Mariner's Compass.
Year: 1896

page_text: Date of Application, 22nd June, 1896-Accepted, 25th July, 1896
COMPLETE SPECIFICATION.
Improvements in or relating to the Mariner's Compass.
I, JOHN SACHEVERELL GISBORNE, of 13 Belitha Villas, Barnsbury, 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 :-
The present invention is for improvements upon the invention protected by my
prior Patent No. 8210 of the year 1895, and has for its object to prevent deviation of
the mariner's compass and to dispense with the necessity for adjustment and the use of
correctors.
According to my present invention, I effect this object by surrounding the compass
needle or needles with a series of vertically disposed electrical coils of equal resistance
connected up and placed in the circuit of a battery or other suitable source of
electrical energy. The said coils should be placed as near together as possible and
must be so arranged that a line drawn through any two opposite coils will pass
through the axial line of the compass.
The poles.of the coils being arranged as hereinafter described, no matter what the
error of the compass, directly a current is sent through the coils the needle will
settle down to magnetic north and will remain constant in that position so long as the
coils are excited.
I will now more fully describe my invention and the manner of performing the
same having reference to the accompanying drawings in which similar letters refer
to corresponding parts in all the figures, and wherein
Fig. 1 is a vertical section and Fig. 2 is a sectional plan on line - Fig. 1,
representing a compass having my invention applied thereto. Fig. 3 is a vertical
section of a modified arrangement. Figs. 4 and 5 are diagrams.
Referring to Figs. 1 and 2, a is the compass bowl within which the compass
needle is suspended from the compass card c by a convenient light framework d.
ee are a series of electrical coils, each of equal resistance, disposed vertically side
by side around the bowl a, each coil being composed of insulated copper wire wound
upon a non-magnetisable core. Magnetisable cores should not be employed as they
would be liable to pick up magnetism from the ship and thus to cause errors in the
compass. A convenient method of retaining the coils in position consists in providing
a series of pockets fixed in any convenient manner around the bowl a, into which
pockets the coils can readily be dropped. g is the protective outer case of the
instrument and represents a battery.
The series of coils e may either be connected up or arranged so that all north
poles or all south poles are uppermost or undermost, or they may be connected up
or arranged so that the poles alternate, the north pole of one coil being next to the
south pole of the adjacent coil throughout the series, and this latter arrangement I
prefer to adopt. One or other of these arrangements must however be employed
as it will not answer to arrange the poles indiscriminately. When the poles alternate
the number of coils employed must be double some odd number so that the poles
of each pair of diametrically opposite coils will be in reverse positions. When like
poles are adjacent the coils would be connected up as shewn in Fig. 2 and also in
the diagram Fig. 4, i.e. the commencement of one coil would be connected with
the finish of the adjacent coil. In the case of alternating poles the coils would
be connected up as illustrated in the diagram Fig. 5. This is of course obvious to
any electrician.

page_text: By way of guidance in carrying out my invention, I may say that in an instrument
I have constructed, and which gives satisfactory results, I have employed fourteen
coils e, each coil being composed of 24 gauge copper wire having two or three coverings
of silk and wound upon a core t" in diameter and 24" long so as to produce a coil
of 1" in diameter. The current used was generated by a battery of six E.B. dry
cells. The strength of the current may however vary considerably, and it is only
necessary to see that the same is not too weak.
I prefer to employ a single magnetic needle only, as illustrated, and to place the
same a short distance, about ", from the top or bottom of the coils, since the latier
exert a greater effect upon the needle when the same is placed thus near the poles
than when placed nearer the middle of the coils. Preferably the needle would be
disposed near the upper ends of the coils as represented in the drawings, so as to
reduce oscillation as much as possible.
If desired, I may combine with the invention above set forth, the invention
described in the Specification to my said prior Patent No. 8210 of the year 1895.
Fig. 3 shews this combination, gl and h¹ being the silk covered copper wires of
two parallel wound coils which surround the bowl a and cover the bottom thereof.
These two coils are of equal resistance and their wires g' are connected at their
ends so as to form a single circuit through which an electric current is passed in
reverse directions around the needle as clearly shewn in the diagram Fig. 4. The
coils e are disposed around the two parallel wound coils g¹ and are placed in circuit
with the latter, the connections being also clearly shewn in the diagram Fig. 4. In
this, as in the first described arrangement, the coils e may be arranged with like poles
uppermost or undermost, or the adjacent poles may alternate. By the use in
combination with my present invention of the coils gh' wound as described upon
the bowl a so as to cover the bottom thereof, "heeling error" will be entirely
prevented.
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 :-
1. In the mariner's compass, the use in combination with the compass needle or
needles, of a series of vertically disposed electrical coils of equal resist ince connected
up and placed in the circuit of a battery or other source of electrical energy, substantially
as described.
2. In the mariner's compass, the combination with the compass needle or needles
of the parallel wound coils g h arranged as described, and the series of vertically
disposed coils e surrounding the latter, the coils g', ', and e being all connected up
and placed in the circuit of a battery or other source of electrical energy, substantially
as described and illustrated.
Dated this 22nd day of June 180
E. P. ALEXANDER & SON,
Chartered Patent Agents,
19, Southampton Buildings, Chancery Lane, London, W.C., Agents.