IMPROVEMENTS IN APPARATUS OR MEANS FOR CORRECTING OR COM- PENSATING FOR THE DEVIATIONS OF THE MARINER'S COMPASS
Year: 1872

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn
t
Fields, in the County of Middlesex, Gentleman, for, the Invention
of "IMPROVEMENTS IN APPARATUS OR MEANS FOR CORRECTING OR COM-
PENSATING FOR THE DEVIATIONS OF THE MARINER'S COMPASS."-A com-
munication from abroad by Louis François Alexandre Arson, of
Paris, in the Republic of France.
Sealed the 9th July 1872, and dated the 31st January 1872.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson
at the Office of the Commissioners of Patents, with his Petition, on
the 31st January 1872.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the
County of Middlesex, Gentleman, do hereby declare the nature of the
said Invention for " IMPROVEMENTS IN APPARATUS OR MEANS FOR CORRECTING
OR COMPENSATING FOR THE DEVIATIONS OF THE MARINER'S COMPASS," a com-
munication to me from abroad by Louis François Alexandre Arson, of
Paris, in the Republic of France, Engineer, to be as follows:-
.This Invention relates to a simple contrivance for compensating for
deviations in the mariner's compass. In the Specification of Letters

page_text: Patent granted to me, and bearing date the 16th day of September 1869,
No. 2705, an apparatus was described whereby the compensation for the
permanent magnatism of the ship was effected substantially by fixed
bars and a rotating bar; the fixed bars effected the fraction of the
compensation which may be considered as constant, whilst the rotating
magnet furnished at each orientation the difference, which completes
exactly the equilibrium.
Now according to the present Invention this compensation for the
permanent magnetism is completely effected by a single magnet placed
in a determined and constant vertical position, the distance of its poles
from the needle being capable of variation.
In carrying out this Invention it is proposed to employ a permanent
magnet, composed by preference of steel wires contained within a
sheath, placed vertically near the needle of the compass and capable of
rising and falling by the action of an eccentric or cam, which is rotated 1
by gearing so arranged as that the said eccentric will make two revolu-
tions for one complete revolution of the ship. Thus the eccentric will
make a complete revolution whilst the ship turns from north to south,
and the magnet will present its upper pole to the point nearest to the
needle when the ship turns to the east or to the west, and to the point 2
the furthest removed from the needle when the ship turns to the north
or south..
-
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John Henry Johnson in the Great Seal Patent
Office on the 26th July 1872.
: .
'
{TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
HENRY JOHNSON, of 47, Lincoln's Inn, Fields, in the County of
Middlesex, Gentleman, send greeting.
2
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirty-first day of January, in the year 3
of our Lord One thousand eight hundred and seventy-two, in the
35th year of Her reign, did, for Herself, Her heirs. and successors,
give and grant unto me, the said John Henry Johnson, Her special

page_text: license that I, the said John Henry Johnson, my executors, adminis-
trators, and assigns, or such others as I, the said John Henry Johnson;
my executors, administrators, or assigns, should at any time agree with,
and no others, from time to time and at all times thereafter during
the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN APPARATUS OR MEANS FOR CORRECTING OR COMPENSATING
FOR THE VARIATIONS OF THE MARINER'S COMPASS," a communication to mo
from abroad by Louis François Alexandre Arson, of Paris, in the
Republic of France, upon the condition (amongst others) that I, the
said John Henry Johnson, my executors or administrators, by an
instrument in writing under my hand and seal, should particularly
describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be
filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said John Henry Johnson, do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained
in and by the following statement, reference being had to the accom-
panying Drawings, and to the letters and figures marked thereon, that
is to say:
1
The said Invention relates to a simple contrivance for compensating
for deviations in the mariner's compass. In the Specification of Letters.
Patent granted to me, and bearing date the Sixteenth day of September
One thousand eight hundred and sixty-nine, No. 2705, an apparatus was
described whereby the compensation for the permanent magnetism of
the ship was effected substantially by fixed bars and a rotating bar; the
fixed bars effected the fraction of the compensation which may be.
considered as constant, whilst the rotating magnet furnished at cach_
oricutation the difference which completes exactly the equilibrium.
Now according to the present Invention this compensation for the
permanent magnetism is completely effected by a single magnet placed
in a determined and constant vertical position, the distance of its poles"
from the needle being capable of variation.
.
In carrying out this Invention it is proposed to cimploy a permanent;

page_text: magnet, composed by preference of steel wires contained within a sheath,
placed vertically near the needle of the compass and capable of rising
and falling by the action of an eccentric or cam, which is rotated by
gearing so arranged as that the said eccentric will make two revolutions
for one complete revolution of the ship. Thus the eccentric will make
a complete revolution whilst the ship turns from north to south, and the
magnet will present its upper pole to the point nearest to the needle
when the ship turns to the east or to the west, and to the point the
furthest removed from the needle when the ship turns to the north or
south.
And in order that the said Invention may be fully understood I shall
now proceed more particularly to describe the same, and for that purpose
shall refer to the several Figures on the annexed Sheet of Drawings, the
same letters of reference indicating corresponding parts in all the Figures.
Figure 1 is a vertical section of the compensating apparatus put 1
together in its place; Figure 2 is a horizontal section of the same
taken along the line 1-2 (Figure 1); Figure 3 is a view at right angles
to Figure 1; and Figure 4 is a plan with the compass and its cover.
removed.
The compass ✗ is suspended in the ordinary manner in the case B, 2
which is secured to the stand or support m of the outer case M, which
protects the whole of the mechanism. The magnet or compensating
bar is composed of a suitable number of magnetized tempered steel
wires, which are introduced into the sheath a, b, whereby they are
caused to partake in the rising and falling motion to which it is 2
subjected by its connection with the frame K of the cam or eccentric E,
such cam or eccentric being fast on the boss of the bevel wheel D².
The wheel D² is arranged so as to make two revolutions while the ship
performs a single revolution; the eccentric E therefore makes a complete
rotation whilst the ship passes from north to south, and the magnet is 3
able to present its upper pole to the nearest point of the needle when
the ship passes into the east or the west, and to the most distant point
when the ship passes into the north or the south. The stroke of the
eccentric is sufficient to cause the power of the magnet to vary in the
proportion of from 1 to 2, according as it is considered in the east or in 3
the north, and the law of this variation, which produces the displace-
ment of the magnet, is such that it fulfils the conditions of equilibrium
•

page_text: in each intermediate point. The compensation is therefore accurately.
obtained in each orientation.
The magnet is regulated to this apparatus in the following manner,
videlicet: Two deviations having been observed in two rectangular
positions, say the north and the east, for example, the angle (xoxyo)
which the plane of the disturbing poles forms with the line of direction
or longitudinal axial line of the vessel is deduced therefrom.
The ring or hoop C which carries the wheel D³, and which is moveable
on the case B having been brought into such a position that the axis of
the wheel D³ will form with that of the ship the angle (xoxyo), and
having been permanently secured in that position by a pin inserted in a
hole drilled for that purpose through the parts, the position of the
eccentric E on its axis is then to be adjusted. This second part of the
operation is as simple as the préceding. The wheel D³ is moved away,
until it is out of gear with the wheel D', and it is maintained is such a
position as to admit of the eccentric being placed at the lowest point of
its stroke. The wheel D¹ is in gear with the wheel D, which is keyed on.
to a shaft carrying a fly wheel V and a small bevel wheel i, which latter
wheel is in gear with the bevel wheel of the repeating apparatus I,
the principal part of which consists of a copper dial x, which is divided,
in a similar manner to the card of the compass X. By acting upon the.
wheel V the moveable parts are caused to turn, so that the repeating
dial x, which is secured on the top of the copper case M enclosing the
apparatus, indicates the same number of degrees (xoxyo). The wheels
D' and D are then brought into and will continue in gear. It will be
readily understood that the position of the eccentric E will be regulated
by this method, since the ship performing a partial revolution to the
extent of the angle (xoxyo), and the apparatus being managed by the
observer according to the prescribed rules, the disturbing magnet of the
ship and the compensating magnet of the apparatus will pass along
at the same time in the plane of north to magnetic south. The position
of the magnet being thus regulated so as to meet the double condition
of orientation and relative power, and the vessel being brought into the
north or into the cast, the necessary number of wires of magnetized
tempered steel are introduced in order to effect the exact compensation
of the permanent magnetism.
This operation is more rapid than that which is required to regulate
the three constituent parts of the magnet in the rotatory system. The

page_text: system in which a single magnet is employed and constantly maintained
in a vertical position also presents an advantage over that of the
rotatory magnet, which renders it preferable.
. :
In the oscillations of the ship the poles of this magnet, which is
contained in the plane of the disturbing poles, assume the same inclina- t
tions as the latter, and are consequently subjected to the same variations
in the intensity; the equilibrium is therefore undisturbed.
The outer case M rests upon a stand or support m, which admits of
the apparatus being transported without the necessity for taking it to
pieces, and of its being readily fixed on the ship's deck in the place
which has been determined on.
Having now described and particularly ascertained the nature of the
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that what I consider
to be novel and original, and therefore claim as the Invention secured ]
to me by the herein-before in part recited Letters Patent is, the
employment of a single bar or magnet which is constantly maintained.
in a vertical position and caused to rise and fall by the aid of an
arrangement of frame actuated by a cam or eccentric for the purpose of
compensating for the permanent magnetism of ships.
In witness whereof, I, the said John Henry Johnson, have to
this my Specification set my hand and seal, the Twenty-sixth
day of July One thousand eight hundred and seventy-two.