IMPROVEMENTS IN CORRECTING THE DEVIATIONS OF THE MARINER'S COMPASS AND DIPPING NEEDLE, AND IN APPARATUS EMPLOYED THEREIN
Year: 1869

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn
Fields, in the County of Middlesex, Gentleman, for the Invention
of "IMPROVEMENTS IN CORRECTING THE DEVIATIONS OF THE MARINER'S
COMPASS AND DIPPING NEEDLE, AND IN APPARATUS EMPLOYED THEREIN."-A
communication from abroad by Louis Francois Alexandre Arson,
of Paris, in the Empire of France, Engineer.
Sealed the 30th November 1869, and dated the 16th September 1869.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at
the Office of the Commissioners of Patents, with his Petition, on
the 16th September 1869.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of Middlesex, Gentleman, do hereby declare the nature of the said In-
vention for "IMPROVEMENTS IN CORRECTING THE DEVIATIONS OF THE MARINER'S
COMPASS AND DIPPING NEEDLE, AND IN APPARATUS EMPLOYED THEREIN," a com-
munication from abroad by Louis Francois Alexandre Arson, of Paris, in
the Empire of France, Engineer, to be as follows :-
This Invention relates more particularly to the correction of the
deviations of the mariner's compass arising from the perturbing in-:

page_text: to the correction of the deviations of what is known as the dipping
needle.
According to this Invention it is proposed to apply to the mariner's
compass a fixed and a moveable compensator. The former consists of
an ordinary mariner's compass of great sensibility suspended in the
centre of a circular frame, which is attached by four radiating arms to
the under side of the deck and properly protected from injury. On this
frame are fitted in a radial direction two boxes, each of which contains
a magnet capable of effecting the fixed correction of the needle, such
boxes being capable of adjustment to any radial position in the frame
round the compass. These magnets should be as light as possible, but
powerfully magnetized in order to diminish the free magnetic action
which they exert independently of their fixed action. By this arrange-
ment the deviation produced by the action of any part of the hull which
may be in a magnetic state and thereby exerts a fixed influence upon
the needle may be compensated by the counter influence of the adjust-
able magnets above referred to when properly placed. The moveable
compensator is placed in the middle of the frame and embraces the
compass; it consists essentially of a body of soft iron, which is conse-
quently magnetic like the hull. This soft iron body is composed of a
riband of soft iron wire gauze which has been tinned after weaving, such
riband being coiled upon an elongated open frame or bobbin, in the
opening in which the compass is situate. This frame is carried by a
horizontal toothed wheel concentric with the compass and capable of
receiving a rotatory motion for adjustment by the aid of a spur pinion
and winch handle or otherwise. The bobbin or open oblong frame is
full to slide longitudinally in grooves along the spur wheel. The
various parts of the compensator with the exception of the adjustable
magnets are constructed of copper. In ships where the compass is
situate in the longitudinal centre of the hull the moveable compensator
should be so situate as to turn on its magnetic centre, but under all
other conditions it is so placed as to turn round a point which divides
its length in the same proportions as those of the ship, that is to say,
supposing, for example, the compass to be situate at one quarter the
length of the hull the compensator should be entered at a quarter of
its own length. As it is found impracticable to obtain soft iron entirely
free from all trace of fixed polarization it is necessary to neutralize this

page_text: defect existing in the moveable soft iron compensator last referred to, and
this may be readily and simply effected by applying the same means as
those employed for correcting the fixed magnetic influences of the hull
upon the needle already described, that is to say, by the employment
of two magnets enclosed each in a copper box resting on a plate which is
made adjustable along the frame or bobbin of the soft iron riband. In
lieu of using tinned iron wire gauze sheets of tin plate inclosed in
suitable copper boxes may be substituted. The apparatus being disposed
as above described it is evident that if the adjustable compensator be so
placed as to effect an opposite deviation equal to that produced by the
ship the needle which will be subjected to equal and opposing influences
will not deviate. To effect this adjustment with certainty the compen-
sator carries a dial similar to the compass card which indicates the
exact reverse deviation of the same. The compensator for the dipping
needle is constructed on the same principles as that for the mariner's.
compass, but its position of course is adapted to suit the nature of the
instrument to be compensated.
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 16th March 1870.
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.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Sixteenth day of September, in the year
of our Lord One thousand eight hundred and sixty-nine, in the thirty-
third year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said John Henry Johnson, Her special
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

page_text: "IMPROVEMENTS IN CORRECTING THE DEVIATIONS OF THE MARINER'S COMPASS AND
DIPPING NEEDLE, AND IN APPARATUS EMPLOYED THEREIN,' a communication
to me from abroad by Louis Francois Alexandre Arson, of Paris, in the
Empire of France, Engineer, 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 de-
scribe 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 imme-
diately 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 accompanying
Drawings, and to the letters and figures marked thereon, that is to
say:
The compass of iron ships is exposed to three kinds of disturbing
influences, videlicet :-
First. The attraction which soft iron excrcises indifferently on both
poles of the needle with an equal intensity.
Second. The relatively fixed attractive or repulsive action which certain
parts possess, and which imparts to them all the characteristics of
magnets.
Third. The action which the free magnetic fluid which is always
present in soft iron exhibits by putting the iron into the state of an
instantaneous magnet.
The first action is self-compensating when it is exercised by a con-
tinuous and closed body, and when the magnetic needle is disposed in a
point where the whole of the actions exercised upon it are symme-
trically distributed. This is the case when the needle is situate in the
central plane of a vessel at whatever distance it may be from the fore or
aft.
With respect to the action of the magnetized iron, certain parts of
the hull, although composed of soft iron, are magnetized, and exercise
a constant action, which can only be compensated by a similar action
produced by a permanent magnet suitably disposed. This method of

page_text: compensation has already been adopted by some navigators who have
judiciously recognized its necessity.
Every time that soft iron is hammer hardened it assumes the character
of a permanent magnet, and becomes comparable to magnetic tempered
steel. It is well known that powerful magnets may be produced with
soft iron suitably hammer hardened, for example, with iron wire, which
it is simply necessary to twist while it is maintained in the direction of
the inclination. Now rivets used to unite the plates, being hardened
by hammering form so many permanent magnets, which combined
exercises a very powerful action. This is the explanation of the state of
magnetization which affects the hulls built in the same yard, the
influence of which on the compass is always similar. It appears how-
ever that the magnets thus produced are not perfectly durable. The
causes which weaken or modify them are perhaps little understood, but
it is always their direction and intensity which are modified, whence it
follows that their correction necessitates the use of a means which may
be modified and adjusted with facility, which it is the object of the
present Invention to provide.
And in order that the said Invention may be fully understood, I shall
now proceed more particularly to describe the same, and for this purpose
shall refer to the several Figures on the annexed Sheet of Drawings, the
same letters of reference indicating corresponding parts in all the corre-
sponding Figures.
Fig. 1 is a longitudinal section, Fig. 2 a corresponding plan, and
Fig. 3 a transverse section taken along the line 1-2, Fig. 2, of a com-
pensator constructed according to this Invention.
The compensator is formed of an ordinary mariner's compass B of
great sensibility suspended in the centre of an apparatus combining both
methods of correction. The whole is carried by a support A, which is
attached by four arms underneath the deck of the ship or in any other
suitable place.
With respect to the fixed compensator, on the arms of the support A
move two boxes c, c, intended to contain magnets capable of making the
permanent correction which is to counteract the effect of the per-
manently magnetized portions of the vessel. One of these boxes is
shewn in section at Fig. 3. These magnets are necessarily bars of steel
tempered and magnetized; they should be as light as possible, and also
strongly magnetized in order to diminish the free magnetic action which

page_text: they exercise independently of their permanent action. For the same
reason it is desirable always to employ two at once, disposed in the two
symmetrical portions of the apparatus for the purpose of neutralizing this
magnetic action.
The moveable corrector or compensator is disposed on the centre of
the support A and around the compass. It consists essentially of a body
of soft iron, which is consequently magnetic like the hull. In the
apparatus shewn in the Drawing this body is composed of a band of wire
gauze D wound on a bobbin d of an oblong form, which is connected to a
spur wheel E, which causes the bobbin to turn around the geometrical
axis of the compass. The bobbin d slides on the spur wheel E by means
of the tongue d', which slides in a corresponding groove, as shewn in
Fig. 3. The spur wheel E is actuated by the pinion e, the axis of which
carries the handle m. The whole of the parts are composed of copper
with the exception of the magnets and the compensator.
With regard to the position of the compensator, in vessels in which
the compass is disposed in the centre of their length, the compensator D
should be mounted so as to turn around its magnetic centre; under
any other condition it is so placed as to turn around a point which
divides its length in the same proportions as those of the vessel, for
example, if the compass is situate at one quarter the length of the
vessel the compensator D is centred at one quarter its own length.
In order to correct the influences of permanent magnetization which
the hull exercises on the compass permanent magnets may be employed
enclosed in boxes H, H³, and fixed on the body, which is the seat of the
disturbing action, and turning with it. It is evident, moreover, that its
power must be diminished in a suitable proportion. The permanent
magnets intended to effect this compensation are disposed in front on a
moveable piece h, which turns around the geometrical axis of the compass
and is capable of occupying any suitable position in relation to the
cardinal points; its distance from the centre may also be varied as
much as necessary. Fig. 3 shews the construction of this piece h.
Figs. 4 and 5 are sections of a moveable compensator, in which the
wound wire gauze is replaced by a certain number of tin plates disposed
in the boxes or sides of the compensator. The correction of this com-
pensator is effected in a similar manner to that of the compensator
composed of wire gauze. All things being so arranged as to carry out
these principles it is evident that if the compensator be directed so as to

page_text: always assume a deviation equal and opposite to that of the vessel, the
compass being then subjected to two equal and contrary actions will not
be displaced. Moreover, the means employed to bring the apparatus
into this position are exceedingly simple.. The compensator is provided
with a dial similar to that of the compass, and all that is required is to
cause it to assume a deviation always equal but in the reverse direction
to that of the ship, as, for example, to the east when the ship turns to
the west.
I shall now proceed to describe the methods employed for regulating
the fixed compensators.
The fixed compensator of the ship is the first apparatus to be adjusted,
and the compensation which it admits of producing should be obtained
before proceeding to the mounting of the moveable compensator. The
same physical laws, moreover, come into play in both these operations,
and what follows applies equally to both. The proposed apparatus is
provided with all the necessary arrangements to admit of the operations
being performed with facility. The needle, may be caused to deviate
from its normal position by the influence of the permanent magnetization
of the hull, and this deviation may be due to two special cases, which it
is important to distinguish in order to effect the exact compensation.
The permanent actions exercised by the hull are reduced to a resultant
composed necessarily of two equal and contrary forces acting around the
needle under the form of a pair. Let these forces be represented by the
lines o, b¹, o, a', (Fig. 6,) they will combine with the action of the earth
to act on the compass, which will necessarily assume an intermediate
position a, b. The correction will simply consist in the use and suitable
direction with respect to the cardinal points of a magnet a", bu, so
disposed that it will produce an equal and contrary action to that
exercised by the pair a', b'. The other cause capable of producing
precisely the same effect is such as would be produced by a permanent
magnetization, the sum of which is represented by two poles a¹, b',
(Fig. 7). The correction would be then obtained by the position a", 6",
of the permanent compensator; but it will be observed that this differs
essentially from the preceding in its direction with respect to the cardinal
points. The choice between the two methods will not be, however,
difficult to determine. After having made the first compensation when
the vessel is directed due north, for example, the ship is turned round
90°. If the direction of the correction has been well chosen it will

page_text: will be augmented.
The principle of the composition of the apparatus herein-before
described consists in producing a deviation equal to that which it is
required to correct, but in the reverse direction, and this object is
attained by means of a similar apparatus to that which produces the
disturbance. The law therefore according to which the disturbance is
produced and corrected is not of much interest, but the expression of
these deviations is so well defined that it is important that it should
engage attention. If the method of curves drawn on rectangular axes
be employed the expression is then of some interest on account of its
regularity, but it has not the entire character, which may be imparted
to it by drawing it around a circumference, which serves as a base to it.
The ordinates are then radii, having outside the circle lengths pro-
portional to the deviations. When the ship turns to the west the
deviations are produced to the east, and the maximum is exhibited in
points, which vary with the position of the compass in the ship. If the
compass be in the centre of the length or at least in the magnetic centre
the deviation is described by four similar curves, which meet the base
circle at the four cardinal points. If the compass is situate between this
central point and the stern the curve loses it regularity, but it is still
composed of portions which are symmetrical in relation to the rectan-
gular axes passing through the four cardinal points. These characteristics
are not merely interesting, they offer this resource, that a vessel may
draw out the curve of its deviations and prepare beforehand the apparatus
which will effect their exact compensation. It is worthy of observation
that when the compensator has been suitably arranged and adjusted at
any given time and in any latitude it continues to fulfil the same
conditions for any period and in all possible latitudes. Time will only
produce variation in the state of permanent magnetization of the ship,
and since this can be constantly corrected by the suitable arrangement
of the permanent magnets the power of the compensating apparatus
will always continue in the proper proportion to the magnetic intensity
of the soft iron of the ship. It is evident also that as the action of the
soft iron of the vessel is neutralized by that of the soft iron of the
compensator, when the power of the one varies under the influence of
change of latitude the other will vary in the same proportion, and the
equilibrum will not be disturbed. It is necessary to observe that the

page_text: dipping needle is like the preceding, subject to deviations which affect
its indications. If it be considered necessary to make the correction it
may be effected with the same simplicity and certainty by means of a
special apparatus based on the principles herein-before described. This
adjustment would moreover be effected in a more simple manner and
with greater facility. The dipping needle is not sensible to the disturbing
influences, except through the component, which they present in the
plane of the inclination, and a careful examination of the consequence of
this shews that this condition greatly limits the influence exercised;
nevertheless in a wide range of latitude the influence might be sufficiently
appreciable to warrant the use of a corrector. In this case the apparatus
herein-before described is applicable without changing the principle, but
merely with a simple modification in the position.
With regard to. the actions due to the soft iron, the iron exercises on
the magnetic needle an attraction which is distinguished from that
which magnetized bodies exercise by a characteristic which leaves us
in no doubt whatever, videlicet, it attracts equally both poles. When
the needle of a compass is caused to deviate on the same side by a hull
which makes a half turn around it this motion cannot be explained by
magnetic action, but it must be attributed to the attraction of the iron
for the needle. There can be no doubt as to the conclusion when a
vessel leaving North Cape clears South Cape. Under these conditions
the magnetism of induction cannot perform any part. This disturbance
will require to be counteracted by the action of a soft iron body
exhibiting the least possible magnetism and suitably disposed in a fixed
position, as shewn in elevation and plan Figs. 8 and 9. A sphere S of
wrought or cast iron will offer the maximum of attractive action due to
the material and the minimum of magnetic action. It should be
suitably directed with respect to the cardinal points at a distance from
the centre greater than the length of the needle, and in such a manneṛ
that it will neutralize the disturbing action. Its position may be readily
and mathematically determined by moving the piece S in which it is
mounted. The diagram referring to this needle will explain precisely
the direction of the position to be chosen.
I shall now proceed to refer to the magnetic deviations due to
permanent actions. The principal cause of the deviations of the com-
pass is ordinarily due to permanent actions. These have been developed
in the soft iron by the mechanical operations to which it has been

page_text: subjected during the building, and their resultant is characterized by
two opposite poles disposed with respect to the cardinal points according
to the latitude the vessel was in during its construction. These actions
must be met by actions of the same nature, that is to say, permanent
like them, and exercising on the needle attractive and repulsive
influences. It is evident moreover that they should be equal in power
and of an opposite nature to those they are intended to destroy. This
fundamental condition, without which the compensation could only be
effected for one or two positions in an entire evolution, is not however
observed in the method of permanent compensation at present in use, in
fact, it cannot be with the method employed, however careful and skilful
the operator may be. This point, which is the very ground of the
arrangement proposed according to the present Invention, is of so much
importance that it appears necessary to incontestably establish it here.
If we suppose the two poles of a disturbing magnet acting on the needle
at the distance R, Fig. 10, then the poles of a compensating magnet
intended to neutralize it, calling I the intensity of one of the poles
measured at the unit of distance and i the intensity of the compensating
magnet, this state is expressed by the equation,
D D
= (1) (+)
T
in which D' and D" are the distances of a disturbing pole from the two
poles of the needle, and d, d", those of the corresponding compensating
pole. If we substitute for D', D", and d¹, d", their numerical values
taken successively in different assumed positions of the disturbing pair,
we shall find that the proportion should vary; now as according to
the existing method it can only be constant, the compensation cannot be
effected.
: I propose to substitute for the means at present in use the apparatus
shewn in Figs. 11 to 14, by which the compensation may be obtained in
an effective and ready manner. Fig. 11 is a vertical section of the complete
apparatus employed for the compensation; Fig. 12 a corresponding hori-
zontal section taken along the line 1, 2 (Fig. 11); Fig. 13 a vertical
section taken at right angles to Fig. 11; and Fig. 14 a horizontal section
taken along the line 3-4 (Fig: 13). This method supposes the putting
in action of two systems of bar magnets, one of which is stationary and
.the other moveable. The former is composed of two bars B, B', disposed
crosswise the one over the other under the needle A. This part of the
apparatus is similar to that at present in use. The latter (the moveable)

page_text: is composed of a bar C turning around its centre in a vertical plane,
which itself turns round the pivot of the needle. This position may
be more clearly defined by the explanation that the bar is fixed in
the body of the bevel wheel D which actuates the large wheel D¹
carrying the compensator M for the magnetism of induction. h are the
four correcting magnets for the superadded permanent magnetization of
the malleable iron plates. The wheels D and D' are in the proportion of
1 to 2, so that the actuating pinion makes two turns around its own
axis while it performs a revolution round the horizontal bevel wheel D',
and if we recur to the object of using this wheel, which is required to
make a complete revolution when the vessel performs an evolution
round its centre, it will be perceived that the pinion will perform two
revolutions while the vessel makes one. The magnet C which the
pinion carries will thus be enabled to bring successively both poles
towards the needle A during each semi-revolution, that is to say, to
alternately increase and diminish the action of the compensating magnet,
which is what it is required to obtain. In one of the positions, videlicet,
when the disturbing pair passes into the N, S, the moveable magnet
diminishes the action of the fixed magnets in a position perpendicular to
that it augments it. A table of the proportions to be established between
these two actions, the sum of which makes the permanent compensation,
which table is based on the value of the quantities R and r, both of
which are known or readily determinable, furnishes the proportion to be
established between the power of the compensating magnets. These
two descriptions of bars are formed of thin plates of steel enclosed in
copper casings to preserve them from oxidation. The power of the large
stationary bars is also regulated by their depression outside the plane of
the needle A. Their position, which fulfils two important conditions,
namely, first, their being always at right angles the one to the other and
to the axis of the ship, and secondly, their being crossed on the vertical
line let fall from the pivot of the needle, admits of their adjustment into
positions where the magnetism of induction exercises no disturbing
action and simply by means of a quarter revolution.
It is necessary to add that the apparatus shewn in Figs. 11 to 14 by
reason of its combination occupies but little space, may be erected with
facility in any convenient part of the ship without the necessity for any
special arrangement. The pinion D and consequently the large wheel D¹
in the apparatus shewn in Figs. 11 to 14 are moved simply by turning

page_text: the wheel V, which is mounted at the exterior of the box I, which forms
the body of the apparatus. This box is surmounted with a lantern L to
illuminate the compass, which is mounted in the ordinary manner.
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,―
First. The peculiar mode or method of correcting the deviations of the
mariner's compass or of the dipping needle by the use of a fixed and a
moveable compensator constructed, arranged, and combined so as to
operate substantially as herein-before described.
Second. The peculiar mode of neutralizing the fixed polarization of
the adjustible soft iron compensator, as herein-before described.
Third. The peculiar arrangements and combinations of compensators
whereby greater facility for working them and certainty in their
operation are obtained, and which admit of their being mounted in any
required position above or beneath the deck of a ship without the
necessity for any special provision, as herein-before described.
In witness whereof, I, the said John Henry Johnson, have to this
my Specification set my hand and seal, this Fifteenth day of
March One thousand eight hundred and seventy.