IMPROVEMENTS IN THE MARINER'S COMPASS
Year: 1885

page_text: I, FREDERICK ARTHUR PAGET, of 158, Fenchurch Street, London, E.C. and of
No 13 Riemer Gasse, Stadt, Vienna, Engineer, do hereby declare the nature of my
invention for "IMPROVEMENTS IN THE MARINER'S COMPASS " to be as follows:-
The object of this Invention is, by a novel preventive method, to reduce to
vanishing amounts the considerable errors caused in all mariner's compasses now
in use by the magnetic influences of the iron and steel parts of the ship. At present,
the only preventive method occasionally employed in a few vessels is that embodied
in the application of the elevated or mast compass, as recommended by the late
Sir Samuel Brown in 1849, by the late Dr Scoresby, by Mr Towson of Liverpool,
and by many others. These improvements also diminish the frictional error, or
the error due to the friction between the pivot and the stone in the cap of the
ordinary compass. They also diminish the tendency to instability, caused by
the motion of the vessel, which is more especially felt by an ordinary compass
the higher it is elevated above the metacentre of the ship. This invention there-
fore intends to bring the mariner's compass under the almost undisturbed action of
the earth's magnetism, such as was the case before the introduction of iron ships
and of their iron equipments. It aims at obtaining exact indications there.
from without the use of Flinders' bars as proposed by Captain Flinders' R.N.
in 1805; and the use of the system of compensating magnets introduced by
Sir George B. Airy, the former Astronomer Royal, and fully developed by
Professor Sir William Thomson.
Now the maximum distance between the furthest South pole and the furthest
North pole, whether in the single needle or in the system of magnets used in a
properly constructed compass card, has not yet been taken into consideration, either
in calculation or in actual construction, as regards the influence of such length
on the deviations of the compass resulting from the direct action of the ship's
magnetism. The ordinary nine inch compass card has thus often a distance of
nine inches between the furthest poles of its needle, or needles; and, in some
larger cards it is much more. There is no compass in actual use made with a
distance of less than three inches and more between its furthest magnetic poles.
Now I find by experiment that the mutual action of both poles of (say) a fixed
magnet of a given length on another (say) magnetic needle diminishes in all
positions with the distances between the two with all the greater rapidity the

page_text: shorter the distance between the two poles of (say) the magnetic needle. Now it
is obvious that, in an iron ship, it is the iron or steel nearest to the compass which
has most influence in causing compass errors. On this principle, it is clear that
the shorter the needles of a compass which is at a given distance from magnetized
matter, the less will such a compass be liable to be deviated from the magnetic
meridian.
The ordinary mast head compass embodies the truly sound scientific principle of
removing, by increased distance, the compass as much as possible from the influence
of the ship's magnetism. But, besides other practical objections, the distance
required by the ordinary compass to partially free it from error is so high above
the metacentre of the ship, that the vibrations induced prevent the taking of
observations and soon destroy the compass pivot and stone in the cap.
This invention minimizes the deviations by minimizing the length of the needles
with which the compass is constructed. It therefore meets the main radical defect
in all the corrective or compensating methods proposed or at present in use,
inasmuch as such methods cannot encounter changes in the amount and direction
of the ship's magnetism.
Now, a magnetic needle, of the length of (say) a very small fraction of an inch,
could not, from its very shortness, be employed in taking bearings. Even if, for
instance, it were fitted with lengthening points of non-magnetic matter, such as of
thin aluminium wire, or with a small reflecting mirror, it could only indicate the
direction of the ship's head; while, from the moments of inertia being unequal
round the horizontal axes, it would be extremely unsteady under the mechanical
action of. the motion of the vessel.
:
But, as the magnetic moment of such a needle is extremely slight, it can keep
only an unusually small and light card to the magnetic meridian. I therefore
employ two or more such short needles to set to the magnetic meridian a light
transparent disc, preferably of mica or tale, about one quarter of an inch, more or
less, in diameter. On this transparent disc the usual points of the compass and
the divisions of the four quadrants of the circle are preferably photographed; and
it is placed on a pivot with a very fine point, enclosed in a compass-bowl suitably
mounted on gimbals.
Now such a small compass, however accurate, would also, by itself, be practically
useless to the seaman in ascertaining the direction of the ship's head and the
bearings of surrounding objects; while it would be impossible to take azimuths
with such a small instrument. I therefore combine with this miniature compass a
simple optical apparatus capable of magnifying the diagram on the card to a size,
such as from five to nine or more inches in diameter suitable for practice at sea.
A great number of different combinations of lenses and prisms or mirrors may be
adopted for the purpose; accordingly as the card is transparent or not; whether
the image is required to be in a horizontal or a vertical plane; whether the light
employed be solar or artificial.
A combination may be formed with a concave mirror alone, or with a concave
mirror and screen; but this would require powerful artificial light by day as well
as by night; besides affording a very cumbersome apparatus.
The diagram on a transparent card could be projected on to a screen in a dark
chamber by the light from a couple of condensing lenses, through a pair of object
glasses, on the principle of the common magic lantern. But, if day-light .be
employed, this would involve an impracticably complicated apparatus, requiring
very large condensing lenses, a heliostat, a dark chamber, etc. and continual adjust-
ments of the objectives; besides the danger of burning the apparatus by strong rays
of the sun unless an alum tank be adapted thereto.
An apparatus known to opticians as a hand magnifier might also be adopted; but
this would afford a comparatively small amplification and the entire compass card
could not be seen at once.
For magnifying the card to a suitable diameter, I therefore prefer to employ a
simple form of the common microscope having a low power with a large field. It

page_text: may have a relatively strong eye-piece, so that, requiring little light, the instrument
will allow the picture to be seen on a dull day. An ordinary small reflecting
mirror may also be thereto adjusted, for use on a very dark day. At night or
during fogs, it would be lighted up by ordinary binnacle lamps. Should a mirror
set at forty-five degrees be employed to receive the picture from the object glass, it
would be necessary, to avoid optical errors, to make this mirror slightly adjustable and
to initially set it by (say) compass bearings. The miniature compass in its gimbals
must also be made exactly adjustable laterally. As a substitute for the usual
lubber's line, cross-hairs are set in front of the field of vision, which, for this
purpose, is made to extend outside the circumference of the card. The horizontal
cross-hair can be accurately set by means of a common spirit-level
The instrument may also be suitably adjusted with apparatus similar to that in
ordinary use for taking azimuths.
Such a compass as described, combined with a suitable optical magnifying
apparatus, would constitute the standard or reference compass of the iron ship.
For the purpose of my invention, I may construct a very light frame in one
piece, stamped or cut out of a composition of very finely powdered cork, india-
rubber and sulphur, the whole being what is termed hard-vulcanized at a suitable
temperature.

page_text: I, FREDERICK ARTHUR PAGET, of 158 Fenchurch Street, London E.C. and of
No 13 Riemer Gasse, Stadt, Vienna, 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 object of this invention is, by a novel preventive method, to reduce to
vanishing amounts the considerable errors caused in all mariner's compasses now
in use by the magnetic influences of the iron and steel parts of the ship. At
present, the only preventive method (in contradistinction to the usual corrective
or. compensating system) employed in some vessels is that embodied in the appli-
cation of the elevated or mast compass, as recommended by the late Sir Samuel
Brown, in 1849 by the late Revd Dr Scoresby, by Mr Towson of Liverpool,
and by many others. These my improvements also diminish the frictional error or
the error due to the friction between the pivot and the stone in the cap of the
ordinary compass. They also diminish the tendency to instability caused by the
motion of the vessel, which is more especially felt by an ordinary compass
the higher it is elevated above the metacentre of the ship. This invention
therefore intends to bring the mariner's compass under the almost undisturbed
action of the earth's magnetism, such as was the case before the introduction of
iron ships and of their iron equipments. It aims at obtaining exact indications
therefrom without the use of Flinders' bars as proposed by Captain Flinders R.N. in
1805, and the use of the system of compensating magnets introduced by Sir George
B. Airy, the former Astronomer Royal and fully developed by Professor Sir William
Thomson.
Now the maximum distance between the furthest South pole and the furthest
North pole, whether in the single needle or in the system of magnets used in a
properly constructed compass card, has not yet been taken into consideration, either
in calculation or in actual construction as regards the influence of such length on
the deviations of the compass resulting from the direct action of the ship's
magnetism. The ordinary nine inch compass card has thus often a distance of
nine inches between the furthest poles of its needle, or needles and, in some larger
cards, it is much more. There is no compass in actual use made with a distance of
less than three inches and more between its furthest magnetic poles.
Now I find by experiment that the action of (say) a fixed magnet of a given
length on another (say a magnetic needle) diminishes in all positions with the
distances between the two with all the greater rapidity the shorter the distance
between the two poles of the magnetic needle. It is obvious that, in an iron ship,
it is the iron or steel nearest to the compass which has most influence in causing
compass errors. On this principle, it is clear that the shorter the needles of a
compass which is at a given distance from magnetised matter, the less will such a
compass be liable to be deviated from the magnetic meridian.
Newton, in pointing to the analogies and the differences between magnetic force
and gravitation, cites experiments by which he deduced that the action between
two magnets diminishes inversely as the cubes of the distances.
About fifty years
ago. this was proved by Gauss to be strictly correct when both poles of a magnet

page_text: act on both poles of the needle at relatively long distances. A floating needle thus
only points north and south without any motion of translation; while in astatic
needle is exactly balanced; in neither case being affected by the greater proximity
to either pole of the earth. By using very short needles for a compass on an iron
vessel, which is in reality a congeries of different magnets-this action comes into
play at a short distance from the deck.
The ordinary mast head compass embodies the truly sound scientific principle of
removing, by increased distance, the compass as much as possible from the influence
of the ship's magnetism. But, besides other practical objections, the distance
required by the ordinary compass to partially free it from error is so high above
the meta centre of the ship that the vibrations induced prevent the taking of
observations and soon destroy the compass pivot and stone in the cap.
This my invention minimizes the deviations by minimizing the length of the
needles with which the compass is constructed. It therefore meets the main radical
defect in all the corrective or compensating methods proposed, or at present in use,
inasmuch as such methods cannot encounter changes in the amount and direction
of the ship's magnetism-whether such magnetism be sub-permanent or be induced
temporarily by the action of the earth.
Now a magnetic needle of the length of (say) a very small fraction of an inch,
could not, from its very shortness, be employed in taking bearings. Even if, for
instance, it were fitted with lengthening points of non-magnetic matter, such as of
thin aluminium wire or with a small reflecting mirror, it could only indicate the
direction of the ship's head, but not the bearings of. surrounding objects; while
from the moments of inertia, being unequal round the horizontal axis, it would be
extremely unsteady under the mechanical action of the motion of the vessel.
But, as the magnetic moment of such a needle is extremely slight, it can keep
only an unusually small and light card to the magnetic meridian. I therefore
employ one two or more such short needles, to set to the magnetic meridian a
light transparent disc, preferably of mica or talc, about one quarter of an inch,
more or less, in diameter. On this slight transparent disc the usual points of the
compass and the divisions of the four quadrants of the circle are preferably
photographed; and it is placed on a pivot made with a very fine point enclosed in
a compass bowl, the whole being suitably mounted on gimbals.
Now such a small compass, however accurate, would also, by itself, be
practically useless to the seaman in ascertaining the direction of the ship's head,
and the bearings of surrounding objects; while it would be impossible to take.
azimuths with such a small instrument. I therefore combine with this miniature
compass a simple optical apparatus capable of magnifying the diagram. on the card
to a size, such as from five to nine or more inches in diameter, suitable for practice
A great number of different combinations of lenses and prisms or mirrors
may be adopted for the purpose; according as the card is transparent or not;
whether the image is required to be in a horizontal or a vertical plane; whether
the light employed be solar or artificial.
at sea.
A combination may be formed with a concave mirror alone, or with an annular
concave mirror arranged with a small plane mirror above the orifice together with
a screen, but this would require powerful light by day as well as by night, besides
affording a very cumbersome and expensive apparatus, and being liable to the
usual objections to catoptric arrangements.
The diagram on a transparent card could be projected on to a screen in a dark
chamber by the light from a couple of condensing lenses, through a pair of object
glasses, on the principle of the common magic lantern, but, if daylight be employed,
this would involve an impracticably complicated apparatus, requiring very large
condensing lenses, a heliostat, a dark chamber etc. and continual adjustments of the
objectives, besides the danger of burning the apparatus by strong rays. of the sun
unless an alum tank be adapted thereto.
An apparatus known to opticians as a hand magnifier might also be adopted but
this would afford a comparatively small amplification,

page_text: i For magnifying the card to a suitable diameter I therefore prefer to employ a
simple form of the common microscope having a low power with a large field. It
may have a relatively strong eye-piece. An ordinary small reflecting mirror may
also be adjusted thereto for use on a very dark day. At night, or during fogs, it
would be lighted up by ordinary binnacle lamps. Should a mirror, set at
45 degrees, be employed to receive the picture from the object glass, it would be
'necessary, to avoid optical errors, to make this mirror slightly adjustable and to
initially set it by (say) compass bearings. The miniature compass must also be
made exactly, adjustable laterally. As a substitute for the usual lubber's line,
cross-hairs are set in front of the field of vision, which, for this purpose, is made to
extend outside, the circumference of the card. The horizontal cross-hair can be
accurately set by means of a common spirit level.
5
The instrument may also be suitably adjusted with apparatus similar to that in
ordinary use for taking azimuths.
Such a compass as described, combined with .a suitable optical magnifying
apparatus, would constitute the standard or reference compass of the iron ship.
For the purpose of my invention .I may construct a very light frame in one
piece, stamped, or cut out, of a composition of very finely powdered cork, india
rubber and sulphur, the whole.being what is termed hard vulcanized at a suitable
temperature.
On sheet 1. Figures 1 to 22 show different constructions of my microscopic
compass, and its case or bowl, together with methods for accurately adjusting it
to the optical axes of magnifying instruments to be afterwards described.
Figures 1 and 2 are drawn to about the actual size, I prefer to employ; but for
the sake of clearness and facility in delineation, all the other figures are made to
about double the actual linear dimensions.
In all the figures 3 to 18 I have shewn by a, a² the minute magnets employed..
They are preferably about one millimetre or one twenty fifth of an inch long,
one third of a millimetre deep and five hundredths of a millimetre thick. The
material I prefer is tungsten steel, which is rolled into thin foil or leaf. On being
cut out they are glass hardened. In all instances they are shewn suspended
edgewise, and, being let into and cemented within thin saw-cuts made in a small
cap so constructed as also to hold the compass card.
:
In figures 3 to 8 this cap ẞ is screwed at its bottom end, having a rim against
which the card is held by the annular nut 32. The material of the cap and nut
consists by preference of a novel alloy, compounded of magnesium melted up with
about five per cent by weight of aluminium. I find that this proportion of
aluminium makes the magnesium workable and tough; in pure magnesium
it is impossible to cut a sound thread or to fit a stone. I thereby obtain a
cap very much lighter than one of aluminium of the same size. The cap is
fitted with a small diamond, &, constituting the centre on which the whole
compass turns on the pivot e. I find that there is much less friction with a
diamond than with an oriental ruby or a sapphire, and the minuteness of the
compass enables me thus to employ commercially the most suitable material for
a' compass centre. A further advantage consists in the diamond being generally of
a lower specific gravity. Figure 3 shews the fine pivot e of iridium or of platino-
iridium soldered into a screw which is held by a bush and nut fitted in the glass
bottom 6 of the compass case.
"In Figure 5, this pivot e is shaped to a double cone, fitted tight into and
cemented to the glass bottom b of the case. In. Figures 7 and 8 this bottom is
constituted of one of the lenses of the objective. The top lens of the illuminating
apparatus, such as that of Professor Abbe, could be used in the same way, when
the light is taken from below. By this arrangement there results an important
saving in light, and the instrument is simplified, as it is thereby unnecessary to
use such means for bringing the compass into the optical axis as those shewn in
Figures 19, 20, 21, and 22 to be fully described further on.

page_text: 1 Figures 9 and 10 indicate, in elevation and plan respectively, and also to about
double the linear dimensions, a screw key for screwing up the parts B, and B₂ of.
the particular cap shewn in Figures 1 to 8 while being held in the holder
Figures 11 and 12.
Figures 13 and 14 indicate another form of cap. The diamond therein (6) is
fitted in such a manner that it is not about flush with the top, as, for instance, in
Figure 3, but so as to leave metal for the saw-cuts above the stone, in order that
the magnets may be brought nearer to each other, and each of them 30° from the
diameter. The small compass card is fixed by Canada Balsam or other suitable
cement, to the bottom lip turned on the cap. In this instance the small magnets
are shewn in two pairs, the steel foil being, in such a case, only a little more than
one thousandth of an inch in thickness.
Figures 15 and 16 indicate a cap again somewhat different from that shewn in
Figures 3 to 8, not being screwed but the card cemented to the bottom lip. This
shape can also be made of ebonite or of the peculiar cork composition hereinafter
described.
Figures 17 and 18 shew a cap made of one piece of diamond or of oriental ruby,
shaped out as shewn. It is cut with two parallel incisions for the small magnets;
the card being also cemented to the bottom rim. Figure 2 shews the actual size
I prefer to employ for the micro-photographic compass card more fully indicated in
Figure 4. It consists of a thin sheet of mica or tale, on which the points and
divisions of the compass are photographed from an original of large size. Mother
of pearl, horn, glass oiled paper, celluloid, ivory etc. could also be used, but the
material I prefer to adopt is a thin sheet of sound Siberian mica.
Figures 19 to 22 indicate methods for accurately adjusting the microscopic
compasses contained in the bowls or holders C, shewn by Figures 1 to 5 to the
optical axis of the magnifying instrument employed. In Figures 19 and 20 the
light is considered as coming from above. The holder is screwed into the guide d,
which can be traversed by two set screws e and ƒ spaced at an angle of about 120°
against a stiff brass spring g.
In Figure 21 the light comes from below, being reflected from a mirror through
an illuminating lens h upon the well known plan of Professor Abbe of Jena. The
guide d is also held laterally by a curved spring g and made to traverse by the set
screw e a slot k allowing the holder to be turned round a quadrant of the circle.
A stiff conical spring i may be adapted to keep the holder from shaking.
On Sheet 2 of the drawings is shewn a compass for taking azimuths. Figure 1
illustrates the entire apparatus erected on a pillar P to be placed in a suitable part
of the ship; Figure 2 is a side elevation, Figure 3 a plan with the prismatic
azimuth arrangement taken off the top of the instrument; Figures 4 and 5 are
longitudinal cross-sections, and Figure 6 is a plan of the whole.
The casing or bowl for holding the microscopic compass together with its adjusting
arrangement is indicated by A. This was already shewn by itself on an enlarged
scale in Figures 21 and 22 of Sheet 1.
The illuminating lens (sheet 1) has been left out of Sheet 2. The light from
the mirror D, concentrated by the illuminating lens or lenses, is transmitted through
the transparent compass card and through the single compound or compound
achromatic objective B. (Figure 4) projecting an enlarged image of the compass
card (which it is necessary, in this instance, to reverse) on, to the horizontal semi-
transparent glass screen C. This screen C may also be a segment of a sphere as
shewn in Figure 5.
In Figure 4 it is of about the same size and takes about the same position
relatively to the azimuth arrangement as the glass cover of an ordinary azimuth
compass. The bottom side of said glass is treated with a diluted solution of fluoric
acid, the smooth dull surface thus obtained being much more suitable than that,
arrived at by grinding the surface with sand or emery. A varnish of, collodion
could also be used as far as the optical effect goes, but this surface could not so
well withstand rough usage at sea. Instead of the usual vertical lubber's line on the.

page_text: inside of the compass bowl, the glass screen is marked with a horizontal line L
through its diameter, (see Figure 3) constituting a true fore and aft line.
It is of course necessary to keep the direct rays of light from the screen, so that
the enlarged image of the card from the single compound or compound achromatic
object glass may not be interfered with; at the same time shewing the lubber's
line and any portion of the card that is to be observed. The top of the apparatus
is therefore provided with a cover d Figures 1, 2 and 3 (Sheet 3) to which the
prismatic azimuth arrangement is fixed, turning with it. This portion of the
compass with the sights, & can be exactly the same as that used by the British
and other Admiralties; and need not be further described.
The almost sole difference is that the prismatic lens for observing the outer
divisions of the magnified microphotographic card is connected with the cover d by
a rectangular tube p Figure 1, sheet 3 in order to exclude side-rays of light from
the picture on the semi-transparent glass screen C.
The screen is adjusted to the top of the magnifying apparatus in the same way
as with the glass cover of the Admiralty Azimuth compass. Into a hole in its
centre is fixed a brass pin b turned out with a head, on the bottom part of which
the glass disc is held by a washer c fixed with small screws. On the upper side
of the head of the central pin is adjusted a boss e cast with spokes e¹ connected
with the outer rim e2 on which is fixed the cover d and the azimuth apparatus. .
In order that the lubber's line and the required portion of the image of the card
may be seen, without admitting too much light, a circular hole is cut out of the
cover d under which aperture is fitted a central disc f resting at its outer circum-
ference, as shewn, on a rim fixed to the cover. Out of this disc f is cut a
segment; which opening may itself be covered or uncovered as required by a
seginental plate f" shaped as shewn by the dotted lines in the plan, Figure 2, and
which can be turned on a small pin in the centre by a small knob ƒ³.
The degrees on the image, further enlarged by.the prismatic lens are seen in the
same position by applying the eye in the ordinary manner.
In order to prevent the image being blurred by light reflected from the sides of the
conical casing c, (Figure 4 Sheet 2) it is lined with velvet, or cloth, or paper, cloth.
The whole apparatus rests as shewn in Sheet 2 on a plate p which can be
adjusted in the top of the pillar P, and held by a lateral set screw as shewn in
Figure 4. Into the bottom plate p are fixed three columns E, E, E, to which are
fitted two rings e. e. The middle ring supports the usual gimballing and in such
wise that the point where the centre lines of the gimbals carrying the whole
apparatus intersect coincides with the top of the pivot or the point of suspension
of the card. In order to bring down the centre of gravity of the whole apparatus,
the bottom plate h, carrying the mirror D), is fitted with a leaden counterweight W.
By means of a cup w milled at its outer edge, and screwing into the socket t the
entire apparatus with the gimbals is stopped or fixed in case of a heavy storm or
otherwise. This cap w may be further secured by means of a check nut. Any
undue vibrations, when the apparatus is in use, are instantly checked by means of
three equidistant springs 8, 8, 8; held from the central ring e and adjusted behind
the three ties f f f holding the counterweight W to the main plate H so as to
obstruct as little light as possible from the mirror D. These springs consist of
india rubber tubing or brass belices may also be employed. The whole apparatus
might be suspended from springs in the framing or it could also rest on india
rubber pads, in order to check such vibration as is encountered in screw steamers.
The casing on the binnacle pillar P is fitted with glass doors to allow the light
to reach the mirror, and the top is arranged with a movable cover as shown in
Figure 1.
".
On sheet 4 is shewn an apparatus for magnifying the microphotographic card
consisting essentially of an ordinary compound microscope with low powers and
large field.
It is similar in its general features to the inversed form of microscope designed
about 1827 by the late Professor Amici of Florence. The instrument is placed on

page_text: a binnacle and pillar P (Figure 1) at a height convenient for the eye. For night
use the binnacle is provided with the ordinary lamps as shewn. Figure 2 is a
front elevation. Figure 3 a plan, and Figure 4 a longitudinal section of the
apparatus. Figure 5 shews more fully the peculiar construction of plane mirrors
I employ.
In Figure 4. A indicates the microscopic compass in its bowl and adjusting
appliances which are shewn more fully on Figures 19 and 20 Sheet 1. B is the
object glass, which, in this modification of the apparatus, has to be made adjustable
to suit eye sights of differing powers. This can be done by a rack and pinion, or
in this instance, a small lever bis shewn. The enlarged image is thrown down
the casing c on to a mirror C set at an angle of 45° and is further enlarged by the
ordinary system of lenses D D d in the ocular or eye-piece of the instrument.
The eye-glass is fitted with a disc O to protect from side rays that eye not
employed on the eye-glass so that it need not be closed. The optical apparatus is
protected by a strong outer casing fand hemispherical bowl h. This outer casing
has at top a glass cover j with a caoutchouc joint ring and it is fitted with a small
adjustable mirror M to illuminate when necessary, the apparatus. This cover can
be turned round, and the jointed mirror set to the required angle. The whole
apparatus is hung from the top by ordinary gimbals, held in a stout ring e carried-
by the main framing E E, Figures 2 and 3. As with the azimuth compass already
described, the point where the centre lines of the gimbals intersect coincides with
the top of the pivot of the compass.
Vibration is also checked by means of three or more caoutchouc or other
springs SS Figure 2 looped to the fixed ring e and the outer casing. In order to
afford a lúbber's line to. the vertical picture of the card, very fine cross wires are
fixed in front of the field glasses D which with its setting D¹ can be turned round
on a flange D2 against a circular rim on the casing C, and held fast by a set
screw p' passing to the front of the apparatus through the outer casing f. A small
telescope T, on the top of which is adjusted a water level 61, is used to correctly
set the crosswires, and to test the accuracy of the instrument by known bearings.
For the same purpose, there is also fitted to the outer casing at right angles a
second small spirit level b³. By means of a socket F resting on the step H to be
fixed on the pillar P of the binnacle the whole instrument can be turned round.
A cup w milled at its periphery, and screwed into the socket of the framing, as
shown in Figure 4 is employed to take the weight of the instrument off the
gimbal suspension in the same way as with the azimuth compass previously
described.
Figure 5 shows to an enlarged scale a section of the plane mirror C. In order
to obviate the losses of light and the sources of error that would arise from the use
of an ordinary mirror of thick glass, I take a very thin sheet of crown glass.
shown too thick on the drawing, which I have obtained about six hundredths of a
millimeter in thickness. The back of this thin disc of glass is silvered in the
usual manner and the silvering coated with shellac or other suitable protective
varnish so that it cannot be injured by sea water This thin mirror is again firmly
cemented to another disc t¹ of thick glass which may be itself also silvered, to be
used in case the thin plane mirror t should get broken. Two plane mirrors of this
kind' are cemented to each side of a stout.brass disc r, so that the one set may be
used should the other get broken. The whole disc is held to the inner casing c
by means of three adjustable set screws k, spiral springs v being employed, so that
the plane of the mirror can be accurately adjusted by a screw driver from
holes XX, made in the bowl h fitted to the outer casing f.
On sheet 5 is shewn an instrument the construction of which will be easily
intelligible after the previous descriptions. It affords a means of seeing the image
of the microscopic compass from a distance; so that it may be used as a steering
compass. The picture of the microscopic compass A is thrown by the object
glass B on to the mirror C, inclined to 45°, and thence on' to a glass screen D
similar to that used for the azimuth compass shown on sheet 2. By interposing a

page_text: bi-concave lens between the mirror C and the screen D the height of the apparatus
could be diminished. The screen is marked with a line similar to that on the
screen of the azimuth compass to serve as the lubber's line. In front of the screen
is a circular shade s to keep off direct rays of light from this screen which shade;
necessarily partakes of the oscillations given by the ship to the instrument. On
the binnacle Figure 1 is fitted a much larger fixed shade S for the same purpose.
The other details are the same as those described for the compass shown on sheet 3,
the pillar supports E etc. on the other hand being similar to that of the azimuth.
compass illustrated on sheet 2.
On Sheet 3, Figure 4 indicates a small hand magnifier with a microscopic.
compass which may be used for instance in the cabin or on the bridge.
The glass bottom of the bowl of the compass is formed of a portion of the right-.
angled prism B, by which the picture of the reversed microscopic card is totally
refracted through the lens C to the eye of the observer. It is suspended on
gimbals and adjusted by a counterweight D.
Figures 5 and 6 sheet 3 show a light framing for a compass formed out of a new
material. It consists of very fine cork dust worked up with rubber preferably Java
rubber and sulphur between rolls heated by steam. This is then cured in moulds
in the same way as ordinarily carried out with articles of ebonite. While the
weight of the sulphur in the composition should be about half that of the
caoutchouc, varying proportions of cork can be employed. A tough and very light
material results from 100 parts by weight of rubber, 50 of sulphur and from 60 to
70 and more of the fine cork dust..
Some of the benefits of this invention may be obtained by employing a rather
larger size of compass card than that indicated; and by applying a microscope to
a portion of the outer circumference and to the lubber's line. But this would
involve longer magnets and other drawbacks.
The mere notion of minimizing compass deviation by minimizing the length of
the needle is not in itself novel. In a previous British Specification of the
year 1868 (N° 843) when describing a compass constructed with a number of
needles 1 inches to 2 inches in length, I stated that such a compass is "less
deviated, "when placed at a relatively less distance from magnetic matter than
ordinary compasses."
"
It is well known that, already during the last century simple and compound
micrometric microscopes have been applied to measuring the minute movements of
suspended magnets when influenced by changes, in the declination. I am aware
that George Dollond in 1812 proposed to place "a lens between the eye of the
steersman and the compass, by which the compass is magnified" I am also aware
that. telescopes have been applied to magnetic needles by Gauss and other
astronomers..
I am further aware that it has several times been proposed, e.g., by the late
Sir Samuel Brown in 1849, by Captain Franklin in 1867 and by others, to use a
transparent inverted or reversed compass-card with an inclined mirror below it in
order to enable the steersman to see an image of the card in a vertical position;
this combination making it possible to raise the steering compass somewhat higher
above the deck,
I am also aware that the late Sir W. Snow Harris employed in 1850 for his
compass a transparent disc of talc, the points being painted thereon and having a
single needle supporting the disc.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
First A mariner's compass for use in ships that produce compass errors con-
sisting mainly of a microscopic. compass card provided with a minute magnet or
magnets in combination with apparatus for optically magnifying said card so that
its directions become clearly visible within the apparatus itself either by daylight

page_text: or by the ordinary binnacle lamps (or other artificial light) substantially as set
forth.
Second A mariner's compass for use in ships that produce compass errors
consisting mainly of a microsopic compass card enclosed in a case which may be
laterally adjustable and is provided with a minute magnet or magnets in com-
bination with apparatus for optically magnifying said card so that its directions
become clearly visible within the apparatus itself either by daylight or by the
ordinary binnacle lamps (or other artificial light) the whole being suspended from
gimballing checked by springs substantially as set forth.
Third: A microscopic compass card for mariner's compasses fixed to a cap
wherein the thin short steel magnets are arranged close to a diamond or other
stone centre substantially as set forth.
Fourth A microscopic compass card for mariner's compasses made of thin
transparent material and having the points and divisions of the quadrants
appearing on a free and clear annular space or rim, such card being fixed to a
cap made of an alloy of magnesium with a small proportion of aluminium wherein
the thin flat magnets are set edgewiso in saw-cuts or grooves quite close to or in
actual contact with the diamond or other stone centre as described.
Fifth The improved construction of adjustable mirror whereby a saving of
light is effected and a better defined picture is obtained substantially as described
with reference to Figures 4 and 5 sheet 4.
Sixth-The azimuth compass substantially as described with reference to
sheets 2 and 3 in which the transparent microscopic reversed compass card with
lower counterweight and mirror and illuminating lens or leuses and with achro-
matic and aplanatic object glass and semitransparent screen connected with
azimuth appliances is suspended at the level of the card in gimballing checked
by springs.
Seventh-The mariner's compass substantially as described with reference to
sheet 4 in which the image from the microscopic card transparent or otherwise is
projected enlarged by means of an achromatic and aplanatic object glass onto a
mirror set at 45° and thence projected on and further enlarged by an ordinary
system of lenses in a lateral eye piece, the whole being suspended from gimballing
at the level of the card and kept from undue oscillation by means of springs.
Eighth The steering compass substantially as described with reference to
sheet 5 in which the image from the microscopic compass card above is by means
of an achromatic and aplanatic object glass enlarged and thrown upon a mirror set
at an angle of 45° and thence reflected upon a semitransparent screen marked
with a vertical lubber's line and having shades for keeping off the direct light,
the whole being suspended from gimballing at the level of the card and kept from
undue oscillations by means of springs.
Ninth The compass substantially as described with reference to Figure 4
sheet 3 in which the image of the reversed card is totally refracted in the prism
and seen through a hand magnifier.
Tenth-The compass card made substantially of the form described and shown
and of a composition of cork dust india rubber, and sulphur.
JENSEN & SON,
For the Applicant.