Improved Appliance or Instrument for use with Ships' Compasses for Determining Deviations, Compensating Errors, and the like.
Year: 1893

page_text: Date of Application, 26th Apr., 1893-Accepted, 2nd June, 1893
COMPLETE SPECIFICATION.
Improved Appliance or Instrument for use with Ships' Compasses
for Determining Deviations, Compensating Errors, and the like.
A communication by CARL THEODOR EMIL CLAUSEN, of 4, Österfarimagsgade,
Copenhagen, in the Kingdom of Denmark, First Lieutenant Royal Navy.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6, Bank Street,
Manchester, both in the County of Lancaster, and 323 High Holborn, in the
County of Middlesex, Civil 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 annexed sheet of drawings shows a top view of this improved appliance or
instrument for use with ships' compasses for determining deviations, compensating
errors, and the like, which appliance or instrument may be termed a deflector.
At the present day, when quick passages and safe navigation are matters of vital
consequence, it is important at all times, and without any waste of time, to be able
to compensate (that is, correct) or account for deviations of the compass. Bearings
of terrestrial or astronomical points have hitherto been used for compensating the
compass and examining the deviation of it; but such bearings cannot always be
had in foggy and hazy weather, and no control of the deviation and compensation
during a changed state of things can be made without a change of courses
occasioning waste of time.
Apparatus, it is true, have formerly been constructed by means of which com-
pensations of compasses could be made, and deviations ascertained, without
employing bearings; but these did not prove practical, were difficult to use,
and realised no accurate result, having been based upon the direct measurement of
the perturbing forces.
The present invention refers to an instrument to be used for determining the
resultant of the forces, as indicated by the reading of a deflection.
This deflector, the top view of which is shown in the drawing, consists of a
graduated ring R, that has, under its centre, a small pivot made to rest in a conical
hollow of the glass cover of the compass bowl.
A ruler A, furnished with two vertical magnets M and M', the poles of which
are turned opposite to each other, may be turned on a pivot on the top of the ring.
The magnets may be approached to or removed from each other by the screw S,
and their distance apart may be read on the scale I. The one end of the ruler,
that is, the end where the south pole of the magnet turns downwards, is painted
blue.
The pointer V passes through the circumference of the ring and its pivot; it is
set in a fore-and-aft direction on the compass bowl.
In foggy and hazy weather, and, in all cases, when the movements of the vessel
are not too violent, and she steers well, this universal deflector may be used without
bearings for-
1. Compensating both the semicircular and the quadrantal error of the
compass.
2. Finding the deviation of the compass on all courses.
Furthermore, when the quadrantal error is already compensated, it may, without
bearings, be used for-
3. Controlling the place of the corrector-magnets by putting the ship on two
different compass courses.
4. Controlling the deviation on the course steered by compass and reconstructing
the table of deviation by only one change of course.

page_text: course known, for
5. Controlling the compensation of the semi-circular error while keeping course,
and, therefore, also applying the corrector-magnets when the vessel is lying at her
quay, or riding at anchor.
6. Controlling the deviation by reconstruction of the table of deviation while
keeping course.
The use of this universal deflector is based on the following, namely:-
The forces acting on the needle are, the horizontal component of the earth's
magnetism and the horizontal component of the vessel's magnetism. The needle
will be guided by the resultant of these forces, and will consequently point in
different directions when the vessel is put to different courses.
When the magnets of the deflector are at such a distance apart (the normal
adjustment) that, when the instrument is placed on the glass of the bowl, they will
act on the needle with the same power as the horizontal component of terrestrial
magnetic force, the effect will be, if the ruler be placed at right angles to the
direction of the needle, the card being quiet, that the needle deviates 45 degrees,
whereas the deflection will differ from 45 degrees if the magnetism of the vessel
should also act on the compass.
How the normal adjustment can be ascertained, need not be fully explained
here; but directions for the use of the universal deflector will now be briefly
accounted for :-
--
The purpose of the deflector is to measure the deflection of the compass card
on different courses, when the ruler is placed at right angles to the direction of
the needle. As soon as the vessel is put to her course by the compass to be
corrected or examined, the corresponding course must be read on an auxiliary
compass (another of the ship's compasses) and kept by it as steady as possible.
Then the deflector is placed on the glass of the compass bowl, with the
pointer V in the fore-and-aft line, and the blue part of the ruler just over the
North of the card; after which the ruler is turned 90 degrees (little by little)
until its position is at right angles to the original direction.
The needle, of course, will be deflected; and, with a little skill, it may be very
quickly set to rest, when the deflection is read, while the course is exact by the
auxiliary compass.
How to use the deflector for compensation of the compass will now be
instanced-
Deflections on compass courses N.E., etcetera, are indicated by U, U etcetera.
Put the vessel on North after compass. Place the deflector, and find U, (read
on exact course). Bring the compass card back and to rest. Remove the
deflector.
16°
Swing ship's head to East, and find U, as above; the card back and to rest.
Remove the deflector. Turn the ship to South, and determine U₁e While, the
ruler is kept in its athwart position, adjust the fore-and-aft corrector-magnet, so as
to render the deflection
(U+U). Bring back the card and to rest.
Remove the deflector.
Finally, put the ship on West. Find U and adjust the athwart ship corrector-
magnet so as to render the deflection = (U + U₂₁).
Should the average struck by deflections of East and West not be equal to that
struck by deflections of North and South, turn the vessel to West, and then place two
globes abreast of the compass to compensate the quadrantal error until (U¸ + U₂)
1 (U₁ + U₁).
The deflector may also be employed in another way.
8
The use of the deflector for controlling the compensation without change of
course will now be instanced.
The quadrantal error already compensated, magnetic course known.
Find the correct magnetic course and keep it steady. Place the deflector on
the glass, and set the blue part of the ruler as many degrees from the lubber

page_text: line as is the magnetic North point, but to the opposite side. Then adjust the
athwartship corrector-magnet until the compass needle is in a correct fore-and-aft
position. Next turn the blue part of the ruler 180 degrees round through the
North, and, the card being quiet, adjust the fore-and-aft corrector-magnet till
the position of the needle is correct athwartship. After which the card is
brought back and to rest, when the deflector is removed. In order to obtain
a good result, the course of the ship should rather not be nearer than 1 point to
magnetic N., S., E. or W.
Supposing the quadrantal error is already compensated, the corrector-magnets
may, in this manner be adjusted, while the ship is lying at her quay, or riding at
anchor; provided, however, that no large iron bulks, such as other ships, iron
cranes, etcetera, be too near, and, further, that the ship be under steam, ready for
sca, and the propellor in motion.
The quadrantal error not already being compensated, the adjustment of the
corrector-magnets will only be approximate; but, nevertheles, sufficiently exact
to render the final compensation much more easy.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is :--
An improved appliance or instrument for the purposes specified, characterised by
the employment of a graduated ring, and a ruler (A) furnished with magnets (M
and M), the distance of which from the centre can be varied by means of a
screw (S), for the purpose of setting the magnets in such a manner that, on the
instrument being placed on the glass bowl of the compass card, they will act as
effectually on the needle as the horizontal part, of the force of the earth's
magnetism, substantially as herein before described.
Dated this 25th day of April 1893
WM. P. THOMPSON & Co.,
Agents for the Applicant.