A METHOD OR MEANS OF ASCERTAINING AND INDICATING THE DEVIATIONS OR ERRORS OF THE MARINER'S. COMPASS
Year: 1852

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
WALKER, of Plymouth, in the County of Devon, Commander in the Royal
Navy, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Twenty-third day of
February, One thousand eight hundred and fifty two, in the fifteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said William Walker, my exors, admors, and assigns, Her especial
licence, full power, sole privilege and authority, that I, the said William
Walker, my exors, admors, or assigns, or such others as I; the said William
Walker, my exors, admors, and assigns, should at any time agree with, and no
others, from time to time and at all times during the term of years therein
expressed, should and lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, in the Islands of
Jersey, Guernsey, Alderney, Sark, and Man, and in all Her said Majesty's
Colonies and Plantations abroad, my Invention of "A METHOD OR MEANS OF
ASCERTAINING AND INDICATING THE DEVIATIONS OR ERRORS OF THE MARINER'S.
COMPASS;" in which said Letters Patent is contained a proviso that I, the
said William Walker, shall cause a particular description of the nature of my
said Invention, and in what manner the same is to be performed, by an
instrument in writing under my hand and seal, to be enrolled in Her said
Majesty's High Court of Chancery within six calendar months next and

page_text: immediately after the date of the said in part recited Letters Patent, as
in and by the same, reference being thereunto had, will more fully and at large
appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
William Walker, do hereby declare that the nature of my said Invention, and
in what manner the same is to be performed, are fully described and ascertained
in and by the present Specification thereof, reference being had to the
Drawings hereunto annexed, that is to say:-
It is well known to mariners that a powerfully magnetized compass needle is
very useful in smooth water, and the more so the lighter it is for indicating any
change of direction in a ship's course, but that the same becomes almost
valueless when the water is rough and the ship's motion is considerable, or
when the ship is much shaken from any internal cause, such as the action of
steam-propelling machinery, in either of which cases the compass card is
never at rest, but in a state of constant oscillation to the extent of several
points on each side of the ship's course. The helmsman would then prefer to
have a heavier compass card and a weaker needle, that is, an instrument with
more matter and less magnetism in it. To explain how this happens, in
order that compass makers and mariners may the better understand the
necessity which exists for the improvements which form the subject of the
present Patent, and the principles on which they are founded, let A, B, C,
in the diagram, Figure 1, represent the section of a compass needle devoid of
magnetism poised upon a vertical pivot P, and suppose the arm A, C, to be
equal in length and quantity of matter to C, B. Then by the laws of mecha-
nics the needle will rest on the pivot P in a perfectly horizontal position, and
the centre of gravity of the needle will be in the same vertical line with the
point of suspension C of the pivot P. But suppose the needle has been
magnetized in some locality where the magnetic dip is considerable, say at
London, or New York, the needle will then dip as represented in Figure 2,
and its centre of gravity be no longer in the same vertical line with the point
of suspension C of the pivot P; it would, in fact, become unsupported and
unstable, there being more matter on the south than on the north side of the
vertical point. To restore horizontality to the needle under such circumstances,
compass makers are in the habit of weighting the lighter arm (A, C), as repre-
sented in Figure 3, where the weight W is supposed to counterpoise exactly
the tendency of the needle to dip. Of course, the greater the magnetic
power of the needle the heavier must the counterpoise be, and hence arises
another greater source of inaccuracy. For though a heavily counterpoised
needle will vibrate independently enough in smooth water, and form, therefore,

page_text: a tolerably good steering instrument, yet, when the water becomes rough and
the ship begins to pitch or roll, the needle acquires a tendency to maintain a
constant oscillation; for as the velocity of the rolling and pitching motion is
common to both sides of the compass needle, it follows that the momentum of
the heavier side will be the greatest, and continue to exert a constantly dis-
turbing force on the needle till the pitching and rolling motion is at an end.
It has been officially reported, that in a line of battle ship, her compass (a
powerfully magnetized one) performed horizontal vibrations through an arc of
90°, caused solely by the rolling of the ship. In vessels propelled by screws,
the results are still further complicated by the exceeding tremor imparted to
the whole frame of the ship by the action of the propeller and the machinery
by which it is driven, so much so, that in such vessels the pilots are often
obliged to abandon altogether any reliance on the indications of the compass.
Again, compass needles, especially when of great magnetic power, are
extremely sensible to what is called local attraction, that is, to any change of a
ship's local magnetism, resulting from change of geographical position, or
from the presence on board of iron substances.
local disturbing forces can at present only be
bearings of known objects on land, or by correct
and computations made in clear weather at sea.
of my improvements has been to find a means of obviating or neutralizing
these various defects in the existing compass, and to produce an instrument
capable of indicating the course of a vessel with correctness both in fair and
in foul weather, in all localities and under the circumstances of agitation from
external or internal causes above referred to, so that the deviations and errors
of the mariner's compass may, when necessary, be ascertained and indicated.
And errors arising from such
ascertained by taking the
astronomical observations.
Now the general object
Figure 4 of the annexed Drawings exhibits a sectional elevation of an
instrument constructed for this purpose, according to my invention. A, A, is
the compass box constructed as usual of wood, and kept every where free from
iron. C, the bowl, which is made by preference of copper, because that metal
exerts a tranquilizing influence on the needle. c, c, leaden ballast required
for adjusting the bowl on its gimbals. E, E, glass cover of the compass bowl.
P, the vertical pivot. B, a brass bell or cone, which is poised in an inverted
position on the pivot P. F, a fine steel rod or axis set in brass, which is
screwed to the top of the bell B, and carries the compass card c, and main
needle N, S. M, the cap of the needle, which is made of one sixth of the
length of the needle, and has at its apex a jewel, on which the point of the rod F
works, besides which, another perforated agate is fixed in the lower end of the
cap. Care is taken that the axis F shall coincide exactly with the centre of

page_text: gravity of the needle and cap, and also that the weight of the bell B shall
not be more than one third greater than that of the card needle and cap, in
order that as a counterpoise the horizontality of the card may be maintained.
The card should be of equal substance throughout, and when fastened to the
needle a final adjustment should be made by placing it on an inclined pivot,
in order that opposite sides may have equal quantities of matter and be in
equilibrium on the pivot or rod F, on which the card is to perform its hori-
zontal movements. When the needle is thus correctly adjusted and then
(but not till then) magnetized, it will place itself in the direction of the
magnetic meridian; and as the quantity of matter and motion of the card
will always be equal on opposite sides of the rod F, both in fair and in stormy
weather, a compass of this kind is sensitive in smooth water and steady in a
rough sea, and on that account superior to any ordinary compass, that is to
say, there can be no tendency to mechanical oscillation through inequality of
niomentum in the card, whilst the power of needle maintains its northerly.
direction. R is a slender hollow pillar equal in length to the radius of the
compass card, which is passed through the centre of the glass cover E, E,
and fixed (by a nut and washer) in the same vertical plane as the axis F and
the centre of gravity of the main needle N, S. T is a slender rod or style
with steel point, which is contained inside of R, and carries at top a second
or indicator needle N³, S. p' is a screw by which the rod T can be raised or
lowered after the manner of a telescope, so as to increase or diminish the
distance between the two needles, and W is a glass dome which encloses the
entire apparatus to protect it from currents of air and electricity, and rests on
a ring L attached to the outside of the compass bowl. Both needles are
made of precisely the same description of steel, that is, of fine cast steel
forged from a charcoal fire, and of the form represented in Figures 5, 6, and 7.
Both needles are also uniformly tempered throughout, that is to say, instead
of tempering them like ordinary needles in common fires, which is the cause
that such needles so commonly exhibit different degrees of hardness or mag-
netic susceptibility in different parts, I temper them by heating them in
boiling lead and then cooling them in boiling water. The temperature of
boiling lead is a specific quantity, and so also is that of boiling water, conse-
quently every particle of the needles is heated alike and exposed to exactly
the same cooling or indurating influence. The principle on which the second
or indicator needle acts is as follows:-It is known that when two magnetic
needles of different magnitudes, varying, say in the proportions of twenty to
one (which is that adopted in the instrument before described), are freely
suspended in the vertical plane of the magnetic meridian and at a certain

page_text: distance apart, both needles, if uninfluenced by local magnetism, will place
themselves parallel to the magnetic meridian, but with the poles of the lesser
needle inverted. This parallelism, however, can only take place where there
are no local disturbing forces. The earth's magnetism is common to both
needles, and may be regarded as a constant quantity, whilst the attractive force
of the two needles on each other may be varied in the inverse duplicate ratio
of their distance apart; whence it follows that whenever the main needle is
made to deviate from the magnetic meridian by the presence of any local
disturbing force, it will by the magnetic mastery it possesses cause the small
needle to deviate in the same direction. The moment, however, any such
deviation takes place, and the needles are no longer parallel to the magnetic
meridian, the earth's magnetism then exerts a mechanical power on the small
needle (in its inverted position) to turn it round, wherefore the effort which
the small needle makes to attain its natural position (assisted by terrestrial
magnetism) causes a greater deviation than that of the main needle, though
in the same direction. Supposing, therefore, the vertical distance between the
centres of gravity of the two needles to be so adjusted (by means of the
screw p¹) that the deviation of the small needle shall be to that on the com-
pass card as 2 to 1, it follows that the small needle will indicate a deviation
from the north and south of the compass, and exactly equal to the deviation
of the main needle from its correct magnetic meridian, and the amount may
at once be read off through the glass dome on the card in the compass box,
which is graduated on the outer edge to 360 degrees, as the quantity in
degrees to be applied to correct the ship's course. To illustrate this by an
example or two.
Example First. Let the indicator needle point in an exact north and south
direction, or to zero on the compass card, then the axes of the two needles
would be parallel, and no error would be indicated.
Example Second.-If the indicator needle pointed in a direction north
twelve degrees west, and south twelve degrees east, thereby making angles
of twelve degrees with the main needle, this would indicate a westerly
deviation of twelve degrees to be applied to correct the ship's course or
compass bearing.
Example Third:-Should the indicator be seen to point in a N. b. E. (north
by east) and S. b. W. (south by west) direction on the card, this would point
out an easterly deviation or error of one point to be applied to correct the
compass course or bearing.
Example Fourth. For the adjustment of height of the indicator, first,
place the instrument where no local attraction exists, and let the north or zero

page_text: point of the card and lubber's point coincide, the needles will now be parallel.
Second, let the compass be made to deviate by iron, a magnet, or by hand,
10, 20, or 30 degrees east or west on either side of the lubber line, and read
off the pointing of the indicator needle on the card; if this reading agree
with the actual number of degrees the compass is made to deviate, then the
instrument is in correct adjustment, otherwise the indicator needle must be
raised or lowered until the indicated deviation on the card is equal to the
actual deviation given to the main needle in the process of adjustment.
And having now described the nature of the said Invention, and in what
manner the same is to be performed, I declare that what I claim is, the
employment in mariners' compasses of a supplementary indicator needle
poised on an isolated and independent pivot made moveable for adjustment of
magnetic intensity, and placed on a vertical plane passing through the centre
of gravity of the principal and supplementary needles for ascertaining and
indicating the deviations or errors of the mariner's compass, as herein-before
described.
In witness whereof, I, the said William Walker, have hereunto set my
hand and seal, this Ninth day of August, in the year of our Lord
One thousand eight hundred and fifty-two.