A CERTAIN APPA- RATUS OF MATHEMATICAL INSTRUMENTS, FOR THE BETTER ASCERTAINING THE GEOGRAPHICAL POSITION OF VESSELS AT SEA
Year: 1798

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
EDWARDS, of the City of Bristol, Mathematical Instrument Maker, sends
greeting.
WHEREAS His most Excellent Majesty King George the Third did, by
His Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Eighteenth day of April, in the thirty-eighth year of His
reign, give and grant unto me, the said John Edwards, His especial licence
that I, the said John Edwards, during the term of years therein mentioned,
should and lawfully might use, exercise, and vend, within England, Wales,
and the Town of Berwick-upon-Tweed, my Invention of "A CERTAIN APPA-
RATUS OF MATHEMATICAL INSTRUMENTS, FOR THE BETTER ASCERTAINING THE
GEOGRAPHICAL POSITION OF VESSELS AT SEA;" in which said Letters Patent
there is contained a proviso obliging me, the said John Edwards, by an
instrument in writing under my hand and seal, to cause a particular descrip-
tion of the nature of my said Invention, and in what manner the same is to
be performed, to be inrolled in His Majesty's High Court of Chancery within
one calendar month after the date of the said recited Letters Patent, as in
and by the same, relation being thereunto had, may more fully and at large
appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
John Edwards, do hereby declare that my said Invention of a Certain Appa-
ratus of Mathematical Instruments for the better Ascertaining the Geogra-
phical Position of Vessels at Sea, is described in the above Drawings, and the
following description, that is to say:-
The same consists of an improved mariner's or polar compass, whose poles
are made meridional, an improved dipping needle, and a latitudinal instrument,
as hereafter described.

page_text: The mariner's or polar compass, Plate 1st, has not the strait needle, but
a star or a plate, either round or starred into any number of points, or a body
of any other form that will retain the center of magnetic gravity in its own
center. It may be made of any ferrugenious substance that will receive the
magnetic fluid, and variously impregnated, but on the same principle. The
one chosen for exemplification was a round plate of steel, about two inches
diameter, and about one sixteenth of an inch thick, filed into twelve equal
points, pierced in the center for a cap, and balanced. Plate 2nd. This I impreg-
nate as follows:-Holding a set of artificial magnets B, the north end of one
touching the south end of the other above the hand, I place their opposite
ends on the star, at the distance of an angle of half the diameter of the star,
Plate, 2 A, I rub them on any one point of the star and its opposite several
times with an equal pressure, whereby the point so rubbed by the south end of
one magnet becomes the north point of the star, and the point so rubbed by
the north end of the other magnet becomes the south point of the star.
Bringing the magnets in the same position to their first station, I rub them
angularly over the next point east of the north, and its corresponding point
west of the south, with the same degree of pressure and number of times, and
in like manner point to point, till all are impregnated. Fixing the cap therein,
I try it on meridional line. If incorrect, which may happen, pass a magnet.
over such point or points east or west of the north point as will correct the
error, observing to use the north end of the magnet on those points east or
west of the south point, and the south end on those points east or west
of the north point. Fix a card on the impregnated side of the starr, with an
agett cap, and place it on a common or the double center, Plate 3d, which
may be made of any metal not ferrugenius. On its bottom is fixed a center A,
carrying a crane B capt, from the middle of which, about three eighths of an
inch distant, is fixed another center tipt with steel C, on which the card plays.
Then mount it as fancy directs you, without or with the universal dial shewn
in Plate 1st. On the rim of the compass is the semicircle A, having the hours
and minutes of the day divided thereon. At each end there is a joint B, that
connects it with a strait bar C first across the compass bowl over the
glass, that gives the semicircle a vertical motion. On the center of the bar C
is fixt a style having a joint D, that gives it an horizontal and vertical motion.
Near the point of the stile is a rim round it E. When used, direct the point
to the sun to catch its center, which throws its shade on another rim F, near
the joint. Having caught the sun's centre, raise the semicircle to the point of
the stile, and it will give the time of the day pretty accurately during the
whole of the sun's appearance.
N.B. The figure 12 on the semicircle must
be nicely placed exactly over the south point, and the surface level.

page_text: The improvement on the dipping needle, which is enclosed in a brass cylinder
glazed, Plate 4, is in the extreme lightness of the needle A and manner of
suspension; viz, it runs round its axis B, having a shoulder on each side.
The axis B runs also, and in agetts burnished into the screws C, screwed into
the ends of the uprights D. Place this dipping needle on the meridional line
of the polar compass, it will give a more correct dip than any needle now in.
The double center, Plate 3d, placed under the common card with the
strait needle, or I prefer the needle made thus
gives it a cen-
trifugal motion, and keeps it more correct to the variations than compasses now
in usc.
use.
The latitudinal instrument, as described in Plates 5 & 6, is actuated by the
attractive and repulsive power of the magnets, the magnetic center of gravity
altering in every parallel of latitude. It may be varied in its construction, but
not in its principle. On Plate 5 is divided a seniicircular line of proportions.
A, B, is a hand pointing to the degrees of latitude so divided; C are lesser
circles of divisions; D, hand pointing to minutes divided thereon. On Plate 6,
A is the bottom plate; B, pillars on which to screw Plate 5; C, semicircular
artificial magnets; D, a cone or center whereon the horizontal wheel E
traverses; F, a smaller artificial magnet fixt in its exact center to the wheel;
G is lead to balance such magnet; H, an axis on the center of the wheel, with
a square end passing through the Plate 5, to receive the larger hand; I,
pinion of leaves nicely adjusted to the wheel; K, socket with an aget, whereon
the pinion turns; I, an axis on the pinion, having the upper end also square
to receive the smaller hand when passed through Plate 5. Note. The arti-
ficial magnetts may be impregnated in the usual manner, but the larger
magnet C must answer nicely to the line of proportions on Plate 5, and the
smaller magnet F should be about one fifth of the larger magnet, with a curve.
Great nicety is required in adjusting this instrument, the north pole of magnet F
hanging to the south pole of magnet C, and south pole of course to the north
of lower magnet. The large hand B must be nicely fixt so as to hang over
the exact center of the upper magnet F, and the smaller hand to correspond
therewith. Then both hands will be actuated by the magnets, and point out
the latitude on the Plate 5 as you go to the northward or southward.
In witness whereof, I, the said John Edwards, have hereunto set my
hand and seal, this Eighteenth day of May, in the year of our Lord
One thousand seven hundred and ninety-eight.
.
JOHN EDWARDS. (L.S.)

page_text: AND BE IT REMEMBERED, that on the same Eighteenth day of May,
in the year above mentioned, the aforesaid John Edwards càme before our
Lord the King in His Chancery, and acknowledged the Specification afore-
said, and all and every thing therein contained, in form above above written.
And also the Specification aforesaid was stamped according to the tenor of
the Statute in that case made and provided.
Inrolled the same Eighteenth day of May, in the year above written.