A MARINER'S COMPASS ON A NEW CONSTRUC- TION
Year: 1788

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, KENNETH
MC, CULLOCH, of the Minories, within the Liberty of the Tower of London,
send greeting.
WHEREAS His most Excellent Majesty King George the Third, by His
Letters Patent under the Great Seal of Great Britain, bearing date the
Twelfth day of August, in the twenty-eighth year of His reign, did give and
grant unto me, the said Kenneth Mc Culloch, my executors, administrators,
and assigns, especial licence, full power, sole priviledge and authority, that I,
the said Kenneth Mc Culloch, my executors,, administrators, and assigns, or
such other persons as I or they should agree with, and no others, from time to
time and at all times thereafter during the term of years therein expressed,
should and might make, use, and vend, within that part of the Kingdom of
Great Britain. called England, the Dominion of Wales, and Town of Berwick-
upon-Tweed, my Invention of "A MARINER'S COMPASS ON A NEW CONSTRUC-
TION;" in which said Letters Patent is contained a proviso that I, the said
Kenneth Mc Culloch, should within the space of one calendar month next and
immediately after the date of the said in part recited Letters Patent, 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 .inrolled in His Majesty's High Court of Chancery, otherwise
the said Letters. Patent to be void and of no effect (as in and by the said
Letters Patent, referrence being, thereunto had, may more fully and at large
annear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Kenneth Mc Culloch, do hereby declare that the nature of my said Invention,
of a Mariner's Compass on a New Construction, and the manner in which the
same is to be performed, is described in the three several Plans or Drawings
thereof hereon made, mark'd Fig. 1, Fig. 2, and Fig. 3, with the explanations
and referrences thereto as herein-after mentioned (that is to say):-
Fig. 1 represents the Azimuth Compass. A, A, sides of the box or case, of
wood, or any other unmagnetic substance. B, the bottom of the box or case.
C, the brass or metal socket for the brass or metal frame to turn round in.
D, the prop or center, the point of which is rounded or spherical, to support
the compass vessel and magnetic needle. E, E, arms or guides of brass, or
some unmagnetic substances that move in the socket round with the prop D,
which serves as a center. These arms have slitts for admitting two pivotts,
which are fixt in the sides of the compass vessel. F, F, the brass or metal
box or compass vessell, the bottom of which rises in a conical form. G, the
magnetic needle, bent so that the point of the pivot on which it moves round
is a small distance above the center of gravity. H, the center or pointed
pivot of steel, or other hard substance, on which the needle turns. K, K, a
brass or metal azimuth circle round the edge of the card, which metal circle is
divided into degrees and subdivisions. I, I, a ring of lead, or any other
ponderous substance, to ballance the compass vessell. 2 represents the top
of the cone in the compass vessell, having a cavity to receive the three pieces
of bell metal, or other hard pollished substances now to be described. 3, a
piece of bell metal, or other hard substance, formed or turned concave, so as
to give full room for the point of the prop. The upper part of the cavity
must just pass through the surface; this piece is placed in the cavity 2. 4, a
thin plate of agat, bell metal, or other hard substance, lays on the top of 3,
and in contact or rests on the prop or center D. 5, a piece of bell metal or
hard substance, in the center of which is a hollow invented cone, the apex or
point just passing through the peice to the lower surface, to permit the pivet
of steel, or other very hard substance on which the magnetic needle turns,
to move with freedom, and the point to touch or be in contact with the thin
plate marked 4, or all these three pieces last described may be formed of one
peice of metal, but it is then very difficult to execute well, and is not so
durable. 6, a cap of metal or other substance, screws down on the cylindric
part at the top of the cone to keep the pieces 3, 4, and 5, secure, so that the
center of motion of the magnetic needle, and the centre of motion of the
compass vessell may approach very near, and be as nearly as possible
perpendicular to each other, which gives the card a proper stability. 7, the

page_text: stop, with nonius or vernier divisions. This stop is the segment of a hollow
sphere, the same diameter as the azimuth circle round the card. It may be
made of metal, ivory, mother of pearl, or other hard substance.
8, the slide
of the stop, moves in a socket, triangular or otherways, the center of which is
a secant to the point of the prop, and is kept steady by a spring at one side.
It is pushed in or drawn out by the ball or button at 9. 10, a dark glass
moveable on the sight vaine. 11, a magnifying glass, also moveable on the
sight vaine; the focal distance reaches the line on the opposite sight
vaine, on which the dark glass is placed. 12, 12, a bar of metal that
goes across with a long oval hole to see through when you read the divisions on
the nonius 13; upon this bar is placed a magnifying glass, to read the divisions
with greater accuracy. 14, 14, the sight vaines vane screwed fast to the
brass or metal bar. 15, a plate of glass, as in the usual way. 16, a brass or
metal pivet fixed on each side of the compass vessell, in a line with the thin.
metal plate on which the pivet of the needle rests. These two pivets must
have room to traverse up and down in the slit in the arms or guides to 17,
and keeps the compass vessell from turning round in the box or case, but
allows it free liberty to come to an horizontal position.
Fig. 2 represents a section of the Steering Compass, which is the same in
principle as the azimuth, but only more simple, having the arms or guides
screwed fast to the box, being always to remain in the same position. A
common card is only wanted, and neither metal circle or nonius stop, nor are
the vaines necessary.
a, α,
The tops of these form a ring, the
exceed one inch. In this ring or
center of these
Fig. 3 represents a section of another application of the compass.
the compass vessell, is suspended on a metal circle by pivets, which apparatus
is generally called jambols by the workmen. In making these jambols b, b,
I carefully observe that the centres of motion pass exactly through a line
round the middle of the metal circle.
c, c, are two pieces of metal rising
from the bottom of the compass vessell.
interior diameter of that ring need not
hollow space I construct another small set of jambols d, in the
small jambols I suspend a ballance of any weighty substance. This ballance
is composed of two pieces; in the upper part is a hollow inverted cone, to
admit the pivet of one of my magnetic needles. e, the bottom of the ballance,
is screwed into the lower part of the other. On the top of this lower part I
generally place a small piece of pollished aggate, or other hard substance, on
which the point of the pivet of the magnetic needle rests, and by screwing
this piece up to a proper height I bring all the points or centers of motion
as nearly as possible to the same horizontal plain. f, the weight of lead, or

page_text: any ponderous substance, screwed to the bottom of the compass vessell to
bring it more readily to a horizontal position.,
In witness whereof, I have hereunto set my hand and seal, the Eleventh
1. day of September, One thousand seven hundred and eighty-eight.
AND. BE. IT REMEMBERED, that on the Eleventh day of September,
in the twenty-eighth year of the reign of His Majesty King George the
Third, the said Kenneth Mc Culloch came before our said Lord the King in His
Chancery, and acknowledged the Instrument aforesaid, and all and every
thing therein contained and specified, in form above written. And also the
Instrument aforesaid was stamped according to the tenor of the several Statutes
made in the sixth year of the reign of the late King and Queen William and
Mary of England, and so forth, and in the seventeenth and twenty-third years
of the reign of His Majesty King George the Third.