AN IMPROVEMENT IN THE MARINERS' COMPASS
Year: 1818

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
CONSTANTINE JENNINGS, of Carburton Street, Fitzroy Square, in the County of
Middlesex, Esquire, send greeting.
WHEREAS His most Excellent Majesty King George the Third did, by
His Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Seventh day of May;
in the fifty-eighth year of His reign, give and grant unto me, the said Henry
Constantine Jennings, my exors, adññors, and assigns, His special licence, full
power, and authority, that I, the said Henry Constantine Jennings, my exors,
adiors, and assigns, during the term of years therein mentioned, should and
lawfully might, during the term of years therein mentioned, should and lawfully
might make, use, exercise, and vend, within England, Wales, and the Town of
Berwick-upon-Tweed, my Invention of "AN IMPROVEMENT IN THE MARINERS'
COMPASS;" in which said Letters Patent there is contained a proviso, that if
I, the said Henry Constantine Jennings, shall not particularly describe and
ascertain 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, and cause
the same to be inrolled in His Majesty's High Court of Chancery within four
calendar months next and immediately after the date of the said Letters
Patent, that then the said Letters Patent, and all liberties and advantages
whatsoever thereby granted, shall utterly cease, determine, and become void, as
in and by the same, relation being thereunto had, will more fully and at large
appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Henry Constantine Jennings, do hereby declare that the nature of my said
Invention, and the manner in which the same is to be performed, are par-
ticularly described and ascertained in and by the Drawings hereunto annexed,
and the following description thereof (that is to say):-
My Invention is an improvement in the mariners' compass, being a means
of guarding or protecting the magnetic needle of it from all action arising
from iron in its neighbourhood, to which defect all other compasses are liable.
In the accompanying Drawings, Fig. 1 is a plan, and Fig. 2 a section of the
compass, with its needle mounted and fitted up in the usual manner with gimbals,
glass cover, wooden case, &c.; Fig. 3 is a representation of the back of the card,
with the needle firmly screwed to it. a, b, c, and d, are four pieces of iron,
softened by annealing, in the manner to be described hereafter, and the forms of
two of which are also shewn in Fig. 4, which is a section of the card and needle
at the dotted line in Fig. 3; two of these pieces are screwed to the card at each
end of the needle, in the manner shewn at Fig. 3, and are intended to act as
guards against the passage of the magnetic fluid, by absorbing the first quan-
tity of it, the remainder being absorbed by means of iron filings, prepared as
herein-after described, and which are contained in the space between the sides
and bottoms of the brass or copper boxes which enclose the needle and card,
and which space is shewn by the letters e, e, of Fig. 2, as filled up by the said
iron filings, and as covered by the brass or copper ring f, f, in Figs. 1 and 2.
In order to keep the bottoms of the boxes a proper distance apart, the bottom
of the inside box must have four pieces of thin brass or copper tube, soldered
underneath it, each about half an inch high and about one quarter of an inch
in diameter; one of these tubes is to be placed exactly in the centre of the
bottom, and the other three within a quarter of an inch of the sides of the
box, so as to form an equilateral triangle; through the middle tube the stem of
the support of the needle passes, having a screw at its end, on the outside
of the box, upon which a nut being screwed, serves to hold the inner box down
in its place, and prevents it from rising in the centre. The sides of the boxes
are also kept at the distance of half an inch from each other by means of a
groove, which is made on the under side of the ring f, f, Fig. 2, fitting upon
the rim or edge of the inner box; the space between the two boxes must be
completely filled with the prepared iron filings, observing to shake them down
so as to be certain that the bottom and sides are entirely filled and surrounded
therewith, but no mechanical pressure should be employed in that operation.
In order that the manner of fixing the pieces of iron a, b, c, and d, Figs. 2
and 3, on the under side of the card, may be more perfectly understood,

page_text: Fig. 5 is section, and Fig. 6 a front view of one of them on an enlarged-scale,
in both of which 9, 9, represents a brass or copper arm or bracket, bent at a
right angle, rivetted to the piece of iron and secured to the card by two screws
h, h, passing through it. These pieces of iron and the iron filings must be
prepared from iron known to be tolerably pure, such as the best Swedish iron;
they must be softened or annealed by being enclosed in a soft plate iron box,
and intimately mixed either with alumine clay, in fine powder, or which is
better, an argillaceous iron ore, or an oxide of iron, in the proportion of about
one-sixteenth part, which may have a tendency to abstract any carbon which
might exist in excess in the iron, so as to render it liable to become polarized;
this box must be well covered with a soft plate iron lid, and be exposed to a
strong red heat for two hours in an oven or furnace properly constructed, so as
to heat the iron box and its contents all over equally; after which it should
remain in the oven or furnace until it is become cold; the powder which was
as aforesaid mixed with the iron filings must then be partly separated from it
by sifting, and the remainder blown away until the iron remains free from any
admixture thereof, when it will be found to be quite soft and fit for use in
the manner directed.
Pure iron, in a sufficiently divided state, procured in any other manner than
by filing it, may also be employed after being annealed as directed, and indeed
the guards at the ends of the needle may be used alone to partially insulate it,
but the perfect insulation can only be effected by the means pointed out herein.
A modification in the shape of the iron, or little differences in the preparing it,
may be made; but the principle is to render iron pure and soft, and to apply
it on the sides and bottom of the compass box, keeping the sides truly circular
and the bottom perfectly flat, with the needle card, &c. suspended on a point
accurately in the centre of the box. If the manufacturer wishes to prevent
attraction from very large masses of iron, he has only to adapt the thickness of
the prepared iron according to the quantity of iron exposed to the needle; two
inches and a half thickness will, I conceive, insulate from one ton of iron close
to the compass box, and from one hundred tons if at one foot distance, and
so on in proportion as the distance increases. I prefer that kind of needle
which was used by the late Dr. Gowen Knight to that of the common form.
In witness whereof, I, the said Henry Constantine Jennings, have here-
unto set my hand and seal, this
.
day of
1
HENRY CONSTANTINE (L.S.) JENNINGS.

page_text: AND BE IT REMEMBERED, that on the Seventh day of November, in the
year of our Lord 1818, the aforesaid Henry Constantine Jennings came before
our said Lord the King in His Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form above
written. And also the Specification aforesaid was stamped according to, the
tenor of the Statute made for that purpose.
Inrolled the Seventh day of November, in the year of our Lord One