CERTAIN IMPROVEMENTS IN THE MARINER'S COMPASS OR BOAT COMPASS
Year: 1813

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, 1, FRANCIS
CROW, of Feversham, in the County of Kent, Watch Maker and Silversmith,
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 Thirtieth day of
January, in the fifty-third year of his reign, give and grant unto me, the
said Francis Crow, my exors, adiñors, and assigns, His especial licence, full
power, sole privilege and authority, that I, the said Francis Crow, my exors,
adiňors, and assignís, should and lawfully might, during the term of years.
therein mentioned; make, use, exercise, and vend, within England, Wales, and
the Town of Berwick-upon-Tweed, my Invention of "CERTAIN IMPROVEMENTS
IN THE MARINER'S COMPASS OR BOAT COMPASS;" in which said Letters Patent
there is contained a proviso that if I, the said Francis Crow, shall not par-
ticularly 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 six 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) may more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Francis Crow, do -hereby declare the-nature of my said Invention, and

page_text: the manner in which the same is to be performed, are particularly described
and ascertained in and by the Drawings and references thereto hereunto
annexed, and the following description thereof, that is to say :-
The card or index of this compass is constructed of two concave metallic
plates, which are hermetically sealed or soldered together, forming a lens,
within which is contained and firmly fixed a magnetic needle. In the centre
of the superior side of the above-described card or lens is fixed an inverted
hollow cone to receive a metallic point hereafter described; and to the center
of the inferior side of this card or leus is attached a small weight or ballast,
keeping the said cards or lens in an horizontal position, and at the same time
adjusting its pressure on the point of action to about twenty-four grains troy
weight. Upon the superior surface of the said card or lens are marked the
points and degrees of the compass.
The above-described card or lens floats in a liquid, which liquid is contained
in a metallic bowl, suspended by gimbals in a box after the usual manner.
Round the superior part of the bowl is a chamber communicating with its
cavity, and constructed with a spring valve,admitting the escape of expanded
air or the replenishing the liquid in the bowl when required. The liquid con-
tained in the bowl is alcohol, which is not liable to freeze in the greatest
degree of cold. The liquid is confined in the bowl by means of a glass plate
strongly secured and cemented into the said bowl; in the centre of which glass
plate, on the inferior side, is fixed a metallic point, which is received into the
aforesaid hollow inverted cone upon the superior side of the above-described
card or lens, keeping the said card or lens in its place, and at the same time
allowing the utmost freedom of circular motion. To the centre of the external
and inferior surface of the said bowl is attached an arm or rod, at the
extremity of which is fixed a tender spring, which is received by a concave
metallic dish attached to the compass box underneath the said bowl, on the
surface of which dish the said spring freely acts, and stops the vibratory
motion of the said bowl.
I also make use of another method of stopping the vibration of the said
bowl, after the following manner: viz. a piece of hard wood or metal or hard
substance, forming a segment of a sphere (the radius of which arises from the
line of suspention) is attach to the inferior side of the said bowl, acting against
the extremity of a tender spring arising from the side or other part of the
compass box.
The peculiar advantages of the above-described compass, which renders it
superior to other compasses, are as follows:-
(1st). The compass while it retains its true horizontal level, is by the means

page_text: of the spring attached to the bowl, deprived of the oscillation or vibratory
motion to which other mariner's compasses are subject, which motion is com-
municated by the agitation of the vessel or ship.
(2nd). The card or lens, while its circular motion is undiminished, is also,
by means of the medium in which it floats, deprived of the oscillation or
vibratory motion.
(3rd). The wear of the point of action by friction from the pressure of the
card or lens, a fault so detrimental to other mariner's compasses, is in this
altogether obviated, since the pressure upon the point acting in the cone (by
which the card or leus is kept in its place) is equal to the weight of about
twenty-four grains troy weight; whereas, the weight acting on the point of
suspension in the common mariner's compass is seldom less than one ounce
and a half, or seven hundred and twenty grains.
From all the above-enumerated circumstances this improved mariner's com-
pass has been proved to retain its magnetical meridian when exposed to the
utmost effect of the most turbulent sea, even in a boat of the smallest size.
In witness whereof, I, the said Francis Crow, have hereunto set my
hand and seal, this Twenty-fourth day of June, in the year of our
Lord One thousand eight hundred and thirteen.
AND BE IT REMEMBERED, that on the Twenty-fourth day of June, in
the year of our Lord 1813, the aforesaid Francis Crow 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 stampt according
to the tenor of the Statute made for that purpose.
Inrolled the Second day of July, in the year of our Lord One thousand