IMPROVE- MENTS IN COMPASS PROTRACTORS
Year: 1861

page_text: LETTERS PATENT to William Clark, of 58, Chancery Lane, in the County
of Middlesex, Engineer & Patent Agent, for the Invention of "IMPROVE-
MENTS IN COMPASS PROTRACTORS."-A communication from abroad by
Charles B. Wood, of New York, United States of America.
Sealed the 26th April 1861, and dated the 19th January 1861.
PROVISIONAL SPECIFICATION left by the said William Clark at the
Office of the Commissioners of Patents, with his Petition, on the 19th
January 1861.
I, WILLIAM CLARK, of 53, Chancery Lane, in the County of Middlesex,
Engineer & Patent Agent, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN COMPASS PROTRACTORS," to be as follows:-
This Invention consists in the combination with ordinary parallel rulers
of a movable circle graduated as a compass, and divided into degrees, if
desired, in such a manner that by the combined operation of said circle and
the parallel rulers the operations of laying off courses on board ship and of
locating a ship's position on a chart from cross bearings, and also the operation
of plotting a day's work, rendering it unnecessary to keep a traverse table of
corrected courses, and the operation of ascertaining bearings between points,
are greatly facilitated.

page_text: In the accompanying Drawing, Fig. 1 represents a face view of this
Invention, and Fig. 2 is a sectional side elevation of the same; similar letters
of reference in both views indicate corresponding parts.
The instrument at present used for the purpose of laying off courses on
board ship, or for the purpose of locating a ship's position on a chart from
cross bearings, or for the purpose of determining the bearing of surrounding
objects, consists of ordinary parallel rulers. The use of these rulers requires
a tedious operation, and furthermore results obtained by the same are sub-
jected to serious and embarrassing errors. In laying off courses on board
ship with said parallel rulers, the operator is obliged to traverse the chart
from the position of the ship to the compass of reference (an operation com-
monly known by the name of "fleeting" to or from a compass of reference),
which is laid out on the chart according to the true meridian, and then he has
to calculate the magnetic course. In the meantime, perhaps, the table is
uneven, or some rubbish has got under the chart, and during the operation the
rulers have slipped, and the result thus obtained will be altogether erroneous.
And in locating a ship's position from cross bearings, or in determining the
bearings of surrounding objects, it is necessary to traverse the chart with the
parallel rulers once for every bearing under all the inconveniences above
pointed out, and for each bearing a separate calculation has to be made should
magnetic bearings be required; all of which render the operation tedious &
liable to produce erroneous results.
All these difficulties are obviated by the instrument which forms the subject
of this Invention, and which consists of a pair of ordinary parallel rulers A
that are connected to a circle B by means of an arm, being secured to the
centre of said circle by a screw pivot a and nut b. The arm C is secured to
one arm of the rulers in such a manner that the outer edge of the ruler to
which the circle is attached shall be in a direct line with the centre of the
circle. The nut 6 serves for the purpose of clamping the circle when
necessary.
In using the instrument, the first thing necessary to be understood is how
to place it in meridian, which is accomplished as follows:-Place the north &
south points of the circle in a meridian line, or the east and west points in a
longitudinal line; the circle now represents a true compass. To make it
represent a magnetic compass, simply turn the compass to the right or left in
accordance with the variation at the nearest point on the chart, either easterly
or westerly. The circle now represents a magnetic compass, and whatever
position the rulers may be in, either edge will show a magnetic course, which
is indicated by that edge of the ruler which is in line with the centre of the

page_text: circle. Now to lay off a compass course, say north-east, place the circle in
the nearest meridian or line of longitude, turn it to allow for the magnetic
variation (also local, if there should be any); turn the ruler until it indicates a
north-east course, and open the rulers until the other arm reaches the point
from which you desire to lay your course. To locate positions from cross
bearings, say from two points, one bearing north-east, the other east-south-
east; place the instrument in meridian as near the first point as convenient,
turn the circle in accordance with the variation, revolve the rulers until they
indicate north-east, open them until the first point is in contact, and draw a
line; apply the instrument in the same way to the second point, and draw a
line. The position of the ship will be shown by the intersection of these two
lines. To find the magnetic bearings between two points, place that arm of
the rulers which has the scale marked upon it upon the two points as if for
the purpose of drawing a line between them; now open the rulers, and thus
move the circle until it is in meridian; turn the circle for variation, and read
the bearing. To plot a day's work, having a list of your courses and their
distances before you, draw any straight line on a sheet of paper, and assume
it as a meridian; assume any point for a point of departure, and from it con-
struct your first course, taking the distance from the scale on the rulers. The
point which makes your first distance now becomes another point of departure
from which you can construct your second course, taking your distance from
the scale as before, and the point which marks the distance on the second
Now a line
course becomes a point of departure for a third course, and so on.
drawn from the first point of departure to the point which marks the distance
on your last course, will be your course & distance made good. The course
of this line you will find by referring it, by means of the instrument, to the
line you have assumed as a meridian, and the distance by applying the scale.
Of course, in the above operation, the circle must be turned from the true
meridian in accordance with variation and leeway.
The instrument will be found very useful in plotting surveys, also in all
mechanical and architectural drawing, but its principal advantages are as
follows:-1st, the facility with which courses may be laid off on board ship,
which in the old way is attended with much trouble and liability to accumu
late an error in the process of what is called "fleeting" to or from a compass
of reference, particularly if your chart is old and-full of creases, or the table
on which your chart is spread is not freed from all rubbish; 2ndly, the expe-
ditious manner in which a ship's position can be ascertained on a chart from
cross bearings; 8rdly, its convenience in plotting a day's work, rendering it
unnecessary to keep a traverse table of corrected courses; 4thly, the facility

page_text: with which bearings between points can be determined; 5thly, the fact of its
doing away with the liability of applying the magnetic variation wrongly,
which, however careless it may appear, is often done.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Clark in the Great Seal Patent Office on the 18th
July 1861.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
CLARK, of 53, Chancery Lane, in the County of Middlesex, Engineer & Patent
Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Nineteenth day of January, in the year of our Lord
One thousand eight hundred and sixty-one, in the twenty-fourth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said William Clark, Her special licence that I, the said William
Clark, my executors, administrators, and assigns, or such others as I, the
said William Clark, my executors, administrators, and assigns, should at
any time agree with, and no others, from time to time and at all times
thereafter during the term therein expressed, should and lawfully might
make, use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN COMPASS PROTRACTORS," a communication from abroad by
Charles B. Wood, of New York, United States of America, upon the condition
(amongst others) that I, the said William Clark, my executors or administrators,
by an instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said Inven-
tion, and in what manner the same was to be performed, and cause the
same to be filed in the Great Seal Patent Office within six calendar months
next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said William Clark, do hereby declare the
nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement, reference being had to the Sheet of Drawings hereunto annexed,
and to the letters and figures marked thereon (that is to say):-
This Invention consists in the combination with ordinary parallel rulers of a
movable circle graduated as a compass, and divided into degrees, if desired, in
such a manner that by the combined operation of said circle and the parallel

page_text: rulers the operations of laying off courses on board ship and of locating a
ship's position in a chart from cross bearings, and also the operation of
plotting a day's work (rendering it unnecessary to keep a traverse table of
corrected courses), and the operation of ascertaining bearings between. points,
are greatly facilitated.
In the accompanying Drawing, Fig. 1 represents a face view of this Inven-
tion, and Fig. 2 is a sectional side elevation of the same; similar letters of
reference in both views indicate corresponding parts.
The instrument at present used for the purpose of laying off courses on
board ship, or for the purpose of locating a ship's position on a chart from
cross bearings; or for the purpose of determining the bearings of surrounding
objects, consists of ordinary parallel rulers. The use of these rulers requires
a tedious operation, and furthermore results obtained by the same are sub-
jected to serious and embarrassing errors. In laying off courses on board
ship with said parallel rulers, the operator is obliged to traverse the chart
from the position of the ship to the compass of reference (an operation
commonly known by the name of "fleeting" to or from a compass of
reference), which is laid out on the chart according to the truo meridian, &
then he has to calculate the magnetic course. In the meantime, perhaps, the
table is uneven, or some rubbish has got under the chart, and during the
operation the rulers may have slipped, and the result thus obtained will be
altogether erroneous. And in locating a ship's position from cross bearings, or
in determining the bearings of surrounding objects, it is necessary to traverse
the chart with the parallel rulers once for every bearing under all the incon-
veniences above pointed out, and for each bearing a separate calculation has to
be made, should magnetic bearings be required; all of which renders the
operation tedious, & liable to produce erroneous results.
:
All these difficulties are obviated by the instrument which forms the subject
of this Invention, and which consists of a pair of ordinary parallel rulers A
that are connected to a circle B by means of an arm being secured to the
centre of said circle by a screw pivot a and nut 6. The arm C is secured to
one arm of the rulers in such a manner that the outer edge of the ruler to
which the circle is attached shall be in a direct line with the centre of the
circle. The nut 6 serves for the purpose of clamping the circle when neces
sary. In using the instrument, the first thing-necessary to be understood is
how to place it in meridian, which is accomplished as follows:-Place the
north and south points, of the circle in a meridian line-on the east and west
points in a horizontal line; the circle now represents a true compass. To
make it represent a magnetic compass, simply turn the compass to the right

page_text: or left in accordance with the variation at the nearest point on the chart,
either easterly or westerly. The circle now represents a magnetic compass, &
whatever position the rulers may be in, either edge will show a magnetic
course, which is indicated by that edge of the ruler which is in line with the
centre of the circle. Now to lay off a compass course, say, north-east, place
the circle in the nearest meridian or line of longitude, turn it to allow for the
magnetic variation (also local, if there should be any), turn the ruler until it
indicates a north-east course, and open the rulers until the other arm reaches
the point from which you desire to lay your course. To locate position from
cross bearings, say from two points, one bearing north-east, the other east-
south-east, place the instrument in meridian as near the first point as conve-
nient, turn the circle in accordance with the variation, revolve the rulers until
they indicate north-east, open them until the first point is in contact, & draw
a line; apply the instrument in the same way to the second point, and draw
a line. The position of the ship will be shown by the intersection of these two
.lines.
To find the magnetic bearing between two points, place that arm of the
rulers which has the scale marked upon it upon the two points, as if for the
purpose of drawing a line between them; now open the rulers, and thus move
the circle until it is in meridian, turn the circle for variation, & read the
bearing.
To plot a day's work, having a list of your courses and their distances
before you, draw any straight line on a sheet of paper, and assume it as a
meridian, assume any point for a point of departure, & from it construct your
first course, taking the distanco from the scale on the rulers. The point
which marks your first distance now becomes another point of departure, from
which you can construct your second course, taking your distance from the
scale as before, and the point which marks the distance on the second course
becomes a point of departure for a third course, and so on. Now a line
drawn from the first point of departure to the point which marks the distance
on your last course, will be your course and distance made good. The course
of this line you will find by referring it by means of the instrument to the
line you have assumed as a meridian, & the distance by applying the scale.
Of course, in the above operation the circle must be turned from the true
meridian in accordance with variation & leeway. This instrument will be
found very useful in plotting surveys, also in all mechanical and architectural
drawing, but its principle advantages are as follows:-1st, the facility with
which courses may be laid off on board ship, which in the old way is attended
with much trouble and liability to accumulate an error in the process of what

page_text: is called "fleeting" to or from a compass of reference, particularly if your
chart is old and full of creases, or the table on which your chart is spread is
not freed from all rubbish; 2ndly, the expeditious manner in which a ship's posi-
tion can be ascertained on a chart from cross bearings; 3rdly, its convenience
in plotting a day's work, rendering it unnecessary to keep a traverse table of
corrected courses; 4thly, the facility with which bearings between points can
be determined; 5thly, the fact of its doing away with the liability of applying
the magnetic variation wrongly, which, however, careless it may appear, is
often done.
Having described the nature of this Invention and the manner of per-
forming the same, I declare that what I claim as the Invention to be protected
by the herein-before in part recited Letters Patent is, the combination with
ordinary parallel rulers A of a circle B graduated as a compass, and divided
into degrees, if desired, substantially in the manner and for the purposes herein
set forth.
In witness whereof, I, the said William Clark, have hereunto set my
hand and seal, this Seventeenth day of July, in the year of our Lord
One thousand eight hundred and sixty-one.