a ship at sea, also Applicable for Ascertaining the Error of the Compass.
Year: 1887

page_text: Date of Application, 7th Feb., 1887.
Complete Left, 15th Apr., 1887.
Complete Accepted, 27th May, 1887.
vi a ship at sea, also
Applicable for Ascertaining the Error of the Compass.
NORWOOD HARRISON (Master Marinor) Rock Hill House Folkestone Kent do hereby
declare the nature of this invention to be as follows :-
An Instrument for finding readily the total Correction (Deviation & Variation) of
the Mariners Compass from any three fixed objects, the positions of which are known;
it is also for use in placing accurately the position of a vessel without the aid of the
Mariners Compass.
DESCRIPTION.
A Disc of Wood or Metal (if of wood a circumference of metal) graduated on the
top and at the circumference to points and degrees, similar to a compass card.
Working on the centre of this Disc is a hand divided into two unequal lengths the
short part is of the same length as the radius of the Disc, it is pointed, for denoting
when used the points & degrees on the circumference of the Disc; the long part is
graduated to units and tenths; on this part slides a metal circle less the Sector of
about fifteen or twenty degrees. On or near the centre of this circle is an index
denoting the distance the centre of the sliding circle is from the centre of the Disc.
In addition to this hand (just described) there are two others working on their ends
at the centre of the Disc, forming as it were two movable arms, these are somewhat
longer (though their exact length is immaterial) than the radius of the Disc and aro
graduated on the same scale as the former (hand described).
On the centre of the sliding circle there are two hands these are longer by about
one third than the two hands on the centre of the Disc; they are also graduated from
the centre of the circle on the same scale as the others. The short ends of these hands
correspond in length to the radius of the sliding circle, and are intended to show the
angles formed by the long hands on the movable circle. These hands, excepting the
first mentioned, are tightened by screws when set to the angles required.
instrument may be considered as a quadrilateral shifting figure with graduated sides
The
working on the graduated Disc.
Now to find position of Ship and Compass Correction, say off South Foreland weather
cloudy and no sun or stars visible, but the South Goodwin Light, South Foreland
Lights and Dover pier Light visible.

page_text: The angle measured between 'South Foreland and South Goodwin Lights 60° and
between South Foreland and Dover pier Lights 70°. Simultaneously with observing
these angles the South Foreland Low-Light was observed to hear by compass N 26° E.
Now by reference to a chart or to a book of "position of Lights" it will be seen that
the South Goodwin bears from the South Foreland Low Light N 78° E (true) 3.4 miles,
and that the Dover pier Light bears from the South Foreland Low-Light S 54° W
(true) 2.8 m.
Lay one of the arms which move on the centre of the Disc to N 78° E and the
other to S 54° W and clamp them with the screws for the purpose. The centre of
the Disc now represents the South Foreland Low Light and the arms are pointing in
the direction of the South Goodwin and the Dover pier Lights.
Set the short arm of one of the long hands to 60° on the sliding circle & the other
hand to 70°, let the hand which is set to 70° be on that arm of Disc which points in
the direction of Dover pier Light & the other on the arm which points to the South
Goodwin, now clamp them at the centre of sliding circle and work the circle in or out
as required until one hand having the angle set to 70° cuts on the arm of Disc at 2.8
which represents the position of Dover pier Light, and the other long hand which is
set to 60° cuts on 3.4, which represents the position of South Goodwin Light. Now
it will be seen the pointed end of long hand on the Disc is directed to N 13° W-(the
true bearing of the South Foreland Low Light) & on the long arm which cuts
the position of the South Goodwin Light will be seen at the point of intersection 4 the
distance in miles from that Light, and at the point of intersection (at the position of
the Dover pier Light) on the other hand will be seen 2.85 the distance from that place
in miles.
As the true bearing of the South Foreland Low Light was found to be N 13° W.
(true) and the Compass bearing N 26° E. a total correction (Deviation & Variation
combined) of 39° westerly is the result found.

page_text: Applicable for Ascertaining the Error of the Compass.
NORWOOD HARRISON R.N.R. Rockhill House Folkestone Kent Master (extra)
Mariner do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement:-
In reference to Drawing a. a. a disc of metal or wood (if of wood to have a metal
rim b. b. b). bbb is graduated on inner & outer concentric rings to points & degrees.
c. c. a hand working on the centre of disc a. a. the short end of which is pointed and
equal in length to the radius of the inner graduated ring. The long end of c. c. is
graduated to units and tenths and is about 15 to 18 units in length (on the drawing
the units equal .32 of an inch). On this long end of ce slides a metal skeleton like
circle dd which is also graduated to points & degrees, (this circle is about 11 units in
diameter) a segment of about 20 degrees is cut out of this circle on the part of
circumference nearest to centre of disc. On the centre of the circle d. d. are two
movable hands, e. e. these are also graduated to about 18 units, the short ends of these
hands are marked and are for the purpose of measuring the degrees and points on
the "sliding" circle d d.
Near the centre of the "sliding" circle is a small cutter or index g for showing the
distance the centre of d d is from the centre of disc.
Working on the centre of the disc and above the hand c. c. are two movable arms
(each 15 units in length), h. h. these are graduated on the same scale as those already
mentioned. These arms have each an index i fitted to it for denoting the number of
points or degrees on the outer graduated rim of dise; these points or degrees will
also be shown by the opposite edge of h on the inner graduated circle of disc. The
outer graduated ring is for denoting accurately the angles which the arms h h make
from the North or South towards the East & West. is a screw for disconnecting
& connecting the circle dd from the sliding radius kas required 11 are screws for
disconnecting when required the short ends from the long hands ee.
The arms hh. are sufficiently raised from the surface of disc to admit of the sliding
circle dd working under them when required.
The arms on the centre of the disc & the hands on the centre of sliding circle, when
set to the required angles are secured by tightening down the thumb screws m. m.
these thumb screws are shown on a side view at the lower part of the drawing.
Directions for use. To find Compass Error (or total Correction) also position of
Ship. A Light House bears from a beacon N 791° W. 10.4 miles, and a Light Ship
bears from the same beacon S 58° E. (4.5 miles) (both true bearings) on passing N. Ed.
of these marks simultaneous angles between them are taken, that between beacon &
Lt. Ho. is 25° & between beacon & Lt. Ship 37°-Set the arms hh on the disc, one
to N 791° W & one to S 581° E & clamp them with screws m. m. Now fix ff the

page_text: short ends of the long hands ee on the sliding circle to the angles 251° & to 37°, so
that 25 will be on the opposite side of c. c that the arm which lies in the direction of
Lt. Ho. is to cc-& fix 37 on the opposite side. Now move the circle up & down ec
and move cc to the right or left as required until the long hands on ee cut h. h. the
positions of Lt. Ho. and Lt. Ship, 10.4 and 4.5. It will now be seen that the Beacon
bears S 58° W (true); this is shown by the pointed end of c c on the inner graduated
ring of the dise; the difference between this & the compass bearing is of course the
error or correction of the compass. The distance of the beacon from the ship will
be 7.3 as shown by the small index g on c. c. and the respective distances from Lt. Ho.
& Lt. Ship will be shown on e. e. 16.5 and 6.6. Many other useful problems in
navigation can be readily worked by this instrument; it is also applicable for solving
problems in oblique angled trigonometry & is a most valuable instrument for the Coast
Navigator & Nautical Surveyor.
Having now particularly described and ascertained the nature of my said Invention
and in what manner the same is to be performed I declare that what I claim in this
said Invention is novel in its entireness.