AN IMPROVED MODE OF AND APPARATUS FOR FACILITATING THE CALCULATIONS. REQUIRED FOR NAVIGATING SHIPS OR VESSELS
Year: 1859

page_text: LETTERS PATENT to John Barker Berger, of Upper John Street, Fitzroy
Square, in the County Middlesex, Master Mariner, for the Invention of
"AN IMPROVED MODE OF AND APPARATUS FOR FACILITATING THE CALCULATIONS.
REQUIRED FOR NAVIGATING SHIPS OR VESSELS."
Sealed the 3rd February 1860, and dated the 29th November 1859.
PROVISIONAL SPECIFICATION left by John Barker Berger at the Office
of the Commissioners of Patents, with his Petition, on the 29th
November 1859.
I, JOHN BARKER BERGER, of Upper John Street, Fitzroy Square, in the
County of Middlesex, Master Mariner, do hereby declare the nature of the
said Invention for "AN IMPROVED MODE OF AND APPARATUS FOR FACILITATING
THE CALCULATIONS REQUIRED FOR NAVIGATING SHIPS OR VESSELS," to be as
follows:-
My Invention of an improved mode of and apparatus for facilitating the
calculations required for navigating ships or vessels relates to a novel or
improved mode of ascertaining the true course in which to steer a ship or
vessel in any latitude when it is required to sail, upon the principle known as
great circle sailing. Every navigator who has been in the habit of navigating
vessels upon the principle of great circle sailing knows, that as the latitude

page_text: and longitude of a vessel sailing from port to port on the great circle is con-
tinually changing, abstruse and intricate calculations are required to ascertain
the precise course in which it is necessary to steer a vessel in order to keep
her on the great circle, which is, of course, the shortest and most direct line
from point to point.
My improved mode of ascertaining the true course in which to sail a sh.
consists in taking the proper bearings direct from a moveable compass card, or
other equivalent contrivance adapted to a chart, upon which the changing
position of the vessel may be marked from time to time when required to take
an observation.
In carrying out my Invention I prefer to employ a 'spherical or hemi-
spherical surface as my chart, as that form more closely resembles the true
form of the earth than any flat projection, which is more or less liable to error.
Taking, for instance, a hemisphere on which the parallels of latitude and the
meridians of longitude are permanently marked, together with an outline,
if desired, of continents, islands, and other physical features which may be
useful to refer to by the mariner, I prepare a plate on which are to be
accurately marked all the points of the mariner's compass. This compass card
or plate is to be adapted to the pole or zenith of the hemisphere, or to both
poles in the case of a sphere, and is so contrived, that it may be turned round
with facility on its centre on a pin or stud placed there for the purpose. A
quadrant of altitude accurately divided on its bevilled edge is also adapted to
the pin or stud of the compass card, and may be freely turned on the centre
thereof.
In order to make use of my mode of and apparatus for ascertaining the
true course to sail a ship on the great circle, the first operation is by means of
the quadrant (which for this purpose must be removed from the compass
card), to draw on the globe or spherical surface a straight line from the point
or port of departure to the point or port desired to be reached. This line will
be the great circle which it is desired to follow. In order to ascertain the
proper course to steer, so as to follow this line, the exact position (that is, the
true latitude and longitude,) of the ship on any point of this line or great circle
must be first ascertained in the ordinary manner, and marked on the spherical
surface, then place the nut of the quadrant upon the central stud or pin of the
compass card, and bring the graduated edge of the quadrant over the exact
spot where the ship happens to be at that moment, and turn the compass card
until the north pole (supposing the ship is in the southern hemisphere) points
directly to the place where the ship is (that is in a line coincident with tho
graduated edge of the quadrant). If the ship happens to be in the northern

page_text: hemisphere, the south pole of the compass must be directed to the ship's place
on the globe or spherical surface; then, with a curved parallel rule, or other
suitable contrivance, ascertain the line of the compass which is exactly parallel
to the ship's course as laid down on the sphere; this line of the compass will
of course be a line that is drawn across the compass card and passes through
the centre thereof, of course as the ship sails along the line, the course to be
steered by the compass is continually altering, and therefore precisely similar
observations must be made from time to time, say, after having run forty or
fifty miles or more, otherwise the ship will get out of her course. Should it
be found, by taking the latitude and longitude of the ship's place, that she has
got or been driven out of her course, either by making lee-way, or through
baffling winds, then her new course from her actual position to the port of
arrival must be laid down afresh on the globe, and the observations and
calculations made from that line instead of the one previously made, which
must be rubbed out.