IMPROVEMENTS IN ASCERTAINING THE ERRORS OF MARINERS' COMPASSES
Year: 1856

page_text: LETTERS PATENT to Stephen Martin Saxby, of Rock Ferry, in the
County of Chester, Gentleman, for the Invention of "IMPROVEMENTS IN
ASCERTAINING THE ERRORS OF MARINERS' COMPASSES."
Sealed the 2nd January 1857, and dated the 10th July 1856.
PROVISIONAL SPECIFICATION left by the said Stephen Martin Saxby at
the Office of the Commissioners of Patents, with his Petition, on the
10th July 1856.
I, STEPHEN MARTIN SAXBY, of Rock Ferry, in the County of Chester,
Gentleman, do hereby declare the nature of the Invention for "IMPROVEMENTS
IN ASCERTAINING THE ERRORS OF MARINERS' COMPASSES," to be as follows:-
The Invention consists in the applying of a transparent or translucent
diagram concentrically upon another diagram, each of these being ruled in
such manner as (by turning either one of them on its centre) to cause inter-
sections of some of the lines drawn thereon, by means of which intersections
various difficult problems in spherical trigometry can be answered by inspec-
tion. The instrument, whether of cardboard, metal, glass, talc, &c., is specially
useful in very readily giving the true amount of compass error by simple
inspection (particularly useful on board iron ships) at any hour of the day or
night when a known heavenly body is visible.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Stephen Martin Saxby in the Great Seal Patent Office
on the 7th January 1857.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, STEPHEN
MARTIN SAXBY, of Rock Ferry, in the County of Chester, Gentleman, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Tenth day of July, in the year of our Lord One
thousand eight hundred and fifty-six, in the twentieth year of Her reign, did,
for Herself, Her heirs and successors, give and grant unto me, the said
Stephen Martin Saxby, Her special licence that I, the said Stephen Martin
Saxby, my executors, administrators, and assigns, or such others as I, the
said Stephen Martin Saxby, 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 "IMPROVE-
MENTS IN ASCERTAINING THE ERRORS OF MARINERS' COMPASSES," upon the condition
(amongst others) that I, the said Stephen Martin Saxby, 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 Invention, 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.
1
NOW KNOW YE, that I, the said Stephen Martin Saxby, do hereby
declare the nature of the said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say:-
The object of my Invention is to offer a remedy for the evils from local
attraction which affect the compasses of iron ships, and to apply the same
Invention to the simplifying the art of navigation, and nautical astronomy
generally, by diminishing necessity for calculation.
My Invention consists in the placing of a spheric diagram made of trans-
parent substance upon another spheric diagram, and in the turning of one
diagram upon another, and in thus causing the intersection of the lines which
are drawn upon each, by which it is easy to measure sides and angles of
triangles.

page_text: My method of using this Invention is, for instance, thus:-Having the
ordinary data for solving a triangle given, I place such data partly on one
diagram and partly on the other, as convenient, and then by moving the
one diagram upon the other, the one being attached to the other, I cause
certain lines, such as meridians, rhumbs, parallels, or other right or oblique
circles so to intersect in each diagram as to shew plainly, and measure by
inspection the result desired. From the peculiar use in spherics of this
arrangement, I call it a "spherograph." As an example, if I desire to
ascertain the error of a ship's compass, I find the true azimuth of a heavenly
body by the spherograph in the following manner:-The latitude, time, and
declination (or any other three clements) -being- given, I, for instance, raise
the pole of the under sphere above the horizon of the upper sphere according
to the latitude; then, tracing the finger along the hour circle or meridian of
the under sphere till I reach the parallel of given declination, I notice what
azimuth circle on the upper or transparent spheric diagram cuts this inter-
section of the so given time and declination, then this azimuth circle indicates
the true bearing of the heavenly body; and this being compared with the
compass bearing of the same heavenly body, the deviation is the compass
error. I use the different lines of the ordinary sphere in different diagrams
to suit different purposes, according to the elements or arguments given, or as
most-adapted to the object in view; as, for example, where the true azimuth
of a star is required, I revolve one diagram, which has the stars or planets
delineated spherically upon it, upon another surface having the hours marked
thereon, and thus I find at once by inspection the star's distance from the
meridian of the place, and enter the spherograph with such distance as if it
were time from noon, and then proceed to find the azimuth as if I were
using the sun, as before described. The spherograph furthermore greatly
simplifies great circle sailing from the facilities it affords for measuring by
inspection the angles and sides of the spheric triangles on which such
"sailing" depends. One form of the spherograph is capable of working all
such questions; but to suit the needs and convenience of navigators and
students, the spherograph is divided into "parts," each having ample in-
struction and a "key" attached thereto, whereby to fully enable persons to
understand and use it.
Having now described my Invention, and the mode of using it, in such
plain terms that any one who is conversant with the known doctrines of the
sphere can fully comprehend it, I will now describe the Drawings attached
hereto for illustration.

page_text: Figure 1 represents a sphere on stereographic projection, and has meridians
and parallels of latitude drawn, the former through every fifth degree, the
latter through every second degree. Figure 2 represents a stereographic
delineation of azimuth circles and almacanthars, on a semicircle of which
the diameter represents the horizon. Figure 3 represents the usual sphere
drawn to a time and place, and illustrates the other diagrams. Either the
one or the other may be transparent, and I attach them loosely but accurately
by their centres. According to the data presented I turn the one figure upon
the other until the things given (or marked thereon for the moment) upon the
one figure or diagram coincide with or intersect that which is given in the
other, and thus spheric triangles are easily formed and measured by inspection
by means of the forms given to the spherograph to suit each case.
I specially claim as my Invention the using of spheric diagrams with a
central or limited motion for the measuring of sides and angles of spheric
triangles such as that of which an azimuth circle forms one side, one such
diagram being composed of translucent or transparent substance or substances.
In witness whereof, I, the said Stephen Martin Saxby, have hereunto
set my
hand and seal, this First day of January, in the year of our
Lord One thousand eight hundred and fifty-seven.
Witness,
ALEX. Ross, of Liverpool.
S. M. SAXBY. (L.S.)