IMPROVEMENTS IN MARINERS' COMPASSES
Year: 1856

page_text: LETTERS PATENT to Charles Robertson, of 68, Mark Lane, Ship Master,
for the Invention of "IMPROVEMENTS IN MARINERS' COMPASSES."
PROVISIONAL SPECIFICATION left by the said Charles Robertson at
the Office of the Commissioners of Patents, with his Petition, on the
19th January 1856.
I, CHARLES ROBERTSON, of 68, Mark Lane, Ship Master, do hereby declare
the nature of the Invention for "IMPROVEMENTS IN MARINERS' COMPASSES" to
be as follows :-
The object of my Invention is to enable the navigator to detect at any time
the amount of variation and deviation of the compass in iron and other ships.
On the glass which covers the compass card an index or pointer is mounted,
which turns on a centre in the middle of the glass. On this index a style is
mounted, from which a shadow is thrown by the sun, and the index is set to
the direction of the shadow, which, if the time be noon, will be due north and
south, and at any other time the due north and south is readily calculated
from the direction of the shadow. There is also a sight placed at the end of the
index, by which the direction of the sun is directly observed, and-the index set
accordingly when the sun is near the horizon.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Charles Robertson in the Great Seal Patent Office on the
12th July 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
ROBERTSON, of 68, Mark Lane, Ship Master, 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 fifty-six, in the nineteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Charles Robertson, Her special licence that I, the said Charles
Robertson, my executors, administrators, and assigns, or such others as I,
the said Charles Robertson, 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 "Iм-
PROVEMENTS IN MARINERS' COMPASSES," upon the condition (amongst others) that
I, the said Charles Robertson, my executors or administrators, by an instru-
ment 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.
,
NOW KNOW YE, that I, the said Charles Robertson, 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 enable the navigator to detect at any
time the amount of variation and deviation of the compass in iron and other
ships. On the glass which covers "the compass card an index or pointer is
mounted, which turns on a centre in the middle of the glass. On this
index a style is mountod, from which a shadow is thrown by the sun,
and the index is set to the direction of the shadow, which; if the time
be noon, will be due north and south, and at any other time the due north
and south is readily calculated from the direction of the shadow. There is
also a sight placed at the end of the index, by which the direction of the
sun is directly observed, and. the index set accordingly when the sun is near
the horizon.

page_text: DESCRIPTION OF THE DRAWING.
Figure 1 shows a vertical section of the instrument, and of the compass on
which it is mounted; Figure 2 is a plan of the same parts. a is the glass
which covers the compass card, having at its centre the brass socket b; c is an
index or pointer, made of brass, and whitened or enamelled on its surface to
render the shadow clearly visible; d is a pin, fixed to the pointer c; it works
freely in the socket b; e is a vertical style, fixed to the index or pointer c;
at c' the pointer is made wide, as shown, to receive the shadow of the style.
When observing the shadow of the style, c is brought to correspond with the
black line on the index or pointer, and then the direction of the pointer is
compared with the compass card below, and the difference either is or readily
gives (according to the time of observation) the amount by which the north
of the compass differs from the true north. 9 is a joint which fits on the end
of the style to lengthen the shadow when the instrument is used in low
latitudes; h is a sight point, which is used when observing the sun directly
when near the horizon, the shadow being then too faint to allow of an accurate
result being obtained from it; and when thus observing, a piece of colored glass
is interposed between the sun and the eye to moderate the light. The instru-
ment is shown at Figure 3; it consists of a frame i, containing the piece of
colored glass, and turning about a centre i¹ on the socket 2, which fits on to
the style e.
Having thus described the nature of my Invention, and the manner of
performing the same, I would have it understood that I do not confine myself
to the exact details described; but what I claim is, the use of an index or
pointer carrying a style, and mounted over and independant of the compass
card, as described.
In witness whereof, I, the said Charles Robertson, have hereunto set
my hand and seal, this Nineteenth day of May, in the year of our
Lord One thousand eight hundred and fifty-six.