IMPROVEMENTS IN MARINERS' AND AZIMUTH COMPASSES
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by the said James Readman at the
Office of the Commissioners of Patents on the 1st December 1880.
JAMES READMAN, of Norton, in the County of Durham. "IMPROVEMENTS IN
MARINERS' AND AZIMUTH COMPASSES."
In mariners and azimuth compasses as now made and used the motions of the
compass cards produce currents of air within the compass bowl, so that the compass
cannot be relied upon to give a true indication.
The object of my Invention is to remedy this defect, and for this purpose I
cause the compass card to move in a vacuum, so that being shielded from external
influences the north pole of the magnetic needle will then always point truly to the
north magnetic pole of the earth. In carrying out my Invention I cover the
compass bowl hermetically with a sheet of plate glass of sufficient strength to bear
the atmospheric pressure, and then by means of an air pump or suitable exhausting
apparatus I produce as perfect a vacuum as possible within the compass bowl.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said James Readman in the Great Seal Patent Office on the
26th May 1881.
JAMES READMAN, of Norton, in the County of Durham.
MARINERS AND AZIMUTH COMPASSES."
"IMPROVEMENTS IN
In mariners and azimuth compasses as now made and used the motions of the
compass cards produce currents of air within the compass bowl, so that the compass
cannot be relied upon to give a true indication.

page_text: The object of my Invention is to remedy this defect, and for this purpose
I cause
the compass card to move in a vacuum, so that being shielded from external
influences the north pole of the magnetic needle will then always point truly to
the north magnetic pole of the earth. In carrying out my Invention I cover the
compass bowl hermetically with a sheet of plate glass of sufficient strength to bear
the atmospheric pressure, and then by means of an air pump or suitable exhausting
apparatus I produce as perfect a vacuum as possible within the compass bowl. As
the card can be moved with much less power than those which move in air or
other medium, much lighter needles can be employed than those hitherto used.
One manner in which my Invention may be carried into effect is represented in
Figure 1 of the annexed Drawings, which is a vertical section of a mariner's
compass; a is the bowl, and b the card pivoted in any ordinary manner; c is a
sheet of plate glass with which the bowl is hermetically covered, and which is
strong enough to bear the atmospheric pressure; d is a screw ring to secure the
plate c in position. In the bottom of the bowl I drill a vertical hole e about th of
an inch in diameter, more or less, also a horizontal hole e¹ of like diameter,
extending from the side of the bowl to the bottom of the hole e. I then make the
hole e' of conical form, as shown, and I insert into it a brass or other soft metal
tube f, the inner end of which I solder into the hole e'. The glass c, having been
secured in place, I connect the tube with an air pump and produce a vacuum in
the bowl a. When the vacuum is formed I compress the sides of the tube f, as
indicated in dotted lines, by means of pliers or other suitable tool, so as to her-
metically close it, and I then sever the tube outside the compression; after which
I solder up the hole e¹ so as to make it flush with the surface of the bowl. Some-
times in order to ensure that the closing of the tube by the pliers shall be hermetic,
I varnish the inside of the tube before inserting it into the hole e.
Figure 2 represents in vertical section, and Figure 3 in elevation taken at right
angles to Figure 2, a somewhat modified way of carrying my Invention into effect;
is a hoop or ring which exactly fits the outside of the bowl. I drill a hole e, e¹,
through the hoop g and through the side of the bowl a, and I screw or otherwise
fix into the hole e¹ in the hoop a tube f which I connect with the air pump. After
having produced the required vacuum in the bowl I turn the hoop g partly round,
so as to bring an unperforated part opposite the hole e and thereby close the hole ;
to ensure that the closing shall be hermetic, part of the hoop moved over the hole
may be faced with leather or other like suitable material. I then fix the hoop in
place by running solder into the hole e' and into 3, or other suitable number of
other holes e² which I form for the purpose in the hoop.
Having now described the nature of my said Invention, and in what manner the
same is to be performed, I declare that I claim,―
Making mariners' and azimuth compasses in such manner that their cards move
in a vacuum, substantially as hereinbefore described.
In witness whereof, I, the said James Readman, have hereunto set my
hand and seal, this Twenty fourth day of May, One thousand eight hundred
and eighty one.