IMPROVEMENTS IN THE MARINER'S COMPASS AND IN THE MEANS FOR PROVISIONAL SPECIFICATION FOR ASCERTAINING AND CORRECTING ITS ERRORS
Year: 1883

page_text: LETTERS PATENT to Sir William Thomson Knight of Glasgow College,
Doctor of Laws and Professor of Natural Philosophy in the University and
College of Glasgow in the County of Lanark North Britain for an Invention
of "IMPROVEMENTS IN THE MARINER'S COMPASS AND IN THE MEANS FOR
PROVISIONAL SPECIFICATION left by the said Sir William Thomson at
the Office of the Commissioners of Patents on the 8th December 1883.
Sir WILLIAM THOMSON Knight of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow in
the County of Lanark, North Britain " IMPROVEMENTS IN THE MARINER'S
COMPASS AND IN THE MEANS FOR ASCERTAINING AND CORRECTING ITS ERRORS
"
This Invention, which relates to Improvements in the Mariners Compass and in
the means for ascertaining and correcting its errors, consists as follows:-
First. An improvement in the appliance for taking bearings on the same
principle as the Azimuth mirror described in the Specifications filed in pursuance
of a certain proviso in two previous Patents granted to me and respectively
numbered 1339 A.D. 1876 and 4876 A.D. 1876.
Second. An improvement in the compass card.
Third. An improvement in the correctors for correcting the semicircular error.
Fourth. Improvements in the Compass bowl.
The improvement in the azimuth mirror consists in the substitution of a totally
reflecting prism instead of an ordinary mirror as described in my aforesaid Specifica-
tions. The advantages of the prism are (First) It does not absorb so much light as
the mirror and allows of objects being seen more distinctly when there is not much
light or when they are at a great distance, (Second) In the azimuth instrument
with mirrors it has been found that, when exposed to much wet or damp, the
silvering of the mirror comes off. With the prism this defect is entirely done
away.
The prism is made so as to be able to turn round on a horizontal axis so that
bearings can be taken either by reflecting the object in the prism and looking

page_text: direct through the lens at the degrees of the compass card or by reflecting the
degrees of the card in the prism and looking over the prism at the object the
bearing of which is required.
Another improvement in the Azimuth mirror is the use of an eccentric lens to
facilitate the adjustment of the instrument.-I also arrange the instrument so as
to be able to use two or more lenses of different focal length, one for taking bearings
of objects on the horizon and the others for taking bearings of Sun or Stars at
different altitudes.
The improvement in the compass card consists in the construction of the degree
divisions so that they can be used for steering and read off by direct numbers
engraved on a circle while each degree has its number engraved on it inverted so
that when seen by the inverted method of using the azimuth mirror each number
is seen correctly and can be read without difficulty even though only three or four
degrees are seen simultaneously in the field of the mirror and lens.
The improvements in the correctors for correcting the semicircular error consist
in placing the fore-and-aft magnets and thwart-ship magnets in holes nearly
through the centre of the binnacle.-Two vertical rows of fore-and-aft magnets are
used, one row on each side of the middle of the binnacle.-One vertical row of
thwart-ship magnets is used.-The thwart-ship and fore-and-aft holes are bored
alternately so that each thwart-ship magnet when in position may have fore-and-
aft magnets above and below it.-To close in the ends of the magnets and prevent
them being taken out of position I use a revolving metal shutter which turns round
to shut in the magnets and is secured in proper position by lock and key.
The improvement in the bowl is the addition of receptacles fixed in its bottom
for holding quicklime for the purpose. of keeping the air inside dry and preventing
the deposition of moisture on the glass cover.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Sir William Thomson in the Patent Office on the 7th June 1884.
Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow in
the County of Lanark, North Britain "IMPROVEMENTS IN THE MARINER'S
COMPASS AND IN THE MEANS FOR ASCERTAINING AND CORRECTING ITS ERRORS
"
My said Invention, which relates to improvements in the Mariner's Compass and
in the means for ascertaining and correcting its errors, consists as follows:-
First. An improvement in the appliance for taking bearings on the same
principle as the Azimuth Mirror described in the Specifications filed in pursuance
of a certain proviso in two previous Patents granted to me and respectively
numbered 1339 A.D. 1876 and 4876 A.D. 1876.
Second. An improvement in the Compass Card.
Third. An improvement in the correctors for correcting the semicircular error.
Fourth. Improvements in the Compass bowl.
The improvement in the azimuth mirror consists in the substitution of a totally
reflecting prism instead of an ordinary mirror as described in my aforesaid
Specifications. The advantages of the prism are (First) It does not absorb so much
light as the mirror and allows of objects being seen inore distinctly when there
is not much light or when they are at a great distance-(Second) In the azimuth
instrument with mirrors it has been found that, when exposed to much wet or
damp, the silvering of the mirror comes off.-With the prism this defect is entirely
avoided.
The prism is so made as to be able to turn round on a horizontal axis so that
bearings can be taken either by reflecting the object in the prism and looking
direct through the lens at the degrees of the compass card, or by reflecting the
degrees of the card in the prism and looking over the prism at the object, the
bearing of which is required."
Another improvement in the azimuth mirror is the use of an eccentric lens to
facilitate the adjustment of the instrument.-I also arrange the instrument so as
to be able to use two or more lenses of different focal length, one for taking bearings
of objects on the horizon and the others for taking bearings of Sun or Stars at
different altitudes.
The improvement in the Compass Card consists in the construction of the degree
divisions so that they can be used for steering and read off by direct numbers
engraved on a circle, while each degree has its number engraved on it inverted
so that when seen by the inverted method of using the azimuth mirror each
number is seen correctly and can be read without difficulty, even though only
three or four degrees are seen simultaneously in the field of the mirror and lens.
The improvements in the correctors for correcting the semicircular error consist
in placing the fore-and-aft magnets and thwart-ship magnets in holes nearly
through the centre of the binnacle.-Two vertical rows of fore-and-aft magnets are
used, one row on each side of the middle of the binnacle.--One row of thwart-ship
magnets is used.-The thwart-ship and fore-and-aft holes are bored alternately so
that each thwart-ship magnet when in, may have fore-and-aft magnets above and
below it. To close in the ends of the magnets and prevent them being taken out
of position I use a revolving metal shutter which turns round to shut in the
magnets, and is secured in proper position by lock and key.
The improvement in the bowl is the addition of receptacles fixed in its bottom
for holding quicklime for the purpose of keeping the air inside dry and preventing
the deposition of moisture on the glass cover.
Le.
t
:

page_text: And in order that my said Invention may be properly understood I now proceed
more particularly to set forth the system, mode or manner, in' or under which the
same is, or may be used or practically carried into effect, reference being had to the
accompanying Drawings and to the letters and Figures marked thereon, that is to
say:―
In carrying out the first part of my present Invention I construct the azimuth
mirror as represented at Figure 1, in side elevation; at Figure 2, in plan; at
Figure 3, in end elevation; and at Figure 4, in part elevation of the side opposite
to that represented at Figure 1.
The improvement in the azimuth mirror represented at these Figures, consists in
the substitution of the totally reflecting prism a, for the ordinary mirror such as
has been used heretofore for azimuth mirrors.-This prism a, is mounted in the
frame b, which is supported by the bearings c, secured to the body of the
instrument. The shaft d, to which the frame b, is connected is pressed into its
bearings by means of the springs e.-This construction of the instrument admits of
the prism a, being turned round a horizontal axis so that bearings can be taken
either by reflecting the object in the prism and looking direct through the lens,
represented in dotted lines at f, at the degrees of the Compass card or by reflecting
the degrees of the card in the prism a, and looking over the said prism a, at the
object, the bearing of which is required.
Another improvement in the azimuth mirror consists in the employment of the
eccentric lens f, to facilitate the adjustment of the instrument. By the word
eccentric, it is to be understood that the centre of the lens f, is not concentric with
that of the tube g, containing the said lens f.-A further improvement consists in
arranging the instrument so as to admit of the use of two or more lenses of
different focal length.-This form of instrument is represented in part side elevation
at Figure 5, and a lens detached from the said instrument is represented in plan at
Figure 6. With reference to these Figures, it will be seen, that the tube g, is
provided with the openings h, for the reception of the lenses f, one of which is
shewn in position within the said tube g.-The lenses f, are mounted in the frames i,
which are provided with the binding screws j, for securing the lenses within the
tube g, when in their proper position. Of the openings h,the upper one is used for
the lens f, when the bearings of the Sun or Stars or other objects at high altitudes
are required, and the lower one is used for a similar lens of shorter focal length,
when the bearings of objects on the horizon are required.
The improvement in the compass card as represented in plan at Figure 7, and in
side elevation at Figure 8, consists in the construction of the degree divisions in
such a manner that they can be used for steering and read off by direct numbers
engraved or otherwise marked on a circle as shewn by the large figures marked
on the Compass Card represented at Figure 7, while each degree has its number
inverted engraved or otherwise marked upon it as shewn by the small figures at
Figure 7, so that when seen by the inverted method of using the azimuth mirror
each of the small numbers is seen correctly and the bearing of an object can be
read off without difficulty, even though only three or four degrees are seen
simultaneously in the field of the mirror or prism a, and lens f.
The improvements, in the correctors for correcting the semicircular error, as
represented in front elevation at Figure 9, and at Figure 10, in transverse section
taken on the line A, B, Figure 9, consist in placing the fore-and-aft magnets k, and
thwart-ship magnets l, in holes nearly through the centre of the binnacle m.- _Two
vertical rows of the fore-and-aft magnets k, are used, one on each side of the centre
of the binnacle; and one vertical row of thwart-ship magnets l, are used.-The
holes for the reception of the fore-and-aft and thwart-ship magnets are bored
alternately, so that each fore-and-aft magnet may have thwart-ship magnets above
and below it and vice versa.-To close in the ends of the magnets k, and I, and
prevent them being taken out of position, I use the revolving metal shutter n,
which is provided at a part of its circumference, with an opening as represented in
dotted lines at o, at Figure 9, of the accompanying Drawings, through which

page_text: opening the magnets ke, and I, may be drawn after the shutter n, has been turned
round into the necessary position.-The staples p, are provided on the binnacle
standard m,
and the staples, are also provided on the revolving shutter n.―These
staples afford the means for securing the magnets in position either by the
employment of two padlocks, or as represented at Figures 9, and 10, of the
accompanying Drawings, by the bolt 8, with the end of which the padlock t, is
caused to engage; or the revolving shutter n, may be secured in position by any
other suitable means.
The improvement in the compass bowl consists in the addition of a receptacle or
receptacles formed in the bottom of the said bowl, for holding quicklime for the
purpose of keeping the air inside dry and preventing the deposition of moisture on
the glass cover.-This improvement is represented at Figures 11, and 12, as applied
respectively to the compass bowls of a standard binnacle and for a wheel-house
binnacle both of which are represented in section at these Figures.-In these
Figures, it is shewn that the receptacle is formed by the perforated plate u,
between which and the plate v, of the bowl proper, the quicklime w, is placed.
Having now described and particularly ascertained the nature of my said
Invention and the system, mode or manner in or under which the same is or may
he used or practically carried into effect, I would observe in conclusion that
what I consider to be novel and original and therefore claim as the Invention
secured to me by the bereinbefore in part recited Letters Patent is :-
First: The improved Azimuth mirror_as hereinbefore described and shewn at
Figures 1, to 6, inclusive of the annexed Drawings.
Second: The improved marking of the Compass Card as herein before described
and shewn at Figures 7, and 8, of the annexed Drawings.
Third The improvement in placing the correctors in the binnacle, and the
revolving shutter for closing the same in the magnet holes as herein before described
and shewn at Figures 9, and 10, of annexed Drawings.
Fourth The improvement in the compass bowl consisting in providing a
receptacle or receptacles for holding quicklime for the purpose of keeping the air
inside the compass box dry substantially as hereinbefore described and shewn at
Figures 11, and 12, of the annexed Drawings.
In Witness Whereof I, the said Sir William Thomson have hereunto set my
hand and seal this fifth day of June in the year of our Lord One thousand eight
hundred and eighty four.
WILLIAM THOMSON
(L.S.