Improvements relative to the Sun Compass for Rendering it Suitable as Correction Apparatus directly connected with the Magnetic Compass
Year: 1897

page_text: Date of Application, 19th Nov., 1897-Accepted, 24th Dec., 1897
COMPLETE SPECIFICATION.
"Improvements relative to the Sun Compass for Rendering it
Suitable as Correction Apparatus directly connected with the
Magnetic Compass."
I, CHRISTIAN NILSEN EITREM of Krageo Norway Master Mariner do hereby
declare the nature of this invention and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement:
The sun compasses with bearing taking device for ascertaining the deviation of
a magnetic compass from the proper variation direction have all heretofore been
so constructed that they had first to be adjusted according to the diametric plane of
the vessel in some part of the deck suitable for observation. But in these sun
compasses it is very difficult to make a wholly correct deviation trial. To bring
the steering line of the sun compass in line with the diametrical plane of the vessel
requires even a very exact adjustment and when the vessel rolls it is almost im-
possible to avoid that the sun compass is shifted more or less out of its adjustment,
so that the calculations have become more or less unreliable. These observations
have besides been so much more laborious because the reading of the sun compass
and the reading of the magnétic compass have to be done in two places, requiring
at least two men for making a deviation trial.
In the present invention these inconveniences and defects are obviated by so
arranging the sun compass, that it can be used in combination with the magnetic
compass the former with its bearing taking device serving as a correction apparatus
which after the usual calculations and bearing takings itself directly indicates the
deviation.
The arrangement and application of a sun compass are supposed to be known
and in the sequel I shall only describe. the improvements and arrangements in
connection with it for attaining the object here in view.
Fig 1 of the accompanying drawings is a part sectional elevation of an ordinary
magnetic compass with superposed improved sun compass and bearing taking
device. Fig 2 is a plan of same, and figs 3 and 4 details.
The most characteristic part of this sun compass is the foundation part. This
is suitably made in the form of a metal cross a having its four ends bent down as
at b where set screws c are provided for fixing it to the bowl d which surrounds the
magnetic steering compass; and as the latter always has a fixed exactly adjusted
position in the length axis of the vessel, and its fixed steering line e always
practically exactly coincides with the diametric plane of the vessel it will be under-
stood that the foundation plate a very readily can be adjusted according to that
plane, as the wire or hair line f stretched diametrically over the cross a has only
to be made to coincide with the steering line e of the compass bowl, see fig 2. The
sun compass is furthermore arranged horizontally as the heeling pivots of the
steering compass become common for both compasses. The cross a has a central
pivot upon which is placed the rose h of the sun compass, with intermediate
discs and and also the socket fitting well on the pivot and screw threaded out-
side. Upon the disc i is placed the bearing taking device consisting of the
2

page_text: ruler m with the diopters an². The ruler with a central hole fits on the socket
and has a sight line o. The bearing taking device is also provided with a pointer
or hand on the outside of the diopter 2. The bearing device can be screwed to
the rose by the nut q on the socket 7, and finally the rose h can be screwed to the
cross a by means of the nut r on the screwed upper end of the pivot g against the
socket 7 if the apparatus is desired to be used as bearing disc. The diopter n is
provided with sight slot and the diopter 3 with hair line as usual, and there is
also a hair line or wire t stretched between the two diopters, but only shown in
fig 1 for clearness' sake. s is the rose of the magnetic compass. The rose of the
sun compass is, analogously to it, divided in degrees and points and the dimensions
of the various parts are so chosen that the rose h of the sun compass is a little
larger in diameter than the length of the ruler m in order that the hand p may
show against the divisions of the rose when the bearing taking device is turned
upon the rose h while this latter is so much smaller than the magnetic compass
roses that the divisions on the latter may conveniently be read off simultaneously
with those of the rose h. For this purpose the cross a should be as broken through
and open as possible.
The above described correction apparatus is with its foundation a placed on an
ordinary steering compass so that the line f coincides with the steering line e of
the steering compass. Having found the azimuth of the sun for a certain few
minutes in advance of the time of the clock and having as usual changed the
azimuth by the local variation to the varying (true magnetic) bearing of the sun,
the bearing device is turned on the rose of the sun compass as many degrees as the
calculation shows; the bearing device is then screwed fast to the rose by the
nut q. The bearings with the sun are then taken, by swinging both these parts,
screwed together, until the line t coincides with the line o in the ruler m. One
can then at once read off both the rose of the sun compass and that of the steering
compass and thereby directly show the eventual deviation for the laid course.
For the sun compass shows the proper variation course and that one compared with
the laid course shows the deviation. Fig. 2 shows a point deviation.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1. In sun compasses the application and use of a foundation which is adapted to
be fixed by set screws or other means directly on to the compass of observation for
the purpose that the sun compass may have heeling pivots in common with the
compass of observation and may serve as a correction apparatus, which shows
directly upon the compass of observation the proper varying course that compared
at the same time with the laid course gives the deviation, substantially as set forth.
2. In sun compasses of the kind firstly claimed the cruciform foundation a
having angle bent ends fixed by screws to the bowl of the compass of observation
and having a fixed pivot g around which the rose of the sun compass can turn
said rose being provided with a screwthreaded socket 7 around which again the
bearing taking device m² can turn and can be fixed to the rose by a nut q. on
the socket for the purpose set forth.
3. In sun compasses of the kind firstly claimed and for using the apparatus as
bearing taking disc only the application of a nut r on the pivot g for fixing the
rose to the foundation.
Dated this Nineteenth day of Novemba 1807
JENSEN & SON
77 Chancery Lane London W.C. Patent Agents.