Correcting Devices for Ships' Compasses.
Year: 1887

page_text: Date of Application, 14th Nov., 1887
Specification Accepted, 14th Nov., 1888
Correcting Devices for Ships' Compasses.
1, LEON SIRIEIX of San Francisco, in the County of San Francisco and State of
California, United States of America, Electrician, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement, reference being
had to the sheet of Drawings and to the letters and Figures marked thereon that is
to say :-
My invention has for its object the provision of a simple and effective arrangement
for correcting the deviations of the magnetic needle, whether such deviations arise
from general or local influences.
It is well known that any local attraction such as the proximity of iron or loadstone
will greatly disturb the normal position of the needle and produce more or less
deviation according to the condition under which the needle is placed. This is
especially noticeable on iron or steel vessels or ships or where such magnetic bodies
are carried by wooden vessels. In such cases the deviation of the magnetic needle
is often so great and uncertain as to render it almost useless as a guide to
navigation.
I have discovered that this deviation can be corrected by means of a correcting
compass provided with certain magnetic bars, the principal ones of which are set or
held transversely to the length of the ship, and that the action of the magnetic fluid
passing through these bars will correct the prime needle or compass, and that the
power of this correcting influence can be regulated by the vertical adjustment of the
correcting compass so as to produce a differential or differentiated action upon
the needle of the prime compass, and also that by the addition of inductors of soft
iron, placed at the poles of the correcting compass all quadrantal deviation arising
from induction will be compensated, and the action of the correcting compass aided.
In this specification I use the term differential to designate the position which the
needle assumes when caught between the two forces derived, the one from the
terrestrial magnetism and the other from the sub-permanent and induced magnetism of
the vessel.

page_text: Ine accompanying Drawings illustrate a practical means for carrying the invention
into practice and use.
Figure 1 is a vertical section of the compass box showing the true or prime
compass and the correcting compass. Figure 2 is a perspective view of the compass
box with a portion broken away to show the magnetic inductors and their means for
adjustment.
Figure 3 is a bottom of the prime compass.
Figure 4 is a plan view of the bottom of the compass box.
Figure 5 is a plan view of the upper card of the correcting compass and Figure 6
is a bottom view of the same.
Let A represent the case, binnacle or box in which a compass or magnetic needle B
is mounted in the usual and ordinary way. For the purpose of brevity and
perspicuity the compass B will be termed the prime compass throughout the speci-
fication.
I may divide the case, binnacle, or box A by a horizontal partition into an upper
and a lower compartment or, if preferred, it may have only a single compartment in
which the entire mechanism is placed and mounted.
When the case, binnacle or box is divided into two compartments, the prime compass
is mounted in the upper compartment, and the correcting compass and parts used with
it, in the lower compartment.
On the under side of the prime compass card B, I secure three parallel magnetic
bars of steel or other magnetic metal c d e, placed edgewise. The middle bar d
coincides exactly with the magnetic line indicated on the face of the prime compass
by N and S. while the bars c and e are parallel with it and equi-distant from it
on each side, the distance being 30 degrees from the middle bar.
The correcting compass is mounted upon the pointed upper end of the rod or
spindle k which extends into the hox A', and can be adjusted from the outside thereof;
the correcting compass is mounted beneath the prime compass.
The correcting compass consists of two discs of cardboard, mica or other non-
magnetic substance, the upper disc l being somewhat larger than the lower disc l'in
diameter. These discs are fixed on the central hub or centre pivot block, at a short
distance apart as shown in Figure 1 and are separated by three magnets c¹ d¹ e¹
parallel with each other, and 30 degrees from each other as above stated in relation
to the bars on the prime compass, and for the same reason. The middle bar d¹ is
somewhat heavier than the side bars c¹ e¹ and it is secured on a line corresponding
with N and S. on the face of the upper disc. On the face of the upper disc, I secure
four pairs of narrow magnetic bars n n, placed diagonally across each other and
across the disc so that each pair of bars, from the centre to the periphery of the disc,
will point to one of the cardinal points of the compass, the four pairs of cross bars
or strips forming eight radial pairs leading from the centre outward. The poles of
these small bars are arranged to balance each other, half N and S.
Upon the bottom of the lower compartment of the binnacle or box, I secure a brass
or other non-magnetic bar F by means of a pivot at its middle, which pivot is
preferably the rod. To each end of the bar is secured a short upright block of soft
iron G.
A horizontal slot is made in the side of the case opposite one of the blocks G
through which a threaded pin from the block passes and a thumb or set nut serves to
fix the blocks and the connecting bar in place by tightening the nut against the
outside of the case. By loosening the nut, the bar, with its blocks G, can be adjusted
a distance equal to the length of the slot, in order to put them in the line of the
induced magnetism.
Each of the blocks G has the edge of its inner face bevelled so as to present two
narrow blunt edges J J towards the middle of the bar.
The correcting compass is held in place between the blocks G G by means of
guides or stops so that the magnetic bars c d e¹ set transversely to the length of the
vessel, while their poles coincide with the blocks G. The guides or stops S
magnetic, and the arrangement is such that the correcting compass can be freely
are non-

page_text: adjusted vertically and will be allowed a slight rotary movement to feel its true
position in respect to the parts.
In practice, the case, binnacle or box A is so placed that the soft iron blocks G
are on the sides of the correcting compass next to the sides of the vessel. The
soft iron blocks G will then be induced by the subpermanent magnetism of the
iron side of the ship. The blunt inner edge of the block on one side will be a
south pole and the inner edge of the opposite block will be a north pole, according
to the position of the magnetic poles of the vessel. The correcting compass being
mounted between the two blocks G with liberty for some rotation. The centre bar
will arrange itself exactly opposite the poles of said blocks, and this great
certitude and nicety of position is aided by the parallel flat bars n n on the upper
face of disc l.
These bars compensate the magnetic influence and enable me to reach an
exactness of position which 1 cannot otherwise obtain, as I have found in my
experiments that the employment of these bars in the manner described corrects the
compass to a great nicety, and compensates several degrees of deviation which would
otherwise affect the needle.
With the correcting compass mounted as described, the prime compass will be found
to be completely corrected and deviations compensated for in a manner to render the
prime compass a reliable indicator and guide for navigation.
I have found that good effects are also produced in cases when it is desired to
counteract or correct the magnetic influence of vertical iron on a vessel by the
employment of two blades P of soft iron united by a non-magnetic strip or bar M
in the box or compartment containing the correcting compass.
The strip M is set transversely to the bar, fore and aft.
These supplemental inductors are only needed where there is a great quantity of
induction from vertical iron, and in other cases they may be omitted.
The combined action of the correcting compass and the soft iron blocks G, which
act as inductors, is to correct the deviations due to both sub-permanent and induced
magnetism of the ship.
The constant deviation is compensated by the vertical adjustment of the correcting
compass, and the allowance for magnetic changes of latitude and magnetic longitude
is made in the same way, said changes, as well as the constant deviation, being
ascertained in the usual way by observations.
The semi-circular deviation being ascertained by the soft iron blocks G, in con-
junction with the magnetic bars on the correcting compass, the inductors being
influenced by the magnetism from the ship's sides and in turn influencing the correcting
compass, and the quadrantal deviation is corrected by the soft iron blocks or inductors
according to natural laws governing the induction of soft iron. The polarity as the
ship's course is changed in the azimuth corresponding with the changes of polarity of
the induced magnetism of the ship's sides.
The heeling error is corrected or overcome by the conjunction and arrangement of
the prime and correcting compasses by means of which they are held always parallel
with each other, and so far as my experiments and tests have demonstrated, this
difficulty of the heeling error will not manifest itself to any appreciable extent in
my compass; if it should, it can readily be corrected in the usual manner well known
to seamen.
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 :-
First. A correcting compass provided with two sets of magnetic bars, one set
being underneath the card of the compass, and the other set on the top, in combination
with a prime compass having magnetic bars, substantially as specified.
Second. In a compensating compass, the combination, with a prime compass and a
correcting compass, of the soft iron blocks G G mounted besides and moved with the
correcting compass, as set forth.

page_text: Third. In a compensating compass, the combination, with a prime compass and a
correcting compass, of the soft iron blocks G G mounted besides and moved with the
correcting compass, and means, substantially as described, for adjusting the said
blocks and correcting compass in a horizontal plane, as set forth.
Fourth. In a compensating compass, the combination, with the prime compass and
a correcting compass, of the soft iron blocks G G and bar F on the ends of which
they are mounted, and the guides or stops S S on bar F to hold the correcting
compass within slight limits of rotation, as set forth.
Fifth. In a compensating compass, the combination of a prime and a correcting
compass, and the upright soft iron blades P arranged relatively to the correcting
compass as described to compensate the magnetism from vertical iron substantially as
specified.