Year: 1886

page_text: I ERNEST BISSON of 95 Boulevard Beaumarchais, Paris in the Republic of France,
Engineer do hereby declare the nature of this invention to be as follows:-
This invention consists in a new arrangement of Mariners' Compass, which will
permit of determining the direction of the magnetic meridian on board a ship, no
matter what may be the causes of the deviations produced.
The apparatus consists of two or more needles placed in the same vertical line
in one or more boxes connected together, and suitably slung to permit of swinging
with the movements of the vessel:
One or more of the needles will be mounted so that the distance between them
may be increased or diminished as required. This may be effected by mounting
the needle on a cross bar contained in the case, and connected with a pair of racks
which are worked by pinions on a cross shaft extending through the case.
Hanging from the bottom of the needle case is a bar, which carries at opposite
ends a bracket, which is adjustable laterally by means of an endless screw, and
vertically by a rack and pinion, or any other suitable motion, and carries a
magnitized bar.
Attached to the swinging bar is a graduated ring, which works in connection.
with a pair of pointers attached to the needle case or box.
Inside the box is placed a mirror, which throws a reflected light on the needle.-
The top of the box is also formed with a glass panel, which carries at its centre
a rotating bar provided with sights.

page_text: I ERNEST BISSON of 95 Boulevard Beaumarchais, Paris, in the Republic of France,
Engineer 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:-
The present invention consists in a novel arrangement of Mariners' Compass
which will permit of ascertaining the direction of the magnetic meridian on board
a vessel, whatever may be the causes of deviations that may exist.
In the accompanying drawing, I have shewn, in two Figures, an instrument
constructed according to my invention.
'and
Fig. 1 being a longitudinal vertical section through the centre of the instrument,
Fig. 2 a horizontal section through the line M N of Fig. 1.
A A are two compass cards, provided with compass needles, and floating upon
centres in the usual manner.
BB is the cylindrical box or case of the instrument, supported in gimbals H, H.
C is a fixed glass for giving light to the lower portion of the case B.
D is the cover of the apparatus closing with a bayonet joint, and fitted with
a glass top E to allow the inspection of the upper compass card.
G is the "set off" alidade, or aights for obtaining compass bearings when the
state of the weather permits such bearings to be taken.
K is a cross bar carrying the pivot of the upper compass card, and capable of
sliding up and down on the guide bars L L, and of being raised and lowered by
means of the racks J, J.
PP are milled heads fixed on the ends of the arbor of the pinions p. p. which
operate the racks J.
OO is a rod having right and left handed screws formed upon it, and fitted with
milled heads at its extremities.
QQ are two sockets sliding upon the bar T T, and forming carriages for the
movable alidade. The bar T T is pivotted at S to the centre of the bottom of the
case B, and is capable of a horizontal movement around this centre.
R is a graduated circle attached to, and rotating with the bar T, and, by the
aid of pointers UU fixed on the sides of the case, indicating the direction of
the movable alidade.
V. V. branches of the alidade, adjustable up or down in the sockets Q, and
secured in position by milled head binding screws.
Y. Y. Stirrups intended to hold, by the aid of binding screws, bar magnets upon
the branches of the movable alidade. The purpose of these bars is partly to
counterbalance the horizontal action of the earth's magnetism upon the compass
needles, and partly to counterbalance the local magnetism of the vessel,

page_text: In some cases, it may be found desirable to provide a system or inclined mirrors
placed at such an angle as will admit of both compass cards being read at one
time, either directly, or by the aid of a glass fixed in the case, opposite the
mirrors.
As will be seen, this compass, of which the form, the details of construction,
and the proportions may be infinitely varied, is particularly characterised :-
(1) By the employment of two magnetic needles of the same dimensions, having
their centres placed in the same vertical line, at variable distances apart, but so
that, at their nearest approach to each other, the two needles cannot exercise any
influence the one on the other.
(2) By the employment of an alidade capable of horizontal rotation, armed with
two bar magnets, and adjustable so as to occupy different horizontal planes between
the two compass needles, at the same time that the distance from the centre can
be increased or diminished.
In constructing the apparatus, the following conditions should be observed. The
two needles should be of small dimensions, first, in order that they may have no
effect the one upon the other, and second, to avoid the necessity for too great
dimensions in the branches of the alidade which carry the bar magnets.-The
dimensions of the needles should not exceed one tenth the maximum vertical
distance that the needles can be separated, that is to say, if the maximum of
separation of the needles is forty five centimetres, their length should not exceed
4 centimetres. The upper needle should be capable of being lowered, and the
lower needle raised to half the maximum distance they can be separated, by the
aid of racks and pinions, or by any other convenient means, but independently of
each other, that is, 22+ centimetres, if the maximum distance be 45 centimetres.
A vertical graduated scale may serve to indicate the position of the needles.
The two needles may be enclosed in one case, as shewn in the drawing, or may,
if thought desirable, be enclosed in two boxes connected together by a rigid stem
in either case, the apparatus must be suspended in gimbals.
The two needles may also occupy fixed positions in one case, a third needle being
provided between the other two, on the same vertical line, and which is capable of
being raised and lowered at will.
If the three needles are not contained in one case, the box containing the third.
needle should be capable of receiving vertical adjustment between the two fixed
needles. I consider, however, the single case preferable, as being more simple in
construction and in working.
The movable alidade V. V. must be so arranged that the two branches may be
raised or lowered, and approached or withdrawn to or from the centre at will.
These movements may be obtained by racks and pinions, by screws, or by such:
other means as may be found desirable; the alidade must also be capable of
rotating completely round the central-vertical axis of the instrument, and must.
be provided with a divided circle for indicating its position with respect to the
needles. The branches of the alidade should also be graduated vertically in agree-
ment with the point of departure on the scale which indicates the separation of the
needles.
The mode in which this instrument is to be used to obtain the magnetic meridian
is as follows:-
'
In order to adjust the instrument previous to placing it on board the vessel,
I proceed in the following manner:-I choose a place in some situation where it will
be screened from all magnetic influence other than that of the earth; the two needles
wil take naturally the same direction:-that of the declination of the place.
Two bar magnets are then placed upon the branches V. V. of the movable
alidade, the branches being first raised to a position equi-distant from the two
needles, the needles themselves being separated as far as possible from each other.
These conditions fulfilled, the movable alidade with its magnets is placed at an
angle with the meridian, say 40°, for example, and the magnets are advanced or
;

page_text: withdrawn to or from the centre, until the two needles are separated from the
meridian at an angle one half less than that formed by the movable alidade with
the meridian, or 20°; it will then be certain that the bar magnets exercise on the
two compass needles an action equal to that of the earth.
The instrument may now be conveyed on board the vessel, and in order to
ascertain the magnetio meridian, it will only be necessary to turn the movable
alidade, with its bar magnets, round, until the two needles take the same direction,
at which time the alidade will occupy the plane of the meridian, which will thus
be determined.
But this determination will only be exact if the vessel has not changed its
latitude, that is to say, the action of the bar magnets must always balance that of
the earth's magnetism, which varies with every degree of latitude.
In order to adjust the instrument at sea without displacing it, I proceed in the
following manner :-(a) The alidade with its magnets must be turned round, until
the compass needles take an identical direction, their direction, and that of the
alidade, being carefully noted.-(b)-The bar magnets are next removed, when the
amount of difference in the direction of the two needles is noted.-(c)-The upper
needle is now lowered by means of the racks and pinions J. J., until it takes a
position midway of the separation noted under (b)-(d)-The upper needle is next
raised to its original position; and,-(e)--the branches of the alidade are lowered,
so that the vertical distance of the bar magnets from the lower compass needle
equals the distance it has been found necessary to lower the upper needle, in order
to cause it to take the medium direction indicated under (c).-(ƒ). The bar
magnets are now replaced upon the branches of the alidade, giving to this latter
the direction as described above at (a), in which the needles coincide, and the
branches of the alidade are approached or withdrawn from the centre, until they
impart a new and identical direction to the two compass needles. If this direction
of the needles corresponds with that of the alidade in the operation described at (a),
it may be concluded that the adjustment of the bar magnets is right.
If, on the other hand, the direction of the needles does not correspond with that
of the alidade, the alidade must be raised to a plane equidistant from the two
needles, turned in the direction that the two needles will have taken during the
operation described above, at (f), and the position of the bar magnets must be
varied until the needles are both brought to the position described above at (a).—
The bar magnets will thus be adjusted for the latitude in which the vessel may be
at the time.
+
The meridian may also be ascertained in a much more simple manner, by
observing the instructions: b, c, d, e, only, and replacing the operation (f) by the
following:
(f) The bar magnets are replaced upon the alidade without respect to the
direction it may be in at the time, and the magnets are then approached and with-
drawn until the two needles assume the same direction, which will be that of the
meridian.
'
$
'1
This method has the advantage of rendering permanent the utility of the
instrument; it is only necessary to bring the two needles into coincidence. when-
ever their direction varies, and to effect this, it is sufficient to slide the bar magnets
back wards or forwards upon the movable alidade, besides which, however, it would
be well to certify from time to time, by means of the operations b, c, d, e, that the
height of the alidade does not need alteration.
Having now described and ascertained the nature of my said Invention and the
manner in which it is to be carried into effect, I wish it to be understood that
what I claim is;-)
The new mariner's compass as above described, and consisting essentially of
two vertically adjustable needles A. A or two "fixed" needles and one vertically
adjustable needle placed between the same in a single case or in separate cases, and

page_text: capable, by suitable means (the racks J J, for example), of receiving an independent
vertical motion, such needles being in combination with an alidade, mounted so as
to turn round the axis of the apparatus, and having two branches V V which are
arranged to be vertically and laterally adjustable, and a graduated circle or disc R
for indicating the angle of the alidade with the line which joins the two index
indicators UU, all substantially as set forth.
Dated this 99nd dev of October 1886