A CERTAIN MATHEMATICAL INSTRUMENT CALLED THE MARINE LEVEL, THE PROPERTIES OF WHICH ARE TO SHEW EVERY DEVIATION, FROM THE HORIZONTAL PLANE OF SHIPS AND VESSELS, AND WHICH IS ALSO. APPLICABLE TO VARIOUS PURPOSES IN SURVEYING, LEVELLING, AND ASCERTAINING VERTICAL AND 'PERPEN- DICULAR SITUATIONS
Year: 1801

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
FITZ GERALD, of Gray's Inn, in the County of Middlesex, Esquire, send greeting.
WHEREAS His present Majesty King George the Third,' by His Letters
Patent under the Great Seal of that part of the United Kingdoin of Great
Britain and Ireland called Great Britain, bearing date at Westminster, the
Eleventh day of August now last past, hath given and granted unto me, .the
said William Fitz Gerald, my exécutors, administrators, and assigns; special
licence, full power; sole privilege; and authority, to make, use, exercise; and
vend, within that part of the United Kingdom of Great Britain and Ireland
called England, the Dominion of Wales, and Town of Berwick-upon-Tweed,
during the term of fourteen years therein expressed, my Invention of
"A CERTAIN MATHEMATICAL INSTRUMENT CALLED THE MARINE LEVEL, THE
PROPERTIES OF WHICH ARE TO SHEW EVERY DEVIATION, FROM THE HORIZONTAL
PLANE OF SHIPS AND VESSELS, AND WHICH IS ALSO. APPLICABLE TO VARIOUS
PURPOSES IN SURVEYING, LEVELLING, AND ASCERTAINING VERTICAL AND 'PERPEN-
DICULAR SITUATIONS;" in which said Letters Patent is contained a proviso,
obliging me, the said William Fitz Gerald; by an instrument in writing under
my hand and seal, to cause a particular description of the 'nature of my said
Invention, and in what manner the same is to be performed; to be inrolled in
His Majesty's Chancery within one, calendar month next after the date of the
said recited Letters Patent, as in and by the same, relation being thereunto
had may more fully and at large appear.
-

page_text: NOW KNOW YE, that I, the said William Fitz Gerald, in compliance
with the said proviso, do hereby declare that the said Invention is described in
and by the words and figures following, viz*:-
I take a plate or plane superficies of any metal or of ivory or wood, or any
other material capable of receiving, shewing, and retaining the graduations and
Figures intended to be described on it; this plate or plane may either be
wholly circular or may be formed of any segment or portion of a circle, pro-
vided that at the lower part there be a weight or preponderation, but for every
practical purpose I prefer forms similar to those contained in the Drawings.
Figure 1, A, is a plane or plate of metal, wood, ivory, or other suitable
material as above predicated; its lower part is weighted as at b, (such weight to
be affixed to the plate A by screw or rivet, or any convenient and secure
manner. The plate A to move or vibrate on a à pivot, arbor, or axis, at its centre
of motion c, and it is to be duly divided, figured, and numbered, either according
to the ordinary degrees of the circle or otherwise, at the pleasure of the person
applying it; the central or perpendicular line ought to be made to pass through
the centre of the axis, pivot, or arbor, and through that of the weight at the
lower part. This plate may be either single or double, but the graduations
ought to be made on both sides; or in other words, the plate A, whether single
or double, ought to have its external faces graduated, divided, and figured,
always having regard to the peculiar application or purpose intended for the
instrument. The plate or plane being thus prepared is supended by a pivot,
arbor, or axis at its centre C, to a frame of metal d, d, seen in front and in
profile at Figures 2 and 3, on which it is freely but not loosely to vibrate and
have motion. The said frame terminating in a cylinder as at d, to be received
into another cylinder as at e, Figure 4; but these cylinders may be reversed, d
may be hollow, and e solid. The frame is to be kept suspended either by a
countersink which is to receive the adjusting screw as at f, or more than onc
of such screws, or by a pin and groove called by workmen a riding jack, a rivet,
or any ordinary method; in any case having the adjusting screw f, by which
A and its frame, when turned in the socket e, are retained in any given situa-
tion; if the making the terminating part of the frame d as a socket be preferred,
then the screw f must be attached to the part d. G, Figure 4, (the profile of
the delineation Figure 8) is a plate of any suitable metal or material, made
perfectly true with its projecting cylinder e (whether solid or hollow) at a
right angle, so as that when the pieces A and its frame are vertical, or at zenith
by the index, the plate or shoulder G may be exactly horizontal. The gra-
duated or divided plate A may be made by taking the divisions on each side of
the zenith or 90° from two centers, viz, from each side of the pit or central

page_text: hole, so that the suspending frame may shew by its sides as fiducial edges or
indices, the declination from 90° on each side. Analogous to the space allowed
in dialling for the thickness of the gnomon of a dial, Figure 5 shews that the
semicircular plate A, or other portion of a circle may be made to produce an
analogous effect, having a solid piece of metal proceeding from its upper part,
similar to and for the like use as the upper part of the frame d, Figures 2 and
3, for turning and being adjusted. In which case the degrees and divisions are
pointed out by the vibrating index or pendulum i, suspended by a pivot, axis,
or arbor to the plate at C, and weighted at b, Figure 5; the bottom of the
vibrating index i, representing, and being instead of, the bottom of the plate A,
as in Figure 1, (the same letter kept to the same part throughout) the line of
gravitation to pass precisely through the zenith or 90° of A, and through the
center of gravity of the weight as at c, Figures 1 and 5. The vibrating-index
may be double, in order to point the divisions on both sides of the plate A, if
instead of the weight fastened on the index as in the last described Figure 5,
the part of such index below the central pivot, or the part of the plate A;
Figure 1, below its center, be made as a frame to receive the plate A, or a
similar plate, at right angles. The marine level is then in its completest state;
for it is obvious by inspection, that if the two respective indices of the two
plates A, A, point exactly 90 or zenith in each plate (they being at right
angles with each other) than every right line, whether real or supposed, cross-
ing at right angles the perpendicular line formed by coincidence of the two zeniths
must be exactly precisely and truly an horizontal one, and if we suppose a
truly even plate to represent such lines so crossing, and that by means of the
respective pivots or arbors, and of the turning round of the plate A, Figure 1
and index Figure 5, such plate and index may be adjusted or made to preserve
their vertical gravitation (allowing for vibration, more especially at sca), then
it will follow that the declination of the horizontal plate or plane will be shewn
by the plate A and index, according to the degrees of declination and the point
of the compass or circle towards which such declination of the plate is, and to
which the said plate A and index may at pleasure be turned and, adjusted. On
these two propositions, the uses of the said Invention, whether at sea or by
land, are founded. Then at Figures 6, 7, and 8, is seen a representation of
the marine level as applicable to nautical purposes; and for most of those pur-
poses it will be sufficient that instead of the plate and index Figure 5, or the
upper plate, there shall be a joint with a pivot, axis, or arbor, so that a zenith
line may be engraved with such other lines on each side of the zenith line as
may be thought proper, having, however, only a single perpendicular line on
each end of the pivot or arbor, which may act as an index to the other lines;

page_text: or there may be affixed a portion of a graduated circle and a real index or
pointer, see Figures 6 and 7. The horizontal plate G, G, Figures 4, 6, and
8, marked with a line fore and aft, and as many other lines as may be chosen
(those are probably most convenient which answer to the points of the mari-
ner's compass) is to be screwed or fastened up parallel with either the horizontal
plane or line of floatation of the ship or vessel when launched on the line of
trim in lading or ballast, or such other line as may be preferred; then by
turning round of the plate A, Figure 6, and its frame (directing the edge of
the plate towards any part of the vessel at pleasure) the degrees of declination
from the horizontal plane or line of trim, or the vertical line or other original
linc are shewn by the index upon the plate A; Figures 6 and 8, G, G, repre
sent the horizontal plane or plate as in G; Figure 4, c, represent the cylinder
of such plate. The joint is, instead of an upper plate, and instead of Figure 5.
A is the
Figure 7 shews a marked joint. and pivot with the profile of A.
vibrating plate as A, Figure 1; b, b, the weight; f the punching or adjusting
screw; the whole constituting the marine level and affording the uses following:
To naval officers. Admitting that there is in most ships and vessels a pecu-
liar angle, or that there are peculiar, angles of declination from the horizontal
plane or line of trim, at which, when not sailing large, they sail the best, and
which angle or angles are found by repeated observation and experiment, this
instrument taking the mean of its vibration enables such officers to observe and
note and keep the ship to such; angles or angles, and to avoid an excess., By
detecting every deviation from the vertical line of the ship, the, commander is
enabled to stow the contents of the ship in due time readily and minutely, and
to correct any erroneous disposition or alteration of his stowage.
:
To mercantile navigators.-The frequent variations of the disposition of
cargoes and ballast, incidental to them, render the marine level eminently useful
in regard to stowing, moving, correcting errors of lading by instant inspection;
thereby saving time, trouble, and expence continually occurring, when the
lading is taken in.
To astronomers and geometricians.- It being very material to obtain an
artificial horizon for the purposes of observation by the quadrant or sextant,
the marine level is adapted to gain such artificial horizon; Figure 9 shews
such application. Let there be the two vibrating plates A, the lower, being
the same as the upper, hanging at right angles one with. the other, the lower
being in the Drawing shewn in profile; let the upper surface of the horizontal
plate or plane G be made truly, even, and polished as a speculum; let the
cylinder e be at right angles with the upper, surface of G; let there be four or
more adjusting or regulating screws passing through or connected with the

page_text: plate G as k, k, k, k; let there be a board Figure 10, with a groove or opening
cut in it at EI, so much beyond its center as that it may receive easily the
cylinder e of the horizontal plate or plane G, Figure 9; let the board Figure 10
be steadily supported, as may be done by various means, but most easily by
three legs, for the reception of which there ought to be holes or any other
suitable and adequate method, a stake or staff might answer the purpose,
received into a socket as at l, and driven into the ground; then it is obvious
that by regulating the instrument by means of the screws of the plate G, and
the pinching screw f of e, until the zeniths or 90°, A, in the several Figures
coincide; an artifical truly reflecting horizon is gained on the upper surface of
the horizontal plate or plane G, Figure 9.
Engineers, land surveyors, miners, architects, builders, and others, will, on a
due examination, easily see the properties and uses of this instrument, and its
parts as adaptable to the different purposes of their respective professions.
In witness whereof, I, the said William Fitz Gerald, have hereunto set
my hand and seal this Seventh day of September, in the forty-first year
of the reign of our said Sovereign Lord George the Third, and in the
year of our Lord One thousand eight hundred and one