AN APPARATUS FOR DETERMINING THE PROVISIONAL SPECIFICATION THE MAGNETIC ABER- RATIONS OCCASIONED BY LOCAL ATTRACTION
Year: 1854

page_text: LETTERS PATENT to Matthew Curling Friend, of 44, Ashburnham Grove,
Greenwich, Lieutenant in the Royal Navy, and William Browning, of
111, Minories, in the County of Middlesex, Philosophical Instrument
Maker for the Invention of "AN APPARATUS FOR DETERMINING THE
PROVISIONAL SPECIFICATION left by the said Matthew Curling Friend
and William Browning at the Office of the Commissioners of Patents,
with their Petition, on the 16th December 1854.
We, MATTHEW CURLING FRIEND, of 44, Ashburnham Grove, Greenwich,
Lieutenant in the Royal Navy, and WILLIAM BROWNING, of the Minories,
London, Philosophical Instrument Maker, do hereby declare the nature of
the said Invention for "AN APPARATUS POR DETERMINING THE MAGNETIC ABER-
RATIONS OCCASIONED BY LOCAL ATTRACTION" to be as follows:-
A circular metallic disc or plate of any required diameter is fitted with a
rim or margin perpendicular to its surface, of about one inch in depth, which
rim or margin is divided into degrees and parts of the circle in the ordinary
manner, and the whole is suspended by gimbals, or otherwise, to preserve it in
a horizontal position. In the centre of this disc or plate a pin or stud is fixed,
on which is suspended a horizontal metallic bar, capable of moving round freely

page_text: to any part of the circle, which metallic bar may or may not be furnished
with sight vanes, sight tubes, index, and vernier. Attached to the upper surface
of this bar is a moveable circular plate, divided at the edge or margin into
points and degrees of the compass, in the ordinary manner, which plate may
be fixable at pleasure by tangent or other screws; and at any convenient point
on the periphery or outer rim of the instrument a stop may be placed, to check
unnecessary vibration, and enable the observer to read off the indications on
the plate with facility.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Matthew Curling Friend and William Browning in the Great
Seal Patent Office on the 14th June 1855.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, MATTHEW
CURLING FRIEND, of 44, Ashburnham Grove, Greenwich, in the County of
Kent, Lieutenant in the Royal Navy, and WILLIAM BROWNING, of 111,
Minories, in the City of London, Philosophical Instrument Maker, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Sixteenth day of December, in the year of our Lord
One thousand eight hundred and fifty-four, in the eighteenth year of Her
reign, did, for Herself, IIer heirs and successors, give and grant unto us,
the said Matthew Curling Friend and William Browning, Her special
licence that we, the said Matthew Curling Friend and William Browning,
our executors, administrators, and assigns, or such others as we, the said
Matthew Curling Friend and William Browning, our executors, administra-
tors, and assigns, should at any time agree with, and no others, from time to
time and at all times thereafter during the term therein expressed, should and
lawfully might make, use, exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an Inveu-
tion for "AN APPARATUS FOR DETERMINING THE MAGNETIC ABERRATIONS OCCASIONED
BY LOCAL ATTRACTION," upon the condition (amongst others) that we, the said
Matthew Curling Friend and William Browning, by an instrument in writing
under our hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to be per-
formed, and cause the same to be filed in the Great Seal Patent Office within
six calendar months next and immediately after the date of the said Letters
Patent.

page_text: NOW KNOW YE, that we, the said Matthew Curling Friend and William
Browning, do hereby declare the nature of our said Invention, and in what
manner the same is to be performed, to be particularly described and
ascertained in and by the following statement, that is to say:-
This Invention has for its object the construction and use of an instrument
or apparatus which we denominate a pelorus, for determining the amount of
magnetic aberration occasioned by local attraction in ships or vessels of every
description, whether built of iron, wood, or any other material, or impelled
by wind, steam, or any other motive power, and by the use of which, together
with the improved binnacle compass, herein-after described, the true course of
a ship or vessel may be from time to time accurately ascertained, clear of all
magnetic aberrations of the compass from whatever cause, whether variation
commonly so called, local attraction, or casual disturbance, by the careless
introduction of iron within the influence of the binnacle.
The apparatus and improvements consist, first, in a metallic ring, divided
into degrees and parts of the circle, commencing at zero, which point is placed
when using the instrument to represent or coincide with the head of the ship
or vessel, and the divisions are continued from zero on each side to 180°
degrees.
Secondly, within the before-described ring, and moving freely upon its
centre, a metal bar is provided, which must be furnished with sight vanes, for
the purpose of taking bearings. This metallic bar must also be provided with
verniers at its extremities, for reading off the points indicated upon the before-
named metallic ring.
Thirdly, moving upon the same centre pivot with the before-mentioned
parts, and beneath the above-described metallic bar, is placed a disc or card,
similar in appearance to that of an azimuth compass, but consisting of a
metallic disc without any magnetic needle, and having a silvered or other rim
divided into degrees and parts of the circle in the ordinary manner, which may
be read off from the vernier or marks at each end of the before-described
movable bar, but within the sight vanes, and also at or from the zero of the
ring before mentioned; and this disc or card may be fixed to the bar at any
required point when necessary by a screw nut or any other means.
whole of the before-described apparatus may be suspended by gymbals in a
square box, and balanced by a weight to keep it in a horizontal position, in
the ordinary manner, and it may be adjusted by screws at the supporting
points on either side of the box.
The
Fourthly, as observations can be taken by the above-described instrument,
which we term a "pelorus," with a greater degree of accuracy than is attain-

page_text: able with binnacle compasses such as are usually constructed, it was important
that a corresponding improvement should be made in the ordinary binnacle
compass to enable the two instruments to be used advantageously in conjunc-
tion, and this we have accomplished in the following manner; that is to say,
we use a moveable index, similar to the hand of a clock, attached to the centre
and working upon the upper surface or face of the card of the ordinary binnacle
compass, which card may be divided with a degree of accuracy corresponding
to that of the pelorus. The pelorus, or instrument before described, should
be securely fixed in an eligible position upon any firm support or pedestal
in the vicinity of the binnacle, and elevated so far as to command a view
of the horizon, having the zero point in a line with or parallel to the keel.
When properly adjusted in this position the instrument is complete.
And now having fully described the construction of the apparatus or in-
strument, we will proceed to explain the method of using it for the purposes
described.
To find the local attraction of a ship or vessel before leaving port, bring into
a line with the sight vanes the most distant object of which you can obtain the
view, and while they are in that position set the movable disc or card so that
it may correspond at the zero with the binnacle compass, and screw it tight;
still retaining the view through the sight vanes of the distant objects before
mentioned, swing the vessel completely round, preserving her local position of
centre as much as possible'; at every point of the compass observe the direc-
tion of the ship's head, as exhibited respectively by the pelorus and binnacle
compass the difference between them will be the amount of local attraction
at the various points of comparison. In using the "pelorus" at sea, it is
necessary to observe that the local attraction will vary with the ship's change
of place on the globe; the ordinary corrections will, therefore, be chiefly made
by means of amplitudes and azimuths of the heavenly bodies. If by ampli-
tude, take from the table expressly prepared for the purpose the anticipated
bearing of the body to be observed, which point place on the movable disc or
card coincident with the vernier or mark immediately within the sight vane,
and screw the disc firmly to the bar by means of the nut at the centre; take
the amplitude in the usual way, and at the same moment let the direction of
the ship's head be observed by the binnacle compass, and that of the pelorus
from the card at the zero: their difference will be the gross amount of all
magnetic errors, and will exhibit the ship's true course.
the compass be known and deducted from the gross
difference will be the local attraction in that course. Proceed in the same
manner with the azimuth, except that a quadrant will be required, which must
If the variation of
amount of errors, the

page_text: be set to the altitude at which it is intended the star should be observed. If
the true bearing of the heavenly body cannot be conveniently ascertained
before the observation, as the object may be rising or setting, set the disc or
card due cast or west to the vernier within the sight vane; take the observation
as before, noting the position of the ship's head at the zero, to which apply the
difference of the true bearing from the east or west point when found. Thus,
if the object be taken with the card at west while the true azimuth should
be subsequently found to be west, ten degrees north, the true bearing being
to the right hand of that which was assumed, the difference must be applied
at the point shewn at zero. Thus, an azimuth taken with the card at west
gave the ship's head by pelorus south, twenty degrees east, the star or sun's
true bearing in altitude was found to be west, ten degrees north, which being
to the right hand, must be applied, as before observed, to the point given at
zero, making the true position of the ship's head south, ten degrees east.
Having now described our Invention of an apparatus and improvements for
determining the magnetic aberrations occasioned by local attraction, and the
best means with which we are at present acquainted of carrying the same into
effect, we would observe, in conclusion, that although in the foregoing Speci-
fication we have described various matters which have been long known
and in use, yet we do not mean or intend to claim any such parts as of our
Invention; but that which we consider to be new in the above described
apparatus, and therefore wish to claim as the Invention secured to us by
Letters Patent, is,-
First, the peculiar combination of parts forming the before-described appa-
ratus, which we term a pelorus, especially the moveable metallic disc or card
and its application, as described.
And, secondly, the application and use of the moveable index to work upon
the face or upper surface of the binnacle compass card.
In witness whereof, we, the said Matthew Curling Friend and William
Browning, have heretofore set our hands and seals, this Eighth day of
June, One thousand eight hundred and fifty-five.
Witness,
JOSH. HY. RIDDELL.
MATW CURLING FRIEND. (L.S.)
WILLIAM BROWNING.
(L.S.)