IMPROVEMENTS IN RENDERING MAGNETIC NEEDLES LESS PREJUDICIALLY INFLUENCED BY LOCAL ATTRACTION
Year: 1843

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
BUSH, of Union Street, Deptford, in the County of Kent, Engineer, send
greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Ninth day of November, in the seventh year of Her reign, did,
for Herself, Her heirs and successors, give and grant unto me, the said
William Bush, Her especial licence, full power, sole privilege and authority,
that I, the said William Bush, my exors, adiñiors, and assigns, or such others
as I, the said William Bush, my exors, adñors, or assigns, should at any
time agree with, and no others, from time to time and at all times during
the term of years therein expressed, should and lawfully might make, use,
exercise, and vend, within England, Wales, and the Town of Berwick-upon-
Tweed, my Invention of "IMPROVEMENTS IN RENDERING MAGNETIC NEEDLES
LESS PREJUDICIALLY INFLUENCED BY LOCAL ATTRACTION;" in which said Letters
Patent is contained a proviso, that I, the said William Bush, shall 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 Her said Majesty's High Court
of Chancery within six calendar months next and immediately after the date
of the said in part recited Letters Patent, as in and by the same, reference
being thereunto had, will more fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
William Bush, do hereby declare that the nature of my Invention, and the
manner in which the same is to be performed, are fully described and ascer-
tained in and by the following statement thereof, reference being had to the
Drawings hereunto annexed, and to the figures and letters marked thereon,
that is to say:
My Invention consists of a mode of constructing a marine compass, whereby
the local attraction may be centralized in or near the axis of motion of the mag-
netic needle. It is well known that the magnetic needles used in marine com-
passes are in many cases acted upon very prejudicially by local attraction, so as
to render them very irregular and incorrect in their pointing. Now, according
to my Invention, this local attraction (consequent on there being quantities of
iron and other causes acting near a compass) is caused to be centralized in or
near the axis of motion of the needle, whereby the needle of a compass is less
prejudicially influenced, and will consequently act with more correctness, and, in
fact, will be more similar in its performance and pointing, to what would be the
case were there no iron or other causes of attraction in the locality in which
a compass may be placed.
And in order that my Invention may be fully understood and readily carried
into effect, I will proceed to explain the best means I am acquainted with for
carrying out my Invention.
DESCRIPTION OF THE DRAWINGS.
In Figures 1 and 2, A, A, represent the brass standard frame or compass
box, supporting the universal joint through which the magnetic bars retain
their perpendicular, and act as a pendulum and conductor, and receives the
magnetism of all iron which might surround it; B, B, the compass bowl or
basin in which the magnet and card revolve; C, C, centre magnetic steel or
iron bar, chain, tubes, or other forms of steel or iron, ascending to and support-
ing the needle upon which the magnet and card revolve; D, D, highly mag-
netised bars framed in contact and combination with C', or centre magnetic
bars, chain, or tubes. Note.-It will be observed that the centre magnetic
bars C and D' are placed with the north pole upwards and south downwards,
which may be reversed, and in some cases only a single bar is necessary.
E, E, void or vacant space intervening between D and F, to prevent the
current of magnetic attraction being direct and uniform in the outer and inner
circles; F, F, outer highly-magnetised circumference of framed steel or iron
bars or tubes, with the poles reversed, placing the south pole upwards; or the

page_text: entire combination may be alternated if required. G, G, outer circumference of
brass or other metal, to protect the magnetic bars or tubes from corrosion;
II, nut and screw to fix the centre which supports the needle. Note.-Where
the barometer is required, the magnetic bar C may be removed, and mercury
substituted, as shewn in Drawing No. 2. I, reservoir of mercury within a
magnetised steel or iron cistern, connected with the magnetic tube, through
which the mercury will ascend, serving also as a balance for the bowl or basin,
which is supported by it.
Figure 3 represents the compound magnet, with the four north and four
south points in combination. The current of magnetic attraction will proceed
in a direct line between the four north points, leaving the two points nearest
approximating thereto to form an angle therewith of twenty-two and a half
degrees east and west.
Figure 4 represents a compound magnet of six points, being three towards
the north and three towards the south; but in this case the current of
magnetic attraction proceeds directly through the three points, by the centre
point of which the due north will be determined. Figure 5 is the same in
principal as Figure 4, having four points substituted. The current of mag-
netic attraction runs in this instance through the centre, the angle formed
being forty-five degrees instead of twenty-two and a half, as in former instance.
Figure 6 represents a magnet of three points, being an equal division of the
centre, forming an angle of about one hundred and twenty degrees; and,
in this instance, the single part determines the due north, the remaining two
points being east and west towards the south.
Figure 7 is also a magnet of three points, the south point being in the
direct magnetic line, the south-eastern and south-western parts describing an
angle of ninety degrees with each other, through the centre of which the
north and south points passes.
Figure 8 exhibits the straight bar magnet, with the points directed north
and south, the section of which is shewn in Figure 1. The axis or point
on which the needle of a compass moves, in place of being fixed as heretofore,
is caused to float on mercury or other fluid. J is a cistern of mercury fixed
in the compass bowl, and I prefer the cistern to be of metal lined with glass;
K is a float of cork or other suitable material, having the axis of the compass
fixed therein. This axis slides freely through a stuffing box at the upper part
of the cistern. L is a cone placed under the needle; this cone on its under
slide has an agate to receive the upper end of the axis affixed on the float, and
on its upper surface it has another agate to receive the lower end of the

page_text: point M of the needle; and in case the cone is not used, then the axis
affixed in the float receives the magnetic needle, it being provided with a
suitable agate to receive the point of the axis.
Having thus described the nature of my Invention, and the best means I am
acquainted with for performing the same, I would remark that I do not confine
myself to the precise details shown, provided the peculiar character of the
Invention be retained; but what I claim is, the mode of rendering magnetic
needles less prejudicially acted on by local attraction, by causing the attraction
arising from local causes to be centralized in or near the axis of motion of
magnetic needles. And I also claim the modes of constructing magnetic
needles with three or more points. And, lastly, I claim the floating of an
axis for a magnetic needle by means of fluid.
In witness whereof, I, the said William Bush, have hereunto set my
hand and seal, this Fourth day of May, in the year of our Lord One
thousand eight hundred and forty-four