MENTS IN COMPASS CARDS
Year: 1885

page_text: I, JOHN DANIEL of 95 Walton Breck Road Liverpool in the County of Lancaster,
Master Mariner do hereby declare the nature of my said invention for IMPROVE-
MENTS IN COMPASS CARDS and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement:-
"
The cards commonly used in mariner's compasses are made with one or more
" needles or small bar magnets placed across the card parallel to a line connecting
the points which indicate North and South. These magnets cross at right angles &
line connecting the East and West points, the neutral points of the magnets being
on that line, and extend towards the edge of the card. The magnetic forces which
attract and repel the magnets act therefore only on a point or points near the edge
of the card, any cause occuring to disturb or oscillate the card, acting upon it with
a leverage equal to the distance between the centre of the card and the point of
the magnet..
The object of this invention is to reduce and as far as possible prevent the
oscillation of compass cards at sea, when a ship rolls and swings about without
increasing the weight of the card, or the friction on the pivot point or interfering
with the simplicity of construction of the instrument.
It consists of dividing the needles or magnets into two or more lengths and
placing them on the North and South side of the East and West line of the card,
securing them on or parallel to a line from the North to the South points,
preferably so that two or more needles etcetera will be placed on the same longi-
tudinal axis each having a North and South pole upon which the magnetic forces
may act to attract or repel.
Referring to the annexed drawings by means of which the invention is better
described. Figure 1 is a plan view of the card. The four cardinal points only
are marked, and the needles are shown in dots, in position on the under surface of
the card. Figure 2 is a sectional elevation of the card on a line passing through
the North and South points.
A is the cardboard of ordinary construction, to which the needles or magnets are
attached. The card is fitted with the usual agate centre B, and mounted on the
point C. The magnets D are placed on either side of the East and West line,
with a space between their approaching ends. The arrangement shown and which
I prefer, consists of six short needles, three on the North side and three on the

page_text: South side of the East and West line of the card; with their inner ends distant
from that line, one sixth of the length of one of the outside short needles. The
distance of each side pair of needles from the North and South line should be
equal to one third of the total length of the pair; inclusive of the distance
between their inner poles. The four outside needles are equal in length, but
each middle needle may be one eighth part longer than an outside needle.
The invention however is not limited to the exact arrangement above described,
and shown inasmuch as more than two needles or magnets having the same
longitudinal axis may be placed on the card, a greater or less distance apart, as
may be considered desirable.
From a number of experiments made by me on board of a merchant steamship,
with various kinds of compass cards in all weathers, the divided needle card has
been found to be the most steady and least liable to oscillate; Arising from the
fact that the forces acting on the magnets on the North side of the card to displace
it from a truly horizontal position; and the forces which would cause oscillation
which act suddenly on the same magnets from a side or lateral direction, existing
for a short time only as in the case of an iron ship rolling at sea, are largely
neutralised in the first instance and considerably checked in the second instance by
the same forces acting in a similar manner on the magnets on the South side of the
card, as each magnet has a separate centre not coincident with the centre of
the card.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that I do
not claim broadly a compass card with a number of magnets, or needles attached to
it, but that what I claim is
The manufacture and use of compass cards having needles or magnets placed on
the North side of the card, and needles or magnets placed on the South side of the
card, the longitudinal axes of those on the one side being preferably coincident
with the longitudinal axes of those on the other side, substantially as and for the
purposes described.
Dated this 31st day of August 1885
WM P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, and
323, High Holborn, London,
Patent Agents for the Applicant.