Im- PROVEMENTS IN THE CONSTRUCTION OF SHIPS' COMPASSES, COMMONLY CALLED MARINERS' COMPASSES,' AND IN APPARATUS CONNECTED THEREWITH
Year: 1869

page_text: PROVISIONAL SPECIFICATION left by Herbert Allman at the Office
of the Commissioners of Patents, with his Petition, on the 15th
September 1869.
I, HERBERT ALLMAN, of No. 70, Gower Street, in the County of
Middlesex, do hereby declare the nature of the said Invention for "Im-
PROVEMENTS IN THE CONSTRUCTION OF SHIPS' COMPASSES, COMMONLY CALLED
MARINERS' COMPASSES,' AND IN APPARATUS CONNECTED THEREWITH," to be
as follows:-
My Invention may be generally be described as being improvements
in the construction of "ships' compasses," which improved construction
renders the compass less liable to the influence of what is termed "local
attraction."
The manner in which I construct a compass is as follows:-I employ
a magnetic needle, commonly so called, and pivoted as an ordinary
compass needle, with this difference that I keep one of the poles (say
the south pole) near the centre or pivot, and the north pole at the end
farthest from the pivot or the centre of rotation; this needle I shall call
needle 1, and this pivot I shall call pivot a. To the end of needle
nearest the centre or south pole I fix an arm of brass or other metal

page_text: incapable of retaining magnetism and produced as a continuation of
needle 1 from the centre or south pole. Now on this arm and at some
distance from the south pole (at pivot a at centre), I fix another pivot
which I call pivot b, and on this pivot I place another needle or magnet
which I call needle 2; thus the needle 1 revolves on the fixed centre or
pivot a, having on the brass end another pivot 6 and needle 2, which
needle revolves not only around its own centre 6 but also around the
centre or pivot a on fixed centres. Needle 2 from its movements I call
a-satellite needle. This apparatus being thus arranged the north poles
of both needles will point north. Now if I place a compass card on
centre on pivot a or fixed centre, and having a "radial slot" in which
an upright pin fixed to magnet or needle 2 works, the result of any local
attraction acting on the apparatus will be that both needles will move
their respective north poles in the same direction, but owing to the
position of the centres in relation to one another. The magnet 2 being
connected with the compass card by a pin and slot moves the card in an
opposite or reverse direction to the movement of the needle 1. Thus
if needle 1 moves 2 points east around its centre, the card is kept in
its position due north by the counteracting effect of the needle 2. I wish
it to be understood that the principle of the construction of this
apparatus may be generally described as one magnetic needle revolving
on one centre and carrying other centres, or a centre on which one or
more satellite needles revolve, the entire system moving around one
common centre, the movement of one needle counteracting the move-
ment of the other. It is best that all the magnet described as No.1
should be at one side of centre, its continuation being of brass at other
side of centre to permit the satellite magnets or magnet on the brass end
to work free from its influence. It is necessary that the satellite magnets
or magnet should be some distance removed from the vicinity of the
magnet on which it rotates.