An Improvement in Mariners' Compasses.
Year: 1896

page_text: Date of Application, 16th Sept., 1896-Accepted, 31st Oct., 1896
COMPLETE SPECIFICATION.
An Improvement in Mariners' Compasses.
I, JAMES CASEY of 10 Philpot Lane, London in the County of Middlesex
Consulting Marine Engineer do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
It has often been observed by mariners that the compass is frequently sluggish
in its movements in damp and foggy weather and is apt at such times to be
uncertain in its action owing to a tendency of the compass card or needle to retain
its position notwithstanding that the vessel to which the compass is attached has
to some extent altered its course; this I attribute to the fact that the excessive
moisture of the air has obtained access to the inside of the compass and prejudicially
effects its working by becoming deposited upon the card or needle and upon the
pivot on which the card or needle turns, and retards the movements of the card or
needle.
My improvement in mariners. compasses overcomes this trouble, it consists of
hermetically sealing the case of the compass and exhausting the air from the inside-
thereof.
A further advantage in exhausting the air from a compass is that the hammering
action that takes place between the top of the pivot and the underside of the cap
of the compass card or needle is greatly reduced, as in a vacuum there is nothing
to cause the compass card or needle to leave the pivot, when both are falling at a
speed due to gravity only as it is well known that if two dissimilar substances are
allowed to fall in a vacuum they will both reach the bottom of the vessel in which
they have been placed at one and the same time, but even if the velocity of fall of
the pivot be greater than that due to gravity only, there will still be less hammering
action between the cap and pivot point when the compass is working in a vacuum
than if they were not, and consequently the sensitiveness of the compass needle is
maintained in good condition for a greater period than when working under
ordinary atmospheric conditions.
Figure 1 of the drawing shows the section of a compass. (a) is the metal case;.
(b) the compass card and needle; (d) the pivot; (e) the transparent top;.
ff) rings of indiarubber; (g) a loose metal ring; (h) a screwed ring; (i) a tube
attached to the case (a) to enable the air to be exhausted from it; and (j) is a
valve to close the tube after the exhaustion of the air from within the case.
Figure 2 is a plan of the compass shown in section by Figure 1.
My invention may be applied to other varieties of compass than that shown in
the drawing; and in lieu of exhausting the case (a) the whole compass including
the case may be placed within an outer casing or binnacle specially constructed to
enable the air within it to be exhausted. The air may be exhausted by means of
any ordinary air-pump.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is:
1. Exhausting the air from within the cases of compasses within which the

page_text: 2. The use of compasses within air-tight binnacles or chambers from which the
air has been exhausted.
Dated sh 10 1
a
1000
E. H. G. BREWSTER,
Agent for Applicant.