The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1874-02-26
THE UNITED STATES NAVAL INSTITUTE.
Important Paper by Professor
Green.
Fundamental Requirements OF the Marine
Compass.

AZ thc idst mccbHY VI TIC On1cu Slatcs NdNai
Institute, Professor J. II. G. Coan IN the char,
held at the Lyceum OF the Naval Academy at
Annapolis, Nd, Professor B. r. Greene, United
States Navy. read paper on "ship's Compasses"
Of more tnan ordinary scientific value. The follow
ing Is an absJract:--
The object Of fhis paper, as partly implied in It's
title, was twOi0ldurst, to consider the theoretical
OF the marine compass and, secondly, TO snow
wherein the PRACTICAL conclusions dedncibe from
those principles are likely to De SATISFIED by the
present form OF compass used In the United States
Navy In the treatment OF the first part
OF the subject the three fundamental properties
magnetp0wer, senabilty and steadiness, as es-
sential TO its reliable action and convenient use.
Under The head OF magnetpower the relations OF
the motive and resisting forces, regarded a. CON-
ponents IN the expression OF the moment OF de.
nection OF compass card were pointed out, and
therefrom: while from the latter 1t was inferred
that there exists an angle Of set, whose value for
on the magnet power OF the card, the exterior d.
receive force acting upon it, and the resistance TO
morton OF the caro-. Whence 1t was inferred that
for the card to return exactly or very nearly to It's
previous position OF rest whenever detected from
It. 1t Is necessary either that the amount OF resist
auce be extremely small In comparison with the
product OF the magnet power by the directive
force. OF that this product be extremely large IN
Re erence was made to the fact that the
directive force in different parts OF the earth
traversed by the navigator varies rom about
0ne-half to about twice Its mean value; while It's
variations on board SNIP especially II IRON built,
Were often quite as large on dinerens courses,
quenrly, II, from developed defects OF the
compass, the moment OF resistance should
ss oH Sosu sUau If Ss
It's mean value. even while the magnet power
OF the card remained unimpaired, the angle of
Hence the great Importance, first, OF an ample
supply OF magnet power IN the compass card, not
only enough ior ordinary circumstances, but sur.
Mus for extraordinary occasions or
special requirement; and, secondly OF so high
degree Of permanence IN the magnetic state OF the
card as 1t was possible to have.
The Development OF magnet power In the CON-
pass card was next considered, comprising
single magnets are formed, and Of the conditions
OF their most favorable distribution upon the COM
pass card. or the attainment Of the greatest mag
Dency. Finally, the several methods OF DETECTION,
oscillation and torsion for correctly estimating The
magnet power Of q compass were pointed out,
with their relative advantages in facility OF use at
sea.
OF the compass, showing at the outset That the
angle Of set was TO be regarded as the detect OF
sensibility. He then pointed out the two parts of
the moment OF resistance, consisting OF the mo-
ment OF friction at the pivot and OF the resistance
OF the medium. 1t was shown that the defect OF
however great it might be, even in a
liquid medium, being wholly excluded by
the law OF this resistance, but that IT dld depend
ON the moment of friction. Hence the Importance,
in order to preserve the highest degree OF compass
senslbiliry, OF reducing the several elements Of
frictIona resistance to their smallest practicable
limits, and OF preserving this condition with the
least possible change under different physical cir
The conditions of compass steadlness were then
discussed; and. after noticing the two conditions
Of elevatilg the point OF card suspension and OF
distributing the non-concenIr1c material of the
card. as to insure equal moments of inertia
about all diameters OF the card, the great adyan-
asss 'hs being shown thas the RE
sistance OF such medium was admirably
adapted to the production OF steadiness
And not only this, but the further advantages OF
the auxiliary condition OF buoyant card with
minimum pressure at the pivot was strongly In
sisted on conducting to much greater steadiness,
and as tending to the condition OF sensibly per-
@ in not az the
Upon the BASIS Of the foregoing principles Pro-
lessor Greene next introduced the present navy
compass, and, after indicating the chief points OF
Its construction. reviewed It's several character
OF other compasses OF well known makers. was
given. This, although quite favorable TO the navy
it had vet reached that degree OF develop
ment to which 1t might he ludlctously
pushed. Again, 1t was shown thai with
OF the compass at the pivot (ony about sixty grains
at the mean temperaturel and the proportonally
the highest degree the condition OF sensibility;
and by reference to the numerical results Of
some recent inspection tests 1t was shown to be
practically free rom error In this respect, or
sensbly perfect sensibillty. Finally the extra
ordinary steadiEess OF the navy compass was
1erred to In confirmation OF the conditions pre-
viousy stated to be favorable to the possession of
this property.
Professor ]. Ii. c. Comm. United states Navy,
Superintendent OF the Nautical Almanac" at its
conclusion made some remarks relative to the
great Improvement IN compasses since they had
been made subject OF special scientific investga-
tion, and gave some account OF his own experience
with the navy compass OF thrty-fve years ago.
which were then supplied to our ships from the
varrn chanHlerSf
The thanks OF the Institute were rendered to
Professor Greene for his interesting aud valuable
paper, and paper by Captain LETTERS, Cher OF
Bureau OF Ordnance, was announced Tor the next
meeting. after which the meeting adjourned.