DICTIONARY OF

Centaur(us) 74 Centre of Oscillation
Centaur(us). Bright constellation in southern sky. Indicated by a line drawn through
Arcturus and Spica. Has two navigational stars, and . Approx. R.A. 14 h; Dec. 60°S.
Centering Error. Sextant error due to centre of pivot not being at exact centre of arc. Error
varies with altitude.
Centigrade Scale. Graduation of thermometer in which freezing point of water is 0° and
boiling point is 100°. Is a modification of Celsius scale, and was introduced by Christin, of
Lyons, in 1743.
Central Eclipse. Eclipse in which centres of the two heavenly bodies are exactly in line to
an observer at a specified place.
Central Latitude. Angle at centre of Earth between plane of Equator and a line projected
through observer. As Earth is not a true sphere this angle will differ from angle formed by
downward projection of observer's vertical—which is the 'normal' latitude.
Central Projection (of sphere). Projection of surface of sphere to a tangent plane by lines
from centre of sphere.
Central Sun. Point in the heavens about which the universe may be considered to turn. At
one time was considered to be in constellation of Taurus.
Centre Board. Name often given to a 'drop keel'.
Centre-Castle. The raised part of a ship's hull amidships.
Centre of Buoyancy. That point in a floating body, at which the total moments of buoyancy
in any one direction are balanced by equivalent moments of buoyancy in the opposite
direction.
Centre of Cavity. 'Centre of displacement.'
Centre of Displacement That point, in a floating body, which is the geometrical centre of
the immersed portion.
Centre of Effort. That point, in a sail, at which all wind force may be assumed to act.
Theoretically, it would be the geometrical centre of sail area. In practice, it will be somewhat
away from the theoretical point, due to sail not presenting a perfectly flat surface to wind,
and not being at a uniform angle to wind in all parts.
Centre of Flotation. Geometrical centre of immersed volume of a floating body.
Centre of Gravity. That point, in any body, at which the moments of gravitational force in
any one direction are balanced by the moments of gravitational force in the opposite
direction.
Centre of Gyration. That distance along a radius of a revolving body at which the mass
may be considered to act. With disc of uniform density and thickness the centre of gyration
is 0-707 of radius from centre of rotation.
Centre of Immersion. 'Centre of displacement'.
Centre of Lateral Resistance. Point, in lee side of underwater body of a vessel, at which
the forces resisting leeway are equal in any two opposite directions in the fore and aft line.
Centre of Oscillation. That point, in a pendulum, at which total of moments of forces on
upper side are equal to moments on lower side.