DICTIONARY OF

Duration of Tide 123 Dysa
Duration of Tide. Time interval between occurrence of low water and the following high
water, or between high water and following low water.
Dutchman's Log. Piece of wood thrown overboard, well forward and used for ascertaining
speed of ship by timing its passage between two marks, of known distance apart, on ship.
Duty. Service or work that should rightly be rendered. 2. Tax or custom charge imposed by
a government on goods imported, exported or consumed.
Duty Free. Exempted from customs duty.
Dwarf Star. One of small mass and low candle power, but of enormously high density.
Dwarf star companion of Procyon weighs about 250 tons per cubic inch.
Dygogram. Geometrical construction representing the direction and amount of each force
acting on a magnetic compass.
Dynamical Mean Sun. Imaginary body moving along Ecliptic and travelling from perigee
to perigee at a constant speed and in the same time as that taken by true Sun. Not considered
in navigation.
Dynamical Stability. Of a ship, is amount of work necessary to heel the vessel through a
given angle.
Dynamo. Machine that converts mechanical energy into direct electric current. Effected by
revolution of an armature in a magnetic field.
Dyne. C.G.S. unit of force, representing amount necessary to produce or accelerate, velocity
of one gramme mass by one centimetre per second.
Dysa, Dyso, Diso. 'Dghaisa.'