DICTIONARY OF

Oakum 239 Ocean Plait
Oakum. Rope that has been unlaid and the yarns teased out. Used for caulking seams, filling
fenders, and other purposes.
Oar. Rowing implement made of wood and consisting of a blade, a long shaft and a loom
that forms a hand-grip. Blade may be flat or curved.
Oar Lock. 'Rowlock.'
Oar Propeller. Machine for propelling a boat by actuating an oar in the manner adopted
when sculling with oar over stern.
Oar Swivel. Name once given to a 'crutch'.
Object Glass. That lens, in a telescope or binocular, at which light rays from an object enter
the instrument.
Oblate Spheroid. Solid produced by semi-rotation of an ellipse about its minor axis.
Sometimes applied to a spheroid that rotates on its minor axis—as do Earth and planets.
Oblique Sailing. Sailing obliquely to the meridian, so that latitude and longitude are
changing.
Oblique Sphere. Terrestrial sphere as it appears to an observer who is not at Equator or a
pole. Apparent movement of all heavenly bodies are along circles oblique to horizon.
Obliquity of Ecliptic. Angle between plane of Equinoctial and plane of Ecliptic.
Observation. Measurement of altitude and bearing of a heavenly body. 2. Measurement of
tidal phenomena.
Observed Altitude. Sextant altitude of a heavenly body when corrected for index error.
Observed Distance. Angular distance between two heavenly bodies when corrected for
index error of sextant.
Obstruction. In a chart, signifies something below chart datum that is a possible menace to
navigation.
Occlude. To enclose; to shut up.
Occlusion. Line, on a meteorological chart, indicating the meeting of cold and warm fronts.
Also the interposition of the cold front between the surface and the warm air mass under
which it has intruded.
Occultation. Obscuration of a heavenly body by a nearer body passing between it and an
observer. 2. The hiding of a light by the interposition of a screen.
Occulting. Said of light when its period of visibility is not less than its period of occultation.
Ocean. Originally a great river that was supposed to encircle the habitable world. Now
applied to the great seas that extend between the continents.
Ocean Greyhound. A fast passenger liner.
Ocean Plait. An under and over plaiting of a single rope that is often used for making mats.