English

The act or practice of noting and recor­ding facts and events as for some scientific study. The measure of a quantity whose value is desired. The DATA so noted and recorded. A single measure, at a single setting of an ap­paratus.

OBSERVATIONS of CELESTIAL BODIES, with appropriate instruments. In NAVIGATION, the measure­ment of ALTITUDE and AZIMUTH of CELESTIAL BODIES.

A series of measurements taken in order to provide the information required for the REDUCTION OF SOUNDINGS, and the DATA for TIDAL PREDIC­TION and investigation.

A tower from which one's surroun­dings can be observed, but at which a watch is not habitually maintained, as at a LOOKOUT TOWER. Such towers are temporarily erected for observations in geodetic networks.

Those data from tide observing equip­ment such as tide gauges, staffs, etc. "Actual tides" is an expression often used in referring to "observed ti­des".

In MARINE NAVIGATION, anything that hin­ders or prevents movement, particularly anything that endangers or prevents passage of a vessel. The term is usually used to refer to an isolated danger to NAVIGATION, such as a SUNKEN ROCK or PINNACLE.

Process of progressive decrease of area of warm sector at the EARTH's surface, and its ultimate disappearance, by the junction of the cold AIR MASSES which initially precede the WARM FRONT and follow the COLD FRONT. FRONT between these two cold AIR MASSES, after their junction (also termed occluded front).

The concealment or extinguishment of the light of an AID TO NAVIGATION during the dark periods of its CYCLE. In ASTRONOMY, the conceal­ment of a CELESTIAL BODY by another which crosses the line of view. Thus, the MOON occults a STAR when it passes between the observer and the STAR.

(v.t.). In SURVEYING, to observe with a surveying instrument at a STATION; also to set a surveying instrument over a point for the purpose of making OBSERVATIONS. In OCEANOGRAPHY, to stop a ship at a selected location, an OCEANOGRAPHIC STATION, for the purpose of gathering oceanographic observations.