English

A group of PENCILS of light, as those originating at the many points of an illuminated surface. A BEAM of parallel LIGHT RAYS is a special case in which each PENCIL is of such small cross-section that it may be regarded as a RAY.

A boat-like structure used instead of a light buoy in waters where strong streams or currents are experienced, or when a greater elevation than that of a light buoy is necessary.

Luminous manifes­tations accompanying a sudden electrical discharge which takes place from or inside a CLOUD or, less often, from high structures on the GROUND or from MOUNTAINS.

The geometrical concept of a single element of light propagated in a straight line and of in­finitesimal cross-section; used in analytically tra­cing the path of light through an OPTICAL SYSTEM.

A distinctively marked vessel anchored or moored at a charted point, to serve as an AID TO NAVIGATION. By night it displays a characteristic LIGHT(S), and is usually equipped with other devices, such as a FOG SIGNAL, SUBMARINE SOUND SIGNAL, and RADIOBEACON, to assist NAVIGATION. Also called light vessel.

A cargo carrying system using specially built ships and lighters. Cargoes are loaded into LASH lighters which are towed to a LASH ship where they are embarked. At their destination the LASH lighters are disembarked and towed away to their unloading berths. Special berths or anchorages are sometimes designated for LASH ships.

The graduated curved part of an instrument for measuring angles, as that part of a MARINE SEXTANT carrying the altitude scale, or arc. The circular outer edge of a CELESTIAL BODY. The half with the greatest ALTITUDE is called the upper limb and the half with the least ALTITUDE, the lower limb.