1. The slowly decaying luminescence of the screen of the cathode-ray tube after excitation by an electron beam has ceased. 2. A broad, high arch of radiance or glow seen occasionally in the western sky above the highest clouds in deepening twilight, caused by the scattering effect of very fine particles of dust suspended in the upper atmosphere.

Related Terms

DIELECTRIC STRENGTH

A measure of the ability of an insulating material to withstand electric stress (voltage) without failure. Fluids with high dielectric strength (usually expressed in volts or kilovolts) are good electrical insulators. (ASTM Designation D 877.)

BEAM

The width of a ship. Also called breadth.

BREADTH

The width of a ship.

CARBON RESIDUE

Coked material remaining after an oil has been exposed to high temperatures under controlled conditions.

REFRIGERATOR

A device to transfer heat from a low temperature to a high temperature medium.

ADSORPTION

Adhesion of the molecules of gases, liquids, or dissolved substances to a solid surface, resulting in relatively high concentration of the molecules at the place of contact; e.g. the plating out of an anti-wear additive on metal surfaces.

HALF-TIDE BASIN

A lock of very large size and usually of irregular shape, the gates of which are kept open for several hours after high tide so that vessels may enter as long as there is sufficient depth over the sill. Vessels remain in the half-tide basin until the ensuing flood tide before they may pass through the gate to the inner harbor. If entry to the inner harbor is required before this time, water must be admitted to the half-tide basin from some external source.

HALF-POWER POINTS

Power ratios used to define the angular width of a radar beam. One convention defines beam width as the angular width between points at which the field strength is 71 percent of its maximum value. Expressed in terms of power ratio, this convention defines beam width as the angular width between half-power points. A second convention defines beam width as the angular width between points at which the field strength is 50 percent of its maximum value. Expressed in terms of power ratio, the latter convention defines beam width as the angular width between quarter- power points.

HEELING MAGNET

A permanent magnet placed vertically in a tube under the center of a marine magnetic compass, to correct for heeling error.

HIGH WATER INEQUALITY

The difference between the heights of the two high waters during a tidal day

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