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


  1. The displacement of an electron beam from its straight-line path by an electrostatic or electromagnetic field.
  2. Shape change or reduction in the diameter of a conduit, produced without fracturing the material.
  3. Elastic movement or sinking of a loaded structural member, particularly of the mid-span of a beam.


A device for measuring the speed of water currents in which a perforated disk, which rotates with the current by means of a propeller, is placed in the path of a beam of light that is then reflected from a mirror onto a phototube.


1. An instrument that measures the penetrating power of a beam of xrays or other penetrating radiation. 2. An instrument used to determine the consistency of a material by measurement of the depth to which a standard needle penetrates into it under standard conditions.


Nonscanning radar which transmits signals over a wide beam in the direction of interest.


A shutter that uses a Kerr cell to modulate a beam of light.


[ENG ACOUS] A microphone in which the motion of a membrane is detected using a light beam reflected from it, either with the aid of an interferometer or by detecting the deflection of the beam.


An instrument which makes a plot of pressure in the cylinder of an engine as a function of piston (or volume) displacement, making use of magnification by optical systems and photographic recording; for example, the small motion of a pressure diaphragm may be transmitted to a mirror to deflect a beam of light.


A surface in a bent beam along which material is neither compressed nor extended.


In a beam bent downward, the line of zero stress below which all fibers are in tension and above which they are in compression.


A graph of the bending moment at a section of a beam versus the distance of the section along the beam.

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