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A pane of glass in a welding helmet or goggles which protects the colored lens excluding harmful light rays from damage by weld spatter.

Related Terms


  1. The point at which parallel rays of light meet after being refracted by a lens or reflected by a mirror. Also called FOCAL PO-I NT. 2. A point having specific significance relative to a geometrical figure. See under ELLIPSE, HYPERBOLA, PARABOLA. 3. The true center of an earthquake, within which the strain energy is first converted to elastic wave energy.


An instrument that measures changes in the declination of the earth's magnetic field, consisting of a permanent bar magnet, usually about 0.4 inch (1 centimeter) long, suspended with a plane mirror from a fine quartz fiber 26 inches (515 centimeters) in length; a lens focuses to a point a beam of light reflected from the mirror to recording paper mounted on a rotating drum. Also known as D variometer.


1) A general term for the night illuminations of vessels/navigational aids whose specification is found in collision regulations, lists of lights and port information. 2) A thick plate of glass fitted in a vessel's structure to provide a watertight light ingress.


A telescope which collects light by means of a lens or system of lenses.


An optical instrument used as an aid in viewing or photo- graphing distant objects, particularly celestial objects. A reflecting telescope collects light by means of a concave mirror; a refracting telescope by means of a lens or system of lenses. A Cassegrainian telescope is a reflecting telescope in which the immergent light is reflected from the main mirror onto a secondary mirror, where it is reflected through a hole in the main mirror to an eyepiece; a Newtonian telescope is a reflecting telescope in which the immergent beam is reflected from the main mirror onto a small plane mirror, and from there to an eyepiece at the side of the telescope.


  1. A grooved rim used to hold a transparent glass or plastic window or lens for a meter, tuning dial, or some other indicating device. 2. A sloping face on a cutting tool.


An instrument, used to measure the pressure exerted by a beam of light, in which there are two small, silvered glass mirrors at the ends of a light rod that is suspended at the center from a fine quartz fiber within an evacuated enclosure.


A piece of glass or transparent material with plane, convex, or concave surfaces adapted for changing the direction of light rays to enlarge or reduce the apparent size of objects.


Mounds of riprap maintained at certain light structures to protect the structures against ice damage and scouring action. Sub- merged portions present a hazard to vessels attempting to pass very close aboard.


  1. The transparent or semitransparent glass front of a cathode-ray tube, through which the image is viewed or projected; the inner surface of the face is coated with fluorescent chemicals that emit light when hit by an electron beam. Also known as face. 2. A disk fixed perpendicularly to the spindle of a lathe and used for attachment of the workpiece. 3. A protective plate used to cover holes in machines or other devices.

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