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MANAGERS AND PROJECTIONISTS 19
Definitions
JT is desirable that the projectionist know the meaning of certain terms used in connection with his work, hence we append a somewhat extended list of definitions, making no pretense that it is complete. It is merely designed to define those terms with which the projectionist is likely to come more or less frequently into contact. Hawkins' Electrical Dictionary of electrical terms contains more than 500 pages of definitions. It is an excellent work for such as have need for so complete a list.
ABSORPTION OF LIGHT.— The retaining or absorption by a substance, as a lens, of a portion of the light falling upon its surface or passing through it. The energy of the light thus retained ordinarily is transformed into heat, though in some instances its energy is partly absorbed in the working of chemical change. The absorption by good quality glass is about one per cent per inch of distance traversed by the light.
ACETONE. — A liquid obtained as a by-product in the distillation of wood alcohol. It forms the base of some film cement formulas.
ACTINIC RAY. — A ray of light, or of invisible radiant energy which can induce chemical action. The violet and ultra violet rays are the most powerfully actinic of any of the entire spectrum.
ADHESIVE TAPE.— See insulating tape.
A. H. — An abbreviation for ampere hour.
AIR GAP. — Electrically it means a gap or opening in an electric circuit which is occupied by air only, as the gap in a gas engine spark plug.
ALIVE. — A term used to describe the condition of a wire or other thing when charged with E. M. F.
AMMETER. — An instrument for measuring current flow in amperes,. It is also known as the "Ampere Meter." It is the commercial form of the galvanometer.
AMP. — The most commonly used abbreviation for ampere.
AMPERE. — The unit of electrical current flow. See page 51.