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EARTH LEAD: The wire which connects any electrical apparatus with the earth, and used as a safety precaution in the event of a short circuit. The largest pin in a 3-pin connector is for the wire which will convey to earth the escaping current. The earth lead should be one with a very low resistance. There is no danger from a loose connection if the escaping current is enabled to flow directly to earth, providing, of course, that the projectionist is not standing in a pool of water and making himself a better earth than the one connected. Projectors using a 2-core mains cable may be connected by a copper (earth) wire to a convenient water pipe, care being taken to first remove the paint — the paint may act as insulation. (See Ground).
ECHO: Reflected sound. A continuous echo is known as reverberation. The sound is reflected from different surfaces according to the surface structure. A hard smooth surface will produce a distinct echo with a certain amount of strength, whilst a soft porous surface will break up and scatter the sound so that it cannot be heard as an acho.
EFFICIENCY: The amount of energy supplied to a machine in relation to the amount used for actual performance. A highly efficient electrical motor is one which usefully employs all the current supplied to it.
ELECTRIC CURRENT: An artificially produced or natural flow of electrons and ions carrying negative and positive charges respectively. The actual nature of electricity is unknown.
ELECTROLYTIC CONDENSER: A small condenser having a relatively large capacity.
E.M.F.: Electromotive Force. The pressure of an electric current, measured in volts.
EMULSION: A light-sensitive substance applied to photographic film, in which the photographic print is impressed by means of lightaction.
EXCITER LAMP: A small voltage single "spot" filament lamp which provides light for the photo-cell in reproduction of sound. Exciter rays are for the same purpose but are directed from the projector lamp.
FADER: In projection, the potentiometer controlling soundvolume.
FADING IN: Gradual lighting of the screen, usually by means of a slide-resistance connected to the lamp circuit.
FILAMENTS: In a lamp or valve, the fine strands of wire which heat or light up. The wires which produce heat within an electric iron or fire are known as elements.
FUSE; The fuse is really an electrical safety valve. Usually in the form of a single strand of wire, it will melt and thus break an electrical circuit should the current exceed a certain value. The fuse wire for domestic lighting is usually rated at 5-amps., insufficient for many 16-m.m. projectors, especially those using resistances.
GENERATOR: The machine which converts mechanical energy into electrical energy and produces a flow of electricity. Electricity cannot be "manufactured."
GRAPHITE GREASE: Soft graphite is used in the manufacture of hightemperature grease, and is often used for lubrication in projector mechanisms.
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