=Depolarization.= A term applied to the removal of permanent magnetism, such as that from a horseshoe magnet, a watch, or a bar-magnet. Heat is the common depolarizer, but counter electro-magnetic forces are employed also in the various forms of apparatus known as demagnetizers. =Deposit, Electrolytic.= The metal or other substances precipitated by the action of a battery or other current-generator, as in the plating processes. =Detector.= A portable galvanometer, by means of which a current and its approximate strength can be detected and measured. =Diaphragm.= In telephones and microphones, a disk of iron thrown into motion by sound-waves or by electric impulse. It is usually a thin plate of japanned iron, such as is used in the ferrotype photographic process for making tin-types. =Dielectric.= Any substance through which electrostatic induction is allowed to occur, such as glass or rubber. It is a non-conductor for all electric currents. =Dielectric Resistance.= The resistance a body offers to perforation or destruction by an electric discharge. =Dimmer.= An adjustable choke or resistance coil used for regulating the intensity of electric incandescent lamps. It is employed extensively in theatres for raising or lowering the brilliancy of lights. =Dipping.= The process of cleaning articles by dipping them in acids or caustic soda, preparatory to electro-plating. Simple immersion, with or without current, to put a blush of metal on a cleaned surface. =Dipping-needle.= A magnetic needle mounted on a horizontal bearing so that it will dip vertically when excited by a current passing horizontally about it. The ordinary compass-needle is mounted on a point, and swings freely to the right or left only. =Direct Current.= (_See_ Current, Direct.) =Discharge.= The eruptive discharge from a Leyden-jar or accumulator of a volume of electricity stored within it. The abstraction of a charge from a conductor by connecting it to the earth or to another conductor. =Discharge, Disruptive.= The discharge of a static charge through a dielectric. It involves the mechanical perforation of the dielectric. =Disconnect.= To break an electric circuit or open it so as to stop the flow of current; to remove a part of a circuit or a piece of apparatus from a circuit. =Distillation, Electric.= The distilling of a liquid by the employment of electricity, which, by electrifying the liquid, assists the effects of heat. It is asserted that the process is accelerated by the electrification of the liquid or fluid, but it must be a conductor liquid or electrolyte. Oil, being a non-conductor, is not affected by any electric current, no matter what its specific gravity may be. =Distributing Centre.= The centre of distribution in a system having branch circuits, such as the electric-light or telephone outlets from a main station.