D
Damper. A frame of copper on which the wire in a galvanometer is sometimes coiled. It acts to check the needle oscillations.
A brass or copper sheathing or tube placed between the primary and secondary coils of an induction-coil to cut off induction and diminish the current and potential of the secondary circuit. When the tube is drawn out gradually the induction increases. It is commonly used in medical coils to adjust their strength of action.
D-C. An abbreviation for direct current.
Dead Earth. A fault in telegraph and telephone lines which consists in the ground-wire being improperly grounded, or not fully connected with the earth.
Dead Turns. A term applied to the ten to twenty per cent. of the convolutions or turns of wire on an armature which are considered to be dead. There are supposed to be about eighty per cent. of the turns on an armature that are active in magnetizing the core; the balance are outside the magnetic field and are termed dead, although they are necessary to the production of electro-motive force.
Dead Wire. A wire in the electric circuit through which no current is passing.
A disused or abandoned electric conductor, such as a telegraph wire, or a wire which may be in circuit, but through which at the time of speaking no electrical action is taking place.
Death, Electrical. Death resulting from an electric current passing through the animal body—electrocution; accidental death by electric shock; premeditated death through bringing the body in direct contact with conductors carrying high electro-motive force. High electro-motive force is essential, and the alternating current is most fatal.
Decomposition, Electrolytic. The decomposition or separation of a compound liquid into its constituents by electrolysis. The liquid must be a conductor or electrolyte, and the decomposition is carried on by means of electricity.
The conversion of two or more chemicals into a new compound or substance.
Deflection. In magnetism, the movement of the needle out of the plane. It is due to disturbance, or to the needle’s attraction towards a mass of iron or steel or another magnet.
Demagnetization. The removal of magnetism from a paramagnetic substance. The process is principally in use for watches which have become magnetized by exposure to the magnetic field surrounding dynamos or motors.
Density, Electric. The relative quantity of electricity, as a charge, upon a unit area of surface. It may be positive or negative.
Surface density, as the charge of a Leyden-jar.
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.
Door-opener, Electric. A magnetic contrivance arranged in connection with a lock, by means of which the latch is released by pressing a distant push-button. This device is used in flats and apartment-houses for opening a door from any of the apartments in the house.
Double Filament Lamp. An incandescent lamp having two filaments, one with a high capacity, the other with a low one. The high capacity may be from sixteen to fifty candle-power, the other from one to five. A turn of the bulb in its socket, or the pulling of a string which operates a switch in the socket, cuts out the current from the long filament and sends it through the shorter and finer one, thus giving a weaker light. These “hy-lo” lamps are useful as night lamps in halls, bath-rooms, or in sick-rooms, where a low or weak light is required all night.
Double Pole-switch. A cut-out that is arranged to cut out the circuit of both the negative and positive leads at the same time.
Double-push. A contact-push having two contacts and arranged so that pressure upon it opens one contact and closes the other.
Double Throw-switch. A switch so arranged that it can be thrown into either one of two contacts; a throw-over switch.
Driving-pulley. The broad-faced or channelled pulley on an armature shaft by means of which the power from a motor may be transmitted mechanically.
Dry Battery. (See [Battery, Dry].)
Duct. The space in an underground conduit for a single wire or cable.
Duplex Wire. An insulated conductor having two distinct wires twisted or laid together, but properly insulated from each other.
Dynamic Electricity. Electricity in motion or flowing, as distinguished from static or frictional electricity.
Electricity of relatively low potential or electro-motive force in large quantity or amperage.
Dynamo. An apparatus consisting of a core and field-magnets, properly wound with insulated wire, which, when put into operation by revolving the core or armature at high speed, develops electric current; a mechanical generator of electricity.
Dynamo, Motor. (See [Motor-dynamo].)