Filter Condenser.--A condenser of large capacitance used in combination with a filter reactor for smoothing out the pulsating direct currents as they come from the rectifier.

Fixed Condenser.--Where the plates are fixed relatively to one another.

Grid Condenser.--A condenser connected in series with the grid lead.

Leyden Jar Condenser.--Where gla.s.s jars are used.

Mica Condenser.--Where mica is used.

Oil Condenser.--Where the plates are immersed in oil.

Paper Condenser.--Where paper is used as the insulating material.

Protective.--A condenser of large capacity connected across the low voltage supply circuit of a transmitter to form a by-path of kick-back oscillations.

Variable Condenser.--Where alternate plates can be moved and so made to interleave more or less with a set of fixed plates.

Vernier.--A small condenser with a vernier on it so that it can be very accurately varied. It is connected in parallel with the variable condenser used in the primary circuit and is used for the reception of continuous waves where sharp tuning is essential.

CONDENSITE.--A manufactured insulating compound.

CONDUCTIVITY.--The conductance of a given length of wire of uniform cross section. The reciprocal of _resistivity_.

CONTACT DETECTORS.--See _Detectors, Contact_.

CONTINENTAL CODE.--See _Code, Continental_.

COULOMB.--The quant.i.ty of electricity transferred by a current of 1 ampere in 1 second.

CONVECTIVE DISCHARGE.--See _Discharge_.

CONVENTIONAL SIGNALS.--See _Signals, Conventional_.

COUNTER ELECTROMOTIVE FORCE.--See _Electromotive Force, Counter_.

COUNTERPOISE. A duplicate of the aerial wire that is raised a few feet above the earth and insulated from it. Usually no connection is made with the earth itself.

COUPLED CIRCUITS.--See _Circuit, Coupled_.

COUPLING.--When two oscillation circuits are connected together either by the magnetic field of an inductance coil, or by the electrostatic field of a condenser.

COUPLING, CAPACITIVE.--Oscillation circuits when connected together by condensers instead of inductance coils.

COUPLING, COEFFICIENT OF.--The measure of the closeness of the coupling between two coils.

COUPLING, INDUCTIVE.--Oscillation circuits when connected together by inductance coils.

COUPLING, RESISTANCE.--Oscillation circuits connected together by a resistance.

CRYSTAL RECTIFIER.--A crystal detector.

CURRENT, ALTERNATING (A.C.).--A low frequency current that surges to and fro in a circuit.

CURRENT, AUDIO FREQUENCY.--A current whose frequency is low enough to be heard in a telephone receiver. Such a current usually has a frequency of between 200 and 2,000 cycles per second.

CURRENT, PLATE.--The current which flows between the filament and the plate of a vacuum tube.

CURRENT, PULSATING.--A direct current whose voltage varies from moment to moment.

CURRENT, RADIO FREQUENCY.--A current whose frequency is so high it cannot be heard in a telephone receiver. Such a current may have a frequency of from 20,000 to 10,000,000 per second.

CURRENTS, HIGH FREQUENCY.--(1) Currents that oscillate from 10,000 to 300,000,000 times per second. (2) Electric oscillations.

CURRENTS, HIGH POTENTIAL.--(1) Currents that have a potential of more than 10,000 volts. (2) High voltage currents.

CYCLE.--(1) A series of changes which when completed are again at the starting point. (2) A period of time at the end of which an alternating or oscillating current repeats its original direction of flow.

DAMPING.--The degree to which the energy of an electric oscillation is reduced. In an open circuit the energy of an oscillation set up by a spark gap is damped out in a few swings, while in a closed circuit it is greatly prolonged, the current oscillating 20 times or more before the energy is dissipated by the sum of the resistances of the circuit.

DECREMENT.--The act or process of gradually becoming less.

DETECTOR.--Any device that will (1) change the oscillations set up by the incoming waves into direct current, that is which will rectify them, or (2) that will act as a relay.

Carborundum.--One that uses a _carborundum_ crystal for the sensitive element. Carborundum is a crystalline silicon carbide formed in the electric furnace.

Cat Whisker Contact.--See _Cat Whisker Contact_.

Chalcopyrite.--Copper pyrites. A bra.s.s colored mineral used as a crystal for detectors. See _Zincite_.

Contact.--A crystal detector. Any kind of a detector in which two dissimilar but suitable solids make contact.

Ferron.--A detector in which iron pyrites are used as the sensitive element.

Galena.--A detector that uses a galena crystal for the rectifying element.

Iron Pyrites.--A detector that uses a crystal of iron pyrites for its sensitive element.

Molybdenite.--A detector that uses a crystal of _sulphide of molybdenum_ for the sensitive element.

Perikon.--A detector in which a _bornite_ crystal makes contact with a _zincite_ crystal.

Silicon.--A detector that uses a crystal of silicon for its sensitive element.

Vacuum Tube.--A vacuum tube (which see) used as a detector.

Zincite.--A detector in which a crystal of _zincite_ is used as the sensitive element.

DE TUNING.--A method of signaling by sustained oscillations in which the key when pressed down cuts out either some of the inductance or some of the capacity and hence greatly changes the wave length.