SWITCH, LIGHTNING.--The switch that connects the aerial with the outside ground when the apparatus is not in use.

SYMBOLS, APPARATUS.--Also called _conventional symbols_. These are diagrammatic lines representing various parts of apparatus so that when a wiring diagram of a transmitter or a receptor is to be made it is only necessary to connect them together. They are easy to make and easy to read. See Page 307 [Appendix: Symbols Used for Apparatus].

SYNCHRONOUS GAP.--See _Gap, Synchronous_.

TELEPHONY, LINE RADIO.--See _Wired Wireless_.

THERMAL AMMETER.--See _Ammeter, Hot Wire_.

THREE ELECTRODE VACUUM TUBE.--_See Vacuum Tube, Three Electrode_.

TIKKER.--A slipping contact device that breaks up the sustained oscillations at the receiving end into groups so that the signals can be heard in the head phones. The device usually consists of a fine steel or gold wire slipping in the smooth groove of a rotating bra.s.s wheel.

TRANSFORMER.--A primary and a secondary coil for stepping up or down a primary alternating or oscillating current.

A. C.--See _Power Transformer_.

Air Cooled.--A transformer in which the coils are exposed to the air.

Air Core.--With high frequency currents it is the general practice not to use iron cores as these tend to choke off the oscillations. Hence the core consists of the air inside of the coils.

Auto.--A single coil of wire in which one part forms the primary and the other part the secondary by bringing out an intermediate tap.

Audio Amplifying.--This is a transformer with an iron core and is used for frequencies up to say 3,000.

Closed Core.--A transformer in which the path of the magnetic flux is entirely through iron. Power transformers have closed cores.

Microphone.--A small transformer for modulating the oscillations set up by an arc or a vacuum tube oscillator.

Oil Cooled.--A transformer in which the coils are immersed in oil.

Open Core.--A transformer in which the path of the magnetic flux is partly through iron and partly through air. Induction coils have open cores.

Oscillation.--A coil or coils for transforming or stepping down or up oscillating currents. Oscillation transformers usually have no iron cores when they are also called _air core transformers._

Power.--A transformer for stepping down a commercial alternating current for lighting and heating the filament and for stepping up the commercial a.c., for charging the plate of a vacuum tube oscillator.

Radio Amplifying.--This is a transformer with an air core. It does not in itself amplify but is so called because it is used in connection with an amplifying tube.

TRANSMITTER, MICROPHONE.--A telephone transmitter of the kind that is used in the Bell telephone system.

TRANSMITTING TUNING COILS.--See _Coils, Inductance._

TUNING.--When the open and closed oscillation circuits of a transmitter or a receptor are adjusted so that both of the former will permit electric oscillations to surge through them with the same frequency, they are said to be tuned. Likewise, when the sending and receiving stations are adjusted to the same wave length they are said to be _tuned._

Coa.r.s.e Tuning.--The first adjustment in the tuning oscillation circuits of a receptor is made with the inductance coil and this tunes them coa.r.s.e, or roughly.

Fine Tuning.--After the oscillation circuits have been roughly tuned with the inductance coil the exact adjustment is obtained with the variable condenser and this is _fine tuning._

Sharp.--When a sending set will transmit or a receiving set will receive a wave of given length only it is said to be sharply tuned.

The smaller the decrement the sharper the tuning.

TUNING COILS.--See _Coils, Inductance._

TWO ELECTRODE VACUUM TUBE.--See _Vacuum Tube, Two Electrode._

VACUUM TUBE.--A tube with two or three electrodes from which the air has been exhausted, or which is filled with an inert gas, and used as a detector, an amplifier, an oscillator or a modulator in wireless telegraphy and telephony.

Amplifier.--See _Amplifier, Vacuum Tube._

Amplifying Modulator.--A vacuum tube used for modulating and amplifying the oscillations set up by the sending set.

Gas Content.--A tube made like a vacuum tube and used as a detector but which contains an inert gas instead of being exhausted.

Hard.--See _Hard Tube._

Rectifier.--(1) A vacuum tube detector. (2) a two-electrode vacuum tube used for changing commercial alternating current into direct current for wireless telephony.

Soft.--See _Soft Tube._

Three Electrode.--A vacuum tube with three electrodes, namely a filament, a grid and a plate.

Two Electrode.--A vacuum tube with two electrodes, namely the filament and the plate.

VALVE.--See _Vacuum Tube._

VALVE, FLEMING.--See _Fleming Valve._

VARIABLE CONDENSER.--See _Condenser, Variable._

VARIABLE INDUCTANCE.--See _Inductance, Variable._

VARIABLE RESISTANCE.--See _Resistance, Variable._

VARIOCOUPLER.--A tuning device for varying the inductance of the receiving oscillation circuits. It consists of a fixed and a rotatable coil whose windings are not connected with each other.

VARIOMETER.--A tuning device for varying the inductance of the receiving oscillation currents. It consists of a fixed and a rotatable coil with the coils connected in series.

VERNIER CONDENSER.--See _Condenser, Vernier._

VOLT.--The electromotive force which produces a current of 1 ampere when steadily applied to a conductor the resistance of which is one ohm.

VOLTAGE DIVIDER.--See _Potentiometer._

VOLTAGE, PLATE.--The voltage of the current that is used to energize the plate of a vacuum tube.

VOLTMETER.--An instrument for measuring the voltage of an electric current.