S.P.D.T. ........Single Point Double Throw

S.P.S.T. ........Single Point Single Throw

S.R. ............Self Rectifying

T. ..............Telephone or Period (time) of Complete Oscillation

Tick. ...........Tickler

V. ..............Potential Difference

Var. ............Variometer

Var. Cond. ......Variable Condenser

V.T. ............Vacuum Tube

W.L. ............Wave Length

X. ..............Reactance

GLOSSARY

A BATTERY.--See Battery A.

ABBREVIATIONS, CODE.--Abbreviations of questions and answers used in wireless communication. The abbreviation _of a question_ is usually in three letters of which the first is Q. Thus Q R B is the code abbreviation of "_what is your distance?_" and the answer "_My distance is_..." See Page 306 [Appendix: List of Abbreviations].

ABBREVIATIONS, UNITS.--Abbreviations of various units used in wireless electricity. These abbreviations are usually lower case letters of the Roman alphabet, but occasionally Greek letters are used and other signs. Thus _amperes_ is abbreviated _amp., micro_, which means _one millionth_, [Greek: mu], etc. See Page 301 [Appendix: Useful Abbreviations].

ABBREVIATIONS OF WORDS AND TERMS.--Letters used instead of words and terms for shortening them up where there is a constant repet.i.tion of them, as _A.C._ for _alternating current; C.W._ for _continuous waves; V.T._ for _vacuum tube_, etc. See Page 312 [Appendix: Abbreviations of Common Terms].

AERIAL.--Also called _antenna_. An aerial wire. One or more wires suspended in the air and insulated from its supports. It is the aerial that sends out the waves and receives them.

AERIAL, AMATEUR.--An aerial suitable for sending out 200 meter wave lengths. Such an aerial wire system must not exceed 120 feet in length from the ground up to the aerial switch and from this through the leading-in wire to the end of the aerial.

AERIAL AMMETER.--See _Ammeter, Hot Wire_.

AERIAL, BED-SPRINGS.--Where an outdoor aerial is not practicable _bed-springs_ are often made to serve the purpose.

AERIAL CAPACITY.--See _Capacity, Aerial._

AERIAL COUNTERPOISE.--Where it is not possible to get a good ground an _aerial counterpoise_ or _earth capacity_ can be used to advantage.

The counterpoise is made like the aerial and is supported directly under it close to the ground but insulated from it.

AERIAL, DIRECTIONAL.--A flat-top or other aerial that will transmit and receive over greater distances to and from one direction than to and from another.

AERIAL, GROUND.--Signals can be received on a single long wire when it is placed on or buried in the earth or immersed in water. It is also called a _ground antenna_ and an _underground aerial._

AERIAL, LOOP.--Also called a _coil aerial, coil antenna, loop aerial, loop antenna_ and when used for the purpose a _direction finder_. A coil of wire wound on a vertical frame.

AERIAL RESISTANCE.--See _Resistance, Aerial._

AERIAL SWITCH.--See _Switch Aerial._

AERIAL WIRE.--(1) A wire or wires that form the aerial. (2) Wire that is used for aerials; this is usually copper or copper alloy.

AERIAL WIRE SYSTEM.--An aerial and ground wire and that part of the inductance coil which connects them. The open oscillation circuit of a sending or a receiving station.

AIR CORE TRANSFORMER.--See _Transformer, Air Core._

AMATEUR AERIAL OR ANTENNA.--See _Aerial, Amateur._

ALTERNATOR.--An electric machine that generates alternating current.

ALPHABET, INTERNATIONAL CODE.--A modified Morse alphabet of dots and dashes originally used in Continental Europe and, hence, called the _Continental Code_. It is now used for all general public service wireless communication all over the world and, hence, it is called the _International Code_. See page 305 [Appendix: International Morse Code].

ALTERNATING CURRENT (_A.C._)--See _Current._

ALTERNATING CURRENT TRANSFORMER.--See _Transformer_.

AMATEUR GROUND.--See _Ground, Amateur_.

AMMETER.--An instrument used for measuring the current strength, in terms of amperes, that flows in a circuit. Ammeters used for measuring direct and alternating currents make use of the _magnetic effects_ of the currents. High frequency currents make use of the _heating effects_ of the currents.

AMMETER, HOT-WIRE.--High frequency currents are usually measured by means of an instrument which depends on heating a wire or metal strip by the oscillations. Such an instrument is often called a _thermal ammeter_, _radio ammeter_ and _aerial ammeter_.

AMMETER, AERIAL.--See _Ammeter, Hot Wire_.

AMMETER, RADIO.--See _Ammeter, Hot Wire_.

AMPERE.--The current which when pa.s.sed through a solution of nitrate of silver in water according to certain specifications, deposits silver at the rate of 0.00111800 of a gram per second.

AMPERE-HOUR.--The quant.i.ty of electricity transferred by a current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs.

AMPERE-TURNS.--When a coil is wound up with a number of turns of wire and a current is made to flow through it, it behaves like a magnet. B The strength of the magnetic field inside of the coil depends on (1) the strength of the current and (2) the number of turns of wire on the coil. Thus a feeble current flowing through a large number of turns will produce as strong a magnetic field as a strong current flowing through a few turns of wire. This product of the current in amperes times the number of turns of wire on the coil is called the _ampere-turns_.

AMPLIFICATION, AUDIO FREQUENCY.--A current of audio frequency that is amplified by an amplifier tube or other means.

AMPLIFICATION, CASCADE.--See _Cascade Amplification_.

AMPLIFICATION, RADIO FREQUENCY.--A current of radio frequency that is amplified by an amplifier tube or other means before it reaches the detector.

AMPLIFICATION, REGENERATIVE.--A scheme that uses a third circuit to feed back part of the oscillations through a vacuum tube and which increases its sensitiveness when used as a detector and multiplies its action as an amplifier and an oscillator.