RECEPTOR, BEAT.--A heterodyne receptor.

RECEPTOR, HETERODYNE.--A receiving set that uses a separate vacuum tube to set up the second series of waves for beat reception.

REGENERATIVE ACTION.--See _Feed-Back Action._

REGENERATIVE AMPLIFICATION.--See _Amplification, Regenerative._

RELAY, ELECTRON.--A vacuum tube when used as a detector or an amplifier.

REPEATING COIL.--A transformer used in connecting up a wireless receiver with a wire transmitter.

RESISTANCE.--The opposition offered by a wire or other conductor to the pa.s.sage of a current.

RESISTANCE, AERIAL.--The resistance of the aerial wire to oscillating currents. This is greater than its ordinary ohmic resistance due to the skin effect. See _Resistance, High Frequency._

RESISTANCE BOX.--See _Resistor._

RESISTANCE COUPLING.--See _Coupling, Resistance._

RESISTANCE, HIGH FREQUENCY.--When a high frequency current oscillates on a wire two things take place that are different than when a direct or alternating current flows through it, and these are (1) the current inside of the wire lags behind that of the current on the surface, and (2) the amplitude of the current is largest on the surface and grows smaller as the center of the wire is reached. This uneven distribution of the current is known as the _skin effect_ and it amounts to the same thing as reducing the size of the wire, hence the resistance is increased.

RESISTIVITY.--The resistance of a given length of wire of uniform cross section. The reciprocal of _conductivity._

RESISTOR.--A fixed or variable resistance unit or a group of such units. Variable resistors are also called _resistance boxes_ and more often _rheostats._

RESONANCE.--(1) Simple resonance of sound is its increase set up by one body by the sympathetic vibration of a second body. (2) By extension the increase in the amplitude of electric oscillations when the circuit in which they surge has a _natural_ period that is the same, or nearly the same, as the period of the first oscillation circuit.

RHEOSTAT.--A variable resistance unit. See _Resistor._

RHEOSTAT, CARBON.--A carbon rod, or carbon plates or blocks, when used as variable resistances.

RHEOSTAT, FILAMENT.--A variable resistance used for keeping the current of the storage battery which heats the filament of a vacuum tube at a constant voltage.

ROTATING COIL.--See _Coil._

ROTARY GAP.--See _Gap._

ROTOR.--The rotating coil of a variometer or a variocoupler.

RUHMKORFF COIL.--See _Coil, Induction._

SATURATION.--The maximum plate current that a vacuum tube will take.

SENSITIVE SPOTS.--Spots on detector crystals that are sensitive to the action of electric oscillations.

SHORT WAVES.--See _Waves._

SIDE WAVES.--See _Wave Length Band._

SIGNALS, CONVENTIONAL.--(1) The International Morse alphabet and numeral code, punctuation marks, and a few important abbreviations used in wireless telegraphy. (2) Dot and dash signals for distress call, invitation to transmit, etc. Now used for all general public service wireless communication.

SKIN EFFECT.--See _Resistance, High Frequency._

SOFT TUBE.--A vacuum tube in which the vacuum is low, that is, it is not highly exhausted.

s.p.a.cE CHARGE EFFECT.--The electric field intensity due to the pressure of the negative electrons in the s.p.a.ce between the filament and plate which at last equals and neutralizes that due to the positive potential of the plate so that there is no force acting on the electrons near the filament.

SPARK.--See _Discharge._

SPARK COIL.--See _Coil, Induction._

SPARK DISCHARGE.--See _Spark, Electric._

SPARK FREQUENCY.--See _Frequency, Spark._

SPARK GAP.--(1) A _spark gap,_ without the hyphen, means the apparatus in which sparks take place; it is also called a _spark discharger._ (2) _Spark-gap,_ with the hyphen, means the air-gap between the opposed faces of the electrodes in which sparks are produced.

Plain.--A spark gap with fixed electrodes.

Rotary.--A spark gap with a pair of fixed electrodes and a number of electrodes mounted on a rotating element.

Quenched.--A spark gap formed of a number of metal plates placed closely together and insulated from each other.

SPIDER WEB INDUCTANCE COIL.--See _Coil, Spider Web Inductance._

SPREADER.--A stick of wood, or spar, that holds the wires of the aerial apart.

STAGGER WOUND COILS.--See _Coils, Inductance._

STAND-BY CIRCUITS.--See _Circuits, Stand-By._

STATIC.--Also called _atmospherics, grinders, strays, X's,_ and, when bad enough, by other names. It is an electrical disturbance in the atmosphere which makes noises in the telephone receiver.

STATOR.--The fixed or stationary coil of a variometer or a variocoupler.

STORAGE BATTERY.--See _Battery, Storage._

STRAY ELIMINATION.--A method for increasing the strength of the signals as against the strength of the strays. See _Static._

STRAYS.--See _Static_.

STRANDED WIRE.--See _Wire, Stranded_.

SUPER-HETERODYNE RECEPTOR.--See _Heterodyne, Super_.

SWINGING.--See _Fading_.

SWITCH, AERIAL.--A switch used to change over from the sending to the receiving set, and the other way about, and connect them with the aerial.