LOOSE COUPLED CIRCUITS.--See _Circuits, Loose Coupled._

LOUD SPEAKER.--A telephone receiver connected to a horn, or a specially made one, that reproduces the incoming signals, words or music loud enough to be heard by a room or an auditorium full of people, or by large crowds out-doors.

MAGNETIC POLES.--See _Poles, Magnetic._

MEGOHM.--One million ohms.

METER, AUDIBILITY.--An instrument for measuring the loudness of a signal by comparison with another signal. It consists of a pair of headphones and a variable resistance which have been calibrated.

MHO.--The unit of conductance. As conductance is the reciprocal of resistance it is measured by the _reciprocal ohm_ or _mho._

MICA.--A transparent mineral having a high insulating value and which can be split into very thin sheets. It is largely used in making condensers both for transmitting and receiving sets.

MICROFARAD.--The millionth part of a _farad._

MICROHENRY.--The millionth part of a _farad._

MICROMICROFARAD.--The millionth part of a _microfarad._

MICROHM.--The millionth part of an _ohm._

MICROPHONE TRANSFORMER.--See _Transformer, Microphone._

MICROPHONE TRANSMITTER.--See _Transmitter, Microphone._

MILLI-AMMETER.--An ammeter that measures a current by the one-thousandth of an ampere.

MODULATION.--(1) Inflection or varying the voice. (2) Varying the amplitude of oscillations by means of the voice.

MODULATION, BUZZER.--The modulation of radio frequency oscillations by a buzzer which breaks up the sustained oscillations of a transmitter into audio frequency impulses.

MILLIHENRY.--The thousandth part of a _henry._

MODULATION, CHOPPER.--The modulation of radio frequency oscillations by a chopper which breaks up the sustained oscillations of a transmitter into audio frequency impulses.

MODULATION, GRID.--The scheme of modulating an oscillator tube by connecting the secondary of a transformer, the primary of which is connected with a battery and a microphone transmitter, in the grid lead.

MODULATION, OVER.--See _Blub Blub._

MODULATION, PLATE.--Modulating the oscillations set up by a vacuum tube by varying the current impressed on the plate.

MODULATOR TUBE.--A vacuum tube used as a modulator.

MOTION, WAVE.--(1) The to and fro motion of water at sea. (2) Waves transmitted by, in and through the air, or sound waves. (3) Waves transmitted by, in and through the _ether,_ or _electromagnetic waves,_ or _electric waves_ for short.

MOTOR-GENERATOR.--A motor and a dynamo built to run at the same speed and mounted on a common base, the shafts being coupled together. In wireless it is used for changing commercial direct current into direct current of higher voltages for energizing the plate of a vacuum tube oscillator.

MULTI-STAGE AMPLIFIERS.--See _Amplifiers, Multi-Stage._

MUTUAL INDUCTION.--See _Induction, Mutual._

MUSH.--Irregular intermediate frequencies set up by arc transmitters which interfere with the fundamental wave lengths.

MUSHY NOTE.--A note that is not clear cut, and hence hard to read, which is received by the _heterodyne method_ when damped waves or modulated continuous waves are being received.

NATIONAL ELECTRIC CODE.--See _Code, National Electric._

NATIONAL ELECTRIC SAFETY CODE.--See _Code, National Electric Safety._

NEGATIVE ELECTRICITY.--See _Electricity, Negative._

NON-SYNCHRONOUS GAP.--See _Gap, Non-Synchronous._

OHM.--The resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters.

OHM'S LAW.--The important fixed relation between the electric current, its electromotive force and the resistance of the conductor in which it flows.

OPEN CIRCUIT.--See _Circuit, Open._

OPEN CORE TRANSFORMER.--See _Transformer, Open Core._

OSCILLATION TRANSFORMER.--See _Transformer, Oscillation._

OSCILLATIONS, ELECTRIC.--A current of high frequency that surges through an open or a closed circuit. (1) Electric oscillations may be set up by a spark gap, electric arc or a vacuum tube, when they have not only a high frequency but a high potential, or voltage. (2) When electric waves impinge on an aerial wire they are transformed into electric oscillations of a frequency equal to those which emitted the waves, but since a very small amount of energy is received their potential or voltage is likewise very small.

Sustained.--Oscillations in which the damping factor is small.

Damped.--Oscillations in which the damping factor is large.

Free.--When a condenser discharges through an oscillation circuit, where there is no outside electromotive force acting on it, the oscillations are said to be _free._

Forced.--Oscillations that are made to surge in a circuit whose natural period is different from that of the oscillations set up in it.

OSCILLATION TRANSFORMER.--See _Transformer._

OSCILLATION VALVE.--See _Vacuum Tube._

OSCILLATOR TUBE.--A vacuum tube which is used to produce electric oscillations.

OVER MODULATION.--See _Blub Blub._

PANCAKE OSCILLATION TRANSFORMER.--Disk-shaped coils that are used for receiving tuning inductances.

PERMEABILITY, MAGNETIC.--The degree to which a substance can be magnetized. Iron has a greater magnetic permeability than air.

PHASE.--A characteristic aspect or appearance that takes place at the same point or part of a cycle.

PICK-UP CIRCUITS.--See _Circuits, Stand-by._

PLATE CIRCUIT REACTOR.--See _Reactor, Plate Circuit._

PLATE CURRENT.--See _Current, Plate._

PLATE MODULATION.--See _Modulation, Plate._

PLATE VOLTAGE.--See _Foliage, Plate._

POLES, BATTERY.--The positive and negative terminals of the elements of a battery. On a storage battery these poles are marked + and - respectively.

POLES, MAGNETIC.--The ends of a magnet.

POSITIVE ELECTRICITY.--See _Electricity, Positive._

POTENTIAL DIFFERENCE.--The electric pressure between two charged conductors or surfaces.

POTENTIOMETER.--A variable resistance used for subdividing the voltage of a current. A _voltage divider._

POWER TRANSFORMER.--See _Transformer, Power._

POWER TUBE.--See _Generator Tube._

PRIMARY BATTERY.--See _Battery, Primary._

PREVENTION, KICK-BACK.--A choke coil placed in the power circuit to prevent the high frequency currents from getting into the transformer and breaking down the insulation.

Q S T.--An abbreviation used in wireless communication for (1) the question "Have you received the general call?" and (2) the notice, "General call to all stations."

QUENCHED GAP.--See _Gap, Quenched._

RADIATION.--The emission, or throwing off, of electric waves by an aerial wire system.

RADIO AMMETER.--See _Ammeter, Hot Wire._

RADIO FREQUENCY.--See _Frequency, Radio._

RADIO FREQUENCY AMPLIFICATION.--See _Amplification, Radio Frequency._

RADIO FREQUENCY CURRENT.--See _Current, Radio Frequency._

RADIO INSPECTOR.--See _Inspector, Radio_.

RADIOTRON.--The trade name of vacuum tube detectors, amplifiers,