alternator

ammeter

aerial

arc

battery

buzzer

condenser

variable condenser

connection of wires

no connection

coupled coils

variable coupling

detector

gap, plain

gap, quenched

ground

hot wire ammeter

inductor

variable inductor

key

resistor

variable resistor

switch s.p.s.t.

" s.p.d.t.

" d.p.s.t.

" d.p.d.t.

" reversing

phone receiver

" transmitter

thermoelement

transformer

vacuum tube

voltmeter

choke coil

DEFINITIONS OF ELECTRIC AND MAGNETIC UNITS

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

The _ampere_ is 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.

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

The _coulomb_ is the quant.i.ty of electricity transferred by a current of 1 ampere in 1 second.

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

The _farad_ is the capacitance of a condenser in which a potential difference of 1 volt causes it to have a charge of 1 coulomb of electricity.

The _henry_ is the inductance in a circuit in which the electromotive force induced is 1 volt when the inducing current varies at the rate of 1 ampere per second.

The _watt_ is the power spent by a current of 1 ampere in a resistance of 1 ohm.

The _joule_ is the energy spent in I second by a flow of 1 ampere in 1 ohm.

The _horse-power_ is used in rating steam machinery. It is equal to 746 watts.

The _kilowatt_ is 1,000 watts.

The units of capacitance actually used in wireless work are the _microfarad_, which is the millionth part of a farad, because the farad is too large a unit; and the _C. G. S. electrostatic unit of capacitance_, which is often called the _centimeter of capacitance_, which is about equal to 1.11 microfarads.

The units of inductance commonly used in radio work are the _millihenry_, which is the thousandth part of a henry; and the _centimeter of inductance_, which is one one-thousandth part of a microhenry.