ce the flow of an electric
current in a wire or a coil of wire caused it to acquire magnetic
properties, the opposite might also prove to be true: a magnet could
possibly be used to generate a flow of electricity.

Michael Faraday had worked on this problem for ten years when
finally, in 1830, he gave his famous lecture in which he demonstrated,
for the first time in history, the principle of electromagnetic
induction. He had constructed powerful electromagnets consisting of
coils of wire. When he caused the magnetic lines of force surrounding
one coil to rise and fall by interrupting or varying the flow of
current, a similar current was induced in a neighbouring coil closely
coupled to the first.

The colossal importance of Faraday's discovery was that it paved
the way for the generation of electricity by mechanical means.
However, as can be seen from the drawing, the basic generator produces
an alternating flow of current.(A.C.)

Rotating a coil of wire steadily through a complete revolution in
the steady magnetic field between the north and south poles of a
magnet results in an electromotive force (E.M.F.) at its terminals
which rises in value, falls back to zero, reverses in a negative
direction, reaches a peak and again returns to zero. This completes
one cycle or sine wave. (1Hz in S.I.units).

In recent years other methods have been developed for generating
electrical power in relatively small quantities for special
applications. Semiconductors, which combine heat insulation with good
electrical conduction, are used for thermoelectric generators to power
isolated weather stations, artificial satellites, undersea cables and
marker buoys. Specially developed diode valves are used as thermionic
generators with an efficiency, at present, of only 20% but the heat
taken away from the anode is used to raise steam for conventional
power generation.

Sir Humphry Davy (1778-1829) one of Britain's leading chemists of
the 18th century, is best remembered for his safety lamp for miners
which cut down the risk of methane gas explosions in mines. It was
Davy who first demonstrated that electricity could be used to produce
light. He connected two carbon rods to a heavy duty storage battery.
When he touched the tips of the rods together a very bright white
light was produced. As he drew the rods apart, the arc light
persisted until the tips had burnt away to the critical gap which
extinguished