to get a bird's-eye view of the natural laws which make Radio
possible. So far you have obtained considerable knowledge of
electricity. In fact, right now you know more about the nature of
electricity than the greatest scientists did until a few years ago.
MAGNETS AND MAGNETISM
Natural magnets found in various parts of the world, com-
posed of an “oxide of iron,” called magnetite, have the peculiar
property of attracting pieces of iron or steel when placed near
to them. These natural magnets also have the property of
pointing nearly due North and South when suspended or pivoted.
These natural magnets received from the early mariners the
name Leiderstan (i. e., leading stone). The name was subsequently
changed to the English word Lodestone. When a bar of
Fig. 4
steel is rubbed with a piece of lodestone the steel becomes magnetized
and is known as an artificial magnet. If this steel bar is
dipped into a pile of iron filings some filings will be attracted to
the tips of the bar. Magnets are divided into two classes,
Permanent and Temporary. Permanent magnets are those which
retain their magnetic effect for a long period of time. These
magnets are made of very hard steel. Temporary magnets are
those that retain their magnetism only during the time which
they are in contact or under the influence of another magnet or
are being energized by an electric current. These magnets are
made of soft iron or a real soft grade of steel. A coil of wire
wound around a bar of iron or steel will have magnetic properties
when a current is passed through the wire.
