CHAPTER II
ELEMENTS OF ELECTRICITY
(A) MAGNETISM
11. Discovery of Magnetism.- You are all probably more or less familiar with
magnetism and its mysterious behavior. It is not our purpose to try to explain this
mystery, but rather to state the simple laws of magnetism, so that you may better
understand the operation of the electrical devices of reproducing equipment.
It was known to the ancient Greeks that certain "stones," found in a region of Asia
Minor called Magnesia, had the peculiar property of attracting to themselves small bits of
iron, and that when two of these "stones" were brought near one another there was
sometimes present a force which tended to draw them together, and at other times the
force present tended to keep them apart. The Greeks called the "stones" "magnets" after
the country where they were found.
It was later found that when one of these magnets was hung, suspended by a string,
one portion always turned towards the north. Some of the Mediterranean merchants used
these magnets to aid them in navigation. As a result of this use the magnets were
termed "leading-stones" or "lode-stones."
A still later development arose as a result of the discovery that a piece of iron or
steel when rubbed against a magnet acquired its properties to a somewhat less degree. It
would pick up other bits of iron or steel, attract or repel another bit of iron similarly
treated, and would take up a definite position north and south when freely suspended.
Such a piece of iron or steel is said to be "magnetized." The Italian navigators as early as
the tenth century utilized the tendency of a magnetized steel needle to place itself north
and south. Their first compass consisted of a horizontal card attached to a cork in which
was mounted a magnetized steel needle. The edge of the card was marked with "the
points of the compass," and this whole unit was floated in a bowl of water the edge of
which was marked in line with the keel of the ship.
The original magnets or "lode-stones," which were not really stones, but were
instead a combination of two iron "ores," are called "natural magnets"; and magnets
made by rubbing pieces of iron or steel against "natural magnets" (or by any other means)
are called "artificial magnets."
In examining the action of any magnet, it will be found that in at least two positions
its magnetic properties will be much more pronounced than at others. These points are
termed the "poles" of the magnet.
The space surrounding a magnet in which its influence may be observed is termed
the "magnetic field."
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