Man's physical universe

xanabras

UNIT VII

SECTION 1

MAGNETISM IS

PRODUCED BY THE ORIENTATION

OF MOLECULES

Introduction.

Magnetism has been known since the time of the early Greeks, but

it was not until the past century that it was studied and put to useful

application, except in the mariner's compass.

The ancient Greeks knew of the peculiar property of attracting bits

of iron possessed by certain lustrous black stones brought from Magnesia

in Asia Minor. They were named "magnets" because of their

source. These stones were really pieces of an iron ore, now called

"magnetite."

Later the miners on the island of Samothrace came to know that

certain types of iron would become imbued with this property of magnetism

when rubbed with magnetite.

It was discovered that a piece of magnetite suspended so as to turn

freely about a vertical axis would always come to rest with the same

part of the stone pointing in a northerly direction. This was the first

magnetic compass, and the stone thus came to be known as "lodestone,"

or "leading stone." The origin of the compass is unknown,

but it is

certain that crude ones were in use during the latter part of

the thirteenth century. These early compasses consisted of a magnetic

needle supported so as to float on water. The invention of the compass

was of outstanding significance, for it permitted mariners to undertake

long journeys of exploration, adventure, and commerce.

Only a Few Substances Exhibit Magnetism.

This property, characteristic of certain uncharged substances, to

attract others is called magnetism. Such objects are described as being

magnetic. The only substances which exhibit magnetism to any considerable

extent are iron, cobalt, and nickel. Iron is by far the most

magnetic of all the elements, although certain alloys far surpass its

magnetism — permalloy, an alloy of nickel and iron, and perminvar,

an alloy of nickel, iron, and cobalt, are typical examples. A recent

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