Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1916-12-09
iqiz9zl MIEST NEWS or the MJIQMOBILE TRADE<zazzzz1
20 - AND INDUSTRY c1@@6
EssON
(5y Special Permission from Motor
Aoel

orr which possessed the property oil
attracting small pieces OF iron and
steel. Later the Chinese discovered
tnat II piece of this black stone was
freely suspended by q string IL pos
sessed the very remarkable property
of pointing always In the same direc
tion. nearly north and south; thence
they called the stone ''lodestone," or
leading stone," and used il In this
manner TO assist them in navigating
their ships. The natural magnet, or
lodestone, Is an ore of iron and is
called magnetic.
If a piece Of iron, or, better still,
piece OF hard steel, be rubbed with
a lodestone II will attract light pieces
OF iron; 1t will point approximately
north and south IL freely suspended by
means OF piece Of string, and il can
be used to magnetic other pieces OF
iron or steel. Magnets made in this
manner are called artificial magnets.
Strong artificial magnets, however,
are not made by using the lodestone,
A as IL Is impossible to make them
! strong enough by this method, but by
methods described in a following Sec
ton on INSTRUMENTATION.
Certain parts of a magnet possess
the property of attracting iron and
steel to greater extent than do
other parts, and these parts are called
the poles OF the magnet The poles
CT bar magnet are usually situated
at or near the ends of the bar.
When a magnet is supported on a
sharp pivot or suspended by a light
thread 1t adjusts itself to such a posi-
ton that IL points nearly north and
south. A small elongated magnet thus
suspended is called a magnetic needle.
IL such needle be turned from the
position which it naturally takes and
: is free to swing, II will at once re-
turn, swinging to and fro until it set.
ties down In its original position. This
tendency Of the magnetic needle to set
itself approximately north and south
is the foundation of the compass.
The end of the needle which points
approximately toward the north geo
graphical pole 10 called the north pole
and is usually marked with the letter
N; While the other end of the needle is
called the south pole.
The north pole Of magnet is often
called the positive, or plus ID pole,
and the south pole is often called the
negative. or minus 81, pole. Since
the north, or positive, pole turns to-
ward the north, It is sometimes called
the north seeking pole and the south,
or negative, pole is sometimes called
the south seeking pole.
II pole of magnet is brought near
q magnetic needle il is found 20 at
tract one pole of the needle and repel
tie other pole. The north pole of the
magnet may be determined by observ-
ing the position 1t takes when sus-
pended by a thread and 1t will be
found that the north pole of the mag
net always repels the north pole OF
the needle and always attracts the
south pole OF the needle Similarly, II
viii be found that the south pole of
the magnet always repels the south
pole OF the needle and always at.
tracts the north pole of the needle.
This action shows that there are two
kinds OF magnetic poles, and that
poles OF the same kind repel each
other and poles Of opposite kinds at
tract each other.
Induced Magnetism
II q bar OF soft iron be used in
stead OF magnet II will be found that
either end Of the bar OF soft iron viii
attract either pole of the needle. II
one end Of the iron bar be thrust into
quantity OF fine iron filings and
Withdrawn, only a very few of the
filings viii adhere to the end of the
bar. II, however, one end Of the bar
be thrust into a quantity of filings
and one pole of a permanent magnet
be presented to the other end of the
bar and the combination then with
drawn, large number Of the filings
will adhere to the end of the soft iron
bar. Practically all OF the filings will
fall from the end of the soft iron bar.
II the permanent magnet be. removed
from the other end. The action be-
tween the soft iron bar and the COM
pass needle viii increase with a de-
crease In the distance between them.
Similarly, the ability Of the soft iron
bar TO hold the filings will increase as
the distance between 1t and the pole of
the permanent magnet decreases. In
either case the bar Of soft iron be-
comes magnetized. due to the action
OF the compass needle, or the perman.'
ent magnet, and two magnetic poles
are produced on il. The end of the
bar nearest the magnetic pole on the
compass needle, or permanent mag.
net, will be of opposite sign. while
the end Of the bar furthest away from
the compass needle, or permanent
magnet, is of the same sign as the pole
on the compass needle, or permanent
magnet Magnetism produced in this
manner is called indicted magnetism.
The magnetism induced in a piece
Of iron may induce magnetism in an
other piece, and this in another piece
and so on; and thus magnet may be
maue to support similar pieces of
iron end to end, each of which has
become a magnet by induction. The
magnetism of each successive piece
is weaker than in the preceding piece.
Demangnetixation
Magnets are made TO assume many
different forms. depending in great
measure upon their application. The