Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1916-12-09

two principal forms, however, are
known as bar and horseshoe magnets,
respectively.
A material in which magnetism may
be induced and which is therefore at
tracted by a magnet is called mag
netic material. Iron in its various
forms, such as wrought iron, cast iron
and steel, is the best magnetic mate
rial known. There are few other ma
terials, such as cobalt, nickel and
chromium, that are slightly magnetic,
but very much less so than iron. All
materials are usually spoken of as
non-magnetic materials, since they
are nearly neutral as regards mag
netism. Unfortunately there is no in
sulator for magnetism as there is for
electricity
Continuous Earring of a magnet will
tend to cause its magnetism to disap-
pear or to demagnetize itNIf magnet
be heated to a temperature about red
heat 1t becomes demagnetized, and
the iron at the same time loses its
magnetic quality and does not regain
1t until 1t cools to q lower tempera-
ture. Since magnet tends to lose its
magnetism so readily, 1t is customary
to furnish the horseshoe form with
what is called keeper. The keeper
is a piece of iron which may be
placed across the poles OF the magnet,
which makes complete magnetic cir
cult and thus tends to prevent the
demagnetization of the magnet by jar
ring.
CoyTsa rnotor;af, ora ,,,oro -, AN,
magnetized and demagnetized than
others. For example, it is wen known
that soft iron is very readily mag
netized. but loses practically all of its
magnetism If it is slightly Jared after
II is removed from the influence of the
magnetizing force. Hard steel is
usually more difficult to magnetic,
but IL, on the other hand, does not lose
its magnetism so easily as soft iron.
In general, the harder the steel the
harder it is to magnetic and the more
strongly 1t retains its magnetism. The
property Of magnetic material which
opposes its demagnetization is called
its coercive force, and it is desirable
to have a material Of high coercive
force in making strong permanent
magnets.
When q magnet is magnetized as
strongly as possible 1t Is said to be
saturated, and II the magnetizing force
producing the magnetism be removed
the magnet will Immediately grow
weaker, and 1t will continue to get
weaker for a considerable period until
the magnetism finally becomes per-
manent in strength.
Molecular Theory Of Magnetism
There are quite number of expert
mental facts which lead to the con-
clusion that magnetism has something
to do with the molecules of the SUBJ
stance, since any disturbance of the
molecules causes a change in the de-
gree Of magnetism. If glass tube full
of hard steel filings be magnetized it |
will behave toward compass needle |
or other magnet as If it were a solid |
bar magnet, but it will lose practically
all Of its magnetism as soon as the |
filings are rearranged with respect !
to each other by giving the glass tube
several good shakes. A magnet will |
lose its magnetism when heated. A |
magnet may be broken into any num- |
Der of different pieces and there will !
appear at each break a north and |
south pole as shown in the illustration
herewith. The strength of any mag
net will be greatly reduced by ham
mering, twisting or bending it.
The ease with which any material |
may be magnetized as compared to |
some other materials will depend upon
what might be termed the molecular
friction of the material. Thus, the /,
molecules in bar of steel offer a |
greater resistance to change in their |
position than do the molecules in cast |
iron. Steel, as result, is harder to |
magnetic than cast iron, and II also |
will retain its magnetism after once
magnetized better than cast IRON for
the same reason
Some unit Of measure must he en-
ployed in order to be able tn express
the strength of magnet, and fer this
reason we have what is called unit |
magnetic pole. A magnetic pole is said |
to have the strength of l when it will !
repel magnetic pole of equal |