<h2><SPAN name="CHAPTER_IV" id="CHAPTER_IV"></SPAN>CHAPTER IV.</h2>
<h3>THEORY AND NATURE OF MAGNETISM.</h3>
<p>Iron and steel have a peculiar property
called magnetism. It is an attraction in many
ways unlike the attraction of cohesion or the
attraction of gravitation. It is very certain
that magnetism is an inherent property of the
molecules of iron and steel, and, to a small
degree, other forms of matter. That is to
say, the molecules are little natural magnets
of themselves. It is as unnecessary to inquire
why they are magnets as it is to inquire why
the molecules of all ordinary substances possess
the attraction of cohesion. The one is as
easy to explain as the other. People of all
ages have insisted upon making a greater
mystery of all electrical and magnetic phenomena
than they do of other natural forces.
Ampère's theory is that electric currents are
flowing around the molecules which render
them magnetic; but it is just as easy to suppose
that magnetism is an inherent quality of the
molecule. (The word molecule is here used
as referring to the smallest particle of iron.)</p>
<p>These little molecular magnets, so small<span class="pagenum"><SPAN name="Page_26" id="Page_26"></SPAN></span>
that 100,000 million million million of them
can be put into a cubic inch of space, have
their attractions satisfied by forming into
little molecular rings, with their unlike poles
together, so that when the iron is in a natural
or unmagnetized condition it does not attract
other iron. If I should take a ring of hardened
steel and cut it into two or more pieces
and magnetize them, each one of the pieces
would be an independent magnet. If now I
put them together in the form of a ring they
will cling together by their mutual attraction
for each other. Before I put them together
into a ring each piece would attract and adhere
to other pieces of iron or steel. But as soon
as they are put together in the ring they are
satisfied with their own mutual attraction,
and the ring as a whole will not attract other
pieces of iron.</p>
<p>Suppose the pieces forming the ring—it may
be only two, if you choose—are as small as
the molecules we have described, the same
thing would be true of them. Each molecular
ring would have its magnetic attractions satisfied
and would not attract other molecules outside
of its own little circle. When the iron
is in the neutral state it will not as a mass attract
another piece of iron, because the millions
of little natural magnets of which it is
made up have their attractive force all turned
in upon themselves.<span class="pagenum"><SPAN name="Page_27" id="Page_27"></SPAN></span></p>
<p>Now, if we make a helix, or coil, of insulated
wire and put a piece of iron into it, and pass
a current of electricity through the helix, the
iron becomes a magnet. Why? Because the
electric current has the power to break up
these molecular magnetic rings and turn all
their like poles in one direction, so that their
attractions are no longer satisfied among themselves,
and with a combined effort they reach
outside and attract any piece of iron that is
within reach. In this state we say it is magnetized.
Most people think that we have put
something into the iron, but we have not; we
have only developed and made active its inherent
power. It must be kept in mind that
it takes power to develop this magnetic power
from its state of neutrality and that something
is never made from nothing. When this
power is developed it will do work in falling
back to its natural state. The power is natural
to the molecules of the metal. It is only
being exerted in a new direction. The millions
of little natural magnets have been forced to
combine their attractions into one whole and
exert it on something outside of themselves.
They are under a strain in this condition, like
a bent bow, and there is a tendency to fly back
to the natural position, and if it is soft iron
and not steel, they will fly back as soon as the
power that wrenched them apart and is holding
them apart is taken away. This power is the<span class="pagenum"><SPAN name="Page_28" id="Page_28"></SPAN></span>
electric current. Now break the current, and
the little natural magnets, that have been so
ruthlessly torn from their home circle attachments,
fly back to them again with the speed
of lightning, and the iron rod as a whole is
no longer a magnet. The power to become so
under the electrical strain is in it still—only
latent.</p>
<p>The kind of magnet that we have been
describing is called an electromagnet. It is
a magnet only so long as the electric current
is passing around it. There is another kind
of magnet called a permanent magnet that will
remain a magnet after the current is taken
away. The permanent magnet is made of
steel and hardened; then its poles are placed,
to the poles of a powerful magnet, either electro
or permanent, when its molecular rings
are wrenched apart and arranged in a polarized
position as heretofore described. Now take it
away from the magnet and it will be found to
retain its magnetism. The molecules tend to
fly back the same as those of the soft iron, but
they cannot because hardened steel is so much
finer grained than soft iron, and the molecules
are so close together that they are held in
position by a friction that is called its coercive
force. The soft iron is comparatively free
from this coercive force, because its molecules
are free to move on each other, so that when
they are wrenched out of their natural position<span class="pagenum"><SPAN name="Page_29" id="Page_29"></SPAN></span>
they fly back by their own attractions as soon
as the force holding them apart is taken away.
The molecules of hardened steel are unable to
fly back, although they tend to do it just as
much as in the iron, and so it is called a permanent
magnet. Its molecules also are under
a strain, like a bent bow. (The form of such
a magnet is usually that of a horse-shoe, or U.)</p>
<p>Let us use a homely illustration that may
help us to understand. Let ten boys represent
the molecules in a piece of iron. Let them
pair off into five pairs and each one clasp his
mate in his arms; each one, say, is exerting a
force of ten pounds, and it would require a
force of twenty pounds to pull any one of the
pairs apart. The five pairs are exerting a
force of one hundred pounds, but this force is
not felt outside of themselves. Now let them
unclasp themselves and take hold of a rope
that is tied to a post, and all pull with the
same force that they were using, to wit, ten
pounds each, and all pull in the same direction,
and they would put a strain of one
hundred pounds upon the post, the same power
that they were exerting upon themselves before
they combined their efforts on something
outside of themselves. So with the magnet.
So long as the force of each molecule is wholly
spent upon its neighbor there is nothing left
for exterior use. But as soon as they all line
up and pull conjointly in the same direction<span class="pagenum"><SPAN name="Page_30" id="Page_30"></SPAN></span>
their combined force is felt outside. The
analogy may not be perfect, but it will help
you to get a mental picture of what takes place
in iron when it is magnetized.</p>
<p>We have now described the magnet and the
inherent power residing in the molecular
structure of iron. It is this magic power
slumbering in its molecules and the ability of
the electric current to arouse them to action
at will and to hold them in action and at will
let them fly back to their normal position, that
gives to electricity and magnetism—twin sisters
in nature's household—their great value
as the servants of man. There would be no
virtue in winding up a weight if it could not
run down and do work in its fall. Simply
bending a bow would never send the arrow
flying over its course; it must be released as
well. The magnet could not accomplish the
great work it does if we could only charge it
and not have the ability to discharge it. Without
this ability the electric motor would not
revolve, the electric light would not burn, the
click of the telegraph would not be heard, the
telephone would not talk, nor would the telautograph
write.</p>
<p>I have said that the permanent magnet
would hold its charge after once having been
magnetized. This is true only in a sense and
under favorable conditions. If made of the
best of steel for the purpose and hardened and<span class="pagenum"><SPAN name="Page_31" id="Page_31"></SPAN></span>
tempered in just the right way, it will hold its
charge if it is given something to do. If a
piece of iron is placed across its poles it also
becomes a magnet and its molecules turn and
work in harmony with those of the mother
magnet. These magnetic lines of force reach
around in a circuit. Even before the iron, or
"keeper," as it is called, is put across its
poles there are lines of force reaching around
through the air or ether from one pole to another.
(For a description of Ether see Chap.
V.) This is called the "field" of the magnet,
and when the iron is placed in this field the
lines of force pass through it in a closed circuit,
and if the "keeper" is large enough to
take care of all the lines of force in the field
the magnet will not attract other bodies, because
its attraction is satisfied, like its prototype
in the molecular ring described above.</p>
<p>We speak of lines of force, not that force is
necessarily exerted in a bundle of lines but as
a convenient way of telling the strength of a
magnetic field. The practical limit of the
magnetization of soft iron (called saturation)
is 18,000 lines to the square centimeter. As
long as we give our magnet something to do,
up to the measure of its capacity, it will keep
up its power. We may make other magnets
with it, thousands, yea, millions of them, and
it not only does not lose its power but may be
even stronger for having done this work. If,<span class="pagenum"><SPAN name="Page_32" id="Page_32"></SPAN></span>
however, we hang it up without its "keeper,"
and give it nothing to do, it gradually returns
to its natural condition in the home circle of
molecular rings. Little by little the coercive
force is overcome by the constant tendency of
the molecule to go back to its natural position
among its fellows.</p>
<p>The magnet furnishes many beautiful lessons,
as indeed do all the natural phenomena.
Every man has within him a latent power that
needs only to be aroused and directed in the
right way to make his influence felt upon his
fellows. Like the magnet, the man who uses
his power to help his fellows up to the measure
of his limitations not only has been a benefactor
to his race, but is himself a stronger
and better man for having done so. But,
again, like the magnet, if he allows these
God-given powers to lie still and rust for want
of legitimate use he gradually loses the power
he had and becomes simply a moving thing
without influence or use in a world in which
he vegetates. But let us leave philosophy and
go back to science.</p>
<p>One of the striking exhibitions of magnetism
is found in the earth. The earth itself is
a great magnet; and there is good reason for
believing that it is an electromagnet of great
power. The magnetic poles of the earth are
not exactly coincident with the geographical
poles, and they are not constant. There is a<span class="pagenum"><SPAN name="Page_33" id="Page_33"></SPAN></span>
gradual deviation going on, but as it follows
a certain law mariners are able to tell just
what the deviation should be at a certain time.
The magnetic pole revolves around the polar
axis of the earth once in about 320 years. A
thermal current (one produced by heat) of
electricity seems to flow around the earth
caused by the irregularities of temperature at
the earth's surface, as the sun makes his daily
round. These earth currents vary at times,
and other phenomena are the occasion. This
will be discussed when we come to electric
storms.</p>
<p>The value of the earth's magnetism is seen
most in the science of navigation. A magnetic
needle is only a slender permanent magnet
suspended very delicately, and when not
under local influence it points north and south
on the magnetic axis. The law of its action
may be explained as follows: Take a straight
bar magnet of fairly good power and suspend
a magnetic needle over it. The needle will
arrange itself parallel to the bar magnet. The
north pole of the needle will point toward the
south pole of the bar magnet. In the presence
of the magnet the needle is not affected by the
earth, but yields to a superior force. If, however,
the bar magnet is taken out of the way
of the needle it will immediately arrange itself
north and south. Of course if the earth's
magnetic axis changes the needle will vary<span class="pagenum"><SPAN name="Page_34" id="Page_34"></SPAN></span>
with it. This variation is uniform and in navigation
is reduced to a science, so that the mariner
knows how much to allow for the variation.
Columbus, as heretofore mentioned, was
supposed to have first noticed this variation
and it made him trouble. He did not
know how to account for it, and as his crew
thought the laws of nature were changing because
they were so far from home he saw the
necessity for some sort of explanation. So,
like the brave man that he was, he hatched up
a theory that satisfied the crew, and although
in the light of the closing years of the nineteenth
century it was a questionable one, it
worked well enough in practice to serve his
purpose.</p>
<p>We have already stated that the earth was a
great magnet, and that probably it was an
electromagnet, caused by earth currents circulating
around the globe. You want to know
how the earth can be a magnet unless it has an
iron core like an electromagnet. Magnetism
or magnetic lines of force may be developed
without the presence of iron. When we pass
a current of electricity through a wire, magnetic
lines of force are thrown out at right
angles with the direction of the current. This
will be fully explained further on. If we wind
the wire into a coil, or helix, these magnetic
lines are concentrated. If now we suspend
this helix, or, better, float it on water so that it<span class="pagenum"><SPAN name="Page_35" id="Page_35"></SPAN></span>
can move freely, and pass a current of electricity
through it, the helix will arrange itself
north and south the same as a magnetic needle.
Its attractive properties are feeble in comparison
with that of the iron, but it obeys the
laws of a magnet. The earth is probably a
magnet of this kind, consisting mostly of lines
of force.</p>
<p>However, the iron in the earth is affected
magnetically, as we have evidence in the loadstone.
The earth has the power also to magnetize
iron through the medium of its magnetic
field, that reaches out in lines of force
from pole to pole like those of the artificial
magnet. If we hold a bar of iron in line with
the magnetic axis of the earth and dip it in
line with the dipping needle and then strike it
a few blows on the end, it will be found to be
feebly magnetic. The blows have partly
loosened the molecules and during the moment
that they unclasped themselves the earth's
magnetism has through its lines of force
caught them for a time and held them a little
out of their natural position—as they are in a
state of rest. The peculiar changing light
that we sometimes see in the northern sky,
that is called the Aurora Borealis (Northern
Light), is indirectly due to intense magnetic
lines of force that radiate from the north magnetic
pole of the earth. Those lines of force
are able to cause the rarified air molecules to<span class="pagenum"><SPAN name="Page_36" id="Page_36"></SPAN></span>
become feebly incandescent, giving them the
appearance that we see in a tube that is a
partial vacuum when electricity is passed
through it. While these auroral displays may
be seen almost any night in the far north,
they vary greatly in their intensity, so it is
only once in a while that they are visible in
the temperate latitudes.</p>
<p>What are called magnetic storms occur
occasionally, and at such times the telegraph
service will sometimes be paralyzed on all the
east and west lines for many hours. Strong
earth-currents will flow east and west, and be so
powerful and so erratic that it is sometimes
impossible to use the telegraph. It sometimes
happens that the operators can throw off their
batteries and work on the earth-current alone.
Sometimes it is necessary to make a complete
metallic circuit to get away from the influence
of the earth in order to use the telegraph. Currents
equal to the force of 2,000 cells of
ordinary battery have been developed sometimes
in telegraph wires. This of course is a
mere fraction of what is passing through the
earth under the wire through which the current
flowed. On the 17th and 18th of November,
1882, a magnetic storm occurred that extended
around the globe, as it was felt
wherever there were telegraph wires. These
magnetic storms are attended by brilliant displays
of the aurora, and this fact strengthens<span class="pagenum"><SPAN name="Page_37" id="Page_37"></SPAN></span>
the theory that the earth is a great electromagnet;
for the stronger the electrical current
the more powerful we should expect the
magnetism to be, and this is shown by the
action of the magnetic needle at such times.
The stronger the magnet the more intense will
be the lines of force, and naturally the more intense
the light, if indeed these lines of force
are the cause of the light. There is evidently
some close relation between the two.</p>
<p>Another coincidence is that at the times of
these storms there is an unusual display of
sun-spots. These sun-spots seem to be great
holes that have been blown through the photosphere
of the sun. The photosphere is a great
luminous body of gaseous matter that is believed
to envelop the sun, so that we do not see
the core of the sun unless it is when we
look into one of these spots. In some way, evidently,
the sun affects the earth by radiating
magnetic lines of force which are cut by the
earth's revolution, and so creating currents of
electricity. The sun is the field-magnet, and
the earth is the revolving armature of nature's
great dynamo-electric machine. It would
seem that the radiant energy that comes out
through these spots or these holes in the sun's
envelope, are more potent to develop earth-currents
than the ordinary rays; and so, when
for a brief while in the revolution of the earth
about the sun, these extra potent rays strike<span class="pagenum"><SPAN name="Page_38" id="Page_38"></SPAN></span>
the earth, an unusual energy is developed, and
these unusual phenomena are the consequence.
These phenomena seem to occur periodically;
some years (about eleven) intervening.</p>
<p>All the forces and phenomena of nature are
thus seen to be in a state of unrest. And it is
to this unrest, which does not stop with visible
things, but pervades even the atoms of matter
throughout the universe, that we are indebted
for the ability to carry on all the activities of
life, and for life itself. For universal quiet
would mean universal death. The cyclone and
tornado that devastate and strike terror to a
whole region are only eccentricities of nature
when she is setting her house to rights. The
play of natural forces has disturbed her equilibrium,
and she is but making an effort to
restore it.</p>
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