MAGNETISM.
[Sidenote: The loadstone.]
In some parts of the world a kind of iron ore is found which is called
loadstone. It has a peculiar power. It attracts iron very strongly.
Hold it close to some iron filings, and they will cling to it in quite
a cluster as you raise it up; so, also, you can take up with it a great
many needles, and if it be a large piece of the ore, it will hold
up a very heavy weight. This powder which the loadstone has we call
magnetism.
Now this power in the loadstone can be communicated to iron and steel.
If a loadstone be moved along in a particular way on a piece of iron
or steel several times, the iron or steel will receive this power, and
will act as a magnet, just as the loadstone does. Common iron will not
keep the power long, but steel will.
[Illustration]
[Sidenote: How common magnets are made.]
Most of the magnets that we see are not real loadstone, but they are
steel that has been magnetized by the loadstone. They are commonly
made in a horse-shoe shape, as represented here. They will hold up a
considerable weight of iron, and sometimes twenty-eight times their
own weight; and it is curious that a magnet which holds a weight all
the time will have its power increased. There is no tiring out of its
power; and, on the contrary, if you give a magnet nothing to do, its
power will grow weak--it will not be able to hold up so much weight
as it did at first. It is for this reason that magnets are never left
without a weight hanging to them.
[Sidenote: Toy fishes and ducks moved by a magnet.]
You have perhaps often been amused in making toy fishes or ducks swim
about in the water with a little magnet. You have seen how readily they
follow the magnet, and how quickly they spring forward to hold on to
it, if you happen to put it very near them. This is because each has a
little piece of steel in its mouth which is attracted by the magnet.
[Sidenote: Strangeness of the magnetic power.]
How very strange this power of the magnet is! It is not any thing that
you can see, and yet there the power is. You see what it does. This
unseen power in the magnet takes hold of things and draws them to it,
as our hand, that we see, takes hold of things and draws them to us.
How it does this we do not understand.
This power does not seem to do much at any distance from the magnet. If
you hold your little magnet quite away from the toy duck or fish, it
will not make it move; but bring it near, and now you see it follows
the magnet all about; and if you bring it very near, the little thing,
as quick as a wink, darts forward and clings to the magnet very firmly.
So, too, if you bring an iron weight slowly nearer and nearer to a
large magnet, there does not seem to be any influence from the magnet
upon it till you bring it very near, and then all at once away goes the
weight out of your hand to cling to the magnet. It is as if the magnet
had very short hands that could not reach far; but so far as they do
reach, they are very strong and hold fast. Whenever you get a chance
to see a magnet of considerable size, you can try this experiment.
[Sidenote: The mariner’s compass.]
[Sidenote: How to make one in a simple way.]
You have heard of the mariner’s compass, but perhaps it has never been
explained to you. There is a slender piece of steel in this compass
which always points to the north. It is balanced on a pivot, so that it
can move around easily to the one side or the other. However much it is
jostled, however much you may turn the box of the compass round, this
needle is always tremblingly but surely pointing one way. This needle
is a magnetized piece of steel. We may consider the whole earth, with
all its loadstone and iron, as a great magnet, and it is the influence
of the earth upon the magnetic needle that makes it always point to the
north. You can at any time make a mariner’s compass in a very simple
way. All that you need is a magnetized needle, a piece of cork, and a
bowl of water. Put the cork in the water, and lay the needle across it,
and the needle will point north and south. You see how this is. The
cork moves so readily in the water that the needle in getting right can
turn it as is needed. It will turn almost as easily as the needle does
on its pivot in the compasses that are made.
[Sidenote: St. Paul’s voyage.]
The mariner’s compass, you can see, must be of great use to the
mariner. When he is far out at sea, where no land can be seen, he
always knows by this which way north is, and so he judges how to direct
his vessel in order to reach the desired port. If it were always
sunshine, he would do very well without the compass, for he could tell
by the sun which way was north, and south, and east, and west; but in
stormy weather and in the night he would be at a loss. At such times,
by looking at his ever faithful compass, he knows in what direction to
steer his vessel. You remember about the voyage and shipwreck of the
apostle Paul, related in the 27th chapter of Acts. Nothing was known
about the mariner’s compass then. So “when neither sun nor stars in
many days appeared,” they did not know all this time where the wind was
carrying them. Perhaps if they had had a compass on board they could
have kept the ship from going ashore and being dashed to pieces.
[Sidenote: Electricity and magnetism in the telegraph.]
Magnetism often has a great deal to do with electricity, and some
persons suppose them to be the same thing. Electricity may wake up the
magnetic power to even a wonderful degree. In Morse’s telegraph there
are both electrical machinery and magnetic machinery. The electricity
that comes over the wires excites the magnetic machinery, and it is
this magnetism that delivers the message sent by the electricity. Just
how this operates you can understand better when you are a little older.
_Questions._--What is loadstone? What peculiar power has it? To what
can it communicate this power? What are the magnets in common use?
Why is a weight always kept hanging to a magnet? Tell about the toy
fishes and ducks. What is said about the strangeness of the magnetic
power? Does it do much at any distance from the magnet? Give the
illustrations. What is the mariner’s compass? How can you make one?
What makes the needle always point to the north? How is the mariner’s
compass of use at sea? Tell about St. Paul’s shipwreck. What effect
does electricity often produce upon magnetism? How is it in Morse’s
telegraph?