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.
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.
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.
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, theyare very strong and hold fast. Whenever you get a chance to see a magnet of considerable size, you can try this experiment.
The mariner’s compass.
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.
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 thenight 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.
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?
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?