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.
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?
CHAPTER XXXII.
GRAVITATION.
If I should ask you why things in the air fall to the ground, you would probably say it is because it is downward, and every thing must come down that is not held up in some way. But what is down, and what is up? This I will explain to you.
How it is known that the earth is round.
The earth, as perhaps you know, is as round as an orange, and people can travel around it just as you can pass your finger around over the orange. This, indeed, was one of the ways in which it was found to be round. Another proof of its being round is this: As you see a ship go out to sea, if you watch it for a long time, after a while the body of the ship will go out of sight, and you will see nothing but the sails, and then the sails will gradually go out of sight also. What does this prove? Why, that the water is not flat, as it appears to be to us, but that it makes a part of the rounded surface of the earth. This figure will make this plain to you. The eye that is represented sees the whole ship at b; but when it gets as far as a, the eye can see only the streamer at the top of the mast.