“No,” said his father. “I only know a very little about it, myself. I am going to explain to you some of the facts,—such as I happen to know. So you must all remember this fact, that in the magnet, the attractive power is not distributed over the whole mass, but resides only in the opposite ends. These ends are called poles.”
“Yes, sir,” said Rollo, “we will remember.”
“Now I can make this apparent in another way,” said his father. Then he asked Rollo’s mother to thread a needle; and when it was threaded, he asked Jonas to stand up and hold the thread in such a manner as to let the needle hang over the middle of the table.
Then, when the needle was still, he brought up the middle of the magnet very near to the needle; but it did not move towards it at all. Then he drew the magnet along towards himself, keeping it at the same distance from the needle, and when the end of the bar came opposite to the needle, it immediately leaped out of its place, and adhered strongly to it.
“There is another way still,” continued the lecturer, “better than either of these.”
So saying, he took off the needle, which had adhered to the magnet, and drawing out the thread, he laid the needle itself carefully away upon a distant corner of the table. Rollo took it up, and was going to place it back with the others. But his father told him to put it down again, by itself, where he had placed it, and not to touch any of the things without his direction.
“I am going to show you another way,” he added, “of making it evident that the attractive power of the magnet resides at or near the poles.”
So saying, he opened the sheet of paper, and spread it out upon the table. Then he laid the magnet down upon it.