So he laid a small nail down upon the table, and then touched the middle of the magnet to the nail. It was not attracted at all. Then he moved it along a little, towards one end, and touched it again. Still it was not attracted. Then he moved it along farther and farther; but the nail was not attracted until he got to the end of the bar, and then the nail hopped up and adhered to it quite strongly. "How curious!" said Rollo. His father then repeated the same experiment with the other half of the bar, and found the result the same. The nail did not appear to be at all attracted until he reached the end, and then it was lifted and held by this end, just as it was by the other. "So that, you see," said Rollo's father, "that the attractive power of the magnet resides in the ends." "Well, father, what is the reason?" "I don't know," said his father. "Don't you know, father?" said Rollo. "I thought you were going to tell us all about it." "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. "Now, Jonas," said he, "sprinkle some sand upon it from my sand-box, carefully, and see where the sand will adhere."