Rollo’s father looked over the things which had been arranged upon the table, for a moment, in silence, and then took up Jonas’s magnet.

“This bar is what they call a magnet,” said he; “but all the magnetism is in the two ends.”

“It is?” said Rollo; “and what is the reason of that?”

“You can see that it is so,” said his father, without answering Rollo’s question, “in this way.”

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.”

So Jonas took the sand-box, and held it over the bar, not very high, and moved it slowly along, from one end to the other, and thus sanded the magnet all over. The sand fell off of it, however, freely, at every part except the ends; and Jonas, observing that it seemed to adhere there, held the sand-box a little longer over those places; and thus there was formed a sort of a black bur at the extremities, consisting of an accumulation of the black particles of sand. Rollo’s father then took up the bar carefully, and passed it around, so that all who were seated at the table could examine it closely.

“It is thickest on all the edges and corners,” said Rollo.

“Yes,” said his mother; “and the sand forms little black bristles, pointing off in every direction.”

They all examined it attentively, and observed the little black bristles pointing out every way from the edges and corners at the ends.

“This shows you,” said Rollo’s father, “exactly how the magnetic power, so far as its attractive force on other bodies is concerned, is distributed. You see it resides in the two ends, and the two ends seem to be exactly alike.”

“Yes, sir,” said Rollo, “exactly.”

“They seem to be so,” continued his father; “but the fact is, the magnetism of one end is very different from that of the other.”

“I see that the cluster of sand is a little bigger at one end, than it is at the other,” said Rollo’s mother. She was more observing than the others, and had noticed a little difference, which had escaped the rest.

“That indicates only a difference in degree,” said Rollo’s father; “but there is a difference in kind.”

“What do you mean by that, father?” asked Rollo.

“Why, if the attractive powers at the two ends were both alike in their nature, only one was stronger than the other, then the difference would be in degree; but there is a difference in the nature of the magnetism itself. In fact, the magnetisms of the two ends are of opposite natures in some respects.”

“Why, both ends attract the sand,” said Rollo, “just alike.”

“True,” said his father; “they seem to attract the sand in precisely the same way; and, looking at the bar, as I now hold it up,” he added, “with the sand adhering in the same way at the two ends, one would suppose that they were both magnetic alike. But, in fact, there is a great difference between them.”

All the company looked upon the two ends of the bar, as Rollo’s father held it up, wondering how he would show that there was any difference between them.

“Now, in the first place,” he continued, “we must get the sand off of the ends. Do you think you can get it off for me, Rollo?” said he.

Rollo took the bar very eagerly, and attempted to brush the sand back upon the paper. He succeeded in brushing off a little of it; but the greater portion remained. When he rubbed upon one side, it moved round to the other; and he could not get it off.

“Hand it to me,” said his father, “and I will show you how it can be done.”

He also asked Jonas to hand him the tongs, which were standing by the side of the fire. He then held the tongs over the sheet of paper, in a horizontal position, and gently rapped the end of the magnet against them, letting the end project a little over the tongs. This knocked all the sand off, and left the bar clean as it was before.

“Now let me see,” said he, “what was it that I was going to tell you next?”

“You were going to show us,” said Rollo’s mother, “that there are two different kinds of magnetisms in the two ends of the bar.”

“O, yes,” said he. “In order to do this, I must poise a needle in a new way.”

He then took up one of the corks which Rollo had put upon the table. From one end of this cork, he cut off, with his penknife, a round, flat piece. It was about as large around as a wafer, but somewhat thicker. He cut a little groove along the upper side of this, and laid the same needle which he had before used, and which he had put away upon the corner of the table, into this groove. Then he put the whole carefully into the saucer of water, which he had previously drawn up towards him.

“There,” said he, “we call a cork like that, a float; because it is intended to float a needle upon. Now, you see, the needle being supported by the cork, and the cork floating freely in the water, the needle is at liberty to move in any way.”

Nathan thought it was a very curious experiment to poise a needle so, upon a piece of cork,—even without the magnetism. And he watched it as it slowly moved about, with a face full of interest and curiosity.

The needle swung round a little one way and the other, and finally came to a state of rest. Then Rollo’s father held the magnet in his hands, in such a manner as to point it towards the needle, and then gradually brought it down near the water, just by the side of the point of the needle. The point immediately began to move slowly towards the bar; but Rollo’s father lifted it up suddenly, before the needle had time to touch it. Then he brought the same end of the magnet down upon the other side of the point of the needle, and that drew it back again.

“There,” said he, “you all see that the point of the needle is attracted by the bar, whichever side I put it.”

They all said they saw it very plainly.

“Now,” said he, “I am going to turn the magnet, and bring the other end of it down to the point of the needle; and if the magnetism at this end is the same with that in the other, the point of the needle will of course be attracted by this end too.”

“Certainly,” said Rollo’s mother.

Then he brought down the other end of the bar towards the needle. This other end was a little bigger than the one which he had tried first, because the file had been a little bigger at that end. But the needle, instead of being drawn towards it, as it had been towards the other end, began to move slowly away from it.

“Why, it is going away,” said Rollo.

His father did not answer, but immediately raised the bar and put it down upon the other side of the point, and then the point began to move away back again; being evidently driven away from the large end of the magnet, on whichever side it was presented.

Then Rollo’s father reversed the magnet again; that is, he brought the smaller end towards the needle as at first. The point of the needle was now attracted, that is, drawn towards the magnet; and then when he changed it again, and brought the large end to the needle, it was always repelled; that is, driven away again.

“Now you see,” he said, “that the small end of the magnet attracts the point of the needle, and the large end drives it away. That shows that the magnetism in the two ends is of two different kinds.

“And now,” he continued, “there is one thing more which is remarkable about it; and I want you to observe it very carefully. You see,” he says, “that the small end of the magnet attracts the point of the needle. But if I try it now upon the other end of the needle, where the eye is, it will repel that, just as the large end of the magnet repels the point.”

He tried it, and the result was just as he had said. And he repeated the experiment in a great many ways, and they always found that the large end of the magnet would draw the eye of the needle towards it, and drive the point away; and the small end of the magnet would draw the point of the needle, and drive the eye away. This proved, as Rollo’s father said, some great difference between the magnetisms of the two ends. “And you see,” he added, “that it is a difference in kind, not merely a difference in degree.”

“But one thing seems strange to me,” said Rollo’s mother, “and that is, that both ends of the magnet don’t attract the point of the needle, just as both of them attracted the nail.”

“And the sand,” said Rollo.

“Yes,” added his mother. “When you brought both ends of the magnet, one after the other, to the nail, they both attracted it.”

“And so they did the needle which hung down by the thread,” said Jonas.

“Yes,” said Rollo’s mother; “but now this needle, that is floating upon the water, is half attracted, and half repelled.”

“The reason is,” said Rollo’s father, “that the needle, that is floating upon the water, is a magnet itself, and has two magnetic poles; but the sand, and the nail and the needle that Jonas held up by the thread, were not magnets. They were only common pieces of iron and steel.”

“Why, father,” said Rollo, “that was the very same needle; you laid it away upon the corner of the table.”

“Yes,” said his father; “but it was not a magnet then.”

“When?” asked Rollo.

“Why, when Jonas held it up by the thread.”

“And is it a magnet now?”

“Yes,” said his father. “We will see if it is not.”

So he took the needle off from the float, and put it upon the paper. He then sprinkled a little sand over it, from the sand-box, and, upon taking it up, they all saw that there was a little tuft of black sand both upon the point and at the eye, showing that it was magnetic at both ends.

“It became magnetic,” said Rollo’s father, “only by being touched by the bar magnet; and that was the reason why I put it away by itself as soon as it had touched the bar. I did not want to have it mixed with the other needles, which had not been touched, and which, of course, were not magnetic. Now, if I take one of the needles which has not been touched, and put it upon the float, you will see that both ends of it will be attracted by both ends of the bar.”

So he placed away the magnetized needle upon the corner of the table again, and took another one, and placed it very carefully upon the float. Then he brought down one end of Jonas’s magnet very near the point of the needle. It attracted it. Then he brought it down very near the eye of the needle. It attracted the eye too. Then he turned the magnet, and tried the other end, and he found that that end also would attract both the eye and the point of the needle.

“Try the magnetized needle, and see if that will attract it too,” said Rollo’s mother.

Then Rollo’s father took the magnetized needle from the corner again, and brought the two ends of that, one after another, near to the ends of the needle upon the float. It attracted them just as Jonas’s magnet had done, only a great deal more feebly.

“So, you see that this needle is really a little magnet, just like Jonas’s great one.”

“Only there is no proof that it has the two different kinds of magnetism in the two ends,” said Rollo’s mother.

“We can easily show that,” said his father. He asked Dorothy to get another saucer full of water, while he prepared another float. Then he put the magnetized needle upon the new float, leaving the unmagnetized one upon the old float. They both looked almost precisely alike, each upon its own little disc of cork in its saucer of water.

“There,” said he, “you cannot see any difference between them; but there is a great deal of difference between them; for one is only a common needle of steel, but the other has its two extremities magnetic in opposite ways.”

To prove this, Rollo’s father brought one end of the bar to the point of the magnetized needle, and the point was repelled. He brought it then to the eye of the same needle, and it attracted it. Then he brought the same end of the bar, first to the point, and then to the eye of the unmagnetic needle, and it attracted them both; so it was evident that there was a considerable difference, in reality, between the condition of the two, though there was no difference in external appearance.

“Now you see, from all this,” added Rollo’s father, “that when a magnet touches a piece of steel, like a needle, it immediately makes it a magnet itself; that is, it makes the two ends magnetic, one having one kind of magnetism, and the other the other kind; and then, if you take two magnets, and bring those two poles which have the same magnetism together, they repel one another; and if you bring those together which have different magnetisms, they attract each other.”

“How do you know that they are the same magnetisms that repel, and different that attract?” said Rollo’s mother.

“I will show you,” said his father.

Then he took the needles that he had used off from their floats, and laid them away. He took next two new needles, exactly of a size, and he held them together between his thumb and finger, with the eyes projecting together. Then he rubbed them once or twice upon the end of Jonas’s magnet, saying,

“There, you see I use both of these needles alike. Of course the eyes have both the same magnetisms. Now you will find that when I put one of them upon the float, and then bring the eyes together, they will repel each other; but an eye and a point will attract. So two points will repel.”

“But you have not magnetized the points,” said Rollo’s mother.

“Yes,” said his father. “When we magnetize one end, the other end becomes magnetized, itself, in the contrary way.”

So he put one of the needles upon the float, and then brought the eye of the other down very near to its eye. It was repelled, as he had said it would be. He then brought the two points together, and they were repelled. But if he brought an eye towards a point, or a point towards an eye, they were attracted.

“This is the end of my lecture,” said he, “for to-night.”

“O, father,” said Rollo, “a little more.”

“No more to-night, only to recapitulate,” said he.

“Recapitulate? what is that?”

“Why, tell you, briefly, the substance of what I have explained, so that you may remember it.”

“Well, father,” said Rollo.

“In the first place, a magnet has a peculiar and mysterious attractive power for iron, residing in its two extremities, which are called its poles; and the power which resides in one extremity is, in some way or other, opposite in its nature to that of the other extremity. Each of these poles repels a pole like itself, and attracts one different from itself, in any other magnet.”

Poor Nathan could not understand this grave, philosophical disquisition very well, and he began to get pretty sleepy. He had, however, been somewhat amused, during the greater part of the time, in seeing the corks float about upon the water, with the needles upon them. So his father took the needles off, and let him have the two floats in one of the saucers to play with, a few minutes, while Dorothy put the other things away. He asked her to put all the things away together, so that they could get them ready the next evening, and then he said that perhaps he would give them another lecture.

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