Rollo's Experiments Part 15

"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 brus.h.i.+ng 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."