Rollo’s father gave one or two other lectures upon magnetism, in the course of which Rollo found out a good deal about the subject; and, having learned from his father’s explanations that any magnet, when balanced freely, would point to the north and south, that is, one end to the north and the other to the south, he determined to try the experiment.  He accordingly poised a needle carefully upon a cork, as his father had done in his lecture, and put it in a basin of water upon the platform.  But he did not succeed very well.  The needle would always swing round, and turn its point towards the garden gate; but Rollo knew very well that the garden gate was not north from the platform.  He remembered that the North Star was over the barn, for he and Jonas had noticed it particularly when they had made the dial.  The needle, therefore, ought to have pointed towards the barn, according to his father’s lecture; but it would not.  Rollo took up a straw, and pushed the point of the needle round, and said, “Point there! point there, I tell you!” But all in vain.  The needle would not heed either his pushing or his commands; but, as soon as he let it go, it would immediately swing back into its old position, where it pointed towards the garden gate.

Rollo was just about giving up in despair, when he saw his sister Mary coming in from the garden gate, with a book under her arm.

“O Mary,” said he, “what shall I do?  My needle won’t point right.”

“Why, what is the matter with it?” said Mary.

“It will point over towards the garden,” said Rollo; “look.”

So Mary came up, and looked at his needle.  She saw that it was pointing towards the garden gate.

“Now I’ll push it away,” said Rollo, “and you will see that it comes directly back again.”

So he took up his straw, and pushed the point of the needle away.  The cork moved, turning round rapidly, until at length it swung away towards one side of the basin, and then suddenly drifted up against the side, and stuck there.

“That’s another plague,” said Rollo.  “It will run up to the side of the basin, and stick there.”

“What makes it?” said Mary.

“I don’t know,” said Rollo.

Mary sat down upon the platform, and examined the needle and the surface of the water very carefully.  She observed that the water was heaped up a little against the side of the basin, all around.  She asked Rollo to observe it.

“Yes,” said he, “and the needle and cork run right up that ridge of water.”

“And the bubbles too,” said Mary.

Mary pointed, when she said this, to several little bubbles which were adhering closely to the side of the basin, in another place.

She took up a little straw, and pushed away some of the bubbles from the side of the basin, and then gently moved them back again until they were pretty near, and observed that they would immediately rush up against the side again.  She did not understand this phenomenon, especially as the water was raised a little along the edge by the side of the basin, so that the bubbles and the needle actually appeared to rush up hill.

After examining this for some time, Mary moved the cork float, with the needle upon it, back into the middle of the basin, and then left it to itself.  It slowly moved around until it pointed to the garden gate, as it had done before.

“Now what is the reason?” said Rollo; “that isn’t north.”

Mary looked upon it very attentively for a few minutes in silence, and then said, suddenly,

“O, I see.”

“What?” said Rollo.

She did not answer, but pointed down to the platform by the side of the basin.

Rollo looked where she pointed, and saw the hammer lying there.  He had had it to play with a short time before, and, when he brought the basin of water, he had laid it down by his side.

“What?” said Rollo.

“The hammer attracts the needle,” replied Mary.

“The hammer?” said Rollo.

“Yes,” replied Mary.  “Don’t you know that iron attracts the needle, and it will not point to the north if there is any iron near to draw it away?”

Rollo was just going to take the hammer up, but Mary stopped him, saying,

“Wait a moment.  Let me take it away slowly, and see the effect.”

So Mary told Rollo to watch the needle, while she carefully drew the hammer away.

Rollo did so.  He and Mary both watched the needle.  It was pointing pretty nearly toward the hammer, and when Mary gently moved the hammer away, the needle, released from the influence which the iron exerted upon it, slowly moved back towards the direction of the barn, that is, the direction of a north and south line, which is called the meridian.

“It’s going back! it’s going back!” said Rollo.

Mary said nothing, but watched it carefully.  The needle swung beyond the direction of the meridian a little way, and then came slowly back again.  So it continued vibrating from one side to the other, though to a less and less distance every time.  Finally, it came to a state of rest; but it was not then, however, exactly in the meridian.

“What makes it swing so, back and forth?” said Rollo.

“I don’t know exactly,” said Mary.  “I suppose the force that it moves with, carries it a little beyond, and then it is drawn back again, and that makes the oscillations.”

“Oscillations?” said Rollo, inquiringly.

“Yes.  They call this swinging back and forth, oscillating; and each movement is an oscillation.”

“Is that the name of it?” said Rollo.

“Yes,” said Mary.  “When you tie a little stone to a string, and hold the upper end of the string still, and let the stone swing back and forth, it makes oscillations.”

“I mean to try it,” said Rollo.

“Yes,” said Mary; “and I will help you by and by, after I have studied my philosophy lesson.”

“Your philosophy lesson?” asked Rollo.  “Have you got a philosophy lesson to get?”

“Yes,” said Mary, “in that great book.”

So Rollo took up Mary’s book, which she had laid down upon the platform near Rollo’s apparatus.  He found that the title of it was “Intellectual Philosophy.”

“Intellectual Philosophy?” said Rollo; “and what sort of philosophy is intellectual philosophy?”

“It is the philosophy of the mind,” replied Mary.  “It explains to us about the thoughts and feelings of our minds.”

“Are there any experiments in intellectual philosophy?” asked Rollo.

“Yes,” said Mary, “we can try experiments in intellectual philosophy.”

“What experiments?” said Rollo.

“Why, there is a question whether we always dream when we are asleep.”

“I do,” said Rollo, “every night.”

“Yes, but perhaps not all night long.”

“Yes, I do,” said Rollo.  “I have good long dreams.”

“But,” replied Mary, “you may dream several hours in the night, so as to remember good long dreams in the morning, and yet perhaps you might have been, for some time, perfectly sound asleep, so as not to have any dreams in your mind at all.  Some persons think we dream all the time when we are asleep, and others think we don’t dream all the time.  Now we might contrive some experiments to decide the question.”

“How?” said Rollo.

“Why, you and I might agree to wake each other up several times, from a sound sleep, and then, if we were dreaming at that time, we should probably remember it.”

“Well,” said Rollo, “let us try it.”

“That would be an experiment in intellectual philosophy,” said Mary.

Rollo determined to try the experiment; and then he took Mary’s book, and asked her where her lesson was that day.  She found the place, and Rollo read a little.  He could not understand it very well, and so he concluded that he would rather have Mary go and study her lesson, and then come down and help him make the experiments of oscillation.

Mary accordingly took her book and went in, and left Rollo at his play.