Part 31

"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.

OSCILLATIONS.

In about an hour, Mary came down into the yard in pursuit of Rollo, in order to try the experiments which she had proposed.

When Rollo saw her coming, he left his play, and ran to meet her.

"Well, Mary," said he, "have you come to make the oscillations?"

"Yes," said Mary. "I have brought some thread for strings, and I want you to get some pebble stones--some large, and some small ones."

Rollo went for the pebble stones, while Mary looked about for a suitable place for making the experiments. In a corner of the yard there was a bench under a tree, and the branches came down pretty low. Mary thought that this would be a good place, for she could tie her strings to these branches with the pebbles hanging down below; and she and Rollo could watch the oscillations, while seated upon the bench.

Mary took her station here, and Rollo presently appeared, with the crown of his cap half filled with pebble stones. Mary said they would do finely. She poured them out upon the bench by her side, and Rollo put his cap upon his head again.

"Now, Rollo," said she, "we will study the art of experimenting."

"No," said Rollo, "we are going to study oscillation."

"Yes," replied Mary; "the experiments are to be on oscillations; but what I want principally to teach you, is, the proper way to make experiments."

"Well," said Rollo.

Mary said no more, but she proceeded to tie a small pebble to the end of one of the long threads which she had brought out with her. Then she tied the other end of the thread to the branch of the tree, which was over her head. The pebble then hung down before them, so that both Rollo and herself could plainly see all its motions.