They went to a restaurant near a great round stone, which was perched on the top of a big ledge of rock, and when Freddie wanted to know what it was his father told him.
"That's a rocking stone," said Mr. Bobbsey. "It stands there on a sort of little knob, and it is so nicely balanced that a man, or two or three boys, can easily push it and rock it to and fro."
"Do you mean one man can move that big rock?" asked Bert.
"Yes, he can make it rock, but he can not make it move off the rock on which it rests. Come and try."
Bert and his father pushed their backs against the stone, and, surely enough, they could make it rock an inch or two back and forth. Freddie helped, or at least he thought he did, which is the same thing. But the stone really did rock, and the children thought it was quite a wonderful thing. Sometimes your heavy piano, if it stands on an uneven place in the floor, may be rocked back and forth a little. That's the way it was with the rocking stone. The restaurant where the Bobbseys ate was
