"No, he could not; because you see that, in that way of suspending anything, the moment that it begins to move, it begins to swing off and to rise; so that it cannot be moved at all without being _lifted_ a little. And the more it is moved, the higher it is lifted, so that it would take a great force to move it far away from the centre, where it was hanging. But we can hang it in a way to avoid that difficulty." "How, sir?" said Rollo. Rollo seemed to be very much interested in this conversation. He had dismounted from his father's knee, and stood by his side, listening eagerly. His mother, too, was paying close attention. As for Nathan, he sat still; though it is not by any means certain that he understood it very well. "Let us suppose," said his father, "that the mass of lead, as big as a load of hay, is fastened to one end of a stick of timber." "That would not be strong enough to hold it," said Rollo. "Well, then, to a beam of iron, as large as a stick of timber," rejoined his father. "O," said James, "you could not get such a big bar of iron." "No," replied his father, "only an imaginary one; and that will be just as good as any. Now, suppose the great mass of lead is fastened to one end of this bar, and another one, just like it, to the other end, to balance it. Now, suppose that the lower end of the great chain is secured around the middle of the iron beam, and the upper end to be fastened to some strong support up in the air. Now, we can move the mass of lead without having to lift it at all; for, if we push against it, and make it move, it will move round and round, without rising at all, as it did before, when it was hung up directly by the chain." Rollo's father then went on to explain to them that, in such a case as this, the weight of the two masses of lead would not prevent their moving easily, for they would exactly balance each other. A little child would be able to move them; but still they would move exceedingly slow at first, and it would be hard to stop them, when they were in motion. So, he said, if the earth should cease to attract and draw down any great, heavy body, like a large stone, for example, the smallest child could lift it, though it would come up slowly, just as a very heavy body would move, if it was suspended by a string, or was afloat upon the water. "And so," said Rollo, "if the earth should not attract us, could we push ourselves right up off from the ground?" "Yes," said his father, "most undoubtedly." "What, and go about anywhere in the air?" "Certainly." Rollo began to laugh aloud at this idea, and looked very much interested and pleased. "O, then I wish there was no gravitation," said Rollo; "I do, really." "But, then," continued his father, "if you should get up into the air, you could not get down again." "Why not?" said Nathan, beginning to look a little concerned.