"HAT?" exclaimed Mr. Curtis, in amazement. "You really think that William will lose his weight at the very instant that the car begins to fall?"

"Not only do I think so, but I am absolutely sure of it."

"Why, what grounds have you for such a belief?"

"I understand your astonishment, James, for I confess I long shared your idea that the passengers in the car would retain their weight until they reached the center of the earth. The problem is a most curious one, and is very puzzling at first; but once the conditions are well understood, the explanation is quite natural."

"Well, I'm afraid that, for my part, I don't know enough about physics to understand your