to ask you a few questions, William, on a point that Mr. Curtis and I have been discussing. I understand that you studied physics at school?"
"Only the very elements," answered William, hastily, fearing that his imperfect knowledge was about to be put to the test.
"Well, that ought to be sufficient, for all the problems you will meet with in your trip are elementary ones. But tell me first what you know about the force of attraction at the center of the earth."
"Why, there is no attraction of gravitation at the center of the earth—or rather, the attraction is the same on all sides, so it is neutralized. A body placed at the very center of the earth would weigh absolutely nothing; if I were there at this moment I should weigh nothing at all, not even one tenth of an ounce."
"Your answer is perfectly correct so far, William, and we all agree with you. Now tell us, please, what you think your weight will be during your trip in the car."
"Why, at the beginning I shall weigh just as much as I do now, that is to say, one hundred pounds. But as I go down my weight will be less, because, instead of being attracted downward
