soning. He was right in believing that his weight would be greatest when he was traveling fastest, as the resistance of the air in the tube would then be greatest. He was also right in believing that, if there was no air in the tube, his speed would be greatest when he reached the center of the earth. What he overlooked was the fact that, while the increase in the speed of the car each second was now very small, the resistance offered by the air was considerable. In a word, although he had not yet passed the center, his speed was checked by the air more than it was increased by gravity, so that the car was gradually slowing up. He had passed the point at which objects would have their greatest weight, and from now on all bodies in the car would continue growing lighter and lighter.
"Ah, yes," said William, as he slowly realized the true state of affairs; "I begin to see now where I made my mistake. Under no circumstances could I have weighed more than I generally do on the earth, because, if the resistance in any one second had kept back the car more than thirty-two feet, my speed the next second would of course be less than before, since gravity, even when greatest, only increases my velocity thirty-two feet each second. And my speed being less, the resis-
