"They will not even perceive its presence," replied the doctor. "The eastern side of the tube I shall also strongly charge negatively. Fortunately, the conductors we have along the inside of the tube will enable me to distribute this charge to whichever parts of the surface I desire."
"What good will this electricity do?" asked Flora.
"Why, this. As two electricities of the same kind repel each other, the car will be thus prevented from striking against the side of the tube. In fact, by increasing or diminishing the charge according to circumstances, I shall be able to keep the car always well in the center of the tube."
"Oh, I'm so glad!" exclaimed Flora.
"Not half so glad as I am," responded the doctor, heartily. "But I have n't a moment to lose. The start of the first car has been announced all over the world as taking place tomorrow at eleven o'clock in the morning, and I have all these electrical arrangements to prepare. It's fortunate your father discovered my oversight so opportunely, and that you showed me the way to remedy it. I hardly know to which of you I owe the greatest gratitude. Although we instinctively dislike the faultfinder, he often proves as service-
