"Nonsense!" replied the doctor, with more show of conviction than he really felt. "What could happen to him? The advantage of this railroad over all others is that the trains cannot get off the track, and that collisions are impossible. So, you see, the danger is very slight."
"There's one thing I forgot to ask about, doctor," said Mr. Curtis. "How is William going to renew his supply of air when it gives out?"
"There will not be any need of renewing it," replied the doctor. "The trip will take only one hour, and as the car is as large as a good-sized room, William will have enough air to last him a whole day, at a pinch. As an extra precaution, however, I have put in a tank of liquefied air, which he can turn on in case he needs it."
"Why, in what case could he need more than a day's supply of air?"
"Well, for instance, if the resistance of the air during his fall is so great as to prevent the car from reaching the catches I have placed on the New York end of the tube."
"And what would happen in that case?"
"Why, it would stop short of its destination and then fall back."
"I see; and as it would n't fall back far enough
