"Oh, as to that," said Phaeton, "I've no objection to telling you two about it, now that I have thought it all out. I did not care to tell you before, because I was studying on it."
"All right; go ahead," said Ned, as we seated ourselves on the grass, and Phaeton began.
"It is called the Underground Railway. You see, there are some places—like the city of New York, for instance—where the buildings are so close together, and land is worth so much, that they can't build railroads enough to carry all the people back and forth. And so they have been trying, in all sorts of ways, to get up something that will do it—something different from a common railroad."
"Balloons would be the thing," said Ned.
"No; balloons won't do," said Phaeton. "You can't make them 'light where you want them to. I've thought of a good many ways, but there was some fault in all of them but this last one."
"Tell us about the others first," said Ned.
"I'll show you one of them," said Phaeton, and he drew from his pocket a small sheet of paper, which he unfolded.
"This," said he, "represents the city of New York. A is some place far up-town where people live; B is the Battery, which is down-town where they do the business. I suppose you both know what a mortar is?"