"I'm sorry," answered the youth, trying not to laugh. "We'll see that
it doesn't happen again."

"Yes; that's what you always say," rejoined the motherly-looking
woman, who looked after the interests of Mr. Swift's home.

"Well, we mean it this time," retorted the lad. "We see where our
mistake was; don't we. Mr. Sharp?"

"I think so," replied the other seriously.

"Come on back, and we'll see what damage was done," proposed Tom.
"Maybe we can rig up another container, mix some fresh gas, and make
the final experiment this afternoon."

"Now do be careful," cautioned Mr. Swift, the aged inventor, once
more. "I'm afraid you two have set too hard a task for yourselves this
time."

"No we haven't, dad," answered his son. "You'll see us yet skimming
along above the clouds."

"Humph! If you go above the clouds I shan't be very likely to see you.
But go slowly, now. Don't blow the place up again."

Mr. Swift went into the house, followed by Mrs. Baggert, who was
loudly bewailing the fate of her bread. Tom and Mr. Sharp started
toward the shop where they had been working. It was one of several
buildings, built for experimental purposes and patent work by Mr.