lad were approaching the shop, which, in spite of the explosion that
had taken place in it, was still intact, when an aged man, coming from
a handsome house not far off, called out, "Tom, is anyone hurt?"

"No, dad. We're all right."

"What happened?"

"Well, we had another explosion. We can't seem to get the right mixture
of the gas, but I think we've had the last of our bad luck. We're
going to try it again. Up to now the gas has been too strong, the tank
too weak, or else our valve control is bad."

"Oh dear, Mr. Swift! Do tell them to be careful!" a woman's voice
chimed in. "I'm sure something dreadful will happen! This is about the
tenth time something has blown up around here, and--"

"It's only the ninth, Mrs. Baggert," interrupted Tom, somewhat
indignantly.

"Well, goodness me! Isn't nine almost as bad as ten? There I was, just
putting my bread in the oven," went on Mrs. Baggert, the housekeeper,
"and I was so startled that I dropped it, and now the dough is all over
the kitchen floor. I never saw such a mess."

"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. Swift, near his
home.

"It didn't do so very much damage," observed Tom, as he peered in
through a window, void of all the panes of glass. "We can start right
in."

"Hold on! Wait! Don't try it now!" exclaimed Mr. Sharp, who talked i