s the odd man went
in the house to speak to Tom's father, the two lads busied themselves
about the airship.

This was a large aeroplane, one of the largest Tom Swift had ever
constructed, and he was a lad who had invented many kinds of machinery
besides crafts for navigating the upper regions. It was not as large as
his combined aeroplane and dirigible balloon of which I have told you
in other books, but it was of sufficient size to carry three persons
besides other weight.

Tom had built it some years before, and it had seemed good enough then.
Later he constructed some of different models, besides the big
combination affair, and he had gone on several trips in that.

He and his chum Ned, together with Eradicate Sampson, the colored man,
and Mr. Damon, had been to a wonderful underground city of gold in
Mexico, and it was soon after their return from this perilous trip that
Tom had begun the work of changing his old aeroplane into a speedier
craft.

This had occupied him most of the Winter, and now that Spring had come
he had a chance to try what a re-built motor, changed propellers, and
different wing tips would do for the machine.

The time had come for the test and, as we have seen, Tom had some
difficulty in persuading anyone to go along with him? But Ned finally
got over his feeling of nervousness.

"Understand, Tom," spoke Ned, "it isn't because I don't think you know
how to work an aeroplane that I hesitated. I've been up in the air with
you enough times to know that you're there with the goods, but I don't
believe even you know what this machine is going to do."

"I can pretty nearly tell. I'm sure my theory is right."

"I don't doubt that. But will it work out in practice?"

"She may not make all the speed I hope she will, and I may not be able
to push her high into the air quicker than I used to before I made the
changes," admitted Tom, "but I'm sure of one thing. She'll fly, and she
won't come down until I'm ready to let her. So you needn't worry about
getting hurt."

"All right--if you say so. Now what do you want me to do, Tom?"

"Go over the wire guys and stays for the first thing. There's going to
be lots of vibration, with the re-built motor, and I want everything
tight."

"Aye, aye, sir!" answered Ned with a laugh.

Then he set at his task, tightening the small nuts, and screwing up the
turn-buckles, while Tom busied himself over the motor. There was some
small trouble with the carbure