this afternoon, and some unknown party trying to bring about our downfall
and death in this brazen way only a few hours afterwards."

"And using corrosive acid, too," spluttered the indignant Jack. "I've
heard of ropes being partly cut, even wire stays or struts filed to
weaken them; but this is the limit. Don't I wish they'd caught the skunk
in the act!"

"He'd never have left this aviation camp alive," said Tom sternly. "Why,
the boys would be so furious they'd be tempted to lynch him offhand."

"And I'd be glad to help pull the rope!" snapped Jack. "A more cowardly
act couldn't be imagined than this. Air pilots take great enough chances,
without being betrayed by spies or traitors."

"We'd better say nothing about it," Tom concluded. "I'm going to run
over the entire machine on my own account."

"And I'll do the same, Tom; for a pilot can't be too sure of his mount,
especially when there's such meanness afoot."

They accordingly busied themselves after their individual fashion. Every
brace and stay was looked over carefully and tested as only pilots know
how. Long experience, and many accidents have taught them where the weak
spots lie, and they understand how to guard against the giving way at
these points.

So the minutes passed. Other pilots had already ascended to await the
assembling of the picked squadron at some given altitude. Every minute
or two could be heard the rush of some unit starting forth. There were