the building where Tom's newest invention was housed.

"Look out! They'll hit something!" cried the young inventor, as though
those in the aeroplane could hear him.

Then, just as though they had heeded his warning, the pilots of the
mysterious craft shot her upward, after she had hovered for an instant
over the big shed.

"That was a queer move," said Tom. "It looked as if they lost control of
her for a moment."

"And they dropped something!" cried Mr. Jackson. "Look! something fell
from the aeroplane on the roof of the shed."

"Some tool, likely," spoke Tom. "I'll get it in the morning, and see
what sort of instruments they carry. I'd like to examine that machine,
though."

The queer aeroplane was now shooting off in the darkness and Tom
followed it with the glasses, wondering what its construction could be
like. He was to have another sight of it sooner than he expected.

"Well, we may as well get back to bed," said Mr. Jackson. "I'm tired,
and we've got lots to do to-morrow."

"Yes," agreed Tom. "It's cooler now. Come on, dad."

Tom fell into a light doze. He thought afterward he could not have slept
more than half an hour when he heard a commotion out in the yard. For an