if
it is! We need it." The noise increased, sounding more and more like
wind, but Tom, looking out into the night, saw the leaves of the trees
barely moving.

"If that's a breeze, it's taking its own time getting here," he went on.

The sound came nearer, and then Tom knew that it was not the noise of
the wind in the trees. It was more like a roaring and rumbling.

"Can it be distant thunder?" Tom asked himself. "There is no sign of a
storm." Once more he looked from the window. The night was calm and
clear--the trees as still as if they were painted.

The sound was even more plain now, and Tom, who had sharp ears, at once
decided that it was just over the house--directly overhead. An instant
later he knew what it was.

"The motor of an aeroplane, or a dirigible balloon!" he exclaimed.
"Some one is flying overhead!"

For an instant he feared lest the shed had been broken into, and his
Humming-Bird taken, but a glance toward the place seemed to show that
it was all right.

Then Tom hastily made his way to where a flight of stairs led to a
little enclosed observatory on the roof.

"I'm going to see what sort of a craft it is making that noise," he
said.

As he opened the trap door, and stepped out into the little observatory
the sound was so plain as to startle him. He looked up quickly, and,
directly overhead he saw a curious sight.

For, flying so low as to almost brush the lightning rod on the chimney
of the Swift home, was a small aeroplane, and, as Tom looked up, he saw
in a light that gleamed from it, two figures looking down on him.

Chapter Sixteen

A Mysterious Fire

For a few moments Tom did not know what to think. Not that the sight of
aeroplanes in flight were any novelty to him, but to see one flying
over his house in the dead of night was a little out of the ordinary.
Then, as he realized that night-flights were becoming more common, Tom
tried to make out the details of the craft.

"I wish I had brought the night glasses with me," he said aloud.

"Here they are," spoke a voice at his side, and so suddenly that Tom
was startled. He looked down, and saw Mr. Jackson standing beside him.

"Did you hear the noise, too?" the lad asked the engineer.

"Yes. It woke me up. Then I heard you moving around, and I heard you
come up here. I thought maybe it was a flight of meteors you'd come to
see, and I knew the glasses would be handy, so I stopped for them. Take
a look, Tom. It's an aeropl