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 aeroplane; isn't it?"

"yes, and not moving very fast, either. they seem to be circling around here."

the young inventor was peering through the binoculars, and, as soon as he had the mysterious craft in focus, he cried:

"look, mr. jackson, it's a new kind of monoplane. i never saw one like it before. i wonder who could have invented that? it's something like a santos-dumont and a bleriot, with some features of cornu's helicopter. that's a queer machine."

"it certainly is," agreed the engineer, who was now sighting through the glasses. in spite of the darkness the binoculars brought out the peculiarities of the aeroplane with considerable distinctness.

"can you make out who are in it?" asked tom.

"no," answered mr. jackson. "you try."

but tom had no better luck. there were two persons in the odd machine, which was slowly flying along, moving in a great circle, with the swift house for its center.

"i wonder why they're hanging around here?" asked tom, suspiciously.

"perhaps they want to talk to you," suggested mr. jackson. "they may be fellow inventors—perhaps one of them is that philadelphia man who had the whizzer."

"no," replied the lad. "he would have sent me word if he intended calling on me. those are strangers, i think. there they are, coming back again."

the mysterious aeroplane was once more circling toward the watchers on the roof. there was a movement on the steps, near which tom was standing, and his father came up.

"is anything the matter?" he asked anxiously.

"only a queer craft circling around up here," was the reply. "come and see, dad."

mr. swift ascended to the roof. the aeroplane was higher now, and those in her could not so easily be made out. tom felt a vague sense of fear, as though he was being watched by the evil eyes of his enemies. more than once he looked over to the shed where his craft was housed, as though some danger might threaten it. but the shed of the humming-bird showed no signs of invaders.

suddenly the mysterious aeroplane increased its speed. it circled about more quickly, and shot upward, as though to show the watchers of what it was capable. then, with a quick swoop it darted downward, straight for 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 instant he could not tell what it was, and then, as he grew wider awake he knew that it was the shouting of eradicate sampson, and the braying of boomerang.

but what was eradicate shouting?

"fire! fire! fire!"

tom leaped to his window.

"wake up, massa tom! wake up! de areoplane shed am on fire, an' de humming-bird will burn up! hurry! hurry!"

tom looked out. flames were shooting up from the roof of the shed where his precious craft was kept.