"Now we believe he has joined forces hereabout with ancient enemies of the Federal officers. At least, there is a strange aeroplane reported from both sides of the border, and some fine gems have appeared in the hands of certain suspected dealers in Maine, and as far south as Boston and Providence.
"Bainbridge is known to be a desperate man. Look out for him, Professor. If you are hailed by another machine, better keep away from it," and the secret service agent laughed. "Had I been in your place I would not have halted on this occasion. You certainly can outsail any airship I have ever seen operated."
Mr. Ford seemed quite satisfied that our friends were law-abiding and he ascended to his waiting craft in a few moments; and the Snowbird started onward again through the starlight.
But the warning of the special agent had impressed the boys as well as the professor. Andy Sudds refused to lie down again, although Jack and Mark continued to operate the flying machine. The old hunter sat with a rifle in his hand for the rest of the night. But the professor went to bed.
An hour after midnight a cloud from the west completely masked the moon and the whole heavens became misty. This cloud brought both wind and rain, and low upon its edge the lightning played fitfully.
"There will be a heavy tempest about dawn," Andy promised the boys. "I have seen a thunderstorm gather like this before." "But not while you were in a flying machine," chuckled Jack.
"No, sir. But on a mountain top a tempest looks much the same."
Mark, while at the controls, had scaled the machine down the air-ways until they were not more than fifteen hundred feet from the earth. But the boys decided to let the storm gather beneath them, and so shot the Snowbird up again until the indicator registered three thousand feet.
Near the earth it must have been very warm and sultry; but up here it was down to freezing, and the party were all warmly dressed. The clouds soon hid the whole earth from them and the great flying machine traveled in space, with the star-lit heavens above and the rolling mass of vapor, streaked now and then with lightning flashes, beneath.
The deafening roll of the thunder awoke Washington White from a short nap, and the darkey was not at all sure that he was safe from the lightning bolts.