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. "How d'I know dem bolts won't fly disher way?" he demanded of the boys when they tried to reassure him. "Why, the earth attracts the electric bolt, and that attraction is much stronger than any the _Snowbird_ may have for the electricity in the clouds," Mark told him. "I don't know erbout dat," grumbled Wash. "An' if jest one o' dem crazy lightning bolts should take it into its haid ter segastuate eround disher flying merchine--biff! bang! dat would be erbout all. Dere would be a big bunch o' crape hung on Wash White's do', suah as you is bawn, boy!" But although the roar of the thunder and whining of the wind nearly drowned other sounds in and about the flying machine, save for a freshening of the gale the _Snowbird_ was at first but little disturbed by the tempest which raged with such fury a thousand feet below. Suddenly Mark caught sight of something moving across the red streak in the eastern sky--the light that warned them of the approach of the sun. "What is that--a huge bird?" he demanded of Andy Sudds, pointing this moving figure out to the hunter. Andy's eyes were very keen, for he was used to sighting along a rifle and gazing over long distances in search of game. But he, too, thought the object must be a bird. "I declare, I didn't know birds flew so high," said Mark. "It must be an eagle. No other fowl could fly so high."