He was interrupted by a heavy, throbbing noise in the air over their heads. The fog was too thick to enable them to see what it was, but Ned cried:
“Wind!”
“Of a sort—yes!” admitted Tom. “But it’s wind from the propellers of some sort of an aeroplane! There’s a craft passing overhead.”
When Ned listened more carefully he knew this to be right. Some big dirigible or aeroplane was passing above them, and the throb of her motors and the beat of her propellers could plainly be heard.
“Think that might be the Red Arrow passing us?” asked Ned.
“It’s possible,” Tom admitted. “She’s got powerful motors.”
They looked upward, trying to pierce the fog, and a moment later the wind began to blow, tearing the blanket of vapor apart. It was just in time for Tom and Ned to see, high up, a great craft heading toward the east. But whether it was the Red Arrow or some other machine they could not tell. It seemed likely that it was one which was racing against Tom for the world circuit prize.
Then the fog drifted in again and there was a wall of white all about them. Ned looked at the glass once more and found that it was still dropping. As he took this in he gave a low whistle.
“It’s going to blow and blow soon,” he said to Tom. “How much longer are we going to be here?”
“Not much longer, I hope,” answered the young inventor a bit impatiently. The sight of that big craft passing overhead had made him apprehensive. “I’ll go and find out. Keep her on this course, Ned,” and he turned the steering wheel over to his chum.