The machine dropped still lower.
"An army camp!" exclaimed Hal, when he was at last able to make out the objects below. He shut off his engine, and for a few moments both boys gave their attention to the awe-inspiring sight.
Dimly they could discern the outlines of the great camp. With its thousands upon thousands of huts, it spread out like a great fan, extending almost as far as the eye could see.
"Great Scott!" exclaimed Chester. "There must be a million men down there!"
"Hardly that many," laughed Hal; "but there are a few. I guess we had better go a little higher. We might be seen, and a chance bullet might bring us down in the middle of them."
The machine rose gently again; but, as the airship headed once more upon its course, there was a muffled explosion, and the machine rocked dangerously.
"What on earth is the matter now?" demanded Chester.
Hal bent over his engine.
"I don't know what has blown out," he replied. "But the engine has gone dead."
"Dead!" exclaimed Chester.