"They are," he announced. "We will cross between Orsk and Iroitsk. A safe place. In the morning we will be in Siberia—the land of the exiles."

And they were, morning seeing them flying over a most desolate stretch of landscape. Onward they flew, covering verst after verst of loneliness.

"I'm going to put on a little more speed," announced Tom, after a visit to the storeroom, where were kept the reserve tanks of gasolene. "I've got more fluid than I thought I had, and as we're on the ground now I want to hurry things. I'm going to make better time," and he yanked over the lever of the accelerator, sending the Falcon ahead at a rapid rate.

All day this was kept up, and they were just making an observation to determine their position, along toward supper time, when there came the sound of another explosion from the motor room.

"Bless my safety valve!" cried Mr. Damon. "Something has gone wrong again."

Tom ran to the motor, and, at the same time the Falcon which was being used as an aeroplane and not as a dirigible, began to sink.

"We're going down!" cried Ned.

"Well, you know what to do!" shouted his chum. "The gas bag! Turn on the generator!"

Ned ran to it, but, in spite of his quick action, the craft continued to slide downward.

"She won't work!" he cried.