"At this rate of progress, very soon," answered the exile, after glancing at the map. "We should be at the foot of the Ural mountains in a few hours, and across them in the night. Then we will be in Siberia." And he was right, for just as supper was being served, Ned, who had been making observations with a telescope, exclaimed: "These must be the Urals!" Mr. Petrofsky seized the glass. "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. "Then the intake pipe must be stopped!" answered the young inventor. "Never mind, I'll volplane to earth and we can make repairs. That magneto has gone out of business again." "Don't land here!" cried Ivan Petrofsky. "Why not?" "Because we are approaching a large town--Owbinsk I think it is--the police there will be there to get us. Keep on to the forest again!" "I can't!" cried Tom. "We've got to go down, police or no police." Running to the pilot house, he guided the craft so that it would safely volplane to earth. They could all see that now they were approaching a fairly large town, and would probably land on its outskirts. Through the glass Ned could make out people staring up at the strange sight. "They'll be ready to receive us," he announced grimly. "I hope they have no dynamite bombs for us," murmured Mr. Damon. "Bless my watch chain! I must get rid of that Nihilist literature I have about me, or they'll take me for one," and he tore up the tracts, and scattered them in the air. Meanwhile the Falcon continued to descend. "Maybe I can make quick repairs, and get away before they realize who we are," said Tom, as he got ready for the landing.