"Well, we've got the hardest part of our work yet ahead of us," remarked Tom several hours later when, the lights having been set aglow, they were gathered in the main cabin. There was no danger of being seen now, for they were quite high.
"We've done pretty well, so far," commented Ned. "I think we will have easier work rescuing Mr. Petrofsky's brother than in locating the mine.
"I don't know about that," answered the Russian. "It is almost impossible to rescue a person from Siberia. Of course it is not going to be easy to locate the lost mine, but as for that we can keep on searching, that is if the air glider works, but there are so many forces to fight against in rescuing a prisoner."
They had a long journey ahead of them, and not an easy route to follow, but as the days passed, and they came nearer and nearer to their goal, they became more and more eager.
They were passing over a desolate country, for they avoided the vicinity of large towns and cities.
"I wonder when we'll strike Siberia?" mused Tom one afternoon, as they sat on the outer deck, enjoying the air.
"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.