"I am sorry you witnessed what you did," the professor said to them. "But I could not have this man spoil my plans. Some time ago he discovered my secret, and to keep him from publishing it broadcast I was forced to take him into my confidence. He has given me some aid in getting rare chemicals, but he wants a heavy price. He demands a half interest in the Monarch, and to be taken to the north pole."
"Then you are really going to search for the pole?" asked Jack.
"I am, my boy, and, what is more, I am going to find it. Why, it is simple with the wonderful gas I have discovered. That is the whole secret of what will be my success. It is easy enough to make an airship that will move, but the trouble is no one has yet been able to make a gas strong enough to lift the heavy weight of the ship high into the air. That is where I have the advantage."
"I wish I could see your ship sail," said Jack.
"You may if you like," exclaimed the old man. "Do you remember what I asked you when the knock interrupted us? I asked you if you wanted to go to the north pole. Now I have taken a great liking to both you boys. I haven't even asked your names yet, but I like you. I need some help in running the ship, also in making my explorations in the frozen north. Would you like to go along?"
For a few seconds the boys did not know what to say. It was a strange and sudden proposition. They had been through so many adventures in the last few hours that their brains were fairly bewildered. But to both of them there came a great desire to make this wonderful trip through the air. Before they could make a reply Professor Henderson spoke again:
"Perhaps you had better think it over a bit," he said. "I realize that it comes rather suddenly. Supposing you go to bed, and we'll talk more in the morning. Come, Washington, make up a couple of bunks for the boys in this room. You can sleep in the balloon shed as usual."
In a few minutes the colored man had made rude but comfortable beds on two bunks, like shelves that folded against the wall. Then, with an armful of bed clothes, he retired to the big shed.
"Better use a little more liniment," advised the old man. "I don't want you sore and stiff if you go with me."
Accordingly Jack and Mark rubbed their arms and legs well. Something in the stuff must have been very soothing for they soon fell asleep.