When the ship had risen as far as Tony desired he made Mark send it straight ahead. The boy adjusted the air tube to carry the craft toward the south, but Tony, seeing by a compass in which direction they were headed, ordered Mark to steer due east.
“Fix things so they will stay so, too,” added Tony. “I don’t want to stop until I get a thousand miles away. Then we’ll come down, sail to some sunny island, and enjoy life.”
Mark locked the steering apparatus so as to keep the _Mermaid_ headed due east.
“Now you can go back to your friends,” Tony said. “When I want you I’ll send for you.”
With a heavy heart Mark rejoined the professor and others. He found them with their bonds removed. But to guard against their escape several men were on watch outside the door.
“What are they doing?” asked the professor eagerly as Mark entered, and the boy told him what had taken place.
“They will ruin my ship and spoil the whole trip,” cried the old scientist. “Oh, why did I ever go to the rescue of the scoundrels?”
“Never mind,” said Jack. “Perhaps we may yet outwit them.”
Morning came at last. The ship was still shooting forward at fast speed, in an easterly direction. The sailors had learned, in their short stay aboard, where the food and stores were kept, and they lost little time in getting breakfast. They sent some in to their captives, including a big pot of hot coffee, and, after partaking of this the professor and his friends felt better.
The mate of the _Good Hope_ came in to help clear away the dishes. As he passed Mark he slipped into the boy’s hand a note.
“Don’t read it until you are alone,” he said in a low voice, as he hurried from the room.
As soon as the other sailors had left, Mark glanced at the slip of paper. It bore these words:
“Open when you hear three raps, then two, then three, and keep silent.”
“Do you think he is a friend of ours?” the professor asked.
Mark told him of the mate’s conversation the night previous.
“I think we can trust him,” the scientist went on. “He must intend to pay us a visit when the others are asleep. When we hear the knocks as he specifies we must open the door and let him in.”
All that day the captives were kept in the living room. Once or twice Mark was sent for to make some adjustment to the machinery, but the apparatus, for the most part, was automatic, and needed little attention. The professor, as well as the others, were all impatience for the promised visit of the mate. Still they felt he would not come until night.