"I did," replied Mark.

"Then how did they get below?"

"I—I don't know," said Mark.

The mystery was deepening, yet he did not want to tell Jack just yet.

"Well, that's queer," remarked Jack. "Maybe the captain came up and got them while you were asleep."

"I didn't go to sleep," answered Mark rather crossly.

Jack said nothing more, but took his place in the conning tower, while Mark went below. Thinking to discover if the ghost might by any chance have been one of the persons on the Porpoise, Mark looked into each bunk. From the captain to Washington, all the inmates were peacefully slumbering.

"Queer," murmured Jack, as he took a look into the engine room before turning in. The engine needed no attention, as it worked automatically, and all there was to do was to steer the ship. Even this needed little care as the course was a straight one, and the wheel could be locked, leaving the lookout little to do.

"Did you see anything during your watch?" asked Mark of Jack the next morning.

"See anything? What do you mean?"