Night settled down. Jack, who had the first tour under the new arrangement, had made himself comfortable in the conning tower, and Mr. Henderson had hidden himself in the companionway. His idea was to thus guard both openings into the ship and ascertain whether the ghost came from within or without the craft.
Up to a short time before twelve o'clock nothing out of the ordinary happened. The only sound was the lapping of the waves on the steel sides of the Porpoise, and now and then a splash as a big fish leaped out of the water. There was only the slightest breeze.
Jack who, somehow or other, felt much sleepier than usual, caught himself nodding several times. Once he awoke with a start and realized that he had been dozing.
"Come, come," he remarked to himself, "this will not do at all. This is a fine way to watch for a ghost."
He remained wide awake for perhaps five minutes. Then he was off to the land of nod again. He was just dreaming that he was skating on a pond and was playing snap the whip with a lot of boys, when he awoke with a start.
He felt something pressing on his chest and to his horror, as he looked up, he saw a big towering white object standing over him. A second glance showed him it was a man, or the semblance of one, and the thing's foot was on his chest.
With a terrified scream Jack sprang up, upsetting the ghost, which, the boy thought at the time, seemed rather heavy for an unearthly spirit.
"Did you catch it?" cried the professor.
"No! Yes! I don't know!" yelled Jack, struggling to his feet in time to see the white object glide down the stairs that led from the conning tower into the forward cabin.
"Run after it! We must solve the mystery!" cried Mr. Henderson springing from the companionway up on deck.