Mark had the watch just after midnight, and was sitting in the conning tower, the door of which opened out on the small deck. He had swept the surface of the water with powerful gla.s.ses and was sure there were no ships in sight. So, feeling that he would like to stretch his legs, he walked up and down on the platform.

He had reached the after end, and was about to turn and go back, when he was startled to see between him and the conning tower a white object. At first Mark thought it was a cloud of mist, or something the matter with his eyes. He rubbed them, but the object did not disappear.

Then it moved, and, to his horror Mark saw that it had the shape of a man, tall and thin. The two arms were outstretched, and to Mark's imagination seemed to be pointed toward him.

In spite of trying not to be, Mark was frightened.

He did not believe in ghosts, and had always felt that all stories about them were due to persons' imaginations. Now he saw something that was hard to explain.

As he watched it, the white object turned and glided without making the slightest noise, toward the conning tower. It entered and Mark breathed a sigh of relief.

Perhaps, after all, it was some one from down in the cabin, maybe the professor himself in his night shirt, who had come up to see that all was right.

"I'll go and look," said Mark to himself.

He had to nerve himself for the ordeal, as, in spite of a.s.suring himself that there were no such things as ghosts, he was frightened.

It was absolutely quiet. The only sound was the gentle swish of the water against the sides of the ship. The engine was running so slowly that it caused no noise.

Half way on his journey to the conning tower Mark paused. There, advancing toward him, was the white object. With outstretched arms it glided nearer and nearer until Mark's heart was beating as if it would burst through his ribs. His mouth was dry and he could not have cried out had he tried.

There was a splash in the water off to the left as some big fish sprang out and dropped back again. Involuntarily Mark turned in that direction.

Then he thought of the ghost and looked for it again. To his surprise the white object was nowhere to be seen!

The boy waited a few minutes, and then, s.c.r.e.w.i.n.g up his courage, he went to the tower. There was no one inside, and, along the length of deck nothing was to be seen of the ghost.

"I wonder if I have been asleep and dreaming," the boy asked himself. He gave his leg a pinch, and the sensation of pain told him he was not slumbering.

"Well, I'll say nothing about it," Mark went on to himself. "They'll only laugh at me."

Entering the tower Mark looked for the gla.s.ses in order to make another observation. He could not find them, yet he was sure he had left them on a shelf in the tower.

"I wonder if the ghost took them," he said.

He heard some one coming up the iron stairs of the small companionway that led down into the interior of the ship through the man-hole. At first he thought it was his queer midnight visitor returning. Then the head and shoulders of Jack appeared.

"I've come to relieve you," said Jack. "Your watch is up; it's two o'clock. Here are the night gla.s.ses. I found them on the cabin table. I thought you had them with you."

"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?"

"I mean anything unusual."

"Nothing, only a school of porpoises went past and gave me a little scare. They were like a lot of water kittens at play."

Mark concluded he would say nothing of the white visitor until he ascertained whether any one else had seen it.

It was several nights later, when the ship was once more proceeding slowly along the surface of the water, that the ghost again appeared.

This time Washington had the midnight watch.

But the colored man was not one to remain quiet when he had such a scary visitor, and his yells aroused the ship.

"It's a ghostess! A big white ghostess!" yelled Washington. "I don seen it wid my eyes, an' it waved his arms at me. I's goin' to die suah!"

"What's all this nonsense?" demanded the professor sternly. Then Washington, more or less excitedly, told of what he had seen. It was just as it had happened to Mark.

"You were dreaming," said the professor to Washington. "There are no such things as ghosts."

Every one, from old Andy to Tom and Bill, had been roused by Washington's cries, and listened to his story. At the close of the recital of how the white thing had suddenly disappeared, Washington refused to continue his watch, unless some one stayed with him.

Mark volunteered to do this. He was anxious to see if the ghost would reappear to him. But nothing happened; and the rest of the night pa.s.sed off quietly.

The next day the _Porpoise_ was taken below the surface, in order to allow of better speed being made. She was running along, submerged to a depth of two hundred feet, when there came a sudden jar, and the ship stopped.

"More trouble!" exclaimed the professor.

He opened the slide covering the bull's-eye windows and looked out. All about was swirling muddy water.

"Can you see anything?" the inventor called to Jack, who was in the conning tower.

"We've run into a mud-bank, and are stuck fast," called back the boy.

CHAPTER XIV

DIGGING OUT THE SHIP

"Reverse the engine!" called the professor. "Maybe we can back the ship out."