Watch was kept, for, though they were out of the regular line of ocean travel, there was no telling when a vessel might come along and run them down, for the Porpoise did not show above the waves more than a few feet, and carried no lights.
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 glasses 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 assuring himself that there were no such things as ghosts, he was frightened.