"I am sure of it, for this reason," said the captain, as the officers on the bridge crowded around; "neither of the periscopes is visible, and I can plainly see the boiling that follows a sinking submarine."
The ship was now at full speed, sailing directly over the course where the submarine was sighted. It did not take long for the vessel to cover the mile, and, as they neared the tell-tale spot, the ship was veered slightly out of its course, so that a good view could be obtained of the surface of the water.
"How deep do you suppose that submarine is now?" asked Alfred.
"It is in less than two hundred feet of water; see, the air bubbles are still coming up, although it went down fully fifteen minutes ago."
The steamer slowed down as it came abreast, and the passengers leaned over the side in intense excitement, watching the signs which indicated the death of another sea terror. Even while they were watching one immense boiling zone appeared and settled down, indicating that another air tank had given way, or that the pressure of the sea water had forced the air from one of the innumerable pockets in the interior of the submarine.
Four bells indicated a resumption of the journey. The great funnels began to pour forth smoke in immense volumes, and the ship fairly shook with the revolutions of the twin screws.
"So we are going directly south," said Ralph, who had just examined the compass, and started for the stairway.
"There will be no let-up now," remarked the captain.
Every one understood that forced draught would now be resorted to, both to avoid the likelihood of being torpedoed, and also to enable the ship to reach port at the earliest possible moment. The St. Duneen, although a twin-screw vessel, was not of more than 5,000 tons burden, having been built as a mail carrier for distant ports, in which speed was regarded as the important element in her construction.
As the commander remarked to the captain, after the latter reached the bridge, he felt sure that the speed alone, which he was able to make in an emergency, would baffle any attempt to reach his hull. It seemed so, for the vessel fairly skimmed the surface of the water, and left a trail which could be marked for miles.