“Oh, I can easily catch up to them, and pass them; but that’s just the trouble, I don’t want to do that,” replied the tall lad. “If we get beyond them we’d have to turn, and then we might lose sight of them. I don’t know what to do if they won’t be friendly and let us come aboard.”
“They could easily fool us by just sinking,” spoke Ned. “I don’t see why they don’t do that instead of trying to run away from us on the surface. If that submarine captain knows anything about physics he must know that an object can travel through the air quicker than it can in water.”
“That’s right,” agreed Bob, “but he’s going along at a pretty good clip.”
This was indeed so. The submarine was fairly flying over the surface of the sea, a smother of foam at her stern showing where the propeller, or whatever form of propulsion she used, was working, while at her blunt nose was a long ripple as the water was pushed away on either bow.
“She is certainly making time,” conceded Jerry. “She must have powerful engines.”
“I guess those aboard her were watching us all the time,” came from Ned. “They just waited until they saw us getting too close, and then they started off.”
“Yes, but what I can’t understand,” observed Jerry, “is why they don’t dive, if they want to have us guessing. If she went down, even a few feet, we couldn’t see her, and she might come up ten miles from here. Then we would be out of it.”
“That’s right,” admitted Ned. “But perhaps they had to come up for fresh air, and their tanks aren’t quite filled yet. Of course oxygen can be manufactured aboard a submarine, but you can’t breathe artificial air forever—you’ve got to have fresh air, especially if they run gasoline engines, as they probably do, though the main ones may be operated by electricity from a storage battery.”
“Why do they need so much air for gasoline engines?” asked Bob.
“Because gasoline won’t explode unless it’s mixed with air. The engine simply must have it. So that’s why they’re probably staying on the surface so long—to renew the air in the compression tanks to feed to the motors.”