Ned, who had gained his feet and who clung to one of the hand-rails with which the compartment in the nose of the boat was furnished, now was silent. He watched his chum’s movements with great anxiety, but he did not interfere by either speech or act with Tom’s attempts to govern the craft. The inventor watched the needles of the several indicators connected with the mechanism of the plane. Some of these gyrated crazily when the boat rolled. But there was an arrow on one dial that stood still. This dial had nothing to do with the driving of the plane. At first it did not enter Tom Swift’s mind that this dial—or what it registered—was at all important to the flight of the seaplane. It was the indicator which registered the amount of compressed air that filled the “skin” of the boat. This hollow between the outer and inner hull of the craft had to do with the balance and security of the plane when she had to be brought down into the sea in rough weather. Tom’s experiments with the pigs’ bladders and the hollow bamboo had resulted in an attempt to overcome boisterous waves through the weight of compressed air between the two skins of the boat’s hull. How it was going to work when the _Winged Arrow_ chanced to descend upon a rough sea, was yet to be proved. He noted the unwavering needle on this particular indicator several times while the plane was rolling without getting from it any inspiration at all. Then, suddenly, he uttered a mighty shout, grabbed for the flexible speaking tube, and yelled to his chief mechanician: “Brannigan! Start the pump! Get busy!” “What pump, boss?” was the surprised query from the tail of the boat. “Compressed air! Isn’t but one, Brannigan! Fill the skin!” “All right, boss! Are you goin’ down?” “Not if I can help it. I want to stay up,” answered Tom, and dropped the tube. “What’s the idea?” demanded Ned, staring at him. “I don’t quite know what the idea is myself, yet,” confessed the young inventor. “But something has got to be done, and I am willing to try—Here we go again!” Once more the huge, groaning structure rolled. If it looked bad to those on the ground, consider how the crew of the _Winged Arrow_ felt! The usual kind of an equilibrator—that used in the government of most dirigible balloons and other flying craft—was a part of the _Winged Arrow’s_ equipment, but in this strange case the instrument seemed to have no value at all. The great hull of the seaplane certainly did not balance. Whether Tom drove the mechanism fast or slow, the rolling continued. No matter how strongly the structure was built, such wrenching must of necessity in time wreck the seaplane. They were now a mile or more high in the air. If the plane fell apart at this altitude there would not be the smallest hope of escape for any of her crew. Tom had tried to descend, but she seemed to roll worse on a downward than on an upward slant. “Brannigan! Make use of that pump!” Tom shouted through the tube.