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.