“Aye, aye, sir!” came back the reply. The finger on the dial had begun to move. The vacuum between the jackets of the hull began to fill with air. The plane regained an even keel again for a moment and Tom felt a tremor of the hull which he knew to be from the pressure of the air driven into the vacuum. “What are you doing, Tom?” demanded Ned, putting his lips close to his friend’s ear. “Trying a new one. Great Scott! Ned, if my suspicion is right, I have worked a scheme for balancing an object floating in air which as far as I know is an entirely new trick. I have invented something—perhaps—without the first idea that I was doing anything extraordinary.” “Don’t care what it is,” replied Ned. “But if it is what is stopping the boat from rolling——” “I believe it is! It is a new equilibrator! I believe it is going to work!” “We’re sitting pretty now,” confessed Ned. “Don’t try any more tricks till we are down again.” “Don’t fret.” Tom turned and spoke to Brannigan through the tube again. “Shut off! All right. Look out for yourselves back there. I am going to zoom.” The _Winged Arrow_, once more on even keel, began to descend in a great spiral. Closer and closer she came to the earth. There was Lake Carlopa and the cove from which she had taken to the air. After a time the two friends in the bow of the plane could see the spectators on the shore. Tom Swift had quite recovered from his disturbance of mind. He believed he had by chance discovered something that really was of great value in the management of this type of seaplane. He wanted to talk it over with his father and make other experiments before being sure that he had guessed right. After all, experiments in natural science are the chief paths to invention. Tom thought that he might have hit upon one of those lucky discoveries that often aid in the establishment of worthwhile knowledge. When the seaplane finally took the water, the air chamber had to be relieved of pressure before the hull floated at a proper depth. Mr. Barton Swift noted this at once and turned to see if the well dressed and talkative stranger had taken note of this fact. The man had disappeared. A motor-car shooting away along the road to Shopton suggested the manner in which the stranger might have gone. It was plain that for some reason the man did not wish to meet the younger Swift at this time. Tom’s father was so much interested in his son’s discovery regarding the compressed air chamber and its value as an equilibrator that he forgot to speak of the stranger and his evident interest in the new flying boat. Indeed, all those closely connected with Tom’s experiments and with the success of the _Winged Arrow_, thought of little else for the next few days but the recurrent flights of the plane.