One of the puzzles the Secret Service men had to solve was that of the connection, if any, between the men who had to do with the missing Mr. Nestor and those who had damaged Tom's airship by filing the muffler case so it was weakened and burst. That there was some connection Tom was certain, but he could not work it out, nor, so far, had the government men.
At last the day came when the big government test was to be made. Tom had completed his Air Scout and had refined it to a point where even his critical judgment was satisfied. All that remained now was to give Mr. Terrill a chance to see how silently the big craft could fly, and to this end a flight was arranged.
Tom had put the silencer on a larger machine than the one he and Jackson had used. It held three easily, and, on a pinch, four could be carried. Tom's plan was to take Mr. Damon and Mr. Terrill, fly with them for some time in the air, and demonstrate how quiet his new craft was. Then, by contrast, a machine without the muffler and the new motor with its improved propellers would be flown, making as much noise as the usual craft did.
"I only wish," said Tom, as the time arrived for the official government test, "that Mary could be here to see it. She was the one who really started me on this idea, so to speak, as it was because I couldn't talk to her that I decided to get up a silent motor."
But Mary Nestor was too grief-stricken over her missing father to come to the test, which was to take place late one afternoon, starting from the aerodrome of the Swift plant.
"First," said Tom, to Mr. Terrill, "I'll show you how the machine works on the ground. I'll run the motor while the plane is held down by means of ropes and blocks. Then we'll go up in it."
"That suits me," said the agent. "If it does all you say it will do, and as much as I believe it will do, Uncle Sam will be your debtor, Mr. Swift."
"Well, we'll see," said Tom with a smile.
Preparations were made with the greatest care, and Tom went over every detail of the machine twice to make certain that, in spite of the precautions, no spy had done any hidden damage, that might be manifested at an inopportune moment. But everything seemed all right, and, finally, the motor was started, while Mr. Terrill, and some of his colleagues from the Army Aviation department looked on.
"Contact!" cried Tom, as Jackson indicated that the compression had been made.