"Of course, Dr. Bird," he said formally, "we are very glad to hear any suggestion that you may care to offer. When it comes, however, to a matter of surrendering control of a Post Office matter to the Department of Commerce or to the Treasury Department, I doubt the propriety. Our records are confidential ones and are not open to everyone who is curious. I will inform the proper authorities of your desire to help, but I doubt seriously if they will avail themselves of your offer." * * * * * Dr. Bird's black eyes shot fire. "Idiot!" he said. "If you're a specimen of the Post Office Department, I'll have the entire case taken out of your hands. Do you mean to cooperate with me or not?" "I fail to see what interest the Bureau of Standards can have in the affair." "The Bureau isn't mixed up in it; Dr. Bird is. If necessary, I will go direct to the President. Oh, thunder! What's the use of talking to you? Who's your chief?" "Chief Inspector Watkins is in charge of all investigations." "Carnes, get him on the telephone. Tell him we are taking charge of the investigation. If he balks, have Bolton go over his head. Then get the chief of the Air Corps on the wire and arrange for an army plane to-morrow. There is something more than a mail robbery back of this or I'm badly fooled." "Do you suspect--" "I suspect nothing and no one, Carnes--yet! I'll get a few instruments together to take with us to-morrow. We'll fly over that section until something happens if it takes us until this time next year." * * * * * A three-seated scout plane rose from Langley Field at eight the next morning. Captain Garland was at the controls. In the rear cockpit sat Dr. Bird and Carnes. Inside his flying helmet, the doctor wore a pair of headphones which were connected to a box on the floor before him. Carnes carried no apparatus but his hand rested carelessly on the grip of a machine-gun. The plane cleared Bellefonte at nine-thirty and bore east toward Philipsburg. Captain Garland kept his eyes on his instrument board and on a map. Less than six hundred feet above the ground, he was following the air-mail route as exactly as possible. Overhead a mail plane winged its way east, three thousand feet above them. Fifteen minutes brought them to Philipsburg. Captain Garland shot his plane upward a few hundred feet. "Turn back, Captain," said Dr. Bird into the speaking tube. "Retrace your course a quarter of a mile farther north. At Bellefonte, turn back and go over the same ground another quarter of a mile north. Keep flying back and forth, working your way north, until I tell you to stop." The plane swung around and headed back toward Bellefonte. "Of course, we can't tell exactly what route he followed," said the doctor to Carnes, "but he was new on this run and it is safe to assume that he didn't stray far. We'll quarter the whole area before we stop."