"It's right along here somewhere!" cried the doctor. "Summon everyone to this point and take up twenty-yard intervals." From the north and south the cars came racing in. The instruments were spread out along a new line twenty yards apart. As the borer was located the intervals were decreased to fifteen feet. Dr. Bird thrust a long white rod into the ground. "His path lies under here," he said. "Into the cars and go back a mile and test again." The borer was making slow progress, and it was half an hour before Dr. Bird drove the second stake in the ground. With a transit he took the bearing of the path and laid it out on a large scale map. "We'll stop him between Marr and Ritchie," he announced. "Jones, I am going back and set up my apparatus. Keep track of his movements. If he changes direction, let me know at once." * * * * * The doctor's car tore off to the west. Near Upper Marlboro, he met the convoy of trucks and led them to the selected spot. The trucks were unloaded and the apparatus laid out. Attached to a huge transformer were a dozen strange-looking projectors. What puzzled Carnes most was a huge built-up steel bar wound about with heavy cable. Dr. Bird had this bar erected on a truck and located it with great exactness. The projectors were set up in a battery just east of the bar. "How about power?" asked the doctor. "We'll have it in five minutes," replied one of the men. "A power transmission line carrying twenty-two thousand passes within two hundred yards of here. We are phoning now to have the power cut off. As soon as the line is dead we'll cut it and bring the ends here." The electrician was good at his word. In five minutes the power line had been cut and cables spliced to the ends. The cables were brought to the doctor's apparatus and the main lines were rigged to the ends of the cable wound around the bar. In parallel on taps, the projectors were connected. Huge oil-switches were placed in both lines. "All ready, Doctor," reported the electrician. "Good work, Avent. He'll be here soon, I fancy." A car whirled up and a man leaped out with a surveyor's rod. He set it up on the ground while a companion watched through binoculars. He moved it a hundred yards to the north and then back twenty. When he was satisfied he turned to Dr. Bird. "The direction of movement has not changed," he said. "The path will pass under this stake." Under the doctor's supervision, the truck carrying the bar moved forward until it stood over the surveyor's stake. The battery of projectors moved to a new location a few feet east of the rod. Other cars came racing up. "He's less than half a mile away, Doctor!" cried Jones. "Get your electroscopes out and spot him a hundred yards from this truck." "Very well, Doctor." * * * * *