“Come on!” Russ said, heading for the door. “Let’s go downstairs.”
No sooner had they reached the ground than Prince came crawling out from under a small shed at the edge of the clearing, barking happily and leaping all over Russ Steele. Russ scratched his head, chuckling. “Dick had you pegged dead to rights, you old coward.”
Jerry knelt down solemnly and held out his right hand to the dog. “Shake, old buddy. Us cowards have to stick together.”
The boys waved as the big chopper began to circle the tower in tightening circles, losing altitude until it was almost level with the observation booth. Slowly it cut speed, until at last it seemed to be hanging motionless in space, held aloft by the great whirling rotors. A hatch opened in the bottom of the fuselage, and a crate was let down carefully on the end of a cable. Before it could touch the ground, Russ Steele rushed over and grabbed it, bringing the fragile package gently to earth. Quickly, he unhooked the cable and waved up at the helicopter. The cable was reeled in smoothly, then with a roar of its engines, the copter leaped into the air. Minutes later it disappeared over the treetops.
The boys watched with interest as Russ Steele unpacked the carton and removed two oblong black Bakelite boxes from the packing. They had a very unscientific, unprepossessing appearance.
“Is that all a Geiger counter is?” Jerry said with a trace of disappointment. “The transformer on my old electric trains looks more complicated.”
Russ smiled. “The Geiger counter is very simple, Jerry—especially when you consider how delicate it is and what it can accomplish.”
“How does it work?” Sandy asked.
“We made one in the science lab once,” Quiz said eagerly. “It’s just two electrodes, really. One of the electrodes is a thin metal cylinder; the other is a metal wire enclosed in a glass tube filled with gas—like a neon light. When the counter is brought near any radioactive substance, the rays given off ionize the gas—so it can conduct electricity—allowing the current to jump the gap and close the circuit, the same way it does when you switch on a light—”
“Only instead of a light, it activates an audible indicator,” Russ said. “That’s the clack-clack you hear when the counter detects radioactivity. Look how sensitive it is.” He held one of the black boxes near his wrist watch, and it began to chatter vigorously.