il is
an antenna. It's shooting out electro-magnetic waves of very high
frequency. When those waves hit anything, some are reflected. The
reflected waves are picked up by the tube inside the coil. You with me?"

"Way ahead of you," Chahda said. "Not all things reflect these waves the
same, huh? Maybe the more dense, the better reflect. So loose earth not
reflect too good, rocks little better, metal very good, and stuff like
crystals best of all."

"Poor native boy," Tony said chidingly. "You knew how it worked all
along."

Rick shook his head. "He's never seen it before, Tony. It's just that
he's pretty quick on the uptake for a poor native boy."

Chahda grinned. "Okay, chums, I'll drop the gag. Go ahead, Rick, I not
know everything yet. Why you testing here?"

"The minerals that make up the rocks and soil here will show a pattern.
We'll mark the pattern on this plastic screen." Rick indicated a circle
of white plastic, scaled like the face of the oscilloscope. "Then, when
we go hunting, we'll be looking for deviations from the pattern. For
instance, there probably is no metal in the ground here. We're looking
for metal. When we find it, the blip on the scope will stand out very
plainly. Got it?"

"Think so. Sounds easy. Let's see it work."

Rick held the tip of the probe at waist level. Tony adjusted the
controls until the scope flickered bright green. A vertical line on the
face of the scope was a much lighter green, nearly white. Then, as Tony
switched the activation circuit, the vertical line formed a pattern that
varied in width from top to bottom. Here and there a blip, a clear
horizontal line, thrust out both ways from the center.

The present pattern was not unlike that of a stylized Christmas tree,
with broad blips representing branches at the base, and increasingly
narrower ones representing the branches at the top. Rick quickly
sketched the pattern on the plastic circle.

"Now watch," he said, and put his rifle on the ground under the probe.

The Christmas tree pattern developed a new element that ruined the
design. It was a strong blip, thrusting out from center, about halfway
up the pattern.

"Steel," Rick said. "Other metals with good reflection qualities would
show blips slightly higher or lower on the scale."

"Some gadget," Chahda said admiringly. "What else you need know?"

"That's all." Tony was already closing the cover to the control panel.
"We're ready to move. Rick, suppose we just