a man-made quake? Tom mulled over the disturbing idea.

"How would I tackle the job myself, if I had to undertake such a project
for national defense?" the young inventor mused. He felt a growing sense
of excitement as an idea began to take shape in his mind.

_What about an artificial shock wave!_

An hour later Bud Barclay walked into the laboratory and found Tom
hunched over a jumbled pile of reference books on his workbench.

"What cooks, skipper?" Bud asked.

Tom looked up, his blue eyes blazing. "Bud, I think I may have the
answer!"

Tom got up from his stool and paced about the laboratory. "Suppose the
Brungarian rebel scientists have invented some sort of shock-wave
producer--a device for sending vibrations through the earth's crust or
the mantle underneath."

"Okay, suppose they have," Bud replied.

Tom snatched up a piece of chalk and made some quick diagrams on a
blackboard. "Just this, pal. Let's say they set up two or three stations
around the world for sending out such waves in a definite direction.
Wherever the wave crosses an earth fault or another wave--_boom!_ An
earthquake!"

Bud stared. "No kidding, is that how those rats triggered off all these