ng
until its apex was almost at the other end.

The light dawned. Rick's lips formed the word. "Grain."

Scotty was watching. "What?"

"Grain," Rick said again. "This thing is a small solid-propellant
rocket!"

CHAPTER XV

The Empty Boat

The Swiss torsion clock on Steve Ames's fireplace mantle read 6:49. Rick
and Scotty, in slacks, shirts, and moccasins, sat in armchairs and tried
to stay awake. The small rocket, cleaned and dried, rested on a
newspaper on Steve's table.

"Rockoon," Rick said. "That explains the funny antenna, the presence of
the electronics expert, and why the stingarees are launched."

"Not to me, it doesn't," Scotty retorted. He sipped steaming coffee.
"What was that word you used? Grain?"

Rick nodded sleepily. "That's what solid rocket fuel is called. It's
poured into the casing around a form. The form is withdrawn after the
fuel hardens. The shape is designed to give maximum burning surface.
Since the solid fuel is grainy, it's called grain."

"Logical," Scotty replied with a languid wave of his hand. "All
perfectly logical. I also understand that a rockoon is a combination of
a rocket and a balloon. The balloon carries the rocket up to where the
air is less dense, then the rocket fires and breaks away. How does the
rocket know when to fire?"

"Two ways. A barometric switch can be installed that will act at a
certain altitude, or a signal can be sent from the ground."

"The antenna," Scotty said. "It can send a signal."

"Sure."

"I'm with you all the way, until you say this shows why the stingarees
fly. Why send up rockoons? What's the reason?"

Rick forgot he was holding a coffee cup and waved his hand. He recovered
in time to keep from spilling the hot liquid on Steve's rug. "Scientific
research is usually the reason for rockoons. They carry experiments."

Scotty snorted. "Are you telling me Lefty Camillion has turned
scientist?"

"Nope." Rick yawned. "I take it back. We still don't know why the
stingarees fly. We only know what they are. Where do you suppose Steve
is?"

"That's the eighth time you've asked. He'll be here when that business
of his is over."

The telephone rang. Rick jumped to his feet and beat Scotty to the phone
only because he was four steps nearer. "Hello?"

An unfamiliar voice spoke. "Stay away from the creek, and stay away from
the house. If you don't, your crab-catching buddy is going to be turned
into crab food." The line went dead.