oriented
properly, the ball serving as solution to that biggest of
missile-engineering problems, excess heat. You'd build a huge concrete
launching field, supported all the way down to bedrock, hop in the
ship and start bouncing. Of course it would be kind of a rough
ride....

In the morning, I called my superintendent and told him to get a
substitute for the rest of the week; I was going to be busy.

Then I started working in the machine shop in Farnsworth's basement,
trying to turn out a working model of a device that, by means of a
crankshaft, oleo dampers and a reciprocating cylinder, would pick up
some of that random kinetic energy from the bouncing ball and do
something useful with it, like turning a drive shaft. I was just
working out a convection-and-air pump system for circulating hot air
around the ball when Farnsworth came in.

He had tucked carefully under his arm a sphere of about the size of a
basketball and, if he had made it to my specifications, weighing
thirty-five pounds. He had a worried frown on his forehead.

"It looks good," I said. "What's the trouble?"

"There seems to be a slight hitch," he said. "I've been testing for
conductivity. It seems to be quite low."

"That's what I'm working on now. It's just a mechanical problem of
pumping enough warm air back to the ball. We can do it with no more
than a twenty per cent efficiency loss. In an engine, that's nothing."

"Maybe you're right. But this material conducts heat even less than
rubber does."

"The little ball yesterday didn't seem to have any trouble," I said.

"Naturally not. It had had plenty of time to warm up before I started
it. And its mass-surface area relationship was pretty low--the larger
you make a sphere, of course, the more mass inside in proportion to
the outside area."

"You're right, but I think we can whip it. We may have to honeycomb
the ball and have part of the work the machine does operate a big hot
air pump; but we can work it out."

* * * * *

All that day, I worked with lathe, milling machine and hacksaw. After
clamping the new big ball securely to a workbench, Farnsworth pitched
in to help me. But we weren't able to finish by nightfall and
Farnsworth turned his spare bedroom over to me for the night. I was
too tired to go home.

And too tired to sleep soundly, too. Farnsworth lived on the edge of
San Francisco, by a big truck by-pass, and almost all night I wrestled
wi