showing excitement, too; I could see that his cheeks were ruddier and his eyes even brighter than normal. “But what if you want the cooling and don’t have any work to be done?”

“Simple,” I said. “You just let the machine turn a flywheel or lift weights and drop them, or something like that, outside your house. You have an air intake inside. And if, in the winter, you don’t want to lose heat, you just mount the thing in an outside building, attach it to your generator and use the power to do whatever you want—heat your house, say. There’s plenty of heat in the outside air even in December.”

“John,” said Farnsworth, “you are very ingenious. It might work.”

“Of course it’ll work.” Pictures were beginning to light up in my head. “And don’t you realize that this is the answer to the solar power problem? Why, mirrors and selenium are, at best, ten per cent efficient! Think of big pumping stations on the Sahara! All that heat, all that need for power, for irrigation!” I paused a moment for effect. “Farnsworth, this can change the very shape of the Earth!”

Farnsworth seemed to be lost in thought. Finally he looked at me strangely and said, “Perhaps we had better try to build a model.”

I WAS so excited by the thing that I couldn’t sleep that night. I kept dreaming of power stations, ocean liners, even automobiles, being operated by balls bouncing back and forth in cylinders.

I even worked out a spaceship in my mind, a bullet-shaped affair with a huge rubber ball on its end, gyroscopes to keep it 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