He moves the mirror to the side so they can see the machine sitting at the focus. Bright glare and heat shimmers obscure one end.

“The engine has a hot part and a cold part. The hot part is kept hot by the sunlight. The cold part is kept cold by blowing air over it. Inside, it moves air between the hot and cold parts, and as the air gets hotter or colder it pushes on other moving parts, and that keeps it running. And all the energy that's left over is stored.”