A shell was awaiting us. I paused before entering it to examine the polished surface of runway and great road. It was obsidian⁠—volcanic glass of pale emerald, unflawed, translucent, with no sign of block or juncture. I examined the shell.

“What makes it go?” I asked Rador. At a word from him the driver touched a concealed spring and an aperture appeared beneath the control-lever, of which I have spoken in a preceding chapter. Within was a small cube of black crystal, through whose sides I saw, dimly, a rapidly revolving, glowing ball, not more than two inches in diameter. Beneath the cube was a curiously shaped, slender cylinder winding down into the lower body of the nautilus whorl.

“Watch!” said Rador. He motioned me into the vehicle and took a place beside me. The driver touched the lever; a stream of coruscations flew from the ball down into the cylinder. The shell started smoothly, and as the tiny torrent of shining particles increased it gathered speed.