"The material simply admits all light-vibrations, or perhaps curves them, just as the opacities cut them off," I answered. "A man under the X-ray is partly invisible; this makes him wholly so. He doesn't register, as the people of the motion-picture profession say." "Camouflage," repeated Larry. "And as for the Shining One--Say!" he snorted. "I'd like to set the O'Keefe banshee up against it. I'll bet that old resourceful Irish body would give it the first three bites and a strangle hold and wallop it before it knew it had 'em. Oh! Wow! Boy Howdy!" I heard him still chuckling gleefully over this vision as I passed along the opal wall with the green dwarf. 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. "The corial does not touch the road," explained Rador. "It is lifted so far"--he held his forefinger and thumb less than a sixteenth of an inch apart--"above it." And perhaps here is the best place to explain the activation of the shells or coria. The force utilized was atomic energy. Passing from the whirling ball the ions darted through the cylinder to two bands of a peculiar metal affixed to the base of the vehicles somewhat like skids of a sled. Impinging upon these they produced a partial negation of gravity, lifting the shell slightly, and at the same time creating a powerful repulsive force or thrust that could be directed backward, forward, or sidewise at the will of the driver. The creation of this energy and the mechanism of its utilization were, briefly, as follows: