But Artie told me about the bumblebee, and how there were still some scientists who insisted, according to the principles of aerodynamics, that it was not constructed properly to enable it to fly. And about how men of this short-sighted ilk were still scoffing at the ancient alchemist's talk of the Philosopher's Stone for transmuting metals, even though transmutation of metals was being done every day in atomic piles. And how he'd theorized that there _was_ once a genuine Philosopher's Stone, probably a hunk of pure U-235, that someone had managed to make, which might explain why so many alchemists (lacking, unfortunately, any knowledge of heavy radiations or Geiger counters) sort of died off in their quest for the stone. * * * * * It was nearly lunchtime when he finished his spiel, and I was kicking myself in my short-memoried brain for having let him get onto the subject, when abruptly the joyous glow behind his eyes damped its sparkle a bit. "There _is_ one little hitch--" "I thought it looked too easy," I sighed, waiting for the clinker. "Don't tell me it has to be made out of pure Gallium, which has the regrettable tendency to liquiefy at about thirty degrees centigrade? Or perhaps of the most elusive of its eleven isotopes?" "No, no, nothing like that," he murmured almost distractedly. "It's the force-per-gram part that's weak." "Don't tell me," I said unhappily, "that this thing'll only generate enough force to lift itself?" A feeble ghost of his erstwhile grin rode briefly across his lips. "That's the way it works out on paper," he said. "Which means," I realized aloud, "that it's commercially useless, because what's the good of an anti-gravity machine that can't lift anything except _itself_! It falls into the class of lifeboats that float up to the gunwales in the water while still _empty_. Fun to watch, but impossible to use. Hell, Artie, if that's the setup, then this thing wouldn't be any more help to a space-aiming government than an aborigine's boomerang; it flies beautifully, but not if the aborigine tries to go _with_ it." "However," he said, a bit more brightly, "I've been wrong on paper before. Remember the bumblebee, Burt! _That_ theory still holds up on paper. But the bee still flies." He had me, there. "So you want I should build it anyhow, just on the off-chance that it _won't_ follow the rules of physical logic, and will decide to generate a force above and beyond its own gravitic drag?" "That's it," he said happily. "And even if it only manages to negate its own weight, we'll have an easier time ironing the bugs out of a model than we would out of a diagram. After all, who'd have figured that beyond _Mach I_, all the lift-surfaces on a plane work in _reverse_?"