And his lungs were parched, his lips dry as swabs of cotton. Blood pounded through his temples, throbbing in time to the drone of the chaunter, and a dark mist gathered before his eyes. He tore the blow-pipe from his lips, gasped, "Keep playing!" came the dim, distant howl of Johnny Brown. "Just a few minutes longer, Jonesy! Relief is on the way. Sparks saw us from his turret window five minutes ago!" And Isobar played on. How, or what, he did not know. The memory of those next few minutes was never afterward clear in his mind. All he knew was that above the skirling drone of his pipes there came another sound, the metallic clanking of a man-made machine ... an armored tank, sent from the Dome to rescue the beleaguered trio. He was conscious, then, of a friendly voice shouting words of encouragement, of Joe Roberts calling a warning to those below. "Careful, boys! Drive the tank right up beneath us so we can hop in and get out of here! Watch the Grannies--they'll be after us the minute Isobar stops playing!" Then the answer from below. The fantastic answer in Sparks' familiar voice. The answer that caused the bagpipes to slip from Isobar's fingers as Isobar Jones passed out in a dead faint: "After you? Those Grannies? Hell's howling acres--_those Grannies are stone dead_!" * * * * * Afterward, Isobar Jones said weakly, "But--dead? I don't understand. Was it the sound-waves that killed them?" Commander Eagan said, "No! Grannies absolutely cannot hear. That is one thing we do know about them--though we will soon know a great deal more, now that our biologists have a dozen carcasses to dissect, thanks to you. But Grannies have no auditory apparatus." "But then--what?" puzzled Isobar. "It couldn't be vibration, because our Patrolmen tried shootin' 'em with the vibro-ray pistol, and nothin' never happened--" "Nevertheless," said Dr. Loesch quietly, "it _was_ vibration which killed them, Isobar. That is, of course, only my conjecture, but I believe subsequent study will prove I am correct. "It was the effect of _dual_, or disharmonic vibration. You see, the vibro-ray pistol expels an ultrasonic wave which disrupts molecular construction sensitive to a single harmonic. The Grannies' composition is more complex. It required the impact of two different wave-lengths, impinging on their nerve centers at the same moment, to destroy them." "And the bagpipe--" said Isobar with slowly dawning comprehension--"emits two distinct tones at the same time!" The full meaning of his words flashed upon Isobar. He turned to Commander Eagan, sallow cheeks glowing with new color. "Then--then what means we've licked our problem!" he cried. "We've found a weapon that'll kill the Grannies, and it won't be necessary to live inside Domes no more! Now we can move out into the open and live like human beings!" "Absolutely true!" agreed the Commander. "But _you_ will not be living Outside, Jones. Not right away, anyway."