"Yeah," drawled Wes Farrell, "but what makes it vibrate?"
Don Channing looked down at the crystal. "Where did you get it?" he asked.
Walt Franks chuckled. "I bet you've been making synthetic elements again with the heterodyned duplicator."
Farrell nodded. "I've found a new series sort of like the iron-nickel-cobalt group."
Channing shook his head. There was a huge permanent magnet that poured a couple of million gauss across its gap, and in this magnetic field Farrell had the crystal supported. A bank of storage batteries drove several hundred amperes—by the meter—through the crystal from face to face on another axis, and down from above there poured an intense monochromatic light.
"Trouble is," complained Wes, "that there isn't a trace of a ripple in any of the three factors that work on the thing. Permanent magnet, battery current, and continuous gas-arc discharge. Yet—"
"It vibrates," nodded Channing. "Faintly, but definitely it is vibrating."
Walt Franks disappeared for a moment. He returned with a portable phonograph, which caused Don Channing to grin and ask, "Walt, are you going to make a recording of this conversation, or do you think it will dance to a Strauss waltz?"
"It's slightly bats, so I brought the overture to Das Fledermaus for it," snorted Franks. As he spoke, he removed the pick-up from the instrument and added a length of shielded wire. Then he set the stylus of the phonograph against the faintly vibrating crystal and turned up the gain.
At once a whining hum came from the loud speaker.