"It's eighty-four, all right. From the Martian habit of using twelve as a base, I've calculated the number to be eighty-four."
"Diddle that, too," suggested Jim.
"O.K.," said Barney. "It doesn't take a lot to crank that one around from zero to about fifteen thousand c.p.s. Here she goes!"
Barney took the main dial of the beat-frequency oscillator and began to crank it around the scale. He went up from eighty-four to the top of the dial and then returned. No effect. Then he passed through eighty-four and started down toward zero.
He hit sixty cycles and the jackpot at the same time!
At exactly sixty cycles, a light near the wall dimmed visibly. The wallpaper scorched and burst into a smoldering flame on a wall opposite the dimmed light.
Barney removed the BFO from the vicinity of sixty cycles and Jim extinguished the burning wallpaper.
"Now we're getting somewhere," said Barney.
"This is definitely some sort of weapon," said Jim. "She's not very efficient right now, but we can find out why and then we'll have something hot."