ve an ironic comment. For
the mathematics had been perfectly correct, only Buck Kendall
misinterpreted the answer.

"I've followed the math with mechanism all the way through," he
explained, "and I'm putting power into it. That's all I know. Somewhere,
by the laws of cause and effect, this power _must_ show itself
again--despite what the damn math says."

And in that, of course, Kendall was wrong. Because the laws of cause and
effect didn't hold in what he was doing now.

"Do you want to watch?" he asked at length. "I'm all set to try it."

"I suppose I may as well." McLaurin smiled. "In our close-knit little
community the fate of one is of interest to all. If it's going to blow
up, I might as well be here, and if it isn't, I want to be."

Kendall smiled appreciatively and replied: "Let it be on thy own head.
Here she goes."

He walked over to the power board, and took command. Devin, and a squad
of other scientists were seated about the room with every conceivable
type and combination of apparatus. Kendall wanted to see what this was
doing. "Tubes," he called. "Circuits A and D. Tie-ins." He stopped, the
preliminary switches in. "Main circuit coming." With a jerk he threw
over the last contact. A heavy relay thudded solidly. The hum of a
straining atostor. Then--

An electric motor, humming smoothly stopped with a jerk. "This," it
remarked in a deep throaty voice, "is probably the last stand of
humanity."

The galvanometer before which Devin was seated apparently agreed. In a
rather high pitched voice it pointed out that: "If the Lunar Fort falls,
the Earth--" It stopped abruptly, and an electroscope beside Douglass
took up the thread in a high, shrill voice, rather slurred, "--will be
directly attacked."

"This," resumed the motor in a hoarse voice, "will certainly mean the
end of humanity." The motor gave up the discourse and hummed violently
into action--in reverse!

"My God!" Kendall pulled the switch open with a sagging jaw and staring
eyes.

The men in the room burst into sudden startled exclamations.

Kendall didn't give them time. His jaw snapped shut, and a blazing light
of wondrous joy shone in his eyes. He instantly threw the switch in
again. Again the humming atostor, the strain--

Slowly Devin lifted from his seat. With thrashing arms and startled,
staring eyes, he drifted gently across the room. Abruptly he fell to the
floor, unhurt by the light Lunar gravity.

"I advise," said the moto