at you better go back to the new
station--the one you were going to move to if it kept on getting worse."

"But the instruments...." the Lensman was thinking, not of the
instruments themselves, which were valueless in comparison with life,
but of the records those instruments would make. Those records were
priceless.

"I'll have everything on the tapes in the flitter," Cloud reminded.

"But suppose...."

"That the flitter stops one, too--or doesn't stop it, rather? In that
case, your back station won't be there, either, so it won't make any
difference." How mistaken Cloud was!

"QX," the Chief decided. "We'll leave when you do--just in case."

* * * * *

Again in air, Cloud found that the activity, while still high, was not
too high, but that it was fluctuating too rapidly. He could not get even
five seconds of trustworthy prediction, to say nothing of ten. So he
waited, as close as he dared remain to that horrible center of
disintegration.

The flitter hung poised in air, motionless, upon softly hissing
under-jets. Cloud knew to a fraction his height above the ground. He
knew to a fraction his distance from the vortex. He knew with equal
certainty the density of the atmosphere and the exact velocity and
direction of the wind. Hence, since he could also read closely enough
the momentary variations in the cyclonic storms within the crater, he
could compute very easily the course and velocity necessary to land the
bomb in the exact center of the vortex at any given instant of time. The
hard part--the thing that no one had as yet succeeded in doing--was to
predict, for a time far enough ahead to be of any use, a usably close
approximation to the vortex's quantitative activity. For, as has been
said, he had to over-blast, rather than under-, if he could not hit it
"on the nose:" to under-blast would scatter it all over the state.

Therefore Cloud concentrated upon the dials and gauges before him;
concentrated with every fiber of his being and every cell of his brain.

Suddenly, almost imperceptibly, the Sigma curve gave signs of flattening
out. In that instant Cloud's mind pounced. Simultaneous equations: nine
of them, involving nine unknowns. An integration in four dimensions. No
matter--Cloud did not solve them laboriously, one factor at a time.
Without knowing how he had arrived at it, he knew the answer; just as
the Posenian or the Rigellian is able to perceive every separate
c