of the vortex's existence and
activity were measured and recorded continuously, throughout every
minute of every day of every year. And all of these records were summed
up, integrated, into the "Sigma" curve. This curve, while only an
incredibly and senselessly tortuous line to the layman's eye, was a
veritable mine of information to the initiate.

Cloud glanced along the Sigma curve of the previous forty-eight hours
and scowled, for one jagged peak, scarcely an hour old, actually punched
through the top line of the chart.

"Bad, huh, Frank?" he grunted.

"Plenty bad, Storm, and getting worse," the observer assented. "I
wouldn't wonder if Carlowitz were right, after all--if she ain't getting
ready to blow her top I'm a Zabriskan fontema's maiden aunt."

"No periodicity--no equation, of course." It was a statement, not a
question. The Lensman ignored as completely as did the observer, if not
as flippantly, the distinct possibility that at any moment the
observatory and all that it contained might be resolved into their
component atoms.

"None whatever," came flatly from Cloud. He did not need to spend hours
at a calculating machine; at one glance he _knew_, without knowing how
he knew, that no equation could be made to fit even the weighted-average
locus of that wildly-shifting Sigma curve. "But most of the cycles cut
this ordinate here--seven fifty-one--so I'll take that for my value.
That means nine point nine oh six kilograms of duodec basic charge, with
one five percent over and one five percent under that for alternates.
Neocarballoy casing, fifty-three millimeters on the basic, others in
proportion. On the wire?"

"It went out as you said it," the observer reported. "They'll have 'em
here in fifteen minutes."

"QX--I'll get dressed, then."

The Lensman and the observer helped him into his cumbersome,
heavily-padded armor. They checked his instruments, making sure that the
protective devices of the suit were functioning at full efficiency. Then
all three went out to the flitter. A tiny speedster, really; a torpedo
bearing the stubby wings and the ludicrous tail-surfaces, the
multifarious driving-, braking-, side-, top-, and under-jets so
characteristic of the tricky, cranky, but ultra-maneuverable breed. But
this one had something that the ordinary speedster or flitter did not
carry; spaced around the needle beak there yawned the open muzzles of a
triplex bomb-thrower.

[Illustration: _Ten seconds in