"How?" The big Lensman's query was skepticism incarnate. "It can't be done, except by an almost impossibly fortuitous accident. You yourself have been the most bitterly opposed of us all to these suicidal attempts."
"I know it—I didn't have the solution myself until a few hours ago—it hit me all at once. Funny I never thought of it before; it's been right in sight all the time."
"That's the way with most problems," the Chief admitted. "Plain enough after you see the key equation. Well, I'm perfectly willing to be convinced, but I warn you that I'll take a lot of convincing—and someone else will do the work, not you."
"When I get done you'll see why I'll pretty nearly have to do it myself. But to convince you, exactly what is the knot?"
"Variability," snapped the older man. "To be effective, the charge of explosive at the moment of impact must match, within very close limits, the activity of the vortex itself. Too small a charge scatters it around, in vortices which, while much smaller than the original, are still large enough to be self-sustaining. Too large a charge simply rekindles the original vortex—still larger—in its original crater. And the activity that must be matched varies so tremendously, in magnitude, maxima, and minima, and the cycle is so erratic—ranging from seconds to hours without discoverable rhyme or reason—that all attempts to do so at any predetermined instant have failed completely. Why, even Kinnison and Cardynge and the Conference of Scientists couldn't solve it, any more than they could work out a tractor beam that could be used as a tow-line on one."
"Not exactly," Cloud demurred. "They found that it could be forecast, for a few seconds at least—length of time directly proportional to the length of the cycle in question—by an extension of the calculus of warped surfaces."
"Humph!" the Lensman snorted. "So what? What good is a ten-second forecast when it takes a calculating machine an hour to solve the equations.... Oh!" He broke off, staring.
"Oh," he repeated, slowly, "I forgot that you're a lightning calculator—a mathematical prodigy from the day you were born—who never has to use a calculating machine even to compute an orbit.... But there are other things."
"I'll say there are; plenty of them. I'd thought of the calculator angle before, of course, but there was a worse thing than variability to contend with...."
"What?" the Lensman demanded.