groating nodded. "our problem now is to sift the billions of factors stored in the prog building and discover which of them is that tiny snowball."

the controller, who had been silent in a state of wild suppression all the while, suddenly spoke up. "i tell you it's impossible, mr. groating. how can you dig the one significant factor out of all those billions?"

groating said: "it will have to be done."

"but there's an easier way," the controller cried. "i've been suggesting it all along. let's attempt the trial and error method. we instigate a series of changes at once and see whether or not the future line is shifted. sooner or later we're bound to strike something."

"impossible," groating said. "you're suggesting the end of stability. no civilization is worth saving if it must buy salvation at the price of its principles."

i said: "sir, i'd like to make a suggestion."

they looked at me. the c-s nodded.

"it seems to me that you're both on the wrong track. you're searching for a factor from the present. you ought to start in the future."

"how's that?"

"it's like if i said old maids were responsible for more clover. you'd start investigating the old maids. you ought to start with the clover and work backwards."

"just what are you trying to say, mr. carmichael?"

"i'm talking about a posteriori reasoning. look, sir, a fella by the name of darwin was trying to explain the balance of nature. he wanted to show the chain of cause and effect. he said in so many words that the number of old maids in a town governed the growth of clover, but if you want to find out how, you've got to work it out a posteriori; from effect to cause. like this: only bumblebees can fertilize clover. the more bumblebees, the more clover. field mice attack bumblebee nests, so the more field mice, the less clover. cats attack mice. the more cats, the more clover. old maids keep cats. the more old maids ... the more clover. q. e. d."

"and now," groating laughed, "construe."

"seems to me you ought to start with the catastrophe and follow the chain of causation, link by link, back to the source. why not use the prognosticator backwards until you locate the moment when the snowball first started rolling?"

there was a very long silence while they thought it over. the controller looked slightly bewildered and he kept muttering: cats—clover—old maids—but i could see the c-s was really hit. he went to the window and stood looking out, as motionless as a statue. i remember staring past his square shoulder and watching the shadows of the helios flicking noiselessly across the façade of the judiciary building opposite us.

it was all so unreal—this frantic desperation over an event a thousand years in the future; but that's stability. it's strictly the long view. old cyrus brennerhaven of the morning globe had a sign over his desk that read: if you take care of the tomorrows, the todays will take care of themselves.

finally groating said: "mr. carmichael, i think we'd better go back to the prog building—"

sure i felt proud. we left the office and went down the hall toward the pneumatics and i kept thinking: "i've given an idea to the chief stabilizer. he's taken a suggestion from me!" a couple of secretaries had rushed down the hall ahead of us when they saw us come out, and when we got to the tubes, three capsules were waiting for us. what's more, the c-s and the controller stood around and waited for me while i contacted my city editor and gave him the official release. the editor was a little sore about my disappearance, but i had a perfect alibi. i was still looking for hogan. that, my friends, was emphatically that.

at the prog building we hustled through the main offices and back up the curved stairs. on the way the c-s said he didn't think we ought to tell yarr, the little old coot i'd hood-winked, the real truth. it would be just as well, he said, to let yarr go on thinking i was a confidential secretary.

so we came again to that fantastic clockwork room with its myriad whirling cams and the revolving crystal and the hypnotic bam-bam of the motors. yarr met us at the door and escorted us to the viewing desk with his peculiar absent-minded subservience. the room was darkened again, and once more we watched the cloud of blackness seep across the face of the universe. the sight chilled me more than ever, now that i knew what it meant.

groating turned to me and said: "well, mr. carmichael, any suggestions?"

i said: "the first thing we ought to find out is just what that spaceship has to do with the black cloud ... don't you think so?"

"why yes, i do." groating turned to yarr and said: "give us a close-up of the spaceship and switch in sound. give us the integration at normal speed."

yarr said: "it would take a week to run the whole thing off. any special moment you want, sir?"

i had a hunch. "give us the moment when the auxiliary ship arrives."

yarr turned back to his switch-board. we had a close-up of a great round port. the sound mechanism clicked on, running at high speed with a peculiar wheetledy-woodeldey-weedledy garble of shrill noises. suddenly the cruiser shot into view. yarr slowed everything down to normal speed.

the fat needle nosed into place, the ports clanged and hissed as the suction junction was made. abruptly, the scene shifted and we were inside the lock between the two ships. men in stained dungarees, stripped to the waist and sweating, were hauling heavy canvas-wrapped equipment into the mother ship. to one side two elderly guys were talking swiftly:

"you had difficulty?"

"more than ever. thank god this is the last shipment."

"how about credits?"

"exhausted."

"do you mean that?"

"i do."

"i can't understand it. we had over two millions left."

"we lost all that through indirect purchases and—"

"and what?"

"bribes, if you must know."

"bribes?"

"my dear sir, you can't order cyclotrons without making people suspicious. if you so much as mention an atom today, you accuse yourself."

"then we all stand accused here and now."

"i'm not denying that."

"what a terrible thing it is that the most precious part of our existence should be the most hated."

"you speak of—"

"the atom."

the speaker gazed before him meditatively, then sighed and turned into the shadowy depths of the spaceship.

i said: "all right, that's enough. cut into the moment just before the black-out occurs. take it inside the ship."

the integrators quickened and the sound track began its shrill babble again. quick scenes of the interior of the mother ship flickered across the crystal. a control chamber, roofed with a transparent dome passed repeatedly before us, with the darting figures of men snapping through it. at last the integrator fixed on that chamber and stopped. the scene was frozen into a still-photograph—a tableau of half a dozen half-naked men poised over the controls, heads tilted back to look through the dome.

yarr said: "it doesn't take long. watch closely."

i said: "shoot."

the scene came to life with a blurp.

"—ready on the tension screens?"

"ready, sir."

"power checked?"

"checked and ready, sir."

"stand by, all. time?"

"two minutes to go."

"good—" the graybeard in the center of the chamber paced with hands clasped behind him, very much like a captain on his bridge. clearly through the sound mechanism came the thuds of his steps and the background hum of waiting mechanism.

the graybeard said: "time?"

"one minute forty seconds."

"gentlemen: in these brief moments i should like to thank you all for your splendid assistance. i speak not so much of your technical work, which speaks for itself, but of your willingness to exile yourselves and even incriminate yourselves along with me—time?"

"one twenty-five."

"it is a sad thing that our work which is intended to grant the greatest boon imaginable to the universe should have been driven into secrecy. limitless power is so vast a concept that even i cannot speculate on the future it will bring to our worlds. in a few minutes, after we have succeeded, all of us will be universal heroes. now, before our work is done, i want all of you to know that to me you are already heroes—time?"

"one ten."

"and now, a warning. when we have set up our spacial partition membrane and begun the osmotic transfer of energy from hyperspace to our own there may be effects which i have been unable to predict. raw energy pervading our space may also pervade our nervous systems and engender various unforeseen conditions. do not be alarmed. keep well in mind the fact that the change cannot be anything but for the better—time?"

"fifty seconds."

"the advantages? up to now mathematics and the sciences have merely been substitutes for what man should do for himself. so fitzjohn preached in his first lecture, and so we are about to prove. the logical evolution of energy mechanics is not toward magnification and complex engineering development, but toward simplification—toward the concentration of all those powers within man himself—time?"

"twenty seconds."

"courage, my friends. this is the moment we have worked for these past ten years. secretly. criminally. so it has always been with those who have brought man his greatest gifts."

"ten seconds."

"stand by, all."

"ready all, sir."