"Not necessarily--there may well be different types, each struggling toward civilization. They certainly are on Venus, and they once were on Mars."

"Why haven't we seen anything like that before, in all these months?

Things have been so calm and peaceful that we thought we had the whole world to ourselves, as far as danger or men were concerned."

"We never saw them before because we never went where they lived--you were a long ways from your usual stamping-grounds, you know. That animal-vegetable flower is probably a high-alt.i.tude organism, living in the mountains and never coming as low as we are down here. As for the savages--whatever they are--they probably never come within five kilometers of the falls. Many primitive peoples think that waterfalls are inhabited by demons, and maybe these folks are afflicted the same way."

"We don't know much about our new world yet, do we?"

"We sure don't--and I'm not particularly keen on finding out much more about it until we get organized for trouble, either. Well, here we are--just like getting back home to see the 'Hope,' isn't it?"

"It _is_ home, and will be until we get one of our own on earth," and after Stevens had read his meters, learning with satisfaction that the full current was still flowing into the acc.u.mulators, he began to cut up the meat.

"Now that you've got the power-plant running at last, what next?" asked Nadia, piling the cuts in the freezer.

"Brandon's ultra-radio comes next, but it's got more angles to it than a cubist's picture of a set of prisms; so many that I don't know where to begin. There, that job's done--let's sit down and I'll talk at you awhile. Maybe between us we can figure out where to start. I've got everything to build it lined up except for the tube, but that's got me stopped cold. You see, fields of force are all right in most places, but I've got to have one tube, and it's got to have the hardest possible vacuum. That means a mercury-vapor super pump. Mercury is absolutely the only thing that will do the trick and the mercury is one thing that is conspicuous by it's absence in these parts. So are tungsten for filaments, tantalum for plates, and platinum for leads; and I haven't found anything that I can use as a getter, either--a metal, you know, to flash inside the tube to clean up the last traces of atmosphere in it."

"I didn't suppose that such a simple thing as a radio tube could hold you up, after the perfectly unbelievable things that you have done already--but I see now how it could. Of course, the tubes in our receiver over there are too small?"

"Yes, they are only receiver and communicator tubes, and I need a high-power transmitting tube--a fifty-kilowatter, at least. I'd give my left leg to the knee joint for one of those big water-cooled, sixty-kilowatt ten-nineteens right now--it would save us a lot of grief."

"Maybe you could break up those tubes and use the plates and so on?"

"I thought of that, but it won't work--there isn't half enough metal in the lot, and the filaments in particular are so tiny that I couldn't possibly work them over into a big one. Then, too, we haven't got many spare tubes, and if I smash the ones we're using, I put our communicators out of business for good, so that we can't yell for help if we have to drift home--and I still don't get any mercury."

"Do you mean to tell me there's no mercury on this whole planet?"

"Not exactly; but I do mean that I haven't been able to find any, and that it's probably darned scarce. And since all the other metals I want worst are also very dense and of high atomic weight, they're probably mighty scarce here, too. Why? Because we're on a satellite, and no matter what hypothesis you accept for the origin of satellites, you come to the same conclusion--that heavy metals are either absent or most awfully scarce and buried deep down toward the center. There are lots of heavy metals in Jupiter somewhere, but we probably couldn't find them.

Jupiter's atmosphere is one ma.s.s of fog, and we couldn't see, since we haven't got an infra-red transformer. I could build one, in time, but it would take quite a while--and we couldn't work on Jupiter, anyway, because of its gravity and probably because of its atmosphere. And even if we could work there, we don't want to spend the rest of our lives prospecting for mercury." Stevens fell silent, brow wrinkled in thought.

"You mean, dear, that we're..." Nadia broke off, the sentence unfinished.

"Gosh, no! There's lots of things not tried yet, and we can always set out to drift it. I was thinking only of building the tube. And I'm trying to think ... say, Nadia, what do you know about Cantrell's Comet?"

"Not a thing, except that I remember reading in the newspapers that it was peculiar for something or other. But what has Cantrell's Comet got to do with the high cost of living--or with radio tubes? Have you gone cuckoo all of a sudden?"

"You'll be surprised!" Stevens grinned at her puzzled expression.

"Cantrell's Comet is one of Jupiter's comet family and is peculiar in being the most ma.s.sive one known to science. It was hardly known until after they built those thousand-foot reflectors on the Moon, where the seeing is always perfect, but it has been studied a lot since then.

Its nucleus is small, but extremely heavy--it seems to have an average density of somewhere around sixteen. There's platinum and everything else that's heavy there, girl! They ought to be there in such quant.i.ty that even such a volunteer chemist as I am could find them!"

"Heavens, Steve!" A look of alarm flashed over Nadia's face, then disappeared as rapidly as it had come into being. "But of course, comets aren't really dangerous."

"Sure not. A comet's tail, which so many people are afraid of as being poison gas, is almost a perfect vacuum, even at its thickest, and we'd have to wear s.p.a.ce-suits anyway. And speaking of vacuum ... whoopee!

We don't need mercury any more than a goldfish needs a gas-mask. When we get Mr. Tube done, we'll take him out into s.p.a.ce, leaving his mouth open, and very shortly he'll be as empty as a flapper's skull. Then we'll seal him up, flash him out, come back here, and start spilling our troubles into Brandon's sh.e.l.l-like ear!"

"Wonderful, Steve! You do get an idea occasionally, don't you? But how do we get out there? Where is this Cantrell's Comet?"

"I don't know, exactly--there's one rub. Another is that I haven't even started the transmitter and receptor units. But we've got some field-generators here on board that I can use, so it won't be so bad.

And our comet is in this part of the solar system somewhere fairly close. Wish we had an Ephemeris, a couple of I-P solar charts, and a real telescope."

"You can't do much without an Ephemeris, I should think. It's a good thing you kept the chronometers going. You know the I-P time, day, and dates, anyway."

"I'll have to do without some things, that's all," and the man stared absently at the steel wall. "I remember something about its...o...b..t, since it is one thing that all I-P vessels have to steer clear of. Think I can figure it close enough so that we'll be able to find it in our little telescope, or even on our plate, since we'll be out of this atmosphere.

And it might not be a bad idea for us to get away, anyway. I'm afraid of those folks on that s.p.a.ce-ship, whoever they were, and they must live around here somewhere. Cantrell's Comet swings about fifty million kilometers outside Jupiter's...o...b..t at aphelion--close enough for us to reach, and yet probably too far for them to find us easily. By the time we get back here, they probably will have quit looking for us, if they look at all. Then too, I expect these savages to follow us up. What say, little ace--do we try it or do we stay here?"

"You know best, Steve. As I said before, I'm with you from now on, in whatever you think best to do. I know that you think it best to go out there. Therefore, so do I."

"Well," he said, finally, "I'd better get busy, then--there's a lot to do before we can start. The radio doesn't come next, after all--the transmitter and receptor units come ahead of it. They won't mean wasted labor, in any event, since we'll have to have them in case the radio fails. You'd better lay in a lot of supplies while I'm working on that stuff, but don't go out of sight, and yell like fury if you see anything. We'd both better wear full armor every time we go out-of-doors--unless I'm all out of control we aren't done with those savages yet. Even though they may be afraid of the demons of the falls, I think they'll have at least one more try at us."

While Nadia brought in meat and vegetables and stored them away, Stevens attacked the problem of constructing the pair of tight-beam, auto-dirigible transmitter and receptor units which would connect his great turbo-alternator to the acc.u.mulators of their craft, wherever it might be in s.p.a.ce. From the force-field generators of the "Forlorn Hope"

he selected the two most suitable for his purpose, tuned them to the exact frequency he required, and around them built a complex system of condensers and coils.

Day after day pa.s.sed. Their larder was full, the receptor was finished, and the beam transmitter was almost ready to attach to the turbo-alternator before the calm was broken.

"Steve!" Nadia shrieked. Glancing idly into the communicator plate, she had been perfunctorily surveying the surrounding territory. "They're coming! Thousands of them! They're all over the bench up there, and just simply pouring down the hills and up the valley!"

"Wish they'd waited a few hours longer--we'd have been gone. However, we're just about ready for them," he commented grimly, as he stared over her shoulder into the communicator plate. "We'll make a lot of those Indians wish that they had stayed at home with their papooses."

"Have you got all those rays and things fixed up?"

"Not as many as I'd like to have. You see, I don't know the composition of the I-P ray, since it is outlawed to everybody except the police.

Of course I could have found out from Brandon, but never paid any attention to it. I've got some nice ultra-violet, though, and a short-wave oscillatory that'll cook an elephant to a cinder in about eight seconds.

We'll keep them amused, no fooling! Glad we had time to cover our open sides, and it looks as though that meteorite armor we put over the projectors may be mighty useful, too."

On and on the savages came, ma.s.sed in formations showing some signs of rude discipline. This time there was neither shrieking nor yelling; the weird creatures advanced silently and methodically. Here and there were ma.s.sed groups of hundreds, dragging behind them engines which Stevens studied with interest.

"Hm ... m ... m. Catapults," he mused. "You were right, girl of my dreams--armor and bows and arrows wouldn't help us much right now.

They're going to throw rocks at us that'll have both ma.s.s and momentum.

With those things they can cave in our side-armor, and might even dent our roof. When one of those projectiles. .h.i.ts, we want to know where it ain't, that's all."

Stevens cast off the heavily-insulated plug connecting the power plant leads to his now almost fully charged acc.u.mulators, strapped himself and Nadia into place at the controls, and waited, staring into the plate.

Catapult after catapult was dragged to the lip of the little canyon, until six of them bore upon the target. The huge stranded springs of hair, fiber, and sinew were wound up to the limit, and enormous ma.s.ses of rock were toilsomely rolled upon the platforms. Each "gunner" seized his trip, and as the leader shrieked his signal the six ponderous ma.s.ses of metalliferous rock heaved into the air as one. But they did not strike their objective, for as the signal was given, Stevens shot power into his projectors. The "Forlorn Hope" leaped out of the canyon and high into the air over the open meadow, just as the six great projectiles crashed into the ground upon the spot which, an instant before, she had occupied.

Rudimentary discipline forgotten, the horde rushed down into the canyon and the valley, in full clamor of their barbaric urgings. Horns and arms tossed fiercely, savage noises rent the air, and arrows splintered harmlessly upon steel plate an the mystified and maddened warriors upon the plain below gave vent to their outraged feelings.

"Look, Nadia! A whole gang of them are smelling around that power plug.

Pretty soon somebody's going to touch a hot spot, and when he does, we'll cut loose on the rest of them."

The huge insulating plug, housing the ends of the three great cables leading to the converters of the turbo-alternator, lay innocently upon the ground, its three yawning holes invitingly open to savage arms. The chief, who had been inspecting the power-plant, walked along the triplex lead and joined his followers at its terminus. Pointing with his horns, he jabbered orders and three red monsters, one at each cable, bent to lift the plug, while the leader himself thrust an arm into each of the three contact holes. There was a flash of searing flame and the reeking smoke of burning flesh--those three arms had taken the terrific no-load voltage of the three-phase converter system, and the full power of the alternator had been shorted directly to ground through the comparatively small resistance of his body.

Stevens had poised the "Forlorn Hope" edgewise in mid-air, so that the gleaming, heavily armored parabolic reflectors of his projectors, mounted upon the leading edge of the fortress, covered the scene below.

As the charred corpse of the savage chieftain dropped to the ground, it seemed to the six-limbed creatures that the demons of the falls had indeed been annoyed beyond endurance by their intrusion; for, as if in response to the flash of fire from the power plug, that structure so peculiarly and so stolidly hanging in the air came plunging down toward them. From it there reached down twin fans of death and destruction: one flaming and almost invisibly incandescent violet which tore at the eyes and excruciatingly disintegrated brain and nervous tissues; the other dully glowing an equally invisible red, at the touch of which body temperature soared to lethal heights and foliage burst cracklingly into spontaneous flame.

In their ma.s.sed hundreds, the savages dropped where they stood, life rived away by the torturing ultra-violet, burned away by the blast of pure heat, or consumed by the conflagrations that raged instantly wherever that wide-sweeping fan encountered combustible material.

In the face of power supernatural they lost all thought of attack or of conquest, and sought only and madly to escape. Weapons were thrown away, the catapults were abandoned, and, every man for himself, the mob fled in wildest disorder, each striving to put as much distance as possible between himself and that place of dread mystery, the waterfall.