"For any given frequency, _f_, and phase angle, _theta_, you integrate, between limits zero and _pi_ divided by two, sine theta d...."

"Hold it--I'm sinking!" Nadia exclaimed. "I don't integrate at all unless it is absolutely necessary. As long as you stick to general science, I'm right on your heels, but please lay off of integrations and all that--most especially stay away from those terrible electrical integrations. I always did think that they were the most poisonous kind known. I want only a general idea--that's all that I can understand, anyway."

"Sure, I forgot--guess I was getting in deeper than is necessary, especially since this whole thing of beam transmission is pretty crude yet and is bound to change a lot before long. There is so much loss that when we get more than a few hundred million kilometers away from a power-plant we lose reception entirely. But to get going again, the receptors receive the beam and from them the power is sent to the acc.u.mulators, where it is stored. These acc.u.mulators are an outgrowth of the storage battery. The theory of the acc.u.mulator is...."

"Lay off the theory, please!" the listener interrupted. "I understand perfectly without it. Energy is stored in the acc.u.mulators--you put it in and take it out. That's all that is necessary."

"I'd like to give you some of the theory--but, after all, it wouldn't add much to your understanding of the working of things, and it might mix you up, as some of it is pretty deep stuff. Then, too, it would take a lot of time, and the rest of your friends would squawk if I kept you here indefinitely. From the acc.u.mulators, then, the power is fed to the converters, each of which is backed by a projector.

The converters simply change the aspect of the rays, from the energy aspect to the material aspect. As soon as this is done, the highly-charged particles--or whatever they are--thus formed are repelled by the terrific stationary force maintained in the projector backing the converter. Each particle departs with a velocity supposed to be that of light, and the recoil upon the projector drives the vessel, or car, or whatever it is attached to. Still with me?"

"Struggling a little, but my nose is still above the surface. These particles, being so infinitesimally small that they cannot even be detected, go right through any substance without any effect--they are not even harmful."

"Exactly. Now we are in position to go ahead with the lights, detectors, and so on. The energy aspect of the rays you can best understand as simply a vibration in the ether--an extremely high frequency one.

While not rigidly scientific, that is close enough for you and me.

n.o.body knows what the stuff really is, and it cannot be explained or demonstrated by any model or concept in three-dimensional s.p.a.ce. Its physical-mathematical interpretation, the only way in which it can be grasped at all, requires sixteen coordinates in four dimensions, and I don't suppose you'd care to go into that."

"I'll say I wouldn't!" she exclaimed, feelingly.

"Well, anyway, by the use of suitable fields of force it can be used as a carrier wave. Most of this stuff of the fields of force--how to carry the modulation up and down through all the frequency changes necessary--was figured out by the Martians ages ago. Used as a pure carrier wave, with a sender and a receiver at each end, it isn't so bad--that's why our communicator and radio systems work as well as they do. They are pretty good, really, but the ultra-light vision system is something else again. Sending the heterodyned wave through steel is easy, but breaking it up, so as to view an object and return the impulses, was an awful job and one that isn't half done yet. We see things, after a fashion and at a distance of a few kilometers, by sending an almost parallel wave from a twin-projector to disintegrate and double back the viewing wave. That's the way the lookout plates and lenses work, all over the ship--from the master-screens in the control room to the plates of the staterooms and lifeboats and the viewing-areas of the promenades. But the whole system is a rotten makeshift, and...."

"Just a minute!" exclaimed the girl. "I and everybody else have been thinking that everything is absolutely perfect; and yet every single thing you have talked about, you have ended up by describing as 'unknown,' 'rudimentary,' 'temporary,' or a 'makeshift.' You speak as though the entire system were a poor thing that will have to do until something better has been found, and that n.o.body knows anything about anything! How do you get that way?"

"By working with Brandon and Westfall. Those birds have got real brains and they're on the track of something that will, in all probability, be as far ahead of Roeser's Rays as our present system is ahead of the science of the seventeenth century."

"Really?" she looked at him in astonishment. "Tell me about it."

"Can't be done," he refused. "I don't know much about it--even they didn't know any too much about some of it when I had to come in. And what little I do know I can't tell, because it isn't mine."

"But you're working with them, aren't you?"

"Yes, in the sense that a small boy helps his father build a house.

They're the brains--I simply do some figuring that they don't want to waste time doing."

Nadia, having no belief whatever in his modest disclaimer, but in secret greatly pleased by his att.i.tude, replied:

"Of course you couldn't say anything about an unfinished project--I shouldn't have asked. Where do we go from here?"

"Down the lining of the hull, outside the pa.s.sengers' quarters to the upper dirigible projectors," and he led the way down a series of steep steel stairways, through bulkheads and part.i.tions of steel. "One thing I forgot to tell you about--the detectors. They're worked on the same principle as the lights, and are just about as efficient. Instead, of light, though, they send out cones of electro-magnetic waves, which set up induced currents in any conductor encountered beyond our own sh.e.l.l.

Since all dangerous meteorites have been shown to contain conducting material, that is enough to locate them, for radio finders automatically determine the direction, distance, and magnitude of the disturbance, and swing a light on it. That was what happened when that light swung toward us, back there in the prow."

"Are there any of those life-boats, that I've heard discussed so much lately, near here?" asked the girl.

"Lots of 'em--here's one right here," and at the next landing he opened a vacuum-insulated steel door, snapped on a light, and waved his hand.

"You can't see much of it from here, but it's a complete s.p.a.ce-ship in itself, capable of maintaining a dozen or fifteen persons during a two-weeks' cruise in s.p.a.ce."

"Why isn't it a good idea to retain them? Accidents are still possible, are they not?"

"Of course, and there is no question of doing away with them entirely.

Modern ships, however, have only enough of them to take care of the largest number of persons ever to be carried by the vessel."

"Has the _Arcturus_ more than she needs?"

"I'll say she has, and more of everything else, except room for pay-load."

"I've heard them talking about junking her. I think it's a shame."

"So do I, in a way--you see, I helped design her and her sister-ship, the _Sirius_, which Brandon and Westfall are using as a floating laboratory. But times change, and the inefficient must go. She's a good old tub, but she was built when everybody was afraid of s.p.a.ce, and we had to put every safety factor into her that we could think of. As a result, she is four times as heavy as she should be, and that takes a lot of extra power. Her skin is too thick. She has too many batteries of acc.u.mulators, too many life-boats, too many bulkheads and air-breaks, too many and too much of everything. She is so built that if she should break up out in s.p.a.ce, n.o.body would die if they lived through the shock--there are so many bulkheads, air-breaks, and life-boats that no matter how many pieces she broke up into, the survivors would find themselves in something able to navigate. That excessive construction is no longer necessary. Modern ships carry ten times the pay-load on one-quarter of the power that this old battle-wagon uses. Even though she's only four years old, she's a relic of the days when we used to slam through on the ecliptic route, right through all the meteoric stuff that is always there--trusting to heavy armor to ward off anything too small for the observers and detectors to locate. Now, with the observatories and check-stations out in s.p.a.ce, fairly light armor is sufficient, as we route ourselves well away from the ecliptic and so miss all the heavy stuff. So, badly as I hate to see her go there, the old tub is bound for the junk-yard."

A few more flights of stairs brought them to the upper band of dirigible projectors, which encircled the hull outside the pa.s.sengers' quarters, some sixty feet below the prow. They were heavy, search-light-like affairs mounted upon ma.s.sive universal bearings, free to turn in any direction, and each having its converter nestling inside its prodigious field of force. Stevens explained that these projectors were used in turning the vessel and in dodging meteorites when necessary, and they went on through another almost invisible door into a hall and took an elevator down to the main corridor.

"Well, you've seen it, Miss Newton," Stevens said regretfully, as he led her toward the captain's office. "The lower half is full of heavy stuff--acc.u.mulators, machinery, driving projectors, and such junk, so that the center of gravity is below the center of action of the driving projectors. That makes stable flight possible. It's all more or less like what we've just seen, and I don't suppose you want to miss the dance--anyway, a lot of people want to dance with you."

"Wouldn't you just as soon show me through the lower half as dance?"

"Rather, lots!"

"So would I. I can dance any time, and I want to see everything.

Let's go!"

Down they went, past battery after battery of acc.u.mulators; climbing over and around the ever-increasing number of huge steel girders and bracers; through mazes of heavily insulated wiring and conduits; past ma.s.s after ma.s.s of automatic machinery which Stevens explained to his eager listener. They inspected one of the great driving projectors, which, built rigidly parallel to the axis of the ship and held immovably in place by enormous trusses of steel, revealed neither to the eye nor to the ear any sign of the terrific force it was exerting. Still lower they went, until the girl had been shown everything, even down to the bottom ultra-lights and stern braces.

"Tired?" Stevens asked, as the inspection was completed.

"Not very. It's been quite a climb, but I've had a wonderful time."

"So have I," he declared, positively. "I know what--we'll crawl up into one of these stern lifeboats and make us a cup of coffee before we climb back. With me?"

"'Way ahead of you!" Nadia accepted the invitation enthusiastically, and they made their way to the nearest of the miniature s.p.a.ce-cruisers.

Here, although no emergency had been encountered in all the four years of the vessel's life, they found everything in readiness, and the two soon had prepared and eaten a hearty luncheon.

"Well, I can't think of any more excuses for monopolizing you, Miss Newton, so I suppose I'll have to take you back. Believe me, I've enjoyed this more than you can realize--I've...."

He broke off and listened, every nerve taut. "What was that?" he exclaimed.

"What was what? I didn't hear anything?"

"Something screwy somewhere! I felt a vibration, and anything that'd make this mountain of steel even quiver must have given us one gosh-awful nudge. There's another!"

The girl, painfully tense, felt only a barely perceptible tremor, but the computer, knowing far better than she the inconceivable strength and ma.s.s of that enormous structure of solidly braced hardened steel, sprang into action. Leaping to the small dirigible look-out plate, he turned on the power and swung it upward.

"Great suffering snakes!" he e.j.a.c.u.l.a.t.ed, then stood mute, for the plate revealed a terrible sight. The entire nose of the gigantic craft had been sheared off in two immense slices as though clipped off by a gigantic sword, and even as they stared, fascinated, at the sight, the severed slices were drifting slowly away. Swinging the view along the plane of cleavage, Stevens made out a relatively tiny ball of metal, only fifty feet or so in diameter, at a distance of perhaps a mile.

From this ball there shot a blinding plane of light, and the _Arcturus_ fell apart at the midsection, the lower half separating clean from the upper portion, which held the pa.s.sengers. Leaving the upper half intact, the attacker began slicing the lower, driving half into thin, disk-shaped sections. As that incandescent plane of destruction made its first flashing cut through the body of the _Arcturus_, accompanied by an additional pyrotechnic display of severed and short-circuited high-tension leads, Stevens and Nadia suddenly found themselves floating weightless in the air of the room. Still gripping the controls of the look-out plate, Stevens caught the white-faced girl with one hand, drew her down beside him, and held her motionless while his keen mind flashed over all the possibilities of the situation and planned his course of action.