cameron leaned back and looked speculatively at the gravital engineer, vogel. the man could give him considerable assistance, if he would. there was no reason why he shouldn't; but any man who had voluntarily remained on handicap haven as long as vogel had was a doubtful quantity.

"usually we maintain about half earth-normal gravity," cameron said. "isn't that correct?"

engineer vogel nodded.

"it isn't important why those limits were set," cameron continued. "perhaps it's easier on the weakened bodies of the accidentals. there may be economic factors."

"no reason for those limits except the gravital units themselves," vogel said. "theoretically it should be easy to get any gravity you want. practically, though, we get between a quarter and almost full earth gravity. now take the fluctuations. the gravital computer is set at fifty per cent. sometimes we get fifty per cent and sometimes seventy-five. whatever it is, it just is and we have to be satisfied."

the big engineer shrugged. "i hear the units were designed especially for this asteroid," he went on. "some fancy medical reason. easier on the accidentals to have less gravity change, you say. me, i dunno. i'd guess the designers couldn't help it and the reason was dug up later."

cameron concealed his irritation. he wanted information, not a heart-to-heart confession. "all practical sciences try to justify whatever they can't escape but would like to. medicine, i'm sure, is no exception." he paused thoughtfully. "now, there are three separate gravital units on the asteroid. one runs for forty-five minutes while the other two are idle. then it cuts off and another takes over. this is supposed to be synchronized. i don't have to tell you that it isn't. you felt your weight increase suddenly at the same time i did. what is wrong?"

"nothing wrong," said the engineer. "that's what you get with gravital."

"you mean they're supposed to run that way? overlapping so that for five minutes we have earth or earth-and-a-half gravity and then none?"

"it's not supposed to be that way," said vogel. "but nobody ever built a setup like this that worked any better." he added defensively: "of course, if you want, you can check with the company that makes these units."

"i'm not trying to challenge your knowledge, and i'm not anxious to make myself look silly. i have a sound reason for asking these questions. there is a possibility of sabotage."

the engineer's grin was wider than the remark seemed to require.

"all right," said cameron tiredly. "suppose you tell me why sabotage is so unlikely."

"well," explained the gravital engineer, "it would have to be someone living here, and he wouldn't like it if he suddenly got double or triple gravity or maybe none at all. but there's another reason. now take a gravital unit. any gravital unit. most people think of it as just that—a unit. it isn't really that at all. it has three parts.

"one part is a power source that can be anything as long as it's big enough. our power source is a nuclear pile, buried deep in the asteroid. you'd have to take handicap haven apart to get to it. part two is the gravital coil, which actually produces the gravity and is simple and just about indestructible. part three is the gravital control. it calculates the relationship between the amount of power flowing through the gravital coil and the strength of the created gravity field in any one microsecond. it uses the computed relationship to alter the power flowing through in the next microsecond to get the same gravity. no change of power, no gravity. i guess you could call the control unit a computer, as good a one as is made for any purpose."

the engineer rubbed his chin. "fatigue," he continued. "the gravital control is an intricate computer that's subject to fatigue. that's why it has to rest an hour and a half to do forty-five minutes of work. naturally they don't want anyone tinkering with it. it's non-repairable. crack the case open and it won't work. but first you have to open it. mind you, that can be done. but i wouldn't want to try it without a high-powered lab setup."

if it didn't seem completely foolproof, neither did it seem a likely source of trouble. "then we can forget about the gravital units," said cameron, arising. "but what about hand weapons? are there any available?"

"you mean toasters?"

"anything that's lethal."

"nothing. no knives even. maybe a stray bar or so of metal." vogel scratched his head. "there is something dangerous, though. dangerous if you know how to take hold of it."

instantly cameron was alert. "what's that?"

"why, the asteroid itself. you can't physically touch any part of the gravital unit. but if you could somehow sneak an impulse into the computer and change the direction of the field...." vogel was very grave. "you could pick up handicap haven and throw it anywhere you wanted. at the earth, say. thirty miles in diameter is a big hunk of rock."

it was this kind of information cameron was looking for, though the engineer seemed to regard the occasion as merely a social call. "is there any possibility of that occurring?" he asked quietly.

the engineer grinned. "never happened, but they're ready for things like that with any gravital system. they got monitor stations all over—the moons of jupiter, mars, earth, venus.

"any time the gravital computer gets dizzy, the monitor overrides it. if that fails, they send a jammer impulse and freeze it up tight. it won't work until they let loose."

cameron sighed. he was getting very little help or information from vogel. "all right," he said. "you've told me what i wanted to know."

he watched the engineer depart for the gravity-generating chamber far below the surface of the asteroid.