Star Light

The commander gave a gesture of impatience.

“That’s silly. I didn’t try to pick up a complete scientific education from the aliens, since it was obviously going to take too long; but one thing I did gather was that the underlying rules are essentially simple. Once the humans started concentrating on basic rules, they went from sailing ships to space ships in a couple of hundred years. Balloons, powered or not, are simple devices; I understand them perfectly myself. Putting an engine aboard doesn’t change that; the same rules have to be working.”

The technician eyed his commander thoughtfully, and thought briefly of electron tubes and television circuits before replying.

“I suppose,” he said thoughtfully, “that a piece of a tent being blown away by the gale, and a ship being tacked into the wind, are also examples of the same rules at work.”

Barle

He was still trying to shrug off the technician’s remark, but only succeeding in growing more and more doubtful of his situation, some twenty hours later when a messenger called him to the communication room. As soon as he entered, Guzmeen spoke briefly into a microphone; a minute later, a human face which neither of them recognized appeared on the screen.

“I am Ib Hoffman, Easy’s husband and Benj’s father,” the stranger began without preamble. “I’m speaking to you two, Barle

“First, Barle

“You seem to feel that many or most human beings would try to thwart you in this, and I have to admit that some would, though I think we have the most effective one under control now. You can’t be sure that I’m being sincere now, for that matter; you’re tricky enough yourself to expect it of other people. Too bad. How much you believe of what I say is beyond my control; I still have to say it.

“I don’t know how much of the basic situation you set up, but I can guess. I’m nearly sure the Esket disappearance was not genuine. I’m uncertain of the real status of the Kwembly. You probably know more of Dhrawn than you’ve reported. I won’t say I don’t care, because I do; we’re here to learn as much as possible about Dhrawn, and what you don’t tell us is a loss to the project. I can’t threaten you with penalties for breach of contract, since I’m not completely certain you’ve broken it and am in no position to carry out threats. And in any case have less than no desire to even make threats. I do want to persuade you, though, that it will be better for both of us if we do without secrets. We’re at a point where anything less than complete frankness is likely to cost us a lot and cost you everything. To make that point, I’m going to tell you a story.

“You know that human beings breathe oxygen much as you do hydrogen, though being so much larger we need a more complicated pumping system to get it through our bodies. Because of the details of that system, we suffocate if deprived of gaseous, free oxygen within a certain rather narrow range of pressures.

“About three quarters of Earth is covered by water. We ca

“Six of our years ago, when Benj was eleven years old, he made such a device, designing it himself with my assistance. He made the pressure tank and regulator, using ordinary fabricating equipment such as may be found in most home workshops, just as he had made more complex things such as small gas turbines. He tested the parts with my help; they worked perfectly. He calculated how long the air in the tank would last him, and then tested the whole assembly under water. I went along as a matter of common-sense safety, using a commercial diving device.

“I am sure you know the principles of hydrostatics and the gas laws; at least, Easy has given me words for them in your language. You can see that at a certain depth, a lungful of air would have only half its volume at the surface. Benj knew this too, but reasoned that it would still be a lungful as far as oxygen content was concerned, so that a one-hour tank would be a one-hour tank regardless of depth, as long as tank pressure was above that of the water.

“To make a long story short, it didn’t. He ran out of air in less than a third of the calculated time, and I had to make an emergency rescue. Because of the quick pressure change and some human peculiarities which you don’t seem to share, he was very nearly killed. The trouble turned out to be that the human breathing rate is controlled, not by the oxygen in our blood, but by the carbon dioxide, one of the waste products. To maintain a normal equilibrium of that, we have to run normal volumes of air through our lungs, regardless of oxygen content or total pressure; hence, an hour’s air supply at normal pressure is only half an hour thirty-three feet under water, a third of an hour at sixty-six, and so on.

“I don’t want to insult anyone’s intelligence by asking if he understands my point, but I’d like some comment from both of you on that story.”

The answers were interesting, both in nature and arrival time. Barle

“It is obvious that incomplete knowledge can lead to mistakes,” said Barle

Ib smiled sourly at the revelation of yet another human characteristic.

“That’s not just what I had in mind, Commander, though there are valid aspects to what you have just said. I’d like to wait for Dondragmer’s answer before I say any more, though.”

It was another full minute, a slightly strained one, before the voice of the Kwembly’s captain arrived.

“Your account is plain enough and you would probably have been briefer had you not meant to imply more. I suspect that your key point is not so much that your son got into trouble through ignorance, but that he did so even under your experienced adult supervision. I would take the implication to be that even though you aliens do not claim omniscience or omnipotence, we are in a certain amount of danger here no matter how closely you supervise and assist us, and we are adding u