“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 cannot breathe under water without artificial equipment, but the use of such equipment is a common human sport. It consists essentially of a tank of compressed air and a valve system which releases the air to our breathing system as needed; simple and obvious.
“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. Barlennan’s popped from the speaker with very little more than light-travel delay; Dondragmer’s came much, much later, and did not overlap with his commander’s.
“It is obvious that incomplete knowledge can lead to mistakes,” said Barlennan, “but I don’t see why that is especially applicable to the present case. We know that our knowledge can’t be complete, and that our work here is dangerous for that reason. We have always known it. Why emphasize the point now? I’d much rather hear your report on the cruiser you say is in trouble. You make me suspect that you are leading up gently to the information that I have lost another cruiser because of something its designing engineers didn’t know. Don’t worry, I won’t blame you for that. None of us could foresee everything.”
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 unnecessarily to our danger any time we act on our own, like the student chemist who experiments on his own.” Dondragmer had spent much more time at the College than had his commander.
“Right. Just what I meant,” said lb. “I cant…
“Just a moment,” interrupted Easy. “Hadn’t you better relay Don’s remark to Barlennan first?”
“Right.” Her husband gave a one-sentence summary of the captain’s speech, and went on, “I can’t force any policy on you, and would prefer not to even if I could. I don’t expect you to make a complete revelation of everything that’s gone on on Dhrawn since you first built the Settlement. In fact, I’d advise strongly against it; I have enough complications up here with the administration as it is. However, if Easy just happened to get an occasional talk with her old friends Destigmet and Kabremm, just as an example, I would have a better idea of what has gone on and be in a better position to keep things running smoothly at this end. I don’t expect a spot decision on any matter of major policy change, Commander, but please think it over.”
Barlennan, being a sea captain by training and trade, was accustomed to the need for quick decisions. Furthermore, circumstances had already compelled thoughts on similar lines to circulate in his tiny head. Finally, his only really basic policy was to ensure his own survival and that of his crew. He answered Ib promptly.
“Easy may get her talk with Destigmet, but not right away; the Esket is a long distance from here. I will also have to wait to tell you all that I’d like to, because I must first hear from you the details of the trouble you mentioned when you first called. You said that another of my cruisers was in trouble.
“Please tell me just what has happened, so I can plan what help to request from you.
Ib and Easy Hoffman looked at each other and grinned in mingled relief and triumph.
But it was Benj who made the key remark. This was later on, in the aerology lab, when they were recounting to him and McDevitt all that had been said. The boy looked up at the huge globe of Dhrawn, and the tiny area where the lights indicated partial knowledge.
“I suppose you think he’s a lot safer now, down there.”
It was a sobering thought.