“I gather that Grandsuur Ylma has been teaching you about such things,” I grunted. Drain-cleaning made it easy to hide my chagrin. I hadn’t learned about orbits until my second year. This was Barb’s second month.

“A lot of xs and ys and zs!” he exclaimed, which forced a laugh out of me.

“Yes,” I said, “quite a few.”

“You want to know what’s stupid?”

“Sure, Barb. Lay it on me,” I said, hauling a fistful of vegetable trimmings up out of the drain against the back-pressure of twenty gallons of dammed-up dishwater. The drain gargled and began to empty.

“Any sline could stand out on the meadow at night and see some satellites in polar orbits, and other satellites in orbits around the equator, and know that those were two different kinds of orbits!” he exclaimed. “But if you work out the xs and ys and zs of it, guess what?”

“What?”

“They just look like a lot of xs and ys and zs, and it is not as obvious that some are polar and some are equatorial as it would be to any old dumb sline looking up into the sky!”

“Worse than that,” I pointed out, “staring at the xs and ys and zs doesn’t even tell you that they are orbits.”

“What do you mean?”

“An orbit is a stationary, stable thing,” I said. “The satellite’s moving all the time, of course, but always in the same way. But that kind of stability is in no way shown by the xs and ys and zs.”

“Yeah! It’s like knowing all of the theorics only makes us stupider!” he laughed excitedly, and cast a theatrical glance over his shoulder, as if we were up to something incredibly mischievous.

“Ylma is having you work it out in the most gruesome way possible,” I said, “using Saunt Lesper’s Coordinates, so that when she teaches you how it’s really done, it’ll seem that much easier.”

Barb was dumbfounded. I went on, “Like hitting yourself in the head with a hammer—it feels so good when you stop.” This was the oldest joke in the world, but Barb hadn’t heard it before, and he became so amused that he got physically excited and had to run back and forth across the kitchen several times to flame off energy. A few weeks ago I would have been alarmed by this and would have tried to calm him down, but now I was used to it, and knew that if I approached him physically things would get much worse.

“What’s the right way to do it?”

“Orbital elements,” I said. “Six numbers that tell you everything that can be known about how a satellite is moving.”

“But I already have those six numbers.”

“What are they?” I asked, testing him.

“The satellite’s position on Saunt Lesper’s x, y, and z axes. That’s three numbers. And its velocity along each one of those axes. That’s three more. Six numbers.”

“But as you pointed out you can look at those six numbers and still not be able to visualize the orbit, or even know that it is an orbit. What I am telling you is that with some more theorics you can turn them into a different list of six numbers, the orbital elements, that are infinitely easier to work with, in that you can glance at them and know right away whether the orbit goes over the poles or around the equator.”

“Why didn’t Grandsuur Ylma tell me that to begin with?”

I couldn’t tell him, because you learn too damned fast. But if I tried to be overly diplomatic, Barb would see through it and plane me.

Then I had an upsight: it was my responsibility, just as much as it was Ylma’s, to teach fids the right stuff at the right time.

“You are now ready to stop working in Saunt Lesper’s Coordinates,” I announced, “and begin working in other kinds of spaces, the way real, grown-up theors do.”

“Is this like parallel dimensions?” said Barb, who apparently had been watching the same kinds of speelies as I had before coming here.

“No. These spaces I’m talking about aren’t like physical spaces that you can measure with a ruler and move around in. They are abstract theorical spaces that follow different rules, called action principles. The space that cosmographers like to use has six dimensions: one for each of the orbital elements. But that’s a special-purpose tool, only used in that discipline. A more general one was developed early in the Praxic Age by Saunt Hemn…” And I went on to give Barb a calca* about Hemn spaces, or configuration spaces, which Hemn had invented when he, like Barb, had become sick of xs and ys and zs.

I caught up with Fraa Orolo late in the afternoon as he was coming out of a chalk hall, and we stood among page-stuffed pigeonholes and chatted. I knew better than to ask him what he had been getting at earlier with his weird discussion of daytime cosmography. Once he had made up his mind to teach us in that mode, there was no way to get him to say the answer straight out. Anyway, I was more worried about the things he had been referring to earlier. “Listen, you’re not thinking of leaving, are you?”

He got a slightly amused look but said nothing.

“I always worried you were going to go into the labyrinth and become a Hundreder. That would be bad enough. But the way you were talking I got the idea you were going to go become a Feral like Estemard.”

This was Orolo’s idea of an answer: “What does it mean that you worry so much?”

I sighed.

“Describe worrying,” he went on.

“What!?”

“Pretend I’m someone who has never worried. I’m mystified. I don’t get it. Tell me how to worry.”

“Well…I guess the first step is to envision a sequence of events as they might play out in the future.”

“But I do that all the time. And yet I don’t worry.”

“It is a sequence of events with a bad end.”

“So, you’re worried that a pink dragon will fly over the concent and fart nerve gas on us?”

“No,” I said with a nervous chuckle.

“I don’t get it,” Orolo claimed, deadpan. “That is a sequence of events with a bad end.”

“But it’s nonsensical. There are no nerve-gas-farting pink dragons.”

“Fine,” he said, “a blue one, then.”

Jesry had wandered by and noticed that Orolo and I were in dialog, so he approached, but not too close, and took up a spectator’s position: hands folded in his bolt, chin down, not making eye contact.

“It has nothing to do with the dragon’s color,” I protested. “Nerve-gas-farting dragons don’t exist.”

“How do you know?”

“One has never been seen.”

“But I have never been seen to leave the concent—yet you worry about that.”

“All right. Correction: the whole idea of such a dragon is incoherent. There are no evolutionary precedents. Probably no metabolic pathways anywhere in nature that could generate nerve gas. Animals that large can’t fly because of basic scaling laws. And so on.”

“Hmm, all sorts of reasons from biology, chemistry, theorics…I suppose then that the slines, who know nothing of such matters, must worry about pink nerve-gas-farting dragons all the time?”