Chimal suddenly realized what this meant “Then you have nobody who knows anything about repairing this equipment? And it is the air machinery you are talking about, that supplies the breathing air for us all?”

“Yes,” the Master Observer said and led the way through thick, double-locked doors to a vast and echoing chamber.

Tall tanks lined the walls with shining apparatus at their bases. Heavy ducts dived down and there was an all-pervading hum and the whine of motors.

“This supplies the air for everyone?” Chimal asked.

“No, nothing like that. You will read about it there, but most of the air has something to do with green plants. There are great chambers of them in constant growth. This apparatus does other important things with the air, just what I am not sure.”

“I can’t promise that I’ll be able to help, but I’ll do my best At the same time I suggest you get whoever else might be able to work with this.”

“There is no one, of course. No man would think of doing other than his assigned work. I alone am responsible and I have looked at this book before. Many of the things are beyond me. I am an old man,, too old to learn a new discipline. A young man is now being taught the air tender’s craft, but it will be years before he is able to work in here. That may be too late.”

With a new weight of responsibility Chimal opened the book. The first part was an outline of air purification theory which he skimmed over quickly. He would read that in detail after he had a more general knowledge of the function of the machinery. Under apparatus there were 12 different sections, each headed with a large red number. These numbers were repeated on large signs down the wall and he assumed, with some justification, that they related to the numbers in the book. When he glanced up at them he noticed that a red light under 5 was blinking on and off. He walked over to it and saw the word emergency printed under the bulb: he opened the book to section 5.

“Purification Tower, Trace Pollutants. Many things such as machinery, paint and the breath of living people give off gaseous and particulate matter. There are not many of these pollutants, but they do collect over the years and can become concentrated. This machine removes from our air those certain fractions that may be dangerous after many, many years. Air is forced through a chemical that absorbs them…”

Chimal read on, interested now, until he had finished section 5. This tower seemed to be designed to function for centuries without attention; nevertheless provision had still been made to have it watched and monitored. There was a bank of instruments at its base and he went to look at them. Another light was flashing over a large dial, blinking letters that spelled out REPLACE CHEMICAL. Yet on the dial itself the reading was right at the top of the activity scale, just where the book said it should be for correct operation.

“But who am I to argue with this machine,” Chimal told the Master Observer, who had been following him in silence. “The recharging seems simple enough. There is an automatic cycle that the machine does when this button is depressed. If it doesn’t work the valves can be worked by hand. Let’s see what happens.” He pushed the button.

Operation lights flashed on, flickering in response to the cycle, and hidden switches closed. A muffled, sighing sound issued from the column before them and, at the same time the needle on the activity scale moved into the red danger zone, dropping toward the bottom. The Master Observer squinted at it, spelling out the letters with his lips, then looked up, horrified.

“Can this be right? It gets worse not better. Something terrible is happening.”

“I don’t think so,” Chimal said, frowning in concentration over the breviary. “It says the chemical needs replacing. So first I imagine the old chemical is pumped out, and this removal is what gives that false reading on the scale. Certainly the absence of a chemical will give the same reading as a bad chemical.”

“Your argument is abstract, hard to follow. I am glad you are here with us, First Arriver, and I can see the workings of the Great Designer in this. We could do nothing about this without you.”

“Let’s see how this comes out, first. So far I’ve just followed the book and there has been no real problem. There, the new chemical must be coming in, the needle’s going back up again to fully charged. That seems to be all there is to it.”

The Master Observer pointed, horrified, at the blinking warning light. “Yet — that goes on. There is something terrible here. There is something wrong with our air!”

“There is nothing wrong with our air. But there is something wrong with this machine. It has been recharged, the new chemical is working perfectly — yet the alarm goes on. The only thing I can think of is that there is something wrong with the alarm.” He slipped through the sections of the book until he found the one he wanted, then read through it quickly. “This may be it. Is there a storeroom here? I want something called 167-R.”

“It is this way.”

The storeroom contained rows of shelves, all numbered in order, and Chimal had no trouble locating part 167-R which was a sturdy cannister with a handle on the end and a warning message printed in red. CONTAINS PRESSURIZED GAS — POINT AWAY FROM FACE WHEN OPENING. He did as it advised and turned the handle. There was a loud hissing, and when it had died away the end came free in his hand. He reached in and drew out a glittering metal box, shaped like a large book. It had a handle where the spine would be and a number of copper-colored studs on the opposite edge. He had not the slightest idea what its function might be.

“Now let’s see what this does.”

The breviary directed him to the right spot and he found the handle in the face of the machine that was marked 167-R, as was the new one he had just obtained. When he pulled on the handle the container slid out as easily as a book from a shelf. He threw it aside and inserted the new part in its place.

“The light is gone, the emergency is over,” the Master Observer called out in a voice cracking with emotion. “You have succeeded even where the Air Tender failed.”

Chimal picked up the discarded part and wondered what had broken inside it. “It seemed obvious enough. The machinery appeared to work fine, so the trouble had to be in the alarm circuit, here. It’s described in the book, in the right section. Something turned on and would not turn off, so the emergency sounded even after the correction had been made. The tender should have seen that.”

He must have been very stupid not to have figured it out, he continued, to himself. Do not speak ill of the dead, but it was a fact. The poor man had panicked and killed himself when the problem had proven insoluble. This was proof of what he had suspected for a long time now.

In their own way the Watchers were just as slow-witted as the Aztecs. They had been fitted to a certain function just as the people in the valley had.

“I’m sorry, but I still don’t understand it,” Watchman Steel said, frowning over the diagram on the piece of paper, turning it around in the futile hope that a different angle would make everything clear.

“I’ll show you another way then,” Chimal said, going into his ablutory for the apparatus he had prepared. His observer’s quarters were large and well appointed. He brought out the plastic container to which he had fastened a length of strong cord. “What do you see in here?” he asked, and she dutifully bent to look.

“Water. It is half filled with water.”

“Correct. Now what will happen if I should turn it on its side?”

“Why… the water would spill out. Of course.”

“Correct!”

She smiled happily at her success. Chimal stretched out a length of cord and picked up the container by it. “You said it would spill. Would you believe that I can turn this bucket on its side without spilling a drop?”