'Of course.'
'Yes, obvious, but consider, Aristotle says that a heavier mass will fall faster than a lighter mass, because it has more of the predilection to join the Earth. But look. Here are the two iron balls, one big and one small, heavy and light. Place them on the doors, set the device level, using a bubble level, high on your outside wall, where there is a good distance to fall. A minaret would be better, the Tower of Death would be better yet, but even from your wall it will work.'
They did as he suggested, Khalid climbing the ladder slowly to inspect the arrangement.
'Now, pour water in the funnel, and watch.'
The water filled the lower basin until the doors suddenly fell open. The two balls fell. They hit the ground at the same time.
'Ho,' Khalid said, and clambered down the ladder to retrieve the balls and try it again, after hefting them, and even weighing them precisely on one of his scales.
'You see?' lwang said. 'You can do it with balls of unequal size or the same size , it doesn't matter. Everything falls at the same rate, except if it is so light and broad, like a feather, that it floats down on the air.'
Khalid tried it again.
lwang said, 'So much for Aristotle.'
'Well,' said Khalid, looking at the balls, then lofting them in his left hand. 'He could be wrong about this and right about other things.'
'No doubt. But everything he says has to be tested, if you ask me, and also compared with what Hsing Ho and AI‑Razi say, and the Hindus. Demonstrated to be true or false, in the full light of day.'
Khalid was nodding. 'I would have some questions, 1 admit.'
lwang gestured at the alchemical equipment in the yard. 'It's the same
for all this ‑ you could test them, see what's useful and what's not.'
Khalid frowned. lwang returned his attention to the falling balls. The two men dropped a number of different items from the device, chattering away all the while.
'Look, something has to be bringing them down,' Khalid said at one point. 'Bringing them, forcing them, drawing them, what have you.'
'Of course,' said Iwang. 'Things happen by causes. An attraction must be caused by an agent, acting according to certain laws. What the agent might be, however . . .'
'But this is true of everything,' Khalid said, muttering. 'We know nothing, that's what it comes down to. We live in darkness.'
'Too many conjoined factors,' lwang said.
Khalid nodded, hefting a carved block of ironwood in his hand. 'I'm tired of it, though.'
'So we try things. You do something, you get something else. It looks like a causal chain. Describable as a logical sequence, even as a mathematical operation. So that you might say, reality manifests itself thus. Without worrying too much about defining what force it is.'
'Perhaps love is the force,' Bahram offered. 'The same attraction as of persons to persons, extended between things in a general way.'
'It would explain how one's member rises away from the Earth,' lwang said with a smile.
Bahram laughed, but Khalid said only, 'A joke. What 1 am speaking of could not be less like love. it is as constant as the stars in their places, a physical force.'
'The sufis say that love is a force, filling everything, impelling every~ thing.'
'The sufis,' Khalid said scornfully. 'Those are the last people on Earth I would consult if 1 wanted to know how the world works. They moon about love and drink lots of wine and spin themselves. Bah! Islam was an intellectual discipline before the sufis came along, studying the world as it is, we had Ibn Sina and Ibn Rashd and Ibn Khaldun and all the rest, and then the sufis appeared and there hasn't been a single Muslim philosopher or scholar since then who has advanced our understanding of things by a single whit.'
'They have too,' Bahram said. 'They've made it clear how important love is in the world.'
'Love, oh yes, all is love, God is love, but if everything is love and all is one with Allah, then why do they have to get so drunk every day?'
lwang laughed. Bahram said, 'They don't really, you know.'
'They do! And the good fellowship halls fill up with good fellows looking for a good time, and the madressas grow emptier, and the khans give them less, and here we are in the year 1020 arguing over the ideas of the ancient Frengis, without a single idea why things act the way they do. We know nothing! Nothing!'
'We have to start small,' lwang said.
'We can't start small! Everything is all tied together!'
'Well, then we need to isolate one set of actions that we can see and control, and then study that, and see if we can understand it. Then work onwards from there. Something like this falling, just the simplest movement. If we understood movement, we could study its manifestations in other things.'
Khalid thought about that. He had finally stopped dropping things through the device.
'Come here with me,' lwang said. 'Let me show you something that makes me curious.'
They followed him towards the shop containing the big furnaces. 'See how you obtain such hot fires now. Your waterworks drive the bellows faster than any number of puffers ever could, and the heat of the fire is accordingly higher. Now, Aristotle says fire is trapped in wood, and released by heat. Fair enough, but why does more air inake the fire burn hotter? Why does wind drive a wildfire so? Does it mean air is essential to fire? Could we find out? If we built a chamber in which the air was pulled out by the bellows rather than pushed in, would the fire burn less?'
'Suck air out of a chamber?' Khalid said.
'Yes. Arrange a valve that lets air out but won't let it back in. Pump out what's there, and then hold any replacement air out.'
'Interesting! But what would remain in the chamber then?'
lwang shrugged. 'I don't know. A void? A piece of the original void, perhaps? Ask the lamas about that, or your sufis. Or Aristotle. Or just make a glass chamber, and look in it.'
' 1 will,' Khalid said.
'And motion is easiest of all to study,' lwang said. 'We can try all
manner of things with motion. We can time this attraction of things to the Earth. We can see if the speed is the same up in the hills and down in the valleys. Things speed up as they fall, and this might be measurable too. Light itself might be measurable. Certainly the angles of refraction are constant, I've measured those already.'
Khalid was nodding. 'First this reverse bellows, to empty a chamber. Although surely it cannot be a true void that results. Nothingness is not possible in this world, 1 think. There will be something in there, thinner than air.'
'That is more Aristotle,' lwang said.‑‑‑Natureabhors the void." But what if it doesn't? We will only know when we try.'
Khalid nodded. If he had had two hands he would have been rubbing them together.
The three of them walked out to the waterworks. Here a canal brought a hard flow from the river, its gliding surface gleaming in the morning light. The water powered a mill, which geared out to axles turning a bank of heavy metal‑working hammers and stamps, and finally the rotating bellows handles that powered the blast furnaces. It was a noisy place, filled with sounds of falling water, smashed rock, roaring fire, singed air; all the elements raging with transmutation, hurting their cars and leaving a burnt smell in the air. Khalid stood watching the waterworks for a while. This was his achievement, he was the one who had organized all the artisans' skills into this enormous articulated machine, so much more powerful than people or horses had ever been. They were the most powerful people in all the history of the world, Bahram thought, because of Khalid's enterprise; but with a wave Khalid dismissed it all. He wanted to understand why it worked.
He led the other two back to the shop. 'We'll need your glassblowing, and my leather and iron workers,' he said. 'The valve you mention could perhaps be made of sheep intestines.'
'It might have to be stronger than that,' said Iwang. 'A metal gate of some sort, pressed into a leather gasket by the suck of the void.'
'Yes.'
<
br /> No Jinn in This Bottle
Khalid set his artisans to the task, and lwang did the glassblowing, and after a few weeks they had a two‑part mechanism: a thick glass globe to be emptied, and a powerful pump to empty it. There were any number of collapses, leaks and valve failures, but the old mechanists of the compound were ingenious, and attacking the points of failure, they ended up with five very similar versions of the device, all very heavy. The pump was massive and lathed to newly precise fits of plunger, tube and valves; the glass globes were thick flasks, with necks even thicker, and knobs on the inside surfaces from which objects could be hung, to see what would happen to them when the air in the globe was evacu‑ ated. When they solved the leakage problems, they had to build a rackand‑pinion device to exert enough force on the pump to evacuate the final traces of air from the globe. lwang advised them not to create such a perfect void that they ended up sucking in the pump, the compound, or perchance the whole world, like jinni returning to their confinement; and as always, lwang's stone face did not give them any clue as to whether he was joking or serious.
When they had the mechanisms working fairly reliably (occasionally one would still crack its glass, or break a valve), they set one on a wooden frame, and Khalid began a sequence of trials, inserting things in the glass globes, pumping out the air, and seeing what resulted. All philosophical questions on the nature of what remained inside the globe after the air was removed, he now refused to address. 'Let's just see what happens,' he said. 'It is what it is.' He kept big blank‑paged books on the table beside the apparatus, and he or his clerks recorded every detail of the trials, timing them on his best clock.
After a few weeks of learning the apparatus and trying things, he asked Iwang and Bahram to arrange a small party, inviting several of the qadi and teachers from the madressas in the Registan, particularly the mathematicians and astronomers of Sher Dor Madressa, who were already involved in discussions of ancient Greek and classical caliphate notions of physical reality. On the appointed day, when all those invited had gathered in the open‑walled workshop next to Khalid's study, Khalid
introduced the apparatus to them, describing how it worked and indicating what they could all see, that he had hung an alarm clock from a knob inside the glass globe, so that it swung freely at the end of a short length of silk thread. Khalid cranked the piston of the rack‑and‑pinion down twenty times, working hard with his left arm. He explained that the alarm clock was set to go off at the sixth hour of the afternoon, shortly after the evening prayers would be sung from Samarqand's northernmost minaret.
'To be sure the alarm is truly sounding,' Khalid said, 'we have exposed the clapper, so that you can see it hitting the bells. 1 will also introduce air back into the globe little by little, after we have seen the first results, so you can hear for yourself the effect.'
He was gruff and direct. Bahram saw that he wanted to distance himself from the portentous, magical style he had affected during his alchemical transmutations. He made no claims, spoke no incantations. The memory of his last disastrous demonstration ‑ his fraud ‑ must have been in his mind, as it was in everyone else's. But he merely gestured with his hand at the clock, which advanced steadily towards six.
Then the clock began to spin on its thread, and the clapper was visibly smashing back and forth between the little brass bells. But there was no sound coming from the glass. Khalid gestured: 'You might think that the glass itself is stopping the sound, but when the air is let back into the flask, you will see that it isn't so. First 1 invite you to put your car to the glass, so you can confirm that there is no sound at all.'
They did so one by one. Then Khalid unscrewed a stopcock that released a valve set in the side of the flask, and a brief penetrating hiss was joined by the muted banging of the alarm, which grew louder quickly, until it sounded much like an alarm heard from an adjoining room.
'It seems there is no sound without air to convey it,' Khalid commented.
The visitors from the madressa were eager to inspect the apparatus, and to discuss its uses in trials of various sorts, and to speculate about what, if anything, remained in the globe when the air was pumped out. Khalid was adamant in his refusal to discuss this question, preferring to talk about what the demonstration seemed to be indicating about the nature of sound and its transmission.
'Echoes might elucidate this matter in another way,' one of the qadis said. He and all the other visiting witnesses were bright‑eyed, pleased, intrigued. 'Something strikes air, pushes it, and the sound is a shock moving through the air, like waves across water. They bounce back, like waves in water bounce when they strike a wall. It takes time for this movement to cross the intervening space, and thus echoes.'
Bahram said, 'With the aid of an echoing cliff we could perhaps time the speed of sound.'
'The speed of sound!' lwang said. 'Very nice!'
'A capital idea, Bahram,' Khalid said. He checked to make sure his clerk was noting all done or said. He unscrewed the stopcock all the way and removed it, so that they all heard the noisy clanging of the alarm as he reached into the flask to turn off the device. It was strange that the clapper should have been so silent before. He rubbed his scalp with his right wrist. 'I wonder,' he said, 'if we could establish a speed for light too, using the same principle.'
'How would it echo?' Bahram asked.
'Well, if it were aimed at a distant mirror, say ... a lantern unveiled, a distant mirror, a clock that one could read very precisely, or start and stop, even better . . .'
Iwang was shaking his head. 'The mirror might have to be very far away to give the recorder time to determine an interval, and then the lantern flash would not be visible unless the mirror were perfectly angled.'
'Make a person the mirror,' Bahram suggested. 'When the person on the far hill sees the first lantern light, he reveals his, and a person next to the first person times the appearance of the second light.'
'Very good,' several people said at once. lwang added, 'It may still be too fast.'
'It remains to be seen,' Khalid said cheerfully. 'A demonstration will clarify the issue.'
With that Esmerine and Fedwa wheeled in the ice tray and its 'demonstration of sherbets' as lwang termed it, and the crowd fell to, talking happily, Iwang speaking of the thin sound of goraks in the high Himalaya where the air itself was thin, and so on.
The Khan Confronts the Void
So lwang brought Khalid back out of his black melancholy, and Bahram saw the wisdom of lwang's approach to the matter. Every day now, Khalid woke up in a hurry to get things done. The businesses of the compound were given over to Bahram and Fedwa and the old hands heading each of the shops, and Khalid was distracted and uninterested if they came to him with matters of that sort. All his time was taken by conceiving, planning, executing and recording his demonstrations with the void pump, and later with other equipment and phenomena. They went to the great western city wall at dawn when all was quiet, and timed the sound of wood blocks slapped together and their returning echoes, measuring their distance from the wall with a length of string one third of a 11 long. lwang did the calculations, and soon declared that the speed of sound was something like two thousand Ii an hour, a speed that everyone marvelled at. 'About fifty times faster than the fastest horse,' Khalid said, regarding lwang's figures happily.
'And yet light will be much faster,' lwang predicted.
'We will find out.'
Meanwhile lwang was puzzling over the figures. 'There remains the question of whether sound slows down as it moves along. Or speeds up for that matter. But presumably it would slow, if it did anything, as the air resisted the shock.'
'Noise gets quieter the further away it is,' Bahram pointed out. 'Maybe it gets quieter rather than slower.'
'But why would that be?' Khalid asked, and then he and lwang were into a deep discussion of sound, movement, causation and action at a distance. Quickly Bahram was out of his depth, being no philosopher, and indeed Khalid did not like the
metaphysical aspect of the discussion, and concluded as he always did these days: 'We will test it.'
lwang was agreeable. Ruminating over his figures, he said, 'We need a mathematics that could deal not only with fixed speeds, but with the speed of the change of a speed. 1 wonder if the Hindus have considered this.' He often said that the Hindu mathematicians were the most advanced in the world, very far ahead of the Chinese. Khalid had long
ago given him access to all the books of mathematics in his study, and lwang spent many hours in there reading, or making obscure calculations and drawings, on slates with chalk.
The news of their void pump spread, and they frequently met with the interested parties in the madressas, usually the masters teaching mathematics and natural philosophy. These meetings were often contentious, but everyone kept to the ostentatiously formal disputation style of the madressa's theolo ical debates.
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