'I did not think he would be interested in such a small matter.'

'The Khan is interested in everything.'

None of them could tell by Nadir's face whether he was joking or not.

'We would be happy to display the void pump to him.'

'Good. That would be appreciated. But remember also that he wishes specific help with cannonry, and with defence against cannonry.'

Khalid nodded. 'We will honour his wish, effendi.'

After Nadir was gone, Khalid grumbled unhappily. 'Interested in everything! How can he say that and not laugh!' Nevertheless he sent a servant with a formal invitation to the Khan, to witness the new apparatus. And before the visit occurred he had the whole compound at work, developing a new demonstration of the pump which he hoped would impress the Khan.

When Sayyed Abdul Aziz and his retinue made their visit, the globe that was to hold the void this time was made of two half globes, one edge mortised to fit the other precisely, with a thin oiled leather gasket placed between the two before the air was pumped out of the space between them, and thick steel braces for each globe, to which ropes could be tied.

Sayyed Abdul sat on his cushions and inspected the two halves of the globe closely. Khalid explained to him: 'When the air is removed, the two halves of the globe will adhere together with great strength.' He placed the halves together, pulled them apart; placed them together again, screwed the pump into the one that had the hole for it, and gestured for Paxtakor to wind the pump out and in and out again, ten times. Then he brought the device over to the Khan, and invited him to try to pull the two halves of the globe apart.

It could not be done. The Khan looked bored. Khalid took the device out to the central yard of the compound, where two teams of three horses each were held waiting. Their draft harnesses were hooked to the two sides of the globe, and the horses led apart until the globe hung in the air between them. When the horses were steadied, still facing away from each other, the horseboys cracked their whips, and the two teams of horses snorted and shoved and skipped as they attempted to pull away; they skittered sideways, shifted, struggled, and all the while the globe hung from the quivering horizontal ropes. The globe could not be pulled apart; even little charges made by the horse teams only brought them up short, staggering.

The Khan watched the horses with interest, but the globe he seemed to disregard. After a few minutes of straining, Khalid had the horses stopped, and he unhooked the apparatus and brought it over to the Khan and Nadir and their group. When he unscrewed the stopcock, the air hissed back into the globe, and the two halves came apart as easily as slices of an orange. Khalid stripped out the smashed leather gasket.

'You see,' he said, 'it was the force of the air, or rather the pull of the void, that kept the halves together so strongly.'

The Khan got up to leave, and his retainers rose with him. It seemed he was almost falling asleep. 'So?' he said. 'I want to blow my enemies apart, not hold them together.' With a wave of his hand he left.

Inside the Night, Inside the Light

This unenthusiastic response on the part of the Khan worried Bahram. No interest in an apparatus that had fascinated the scholars of the madressa; instead, a command to discover some new weapon or fortification that had eluded the hard search of all the armourers of all the ages. And if they failed, the possible punishments were only too easy to imagine. Khalid's absent hand mocked them from its own kind of void. Khalid would stare at the end of his wrist and say, 'Someday all of me will look like you.'

Now he merely looked around the compound. 'Tell Paxtakor to obtain new cannon from Nadir for testing. Three at each weight, and all manner of powder and shot.'

'We have powder here.'

'Of course.' A withering glare: 'I want to see what they have that is not ours.'

In the days that followed, he revisited all the old buildings of the compounds, the ones he and his old ironmongers had built when they were first making guns and gunpowder for the Khan. In those days, before he and his men had followed the Chinese system and connected the power of their waterwheel to the furnaces, making their first riverpowered blast furnaces and freeing up their crew of young puffers for other work, everything had been small and primitive, the iron more brittle, everything they made rougher, bulkier. The buildings themselves showed it. Now the gears of the waterwheels whirred with all the power of the river, pouring into the bellows and roaring as fire. The chemical pits steamed lemon and lime in the sun, and the puffers packed boxes and ran camels and moved immense mounds of charcoal around the yards. Khalid shook his head at the sight of it all, and made a new gesture, a kind of sweep and punch with his ghost hand. 'We need better clocks. We can only make progress if our measurement of time is more exact.'

Iwang puffed his lips when he heard this. 'We need more understanding.'

'Yes, yes, of course. Who could dispute that in this miserable world. But all the wisdom of the ages cannot tell us how long it takes flashpowder to ignite a charge.'

When the days ended the great compound fell silent, except for the grinding of the watermill on the canal. After the resident workers had washed and eaten and said their last prayers of the day, they went to their apartments at the river end of the compound, and fell asleep. The town workers went home.

Bahram dropped onto his bed beside Esmerine, across the room from their two small children, Fazi and Laila. Most nights he was out as soon his head hit the silk of his pillow, exhausted. Blessed slumber.

But often he and Esmerine woke some time after midnight, and sometimes they lay there breathing, touching, whispering conversations that were usually brief and disjointed, other times the longest and deepest conversations they ever had; and if ever they were to make love, now that the children were there to exhaust Esmerine, it would be in the blessed cool and quiet of these midnight hours.

Afterwards Bahram might get up and walk around the compound, to see it in moonlight and check that all was well, feeling the afterglow of love pulse in him; and usually on these occasions he would see the lamplight in Khalid's study, and pad by to find Khalid slumped over a book, or scribbling left handed at his writing stand, or recumbent on his couch, in murmured conversation with Iwang, both of them holding tubes of a narghile wreathed by the sweet smell of hashish. If Iwang was there and the men seemed awake, Bahram would sometimes join them for a while, before he got sleepy again and returned to Esmerine. Khalid and Iwang might be speaking of the nature of motion, or the nature of vision, sometimes holding up one of Iwang's lenses to look through as they talked. Khalid held the position that the eye received small impressions or images of things, sent through the air to it. He had found many an old philosopher, from China to Frengistan, who held the same view, calling the little images 'eidola' or 'simulacra' or 'species' or 'image' or 'idol' or 'phantasm' or 'form' or 'intention' or 'passion' or,similitude of the agent', or 'shadow of the philosophers', a name that made Iwang smile. He himself believed the eye sent out projections of a fluid as quick as light itself, which returned to the eye like an echo, with the contours of objects and their colours intact.

Bahram always maintained that none of these explanations was adequate. Vision could not be explained by optics, he would say; sight was a matter of spirit. The two men would hear him out, then Khalid would shake his head. 'Perhaps optics are not sufficient to explain it, but they are necessary to begin an explanation. It's the part of the phenomenon that can be tested, you see, and described mathematically, if we are clever enough.'