The Year of Rice and Salt

'To be sure the alarm is truly sounding,' Khalid said, 'we have exposed the clapper, so that you can see it hitting the bells. I 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 I 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!' Iwang 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. Iwang 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 Iwang 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 Iwang brought Khalid back out of his black melancholy, and Bahram saw the wisdom of Iwang'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 an li long. Iwang did the calculations, and soon declared that the speed of sound was something like two thousand li an hour, a speed that everyone marvelled at. 'About fifty times faster than the fastest horse,' Khalid said, regarding Iwang's figures happily.