The Year of Rice and Salt

'It's a wonder things don't change colour when you move,' Bahram said, and the other two went silent, until Khalid started laughing.

'Another mystery! Allah preserve us! They will just keep coming for ever, until we are one with God.'

This thought appeared to please him immensely.

He set up a permanent dark room in the compound, all boarded and draped until it was much darker than his study had been, with shuttered chinks in the east wall that could let in small shafts of light, and many a morning he was in there with assistants, running in and out, arranging demonstrations one way or another. One he was pleased enough with to invite the scholars of the Sher Dor Madressa to witness it, because it so neatly refuted Ibn Rashd's contention that white light was whole, and the colours created by a prism an effect of the glass. If this were so, Khalid argued, then light twice bent would change colour twice. To test this, his assistants allowed sunlight in through the wall, and a first prism's array was spread across a screen in the centre of the room. Khalid himself opened an aperture in the screen small enough only to allow the red part of the little rainbow through it, into a draped closet where it immediately encountered another prism, directing it onto another screen inside the closet.

'Now, if the bend of refraction caused by itself the change in colour, surely the red band would change at this second refraction. But look: it remains red. Each of the colours holds when put through a second prism.'

He moved the aperture slowly from colour to colour, to demonstrate. His guests crowded around the door of the closet, examining the results closely.

'What does this mean?' one asked.

'Well, this you must help me with, or ask Iwang. I am no philosopher, myself. But I think it proves the change in colour is not just a matter of bending in itself. I think it shows sunlight, white light if you will, or full light, or simply sunlight, is composed of all the individual colours travelling together.'

The witnesses nodded. Khalid ordered the room opened up, and they retired blinking into the sun to have coffee and cakes.

'This is wonderful,' Zahhar, one of Sher Dor's senior mathematicians said, 'very illuminating, so to speak. But what does it tell us about light, do you think? What is light?'

Khalid shrugged. 'God knows, but not men. I think only that we have clarified (so to speak) some of light's behaviour. And that behaviour has a geometrical aspect. It seems regulated by number, you see. As do so many things in this world. Allah appears to like mathematics, as you yourself have often said, Zahhar. As for the substance of light, what a mystery! It moves quickly, how quickly we do not know; it would be good to find out. And it is hot, as we know by the sun. And it will cross a void, if indeed there is any such thing as a void in this world, in a way that sound will not. It could be that the Hindus are right and there is another element besides earth, fire, air and water, an ether so fine we do not see it, that fills the universe to a plenum and is the medium of movement. Perhaps little corpuscles, bouncing off whatever they strike, as in a mirror, but usually less directly. Depending on what it strikes, a particular colour band is reflected into the eye. Perhaps.' He shrugged. 'It is a mystery.'

The Madressas Weigh In

The colour demonstrations caused a great deal of discussion and debate in the madressas, and Khalid learned during this period never to speak of causes in any opinionated way, or to impinge on the realm of the madressa scholars by speaking of Allah's will, or any other aspect of the nature of reality. He would only say, 'Allah gave us our intelligence to better understand the glory of his work,' or, 'the world often works mathematically. Allah loves numbers, and mosquitos in springtime, and beauty.'