Rina scowled. ‘What is? By the mothers’ bones, don’t give us children’s stories, man.’

‘Children’s stories? Have you heard of Euhemerus?’

‘Who?’

‘Greek philosopher. Or perhaps Hatti. Died a long time ago. Anyhow he believed that our myths are our oldest account of ourselves. They’re not just stories, you see, though that’s what they teach you in school nowadays. They describe events that really happened. Important events, major, world-changing events. That’s why they were remembered, and written down, and why they became the strange sort of mass memory we call a myth.

‘And any of you could have confirmed the truth of those myths for yourselves, had you gone out in the world and looked, as have I, Pyxeas. If you had learned to read the great book of the world, as I and some others have learned. I have seen the shorelines of lakes long vanished. I have seen ridges of rubble strewn across the continents, left by the retreat of great ice sheets. I have seen valleys gouged by long-melted glaciers. And indeed you could have found the truth in our own Archive. We have records going back millennia – not even the Hatti, not even the Egyptians go back as far as we do—’

‘Oh, Uncle!’ Ywa cried. ‘Get to the point. Why did it start to rain five years ago, all across the Continent?’

‘Because the air got cooler. You must know that the air, invisible all around us, is a jumble of gases. It contains vital air which sustains a flame, and fixed air which is produced by a flame, and other inert components. And water! In the form of vapour.’ He glared at them. ‘Come on, come on! I taught too many of you these basic principles; have you forgotten how to think while I’ve been away?’

Alxa said slowly, remembering her lessons as she spoke, ‘When the air cools, it must drop the moisture it holds.’

He pointed at her. ‘Yes! You have it. The abnormal rainstorms themselves were a sign of the cooling of the air. Then as the rain washed out, the currents of the air were deflected – pushed away by the gathering cold in the north – and settled into a new pattern of persistent and dry winds from the west.’

‘Which,’ Ywa said, ‘eventually brought drought to the southern lands. Is that what you’re saying?’

‘Yes. But why is the air cooling, and indeed the world as a whole? The ultimate cause seems clear . . .’ He dug out a bit of Albian chalk, and rapidly began to sketch on the plaster wall: a spinning sphere, its axis tilted, swooping on a curved path around a scribbled sun. ‘The earth! The world on which we stand, spinning and sailing through the void in a manner long ago determined by the Greek scholars brought to Northland by Pythagoras, and measured in detail by generations of astronomers. It’s a very precise art, you see; you can measure a star’s apparent position in the sky quite exactly . . .’