The party had broken into groups: Pyxeas’ party, the two Arab travellers, and the local men who seemed particularly furtive tonight to Avatak, suspicious, watchful of the others. One of them giggled frequently, a man who had never got over the effects of the high land. Uzzia, too, seemed more reserved than usual, watchful. As did Jamil, his eyes glittering as he glanced at the others. Only the horses seemed unperturbed – and the mule, who cropped at the lush grass with an air of bored indifference.

Pyxeas, typically, showed no awareness of any of this tension. ‘Oh, I wish I had more light!’ he said, squinting at the oracle’s dials in the firelight. ‘But that of course would ruin the seeing. Still, not long to go now, before the moon is snuffed out!’

Jamil glanced at the locals. ‘Play with that toy if you must. But keep it down, will you?’

‘Toy?’

Uzzia touched Pyxeas’ arm. ‘Hush, those men are alarmed about something, and we don’t want to scare them any further.’

‘Let them wallow in their superstitious fear. They are nothing. The eclipse is too significant, and I, Pyxeas, will capture it, and use it to determine my position on the curving belly of the earth.’

Avatak could see that Uzzia was intrigued despite herself. ‘What are you talking about, scholar?’

‘Know that eclipses occur on particular days at precise hours, which can be calculated in advance – years in advance, at that. And that knowledge is encoded into the gears of my oracle. You see? So I know an eclipse is due tonight – I know the exact time it will occur, by Northland’s clocks. Now, to determine my east-west position, all I have had to do is observe the eclipse.

‘Here I have Avatak measuring the local time – the hour at this precise point. Suppose I see, from Avatak’s glass, that the eclipse happens at midnight for me, I mean some particular aspect of it, the moon’s first entry into shadow, or the last exit. But the oracle tells me that the eclipse is scheduled for sunset at Etxelur, for example. Knowing the difference between those two times, I can calculate my arc east-west around the world – do you see? As if I am using the world itself as a gigantic common clock.’

Jamil thought that over, frowned, and spat. ‘Lot of fuss to work out one tiny number.’

The scholar, predictably, grew angry. ‘But with such “tiny numbers” I, Pyxeas, map the heavens! Thus I know that eclipses happen, at full moon or new moon, just as the moon crosses the sun’s path in the sky—’

‘Enough!’ Jamil clamped his hands to his ears. ‘You make my brain boil, old man.’