Discworld – Jingo (Terry Pratchett)

The captain of the Klatchian ship was not an argumentative man when he was anywhere near 71–hour

Ahmed. He just looked at the straining sails and calculated his chances of Paradise.

'Perhaps the dog who cut the sail loose did us a favour!' he shouted, above the roar of the wind.

Ahmed said nothing. He kept looking back. The occasional burst of electric storm light showed the ship behind, aflame with green light.

Then he looked at the cold fire streaming behind their own masts.

'Can you see that light on the edge of the flames?' he said.

'My lord?'

'Can you, man?'

'Er... no...'

'Of course you can't! But can you see where the light isn't?'

The captain stared at him and then looked up again in terrified obedience. And there was somewhere where the light wasn't. As the fizzing green tongues waved in the wind they seemed to be edged with... blackness, perhaps, or a moving hole in space.

'That's octarine!' shouted Ahmed, as another wave sloshed over the deck. 'Only wizards can see it! There's magic in these storms! That's why the weather is so bad!'