of course; nobody could get out. The two marines followed them, not close but not far either.
Joe usually had a good sense of direction, but once they were in Edinburgh proper, he was lost. It was a tangle of marble monuments and chaotic tenements. He got a glimpse downhill once, when they were near the castle, and saw the slums – a labyrinth of wooden buildings clustered around wells in muddy courtyards where chickens and goats scratched, and people had hessian sacking instead of front doors. And then they turned a corner and they were on a broad stone bridge, and on either side were warmly lit inns and shops that sold specialist whisky.
Up a flight of more than a hundred steps was a whole street of blacksmiths.
The workshop Kite chose was back from the road through a twisting little passage. Inside, the workshop smelled of hot metal and the forge, where the coal was cherry red. The blacksmith was a large woman in a heavy apron, hammering out a sword on the anvil. Joe could see the shape already. It sparked under every hammer blow.
She looked like she might hit them with the hammer too, but she must have been expecting them, because she dropped the sword into a cooling barrel and came across to shake Kite’s hand. With evident pride, she offered them some tea. Kite looked impressed. Joe didn’t understand at first, and then realised that India was on the far side of France. It must have been hell to get anything from there to here.
While they drank the tea, he looked around at the equipment. The place was well supplied. The walls were covered in racks and racks of hammers and tongs, pincers, some big enough to make an iron hull for a ship and some small enough for jewellery. The forge pumped out heat and red light, which gleamed on the claymores laid on the workbench. She must have had a commission for a whole regiment.
‘Has the Ajax been in?’ Kite was asking. He was holding his tea in both hands. The two marines were doing the same, and they kept giving the smith adoring looks.
‘Ah, no. Sunk off Calais. How’s your sister?’
‘Lost in action.’
‘Fuck. So what are we making?’ she asked, as if they’d been talking about bad weather before. Kite inclined his head at Joe.
‘Can I explain what this is or are you going to shoot someone?’ Joe said to Kite.
‘No, tell her,’ Kite said, without any hostility. He was sitting with his back to the forge. Joe would have been ferociously hot after ten seconds, but Kite was still wearing his jacket.
‘Right,’ said Joe, and explained what telegraphs were, and how Morse code worked.
He’d had to learn to code as part of the lighthouse-keeping exam. Anyone de Méritens sent anywhere near a lighthouse took it, and after he’d learned, Joe had found the whole transmitting system so fascinating that he’d taken some telegraphs apart at work just for the novelty.
They worked in the same way that arc lamps did: with a spark gap. But where, in a lighthouse, you ran electricity through the two electrodes to get a continuous spark – the light of the lamp – you just needed little blips if you wanted to talk to somebody. If you sparked your spark gap on and off, the electromagnetic field could affect any wire coils nearby. If you gave it enough electricity – 10,000 volts, say – it would affect a coil miles away. The machines were beautiful: all delicate copper coils in the transformers, and electrodes that looked like ball-bearings on sticks. Despite everything, he found himself enjoying drawing the parts out, and showing them how the circuit worked. Kite and the blacksmith listened in silence. One of the marines crossed himself.
‘So, once this is done, you should be able to communicate … eh, over about twenty miles. They did it from France to a lighthouse in England a couple of years ago.’
‘Twenty miles,’ said Kite.
‘It’s not far, but it’ll do you for the siege,’ Joe pointed out, and then realised that Kite had meant twenty miles was long, not short. ‘I need to make a battery, don’t I,’ he added, more to himself, and looked around a bit aimlessly. ‘Where do we get sulphuric acid?’ He paused, because a home-made battery was only going to manage about ten or twenty volts. ‘And – a lot of copper wire.’
It was hard to explain wireless telegraphy to someone who didn’t know