'You could be right at that,' said Fallon. 'So they're mirrors! Where does that get us?'
'Take a closer look,' I advised.
Fallon picked up one of the mirrors and Halstead took the other. After a while Halstead said, 'I don't see anything except the reflection of my own face.'
I don't do much better,' said Fallon. 'And it's not a good reflective surface, either.'
'What do you expect of a metal mirror that's had things dumped on it for the last four hundred years? But it's a neat trick, and I only came upon it by accident. Have you got a projection screen?'
Fallon smiled. 'Better than that -- I have a projection theatre'.
He would have! Nothing small about millionaire Fallon. He led us into a part of the house where I had never been, and into a miniature cinema containing about twenty seats. 'I find this handy for giving informal lectures,' he said.
I looked around. 'Where's the slide projector?'
'In the projection room -- back there.'
'I'll want it out here,' I said.
He looked at me speculatively, and shrugged. 'Okay, IT] have it brought in.'
There was a pause of about ten minutes while a couple of his servants brought in the projector and set it on a table in the middle of the room, acting under my instructions. Fallon looked interested; Halstead looked bored; Mrs. Halstead looked beautiful. I winked at her. 'We're going to have a fine show,' I said. 'Will you hold this mirror, Mrs. Halstead?'
I puttered around with the projector. 'I'm using this as a very powerful spotlight,' I said. 'And I'm going to bounce light off the mirror and on to that screen up there. Tell me what you see.'
I switched on the projector light and there was a sharp intake of breath from Fallon, while Halstead lost his boredom in a hurry and practically snapped to attention. I turned and looked at the pattern on the screen. 'What do you think it is?' I asked. 'It's a bit vague, but I mink it's a map.'
Fallon said, 'What the hell! How does it . . .? Oh, never mind. Can you rotate that thing a bit, Mrs. Halstead?'
The luminous pattern on the screen twisted and flowed, then steadied in a new orientation. Fallon clicked his tongue. 'I think you're right -- it is a map. If that indentation on the bottom right is Chetumal Bay -- and it's the right shape -- then above it we have the bays of Espiritu Santo and Ascension. That makes it the west coast of the Yucatan Peninsula.'
Halstead said, 'What's that circle in the middle?'
'Well come to that in a minute,' I said, and switched off the light. Fallon bent down and looked at the mirror still held by Mrs. Halstead and shook his head incredulously. He looked at me enquiringly, and I said, 'I came across this bit of trickery by chance. I was taking photographs of my tray -- or mirror -- and I was a bit ham-handed; I touched the shutter button by accident and the flash went off. When I developed the picture I found that I'd got a bit of the mirror in the frame but most of the picture was an area of wall. The light from the flash had bounced off the mirror and there was something bloody funny about its reflection on the wall, so I went into it a bit deeper.'
Halstead took the mirror from his wife. 'This is impossible. How can a reflection from a plane surface show a selectively variable pattern?' He held up the mirror and moved it before his eyes. 'There's nothing here that shows.'
'It's not a plane mirror -- it's slightly convex. I measured it; it has a radius of convexity of about ten feet. This is a Chinese trick.'
'Chinese!'
'Old Vivero said as much. '... that stranger from the East which the Moors brought to Cordoba.' He was Chinese. That stumped me for a bit -- what the hell was a Chinaman doing in Spain in the late fifteenth century? But it's not too odd, if you think about it. The Arab Empire stretched from Spain to India; it's not too difficult to imagine a Chinese metal worker being passed along the line. After all, there were Europeans in China at that date.'
Fallon nodded. 'It's a plausible theory.' He tapped the mirror. 'But how the hell is this thing done?'
'I was lucky,' I said. 'I went to the Torquay Public Library and there it was, all laid out in the ninth edition of the Encyclopaedia Britannica. I was fortunate that the Torquay Library is a bit old-fashioned because that particular item was dropped from later editions.'
I took the mirror from Halstead and laid it flat on the table. This is how it works. Forget the gold trimmings and concentrate on the mirror itself. All early Chinese mirrors - were of metal, usually cast of bronze. Cast metal doesn't give a good reflective surface so it had to be worked on with scrapers to give a smooth finish. Generally, the scraping was done from the centre to the edge and that gave the finished mirror its slight convexity.'
Fallon took a pen from his pocket and applied it to the mirror, imitating the action of scraping. He nodded and said briefly, 'Go on.'
I said, 'After a while the mirrors began to become more elaborate. They were expensive to make and the manufacturers began to pretty them up a bit. One way of doing this was to put ornamentation on the back of the mirror. Usually it was a saying of Buddha cast in raised characters. Now, consider what might happen when such a mirror was scraped. It would be lying on its back on a solid surface, but only the raised characters would be in contact with that surface -- the rest of the mirror would be supported by nothing. When scraper pressure was applied the unsupported parts would give a little and a fraction more metal would be removed over the supported parts.'
'Well, I'll be damned!' said Fallon. 'And that makes the difference?'
'In general you have a convex mirror which tends to diffuse reflected light,' I said. 'But you have plane bits where the characters are which reflects light in parallel lines. The convexity is so small that the difference can't be seen by the eye, but the short wavelengths of light show it up in the reflection.'
'When did the Chinese find out about this?' queried Fallon.
