Finn
We only ever see one side of the moon. This is because it takes exactly as long for the moon to make one rotation on its axis as it does for it to complete its orbit of the Earth.
Dad says it’s a bit like a dancer circling, but always facing their partner.
He did a bit of a dance in the kitchen with Mum to show me, while we were studying the moon and space.
It made Mum laugh and then he hugged her.
They don’t hug very often these days, because Dad is too busy with home-schooling me and with organising the sailing camp, even though it’s the summer holidays, and Mum is too busy with her writing.
So the moon never turns its back to the Earth, and this is called Synchronous Tidal Locking.
Some people call the side we never see ‘the Dark Side of the Moon’.
But that’s only because they’re looking at it from one point of view.
It’s more correct to call it ‘the Far Side’, because it does receive sunlight too.
It can shine sometimes, just like the side facing us.
To be able to see it, though, depends on where you’re standing.
I suppose you could say the same about a lot of things.
The moon is also responsible for the tides in the oceans on Planet Earth because of its gravitational pull.
At the moment, with the moon almost full, there are spring tides, which means they are both higher and lower than at other times in the month.
Today, Dad decided we should go out in the dinghy because it would be good practice for me before the sailing camp and he wanted to double-check some of the places he plans on taking the other autistic kids when they are here.
We waited for it to be low tide so we could go out at slack water and then the incoming spring tide would help push us back in when we were returning.
We sailed to where the salt pans are, just beyond the lagoon in the marshes.
The sun and the wind make the shallow seawater in the pans evaporate and then the salt can be collected.
This is where, in the olden days, the donkeys would have worn their stripy trousers and carried baskets on their backs to take the salt to market.
By the time we got there, the sun was lower in the sky, and I had to pull my cap down so my eyes wouldn’t be dazzled by it as it reflected on the water, even though I was wearing my sunglasses too. I really do prefer the night-time.
I thought about the old man in the cemetery and the donkeys he keeps in his orchard.
It must have been hard for them, working in the heat with all the flies nipping at their legs and the salt getting into the bites and making them sting.
I wondered whether that would hurt even more than being stung by a jellyfish.
A big white Moon Jelly floated past the boat just when I was thinking that, but they don’t sting.
Once, though, I found a small brown-ish jellyfish on the beach and I picked it up.
That really hurt, like being burnt if you accidentally touch an electric fence, which I have also done, and I had a bright-red line on my wrist for days.
Dad had to wash it in seawater and scrape my skin to get the filaments off.
Autistic people don’t like being touched at the best of times and that definitely wasn’t the best of times.
A lot of people came over to see what was going on and someone called the police, so Dad had to explain to the policeman that I really was his son, and he wasn’t a Stranger trying to hurt me.
The piles of salt around the pans looked like heaps of snow, but of course snow would melt immediately in the summer heat. There wasn’t too much wind, just a steady breeze, and we made it there and back in good time.
Dad said he was very pleased with how I’d handled the dinghy.
When we were putting it away, he pointed out the bigger boat that we’ll be sailing as a Team when the sailing course starts next week.
The other kids and their parents will be arriving this weekend.
They’re going to stay in some holiday apartments in Saint-Martin, up the hill from the harbour.
At least we don’t have to stay there as well, but Dad says we do have to have supper with everyone every evening and be Sociable.
Being Sociable is another thing autistic kids are definitely not good at, like Working as a Team, but he seems to have forgotten that as well.
When we got back, Mum was busy typing up her notes about Philly’s life. She’ll be off on her writing course next week and Philly will be going home.
I took my laptop out to the porch, where Philly was sitting doing her crossword.
‘How was the sailing?’ she asked.
‘We went to the salt pans. I saw a jellyfish,’ I told her. ‘The tide’s coming in now and it’ll be quite a high one tonight because the moon’s still nearly full.’
She nodded. ‘Maybe we could walk down to the beach after supper to look at it. I’d like that.’
‘OK,’ I said. Usually, I don’t enjoy going to all the effort of walking through the dunes, getting sand in my shoes, and the sun can be way too hot.
But as it would be at night and she only has a few days left I thought it would be Polite to go with her, and she might tell me some more about flying planes in the war and coming to France on a secret mission. As well as how she lost her leg.
I’m really not looking forward to next week at all. I started feeling anxious about it again, so I quickly did another Sudoku to calm my brain down. Then I looked across at Philly and she was watching me.
‘Finished already?’ she asked. ‘You’re very good at puzzles, aren’t you, Finn?’
‘Yes, I am. Can you tell me about poem codes, please? They sound quite interesting.’
‘Oh,’ she said. ‘So you were listening when I was talking to your mother about them, were you?’
‘Yes. You said you used the poem Ben sent you when you went on your secret mission to France. So how do they work?’
‘I’ll show you if you bring me a piece of paper and a pencil.’
‘Shall we use the one Ben gave you?’
‘No,’ she said. ‘That one was given to me. I shall give you one of your own.’
I sat next to her on the porch sofa and breathed in her smell of lavender while she drew a grid running across the page, two squares deep.
‘Before we started using poem codes, agents being sent to France would often take a copy of a particular book with them. The codebreakers back at home would have a copy – not just of the same book but exactly the same edition. Then the agent could send back a series of page numbers, line numbers and word numbers to create a message that could be understood at the other end. Of course, the danger was that if the agent was captured the Germans would then also have a copy of the book and they began to cotton on pretty quickly to what we were doing. Do you know, the average life expectancy of an SOE radio operator in the field could be as short as just six weeks, and that was partly due to the ease with which the Germans began to be able to intercept and decipher those messages. So we needed to come up with a better system. In fact, we were always needing to come up with better systems – that’s part of the work of a cryptographer, continually refining and improving coding systems as the enemy tries to break them.
We came up with the idea of poem codes. Poems could be memorised, so there was no need to carry books around. ’
She googled something on her iPad and showed me it was a poem called Dover Beach , by a man called Matthew Arnold.
‘This one can be yours,’ she said. ‘It’s a favourite of mine, and it seems rather appropriate for a boy who lives on an island and loves being out at night-time.
We’ll take this line, which is quite easy to memorise: The tide is full, the moon lies fair upon the straits .
Do you think you could learn that off by heart? ’
I repeated it straight back to her, along with the rest of the first part of the poem. I’m very good at remembering things even when I’ve only seen them once.
‘Impressive,’ she said, and her eyebrows went up towards her white hair. ‘You’d have made a very good recruit.’
Then she tapped the grid she’d drawn with the end of the pencil that has the little rubber attached. ‘Next, we need to encode the letters. We write the words we’ll be using across the top, one letter in each square. Let’s take the words “ moon lies fair ”. Here, you do it.’
She handed me the pencil and I wrote out the letters.
‘Good. Now we need to write in the code numbers beneath the letters. So the “A” is 1, the next letter alphabetically is “E” so that’s 2. Write those in underneath the letters on the grid and carry on. That’s it, you’re getting the hang of it now.’
Once I’d finished coding the letters, she took the pencil back from me.
‘Very good,’ she said. ‘So now we use the numbers we’ve encoded as our transposition key.
We write them out across the top of a new grid in the same order, like this .
.. And then we can write the message we need to send in columns beneath the key like this, padding the extra spaces with “X”s . ..’
I looked at the new grid. It looked like this:
7 9 10 8 6 4 2 12 3 1 5 11 M A R M I T E L O W S E N D S U P P L I E S X X
‘There are actually some more jars of Marmite in the cupboard where the spaghetti is kept, you know,’ I said.
‘Well, that’s a good thing. But you see how the basic premise works, in principle? We would transmit the coded message in groups of four letters, starting WSEL because they’re under numbers 1 and 2 in our key. See if you can write out the whole coded message.’
She handed me the pencil again and I wrote out:
Wsel Oetp Sxip Mnmu Adrs Exli
She nodded, looking at the work we’d done.
‘It’s not perfect. Any enemy cryptanalyst with an ounce of intelligence might be able to work it out fairly easily, given enough time.
So the next step is to make it more complicated.
We make another grid and re-transpose the message.
That’s called a double transposition code, you see?
And then we send that coding in groups of five letters.
We also need to tell those on the receiving end which keywords we’re using – in the case of your poem it would be line two, words six, seven and eight.
You could easily send that information as a cipher at the start of the message. ’
She showed me how to do the double transposition and we worked on writing out a few messages that would probably have stumped even the cleverest Nazis, according to Philly.
‘So to decipher the message at the other end, you’d need to know the grid layout, with the keywords and the right number of rows, and work it backwards?’ I said.
‘Exactly. That’s one of the jobs the cryptographers at Bletchley Park were doing, day in, day out.
Poem codes were a pretty effective way of sending messages from the field, especially if the agent only used the poem once.
Even more so if the poem wasn’t a well-known one, or if it was something made-up. ’
I took the pencil from her and wrote another coded message on the paper, using the simplest way of coding she’d shown me at the beginning.
She looked at it for a moment, then smiled and said, ‘You’re very welcome, Finn.’
‘Are you going to tell Mum some more of your story now?’ I asked.
‘Would you like to hear some more?’ she said.
‘Yes. I want to know how you got on when you went on that secret mission to France. Was that when you lost your leg?’
She laughed. ‘All in good time, my young friend. But in that case, let’s go and see if Kendra’s ready.’
I collected up the coding we’d done, so I could laminate it later on, and we went inside to find Mum.