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It's good to see ourselves as others see us.
20 miles or so over there is Dover.
This is the view of our coast from France.
We're in Northern France - one small step from Britain,
one giant leap in language and culture.
We're not on our island any more - this is mainland Europe.
Niggly neighbours we may be,
but there's an unbreakable bond between our coasts.
Our shared story is written into the landscape
and it runs in our blood.
From Norman conquest to the D-Day liberation,
a narrow stretch of sea can't separate us.
Now we're following the threads that tug us time and again across the Channel.
And here to meet our French neighbours are the usual familiar faces.
Mark Horton discovers why it was French stone that built England's first castles.
That's completely exhausting!
Alice Roberts is trying to make a good impression.
It's still nerve-wracking.
Miranda Krestovnikoff is throwing some light on the private life of bats.
On a voyage of discovery to an underwater wonderland, Nick Crane is on the French Channel Islands.
I had no idea that there was such a huge landmass lurking beneath the waves.
And Dick Strawbridge explores a secret map that saved D-Day from sinking in the sand.
The old halftrack is getting through there, all right!
This is our coast, and beyond.
We've crossed the English Channel, heading for Mont-St-Michel.
Our French odyssey begins at Cap Gris Nez - or the Grey Nose -
where France is within sniffing distance of England.
Standing on this spot, I'm full of anticipation for our journey along the French coast.
But others have come here to look back at our coast, with conquest in mind.
In 1803, Napoleon eyed up the south coast for invasion, but was held back by the Royal Navy.
Nearly 140 years later it was Hitler who was headed off by the Royal Air Force,
but there are traces of his tyranny left behind.
The footprints of the German army are still deeply embedded along this shore,
but what I find intriguing is that this World War II bunker is built on top of a much earlier fort,
a fort that was put here by Henry VIII.
The earthworks of defensive ditches and mounds still dominate Hitler's bunkers.
Henry VIII's fort was built in 1546, but its shape still scars the landscape,
a quarter of a mile across from ditch to ditch.
Not that there's much left of the walls built into these earthworks.
Daniel Leunens, who's written a history of this coast, is showing me one tantalizing glimpse.
So this is 16th century masonry?
That's right, yes. And this is the entrance of some rooms,
where were stored lots of things -
-Much more beer than wine, anyway!
-Right, how very English!
In Henry VIII's day, this WAS England, a last toe-hold on the continent.
Nearby Calais was at the heart of an English enclave,
a remnant of the former territory in Northern France, and the fort,
inspired by a cutting-edge Italian design, was intended to bolster their position.
Henry clearly planned to stay, he was even going to build a new port around the Cap.
To defend this harbour he needed a fort, but the harbour should never be made.
So they built the defences, but didn't build the thing the defences were here to defend?
That's right, yeah.
The English clung onto this coast for another 12 years,
before being finally booted back across the Channel.
One more spat in a barney that's rumbled on along this shore
between battling siblings either side of the sea.
Connections between Britain and France are the story of this coast,
links across the sea that we'll explore along our journey.
As well as clashing, we've been comfortable coming together, too.
In the 1920s, London's smart set would think nothing of hopping
on a plane to fly directly to the fashionable resort of Le Touquet.
There's a lot about this coastline to make us feel at home,
and at the bracing seaside town of Ault,
the weather isn't the only thing we've got in common.
Nick is getting to grips with foreign terrain which feels strangely familiar.
Think of a coastal landmark that symbolises Britain.
We write songs about them, we treat them as one of our national icons.
But think again.
Welcome to the White Cliffs of France.
I don't know if bluebirds fly over these white cliffs, but they do stretch for almost 150 miles.
They certainly look familiar, but is the similarity more than skin deep?
I'm meeting geologist Rory Mortimore.
He's a man who can tell if this chalk has the same fingerprint as the English cliffs.
Strangely, though, it's not the chalk itself that we're looking at, but what's embedded in it.
You see these black nodules?
These are lumps of flint,
-and this flint has formed around animal burrows into the seabed.
But what is fantastic about the way that the flint forms
is that it's unique at every level in the chalk.
-So at this level you'll see they are tubular.
-Is that one there?
-That's the outside of a tube, there.
When you follow this across the whole of the English Channel area
where the chalk is present, you can identify this layer because of its tubular flint.
-And this sample is of the tubular flint which was collected on the Isle of Wight.
-Isn't that amazing?
So your bit of tubular flint from Southern England matches up this bit of tubular flint here?
It does indeed, matches perfectly.
Which means the chalk on both sides of the Channel was laid down at the same time.
In fact it's still there, under the sea.
For millions of years, we were all part of the same landmass.
There was no England or France, and certainly no Channel.
If you were here, say, 600,000 years ago, you'd have been able to walk
on chalk downland all the way from here to England.
-All the way across there?
-All the way across the Channel.
-The chalk downs ran from here, undulating, all across the South Downs?
Gow was the Channel formed?
By a cataclysmic geological event, Nick, a very spectacular event - what we call a megaflood.
That megaflood started as a trickle
through a chalk ridge that spanned the Channel.
This ridge was holding back a colossal lake, fed by melt water
from glaciers across Northern Europe, and soon to become the North Sea.
When the chalk gave way, it was catastrophic.
It must have been a very extraordinary event,
a very dramatic event, and would have happened in a very short space of time.
That would have isolated Britain from Europe for the very first time.
-And how deep is the Channel now?
-The Channel is surprisingly shallow.
This point is perhaps 30 metres deep.
If you were to imagine taking something like St Paul's Cathedral,
put it on the floor of the English Channel here, most of it would be sticking out.
It's a very shallow sea.
Our shores might be separated by the sea, but we share the same problem - erosion.
Dover's cliffs are crumbling, but because of the way the tides
course through the Channel, the situation here is even worse.
Almost half a metre a year of coast is lost to the sea.
In the town of Ault, they've been battling it for centuries.
Now, this photograph was taken just a few decades ago.
The building on the left here is that cream building down there,
and here is a very beautiful crazy golf course. But just look at this.
This is where the golf course was.
You can't actually fight this sort of erosion, so in Ault they've stopped trying.
Instead of building more sea defences they're going to build a new town,
or rather an extension to the existing one - 400 metres inland.
The primal forces that carved out the Channel are also eating up the coast.
We can't stop it so, like the French, we'll have to learn to live with it.
Just as the elemental forces batter this coast, they can also be strangely uplifting.
In Dieppe, they positively revel in the brisk sea breezes.
And they celebrate them with colourful paper and steel,
canvas and string.
The city's kite festival happens every two years, and thousands turn up to join in.
While most are happy to keep their feet on the ground,
others look to their kites for a thrill - a jump-start, even.
My name is Pierre Cardineaud. I'm the world champion kite jumper.
You look good for a few seconds.
83 metres is the world record,
and over nine metres in height.
There is not enough wind to do a big jump. You can do freestyle,
for example two or three...twists.
It's not to fly, really.
It is a little fly on the jump,
like a fish in the sky or like a bird who is going to... Just a small jump.
20, 30 metres later along...
It is that that I love.
The French know a thing or two about revolutions,
and this coast started one that spread around the globe.
Amateur artist Alice Roberts has packed her paints, heading
for Etretat to explore how this shoreline made a lasting impression on the world of art.
The place I'm looking for is just down here.
Even though I've never been here before, I feel like I know this
particular spot in Normandy very well - from paintings I studied back in school.
And this is what I've been looking for.
La Porte d'Aval. It's been described as an elephant dunking its trunk in the sea.
It's one of the most photographed sites in France, and one of the most painted.
And it's this painting that's brought me here, Cliffs of Etretat, 1883
by Claude Monet, the father of Impressionism.
Impressionist painting was a revolutionary way of capturing colour and light on canvas,
and it all started here on this coastline around 135 years ago.
Unlike many artists of the day, the Impressionists shunned
the comfort of the studio and worked outdoors to experience the elements.
Photography was becoming popular, but these artists were trying
to capture light in a different way, experimenting with oil painting.
I want to see what it is about Normandy that inspired the Impressionists,
and I'm hoping that British artist Rob Perry can help me.
For the last 15 years, Rob's been coming to France to paint.
-Hi, Alice. Nice to meet you.
-How are you?
'He's going to give me a hands-on introduction to Impressionism,
'but we've got to hurry.'
-Let's go for it.
-'It's late in the afternoon with the daylight fading fast.'
Monet worked in the moment with nature's changing moods.
He'd cope in all conditions, maybe even nursing a cold, like me.
-Setting up our easels outside, this is exactly how the Impressionists painted, isn't it?
They were able to do it, of course,
because of the invention of the tube for oil paints.
They didn't have to mix them up with pestles and mortars
like they had in previous centuries.
-So new technology freed them to go outside?
Rob, I really want to get the texture of the sea.
-That is the rocks we're looking at, and I love this sea.
The Impressionists loved to get this kind of vibrant paint surface,
-made of flecks of different colours.
-And this is going to change as we paint it, isn't it?
You've got to work fairly quickly when you're working on the spot.
Monet always worked in very broad touches, you see.
They used these short stabbing brushstrokes, you know?
You hold it like an axe, really.
OK, that's a good tip.
The Impressionists broke with many conventions of the day.
They'd rarely start a painting with an outline sketch -
instead they put colour straight onto the canvas, freehand.
It makes me nervous working this quickly.
-We've got 20 minutes.
They didn't believe in mixing colours on the palette.
They applied it pure, as it came out of the tube.
Hmm... 'I'm beginning to see the challenge of Impressionist painting.'
I simply can't work fast enough to get all these changes of light onto the canvas, and before we know it
the light's gone altogether.
We'll have to give it another try tomorrow.
But before we do, I want to visit the place that first inspired this new artistic movement -
the bustling harbour town of Le Havre.
Monet grew up around here,
and in 1872, he painted this view of the harbour at dawn.
He called it Impression Sunrise, and so coined the term for a completely
new way of looking at the world - Impressionism.
I'm hoping French art historian Emanuelle Riand can tell me more.
So this is the really famous painting, isn't it?
Yes, the first Impressionist painting. It can be said,
he did it from his window,
it was his direct view on the harbour.
And was it well received at the time?
No, because it was very different.
It was probably not...
well drawn enough for them, and too much coloured.
It was very shocking for this time.
What's shocking for me is the speed at which Monet painted.
In one session, he could work on 10 canvases,
and I struggled with one in an afternoon.
I'm determined to have another go.
So the first challenge here is to put this easel up in this wind,
so I've hung a bag with some heavy pebbles in it off the easel.
Now I've just got to choose some colours.
It's still quite grey, so I'm going to have to get my Impressionist eye working.
And in those greys I think I can see some purples in that cliff,
maybe some yellow colours.
Let's have a splurge of that one.
Rob's painting as well, but in his own style.
Although he works outdoors, he isn't exactly an Impressionist as Monet would have recognised.
It's still nerve-wracking.
He's getting the colour onto the canvas as quickly as possible,
but I'm sticking to the Impressionist rules - separate strokes to create an impression of colour.
It's just mad, cos the light changes all the time as well.
You're here for three hours and you pick the bits that you like.
You wait for the sky to change, and you think, "Oh, I like that."
-What do you think, Rob?
-You've got some really nice colour in there.
That's exactly what the Impressionists were after. The sky has come out very well.
I think I'm most pleased with the sky.
I really struggled with the sea.
And it's that elusive quality of light in the sea and the sky
that must have so fascinated the Impressionists,
drawing them back to this coast time and time again.
At Le Havre, a huge gash opens up in the coast.
This is where the sea meets one of the world's mightiest rivers -
A great river demands a great bridge,
and the Pont de Normandie rises to the occasion.
Seven years in the making,
184 steel cables suspend the road over the river.
That's the left bank of the River Seine down there.
Travel about 120 miles in that direction
and you arrive in the famous artistic district of Paris.
But there's another little artistic gem on the left bank of the Seine.
In Honfleur, even the boat builders have an artistic flair.
Their craft helped see off the English
during the Hundred Years War.
When peace was finally declared,
the boat builders of Honfleur used their skills to build a church,
a wooden church.
Started in the 1460s,
its roof reflects its maritime heritage...
..Looking like the upturned hull of a ship.
Oddly, the bell tower is built separately,
maybe to protect the wooden church against lightning strikes,
or perhaps the vibration of the bells. No-one's quite sure.
Honfleur has witnessed a steady stream of traffic
crossing the Channel for centuries.
But in 1066, thanks to William the Conqueror,
it was all heading in our direction.
Invasion came as second nature to these Normans.
After all, originally they were Norsemen,
Viking marauders who'd only been in France 150 years
before they turned their sights on us.
But they left a permanent legacy in stone.
The Normans taught us their tradition of castle construction,
bringing it to Britain.
Among their first big builds, the Tower of London,
and Canterbury Cathedral, and they built them with French stone.
In the heart of Normandy, Mark Horton is on his way
to the city of Caen
in search of that special stone worthy of William's English castles.
In the years after 1066,
the River Orme, that connects Caen to the sea,
would be busy with Norman longboats like this,
transporting great blocks of stone to Britain for building.
Medieval castle expert Pamela Marshall and I are retracing the route to try and discover why.
Caen stone is one of the best.
And I know it seems a long way from England, but he's got this waterway.
He then just whips it across the sea across the Thames, and it's a material that his craftsmen
are well-versed with, they know how to use it.
And he presumably thinks the Anglo Saxon masons are rubbish, anyway?
Possibly. Remember, the Anglo Saxons aren't used to castles at all,
let alone stone ones.
William not only had a mighty river to transport the stone,
but at Caen, he had a ready supply, right beneath his feet.
The city was built on limestone,
a rare limestone containing very few fossils.
Having used it for castles and cathedrals here,
William was determined to bring it to England.
Hidden beneath the streets of modern Caen, there's still a labyrinth
of ancient stone quarries, abandoned since the Middle Ages.
We've come to one tucked away in a quiet corner of the city.
It's only accessible, we're told, because the roof collapsed,
creating a makeshift entrance.
Inside, it's as if the workers had left yesterday.
Look at this, that's where the chariot, the wagon has...
-The wagon has brushed past it!
-Has brushed past it.
Oh, these are fantastic. To split the rock away,
they cut out a wedge shape with chisels
and then insert a dry wooden wedge, which they then wet.
And as the wood expands, it helps the rock to split naturally.
It's extraordinary, it's like a frozen moment in time.
But what was it about the stone that made it so special?
Worth hauling across the Channel?
Who better to ask than a group of modern Norman masons?
Jean Pierre Dauxerre, a former city planner, is passionate about Caen stone.
It's a stone we like to stroke with eyes, with hands.
-Is it possible to break it open?
-Yes, it is.
-Here we go.
-Do it slow. Slowly.
-Give it some welly, shall we? Hey!
-Voila, you are strong.
-I know! Isn't that amazing?!
-Just a few pieces like this, and look what happens.
-It's your work.
There are no fossils or anything in it.
It's the colour of churches, castles.
But the stone now is so soft, just falls apart in one's hands.
Stone becomes hard because water...goes away.
-Evaporates from it.
The stone is quite soft when extracted,
easy to split or cut using even the most basic tools.
And the longer it's exposed to the air, the tougher it gets.
That's completely exhausting!
And without shells or fossils to make it fracture unpredictably,
it can also be finely worked,
which is why it was highly-prized amongst Medieval masons.
The Normans helped shape Britain,
they laid the foundations for some of our greatest buildings.
Although these structures have been extended since,
there's a little bit of Normandy left in most of them.
This is a coast that has known invading armies depart and arrive.
The tranquil stretches of sand give few clues to the turbulent role they played in our recent history.
But on the 6th June 1944,
156,000 Allied servicemen landed here.
These are the D-Day beaches.
This wasn't the most obvious or the easiest place to launch
a massive invasion of mainland Europe,
which is precisely why these beaches were chosen.
The most obvious place to unload tanks and heavy equipment
was somewhere built for the job, a port like Dieppe.
But when the Allies did try to land here in 1942, it ended in disaster.
The Germans had fortified the place.
Canadian and British forces lost over 3,000 men.
It was clear that for a successful invasion,
the Allies would have to arrive where the Germans didn't expect them.
But the British knew the terrible price of trying to fight their way off a beach.
During the First World War, the Allies had attempted to land on the beaches of Gallipoli in Turkey.
Over 100,000 men were killed or wounded
before the mission was abandoned, and a generation of soldiers learned to fear landings on sand.
Former army engineer Dick Strawbridge is exploring
how the Allies prepared for the biggest seaborne assault in history.
The D-Day planners were haunted by the disaster of Gallipoli,
but the beach invasion they were planning would dwarf that operation.
The aim this time was to overwhelm the enemy at high speed,
using tanks and other armoured vehicles,
but the Allies' worry was that they'd get bogged down.
Even with some ruts on the sand, the old half-track is getting through there all right.
So rough-packed sand isn't a big problem.
It wasn't necessarily the sand they were worried about,
it was what was underneath it that the Allies were concerned about.
This whole area is riddled with soft, sticky peat bogs
lurking below the surface.
The sand may appear very smooth, able to support the vehicle's weight, or even mine.
OK, feels nice and solid.
But dig a little deeper and it's a different story.
What have we got? Oh, it's a different colour, completely different colour.
That's a peat bog, being an Ulsterman, I should know about those things.
That is peat, which mean there's definitely no way you'd bring your vehicles over this bit.
There's an awful lot to do to cover this beach.
These peat bogs are the remains of ancient forests submerged when the Channel flooded.
From the air, it's possible to see them as dark patches.
What you can't see are the ones underneath the sand.
Trials on similar beaches in Norfolk had shown that peat had the potential
to bring the invasion to a grinding halt.
Allied intelligence had to identify these areas,
and they had to do so without alerting the Germans.
They used any information they could get their hands on -
old holiday snaps, ancient maps, medieval accounts -
to build a picture of the terrain that lay beneath the surface.
This is what it was all about,
a map of the potential hazards of this beach that was codenamed Gold by the Allies.
Look here, it's dated March 1944.
On the top it says "BIGOT", that's a classification beyond Top Secret used especially for D-Day.
You can see areas here where there's possibly pools that are clay, and they move and change shape,
but the details here, people have made this really accurately.
If you're going to attack this beach,
you need to understand where not to be.
This sort of detail couldn't be gathered from a distance.
Someone had to get onto the beach itself and take samples of the sand,
right in front of the Germans.
At just 23 years old, Major Logan Scott-Bowden found himself leading this vital mission.
He and fellow Royal Engineer Sergeant Bruce Ogden-Smith would be
the first troops to land here, unsupported and six months ahead of D-Day.
These days, it's difficult for Major General Scott-Bowden to travel,
so I've come to see him.
-Sir, lovely to meet you.
-Very nice to see you, Dick.
But first, a small gift from the beaches of Normandy.
What do you think of that?
Ha! Well, I never!
Sand, and the peat layer, just below the sand.
-Does that bring back memories?
Yes, it does indeed.
Major General Scott-Bowden collected his sand sample drilling with a metal auger like I did,
but he had to swim ashore with his at night
and take the samples from within feet of enemy patrols.
The mission was timed for the stroke of midnight, New Year's Eve 1943,
on orders from the highest authority.
Churchill said, "Well, they'll all be celebrating on New Year's Eve,
"they won't be patrolling very much.
"It's a good opportunity."
We were doing the job on a rising tide,
which would obscure our tracks,
but of course one thing we hadn't reckoned on was the time difference.
They were an hour ahead of us and these Germans were clearly...
well on in their New Year celebrations,
so we didn't expect any trouble from them.
But strong tides and unexpected gale force winds
swept the two soldiers a mile from where they were supposed to land.
There was a low search light. Every time the search light came down,
came round, we had to flatten ourselves so it wouldn't pick us up.
We gradually recovered the mile we'd lost.
We loaded the samples into these containers, into each other's containers,
and then we tried to swim out.
And Bruce Ogden-Smith started yelling, so I had to swim slightly back to him.
I said, "What's up?", and he was yelling, "Happy New Year!"
I said, "Swim, you B, or we'll be back on the beach!"
They were elated from the mission, but it was only the first.
A fortnight later they risked it all again to collect more samples,
which confirmed for the D-Day planners the safest places to land.
The invasion was a huge gamble, but thanks to two Royal Engineers,
the Allies knew they wouldn't be fighting the terrain when they hit the beach.
The Germans had also been busy preparing for invasion.
In 1942, Hitler commissioned around 15,000 concrete fortifications
to guard the coast from Norway to Spain, the so-called Atlantic Wall.
Ultimately, it offered little protection,
but the Atlantic Wall remains the most visible reminder of Hitler's presence in this part of Europe.
By contrast there's not so much to mark the Allies' impact on this coast,
except here at Arromanches.
These are the stranded pontoons of the Mulberry Harbour,
the artificial port floated across the Channel by the Allies.
Following D-Day, this is how they landed all the hardware needed
to support the advance through France.
Now the pieces are part of the landscape.
On the beaches and dunes of coastal Normandy,
the remnants of conflict are being colonised by nature.
Miranda Krestovnikoff is looking for signs of life in the debris of war.
They don't seem terribly hospitable, but these abandoned fortifications
attract swarms of visitors each year - tiny, winged visitors.
They're the favourite hang-out of what the locals here call
chauve-souris - literally, bald mice.
That's bats, to you and me.
And this old munitions store has become a particularly popular party spot for the tiny creatures.
So much so that naturalists from the group Mamalogique Normand
are using the location to capture and record details of hundreds of bats.
Working with the French scientists is Shirley Thompson from the UK Bat Conservation Trust.
I have to say, if I was a bat it looks a good place to live, doesn't it?
It certainly does, very out of the way.
Why do they like it here? Why do they roost here?
it's cool because, of course, it goes right in,
it's very stable and it's damp.
It's such an attractive environment, that it's become the focus for a rarely seen event.
Bats are notoriously shy and they hibernate during the winter, which makes them pretty difficult to see.
But for a short time during the autumn they do something quite remarkable - they swarm.
It's believed to be part of the mating behaviour and hundreds of bats can take part.
For the French scientists, it's an opportunity to gather a huge amount
of data on these secretive creatures to use in future conservation work.
Now, it's going to be pretty tricky to spot bats approaching at night.
Wow! That one nearly hit me, did you see?
But Shirley has a secret weapon - a bat detector.
We use a torch of light to go out in the dark, they use a torch of sound.
They send out lots of little shouts, listen for the echoes that come back
if those shouts hit anything, but they're very, very high shouts
and a bat detector takes them in, makes the pitch lower,
plays them out so that we can hear them.
BAT DETECTOR CLICKS
-Fantastic, because we can't see them at all, but we can...
So this is a really useful early warning device because even if we can't see them,
-we can actually hear them.
-That's right, yes.
BAT DETECTOR CLICKS
As we hear more and more bats arrive, it's possible for me to see them using an infrared camera.
Fantastic, and with the echolocation they can detect the fact that there's a net there,
and what's very interesting is that I've got quite a few flying in
over the top of the arch, right over the top of the net.
I think I've got two in the net,
and the ones that are in the net seem to be...
almost attracting other bats in.
There's certainly quite a lot of activity now.
Handling bats is highly specialised, and the naturalists have to be licensed to do it.
But it's a chance to get up close to these remarkable animals.
The Pipistrelle is native to Normandy as well as our own shores.
I think if people actually got up close and personal with bats
they wouldn't be scared of them, people are very scared of bats.
And you see, another problem is that they always look as if they're cross
with their mouths open, but that's because it's shouting.
It's echolocating, it's looking at you with its ears as well as its eyes.
Some bats will fly more than 30 miles to join a swarm,
and the naturalists tonight have identified seven different species...
..including the distinctive Natterer's bat.
See its ears?
It's got a little twist on the top,
and these have such a fine wing membrane, can you see that?
-Very fine membrane.
It's beautiful. This is the best bit, isn't it?
They've been processed, they're absolutely unharmed, unfazed by the whole thing.
Five minutes later you're releasing them.
They've gone to tell their friends.
Let me just turn this on and see if we can hear him.
Off he goes. Go on. Oh, magic!
Out of the dark and into the light.
The coast of France, like, Britain is ringed with lighthouses,
their beams often crossing those of their counterparts across the Channel.
The technology that made it possible came from Normandy,
and it's lit up coasts around the world.
At Gatteville, Dick is finding out how lighthouses were made...
In the 1820s, the French government started to build lots of lighthouses,
but it wasn't just to impress the neighbours.
After years of war with Britain,
the Channel was open for business again.
It became an issue of national interest to keep shipping safe.
The plan was to have every stretch of coast lit up by a lighthouse.
It would have meant building hundreds of oil-burning beacons
if it hadn't been for one local genius called Augustin Fresnel.
He found a way of seriously stepping up their brightness
by using a super efficient lens,
the Fresnel lens.
This one at Gatteville focuses the light so efficiently it can be seen 30 miles out to sea.
It's a big torch, and all that's been done with a 1600 watt bulb.
That's the equivalent of half the energy you use to boil a kettle.
A mathematician and physicist, Fresnel came up with the idea
of a lens made up of circular prisms of glass,
but why didn't he just use a super-sized ordinary lens?
Physicist Jonathan Hare has been looking into Fresnel's invention.
Good to see you, mate. How you doing?
OK, Jonathan, how can we don't use an ordinary shaped lens?
The main problem is that they're so big and bulky.
If you look at a standard lens,
-and then scale this up...
-It's going to get really fat and heavy, isn't it?
It's going to weigh a ton, and be really thick,
which will absorb a lot of the light.
There's a better way of doing it.
If you imagine this is a cross-section of a lens, what Fresnel did,
which was very clever, he realised that it was this curved surface here
which makes it act like a lens.
So he thought, "I'll just take this curved part of the lens and cut that out."
I can show you on here. You can see the bits that I've marked on here.
So if we cut these out and bring them back, we get a very peculiar shape.
-Did you make that yourself?
-You've got your own Fresnel lens!
-Yeah, out of plastic.
I cut it up and polished it, and it is a peculiar looking shape, it's much lighter now.
Oh, yeah, compare that. A significant difference there.
But it is the same lens.
We've taken take this bit here, and cut that off,
and taken these bits here and put that on.
We've taken these bits here and cut that off, and same again,
same again there, and put them all on the one small lens.
-All the important bits are there.
-Does it work?
OK, so here's a standard lens.
The lens is basically focused to a point, and you can see
that it bends the light, just like a lens.
We know that works, cos it's the right shape.
I'll show you how the Fresnel lens works.
We hold that in place, and it should give exactly the same effect as the big one did.
Exactly the same properties.
It's got the same properties.
-And it behaves the same way?
-Exactly the same.
So here's a commercial one, which is a much finer one, but basically it's made of rings.
You can see the rings on it, can you see that?
everybody thinks it's a magnifying glass for reading or
looking at cars, but we know we can do something different.
-If I hold that there, you can capture the rays of the sun.
-That doesn't take very long.
-It is actually a really efficient lens, but look it's as thick as a piece of card.
The focusing power of the lens means it has to be kept moving during
the day to prevent the sun's rays burning out the bulb.
-We can't go in, the mechanism floats on a bed of mercury.
-And that's not nice.
Mercury vapour is not on. But as you see, it must be really efficient.
See that tiny nylon gear that's making it all move?
-It's so perfectly balanced.
It raises the question, why aren't there more Fresnel lenses, because those are great?
Well, the thing is, you wouldn't want them on a camera lens,
because each of the rings of lenses distorts the image.
They're absolutely great for shining out a beam of light, but if you try to use this in a camera...
-It could be an interesting effect, the old Fresnel lens effect.
This lightweight lens, invented in Normandy nearly 200 years ago,
is still lighting the way for ships around the world.
Coastal nations are united by the joy of being beside the sea.
Some Brits, though, are so enamoured of the French and their coast, they've made their home here.
For one English ex-pat, the wide open beaches of Normandy have an irresistible pull.
My name's Sam Delorme, I moved over from England 11 years ago.
I work with steeplechasers and cross-country horses,
but today I've come down to the beach to see a good friend of mine,
Franc de la Noe, train his trotters.
The discipline is called harness racing, it's a very popular sport over here.
In England, I think you're starting to get to know it,
but over here it's very, very big,
and he's very ready to go.
He's gonna to be racing Sunday, so this is going to be one of his important work-outs for that race.
To see a horse rolling after a work-out,
it means he's calm, he's enjoyed himself.
To get them away from the routine, they're like us, it's good for them.
So if they're feeling good, it shows in their racing afterwards.
At this point in our journey, the British Isles are once again within touching distance of France.
At their closest the Channel Islands are only ten miles from the Normandy coast,
but for 800 years they've been loyal to the Crown of England...
well, most of them!
Nick is on a voyage to the French Channel Islands.
It's not often you get a chance to visit a land that magically
emerges from the waves, but that's what Jersey skipper Chris Fairburn
has promised I'll see at the Iles Chausey, the French-owned Channel Islands.
He's made the trip many times, but before we arrive,
there's a small ceremony to perform.
We don't have to hum the Marseillaise if you don't want to.
Would it be a problem for the French if you didn't raise the tricolour?
They have been known to fine people if they don't have the courtesy flag flying.
You mean, there's real tension on...
No, that's just customs men in France finding something to do in a day!
Or maybe they're just keen to remind foreign sailors that
the Chausey Islands are part of France, albeit a very small part.
Compared with the likes of Jersey and Guernsey, the Iles Chausey are tiny.
But as you get closer, they begin to reveal their secrets.
This is a nautical obstacle course.
One wrong turn and you run onto the rocks.
There are islands absolutely everywhere.
The largest is also the only one that's inhabited.
With a native population of about 30, this is the audaciously named Grande Isle, The Big Island.
It's only a mile and a half long, there are no Tarmac roads,
there are no cars or buses and even bikes are banned. Suits me.
I've been told island life revolves around an old fort.
It was built by Napoleon III to defend against a British invasion which never came.
Chausey historian Gilbert Hurel has agreed to show me around.
So, Napoleon built this enormous fort to keep out the English,
but why didn't the English get their hands on the Chausey Islands in the first place?
There was no strategic interest.
It was too small, no shelter for boats, and too close to the French mainland.
This fort was built for nothing,
never been used for military reasons. Now fishermen live in it.
It's quite a sight because you come in from the outside expecting a kind of sense of
military order, and what we have is the most picturesque jumble of fishing paraphernalia everywhere.
It's a wonderful sight.
It's now home to most of the islanders,
out at their day jobs fishing for lobster and shrimp.
Gilbert has offered to help me catch up with one of them.
I've noticed you never look at a map, you don't have any charts...
No, but I know the place by heart.
Here is Freddo coming.
Oh, I see, a little dory like yours.
Frederic LaGronde - Freddo, as everybody knows him -
has been living and fishing on the island for almost 50 years.
-So he's been fishing shrimps, which is a local speciality...
Freddo, is this a good catch?
THEY SPEAK FRENCH
"It's not bad at all."
And when he says it's not bad, it means it's rather good.
He is Norman, you know.
It's a very Norman thing, Gilbert tells me, not to be overly enthusiastic,
and it seems even the islands share this modesty,
until the tide goes out.
This part of France has one of the largest tidal ranges in the world.
The water drops a staggering 14 metres to reveal miles of sandbanks.
This is absolutely incredible, I had no idea
that there was such a huge landmass lurking beneath the waves.
That's where the heart of Chausey beats.
You'd never think, as you come across the top of this bit of the ocean
in a boat, that there's a secret world down here on the seabed
-that you can walk on at low tide.
-You can walk on the seabed, really.
When the tide goes out, the Chausey Islands are an incredible 60 times bigger.
And they still have one more surprise...
..a deserted quarry.
Here's a huge block that has been split,
but they've just abandoned the stone.
Islanders quarried granite here for generations, when the easiest way to transport the heavy stone was by sea.
And it's the route those original quarry ships must have followed that leads us away from Chausey,
because their precious stone cargo helped to build one of France's most distinctive landmarks...
..the monastery at Mont-St-Michel.
Benedictine monks started building here in the 8th Century.
The mount itself was created by the tides,
endlessly striping away the soft earth, leaving hard granite behind,
and looking, for all the world,
as if it was placed there by an unseen hand.
The same tides that submerged the Chausey Islands daily flood through here.
It's not surprising that the monks thought that something supernatural was going on.
But I've more earthly concerns on my mind, like what I'm having for my tea.
I'm on my way out to a farm, but it's a farm unlike any other.
For a start, you can only get to it in amphibious craft.
Here they grow a famous French foodstuff - moules - mussels.
These wooden stakes, called bouchots, are seeded with coiled ropes of young mussels,
and then they're simply left out here to grow.
Mussels wouldn't live long exposed to the air like this,
but the farmers here have learnt to exploit the huge rise and fall of the tide.
When the sea is out they're easy to pick off.
In a few hours they'll all be submerged, so they have to work quickly.
This is just astonishing.
For some reason, I'd imagined that French mussel harvesting would
involved women with wicker baskets wading into the sea with rakes,
but it's anything but.
It's this hydraulic hand that just goes down over the wooden stake
and so easily scoops up the rope of mussels.
It's brilliant, but it's not quite as romantic as I'd hoped.
Alain Chevalier's family have been growing mussels for generations.
OK, give me one.
There's a reason why they cook these things, you know?
Every stretch of coast is unique, like a personality.
But like people, coastlines can have a great deal in common.
In some ways, it feels as if we and the French share the same shore.
And here, at the end of our journey, is one more thing we share with
the French - the monks who built this also did a spot of construction work
on the English coast.
And this is where they built a church - St Michael's Mount, on the Cornish coast.
Next time, we travel from the granite of Cornwall
to the sand of South Wales.
There's a sword...
Wow! Look at that.
I'm clinging onto everything.
If you want to know more about our coast, the Open University
has produced a booklet with ideas and information to inspire you.
For a free copy or to find out more about Open University programmes
on the BBC...
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