Ben Franklin's Balloons

PBS Airdate: October 22, 2014

NARRATOR: It was the first human flight. One-hundred-twenty years before the Wright brothers, a pair of 18th-century French brothers built a series of hot air balloons and took a great leap into the unknown.

TOM CROUCH (Smithsonian National Air and Space Museum): They knew that if you climbed to the top of the mountain, there was still air to breathe, but they weren't sure that if you get a few hundred feet above the surface of the earth, there would still be air to breathe, up there.

NARRATOR: Incredibly, the historic flight that first took a pair of brave voyagers 3,000 feet into the sky might have gone unnoticed in the English-speaking world, if not for an eye-witness account, written by America's first scientific genius, Benjamin Franklin.

BENJAMIN FRANKLIN (Scientist/From His Writings): And presently the Globe was seen to rise. It diminished in Apparent Magnitude as it rose, till it enter'd the Clouds.

NARRATOR: Now, a team of experts, including a direct descendant of the inventors of the hot air balloon, is attempting to build a replica.

JEAN-CLAUDE RAGARU (Historian): Here we have an extremely oversimplified drawing, in effect, "If you make this balloon here, you won't have any problems."

NARRATOR: They hope to recreate that historic flight in a flammable paper and cotton balloon, dangerously powered by an open fire.

TOM CROUCH: They had sponges on long sticks, so that they could, kind of, dab burning spots inside the balloon.

NARRATOR: What was it like to leave Earth for the very first time?

MERCEDES TARAVILLO (Balloon Builder): "It's magic, because you can't see how it works. It must be magic! How can it rise into the air?"

NARRATOR: Relive Ben Franklin's Balloons, right now, on NOVA.

A spring morning in central France: working in the pre-dawn gloom, a team of experts assembles an enormous flying machine. There's been nothing quite like it for 230 years.

MERCEDES TARAVILLO: Careful! There are a lot of hanging parts everywhere.

NARRATOR: In the next several hours, they will attempt to recreate one of the most important achievements in the history of technology: the first human flight.

Over the course of nearly two years, this team has spent countless hours researching, experimenting and struggling to rebuild the first flying machine.

According to eyewitnesses, the original version took two daring Frenchmen on a 25-minute flight, 3,000 feet into the air and changed the world.

TOM CROUCH: No human being had ever made a free flight. That was the first time. They had no idea what was going to happen.

NARRATOR: Now they are about to recreate that historic moment in this untested replica.

In the 18th century, the stakes were high, and even today, the risks are significant. Carefully, they set a brazier full of straw alight, watching anxiously, as the giant structure fills with smoke and flame.

If all goes as planned, they hope to find answers to questions that have fascinated historians for centuries: How dangerous was that first flight more than 200 years ago? How high could the balloon carry them? How far could it travel? And how did those inexperienced pilots somehow manage to guide it and themselves safely back to Earth?

The story of the first human flight begins in Annonay, France, with two brothers, Joseph and Etienne Montgolfier. The Montgolfier family owned a large and highly successful papermaking enterprise.

Joseph, 12th of 16 children, was a born inventor, a dreamer who chafed at the demands of the family business. His younger brother Etienne was the more practical-minded of the two. He had trained in Paris as an architect and was a skilled mathematician. Together, they formed a brilliant team.

In France, the Montgolfier brothers are as famous as the Wright brothers are in the U.S. Thanks to their pioneering creations, in less than two years, beginning in 1783, earthbound humanity discovered how to rise thousands of feet in the air, traverse miles of countryside and, incredibly, fly across the English Channel.

According to Montgolfier family history, it all began with a lucky bit of laundry, left to dry in a fireplace.

Legend has it that Joseph Montgolfier noticed his wife's blouse inflate with hot air and rise, "sparking" the idea for a flying machine. Even so, he failed to grasp why the shirt rose. Not understanding that heat causes air to expand and rise, he mistakenly believed that he had discovered a new substance in the smoke that was lighter than air.

It's not as crazy as it sounds. Scientists had recently discovered that air is actually a mixture of many different gases.

TOM CROUCH: In the 18th century, they were fascinated by the chemistry of the atmosphere, and they began to tease the first constituent gases out of the air.

NARRATOR: By 1776, carbon dioxide, nitrogen and oxygen had all been discovered, as well as hydrogen, an explosive gas that was known to be lighter than air.

So, why not assume that smoke contained yet another type of gas, also lighter than air? The brothers proudly dubbed their so-called discovery, "Montgolfier gas."

GUILLAUME DE MONTGOLFIER (Descendent of the Montgolfier brothers): For my family it represented a huge change. It was a big turning point—in their lives and in their business—that took place on that winter eve, in front of the fireplace.

NARRATOR: Now, Guillaume de Montgolfier, a direct descendant, along with an experienced balloon builder and a team of historians have set out to retrace the steps that led to the groundbreaking first human flight.

The Montgolfier brothers' first experiments took place here, in the winter of 1782. Etienne spent his days running the family's papermaking business, so when the brothers began building the world's first hot air balloons, their first creations were made out of paper.

In the village of Annonay, the appearance of these mysterious objects in the sky sparked talk of witchcraft. To dispel such fears, the brothers decided to stage a spectacular demonstration.

The first public flight of an unmanned hot air balloon took place in a field near the village square. It's a flight that is commemorated each year by some of today's townspeople, among them, many Montgolfier descendants.

The date was June 4th, 1783. Unlike this synthetic reproduction, that first balloon was made of cotton, lined with paper. It was a simple machine, with no gondola.

But at 35 feet in diameter, it was much larger than any of their previous balloons. With a huge crowd in attendance, the Montgolfiers lit a straw fire and slid the firebox under the balloon. When it was fully inflated, the two brothers released the ropes and the balloon rose into the air.

The Montgolfier's balloon soared to an altitude of 6,000 feet in a mere 10 minutes and drifted for nearly two miles. The audience watched in awe: amazed that these two men had made something that could fly.

News of the incredible flight quickly reaches Paris, catching the attention of one of the most renowned thinkers of the day, Benjamin Franklin, who was stationed there and charged with conducting peace talks with the British.

The French revered Franklin for his experiments with electricity and other natural phenomena. He, in turn, was fascinated by recent European discoveries in physics and chemistry, and he took great interest in the astonishing new technology of balloon flight.

MI GYUNG KIM (North Carolina State University): He was a scientific celebrity in Paris. Franklin was very excited about the experiment, because the balloon was impossible to avoid. It's this large object that floats. It caught everybody's attention, as did it Franklin's.

NARRATOR: The French scientific community was equally excited by news of the flight, including a close friend of Franklin's, Jacques Charles. A gifted experimentalist, Charles decided to duplicate the flight by making his own balloon.

TOM CROUCH: He was such a great, sort of, scientific showman. Even Franklin, who came to watch his demonstrations, said that when it came to Jacques Charles, nature could not say no to him.

NARRATOR: But in a providential twist of fate, Charles didn't get the whole story behind the Annonay flight. Apparently, no one had told him that fire had played a key role in the balloon's ascent, so he assumed that the Montgolfiers had filled their balloon with the only known lightweight gas, hydrogen.

Thinking he was merely duplicating the Montgolfier breakthrough, Charles set out to make the world's first hydrogen balloon. He calculated that he required over a thousand cubic feet of hydrogen, a huge quantity for the time. To produce it, he placed a thousand pounds of iron shavings in a closed container, then added 500 pounds of deadly sulfuric acid, also known as "oil of vitriol."

The energetic reaction caused the iron atoms to combine with the sulfur and oxygen in the acid, creating a residue of iron sulfate and liberating lightweight hydrogen atoms, a potential fire risk.

TOM CROUCH: It certainly was dangerous to produce hydrogen. The thing steamed and bubbled. You could hear it making noises, and it got hugely hot. And that's a problem, because you're generating hydrogen.

NARRATOR: Most of what we know about Charles' experiments comes from letters written by Benjamin Franklin to British naturalist Sir Joseph Banks. Preserved at the Royal Society of London, one offers a vivid glimpse of Charles' first balloon flight.

BENJAMIN FRANKLIN (From A Letter to Sir Joseph Banks): And presently the Globe was seen to rise. A little Rain had wet it, so that it shone, and made an agreeable Appearance. It diminished in Apparent Magnitude as it rose, till it enter'd the Clouds, when it seem'd to me scarce bigger than an Orange. I thought it my Duty, Sir, to send an early Account of this extraordinary Fact."

TOM CROUCH: Franklin wants to make sure that, again, his English colleagues, who have never seen anything like this, get a notion of what it looked like and felt like and even sounded like.

NARRATOR: The balloon traveled more than 15 miles, much farther than the Montgolfiers' hot air balloon, before landing in the village of Gonesse, where it caused a panic among terrified peasants.

TOM CROUCH: When a balloon is on the ground, you know, it's not just laying there. The hydrogen inside is sort of moving around, and the balloon is kind of moving, and it had fallen down in the middle of a group of peasants who were frightened by it. So they attacked it with scythes and flails. And, once they destroyed it, they tied it to the tail of a horse and pulled it, in triumph, through the streets of Gonesse. So the world's first hydrogen balloon came to a sad, sad end.

NARRATOR: While Charles conducted his experiments, the Montgolfiers were becoming increasingly famous. Fascinated by accounts of the first flight in Annonay, Louis XVI had invited the Montgolfiers to his court.

MI GYUNG KIM: The King was fascinated by the possibility of flight in the air, so he really wanted to see the invention.

NARRATOR: For Etienne Montgolfier, the King's curiosity represents a vital opportunity.

TOM CROUCH: So the next thing that's going to happen, you know, you've flown a small balloon in Annonay, now you've flown a small gas balloon in Paris, obviously the next thing to do is to fly living creatures.

NARRATOR: But building a hot air balloon to carry a person is a daunting challenge. Their first balloon had only enough buoyancy to carry its own weight. Yet based on that early experiment, the Montgolfier brothers calculated the dimensions of an immense craft, capable of carrying two passengers aloft. But exactly how they built that machine has been lost to history.

So the team, Guillaume de Montgolfier, along with historian Jean-Claude Ragaru, and experienced balloon maker Mercedes Taravillo, will attempt to rediscover the past by building a replica.

They have very little to go on, aside from the clues contained in a cache of recently rediscovered letters, found in a tower at the Château de Brogieux, where the brothers conducted many of their early experiments.

There also exist many 18th-century engravings, based on eyewitness accounts, and fragments of Joseph Montgolfier's notebooks.

MERCEDES TARAVILLO: We would like to find some sketches if possible. That would be wonderful.

NARRATOR: The notebooks contain Joseph's calculations. A gifted, self-taught mathematician, he derived the relationship between the volume of the balloon envelope and the amount of weight it could lift, taking into account air temperature and other variables.

These centuries-old notes reveal the impressive size of the balloon, but no blueprint or remnants of the original craft have survived. Fortunately, Jean-Claude Ragaru knows of a drawing by Joseph Montgolfier, which gives a rough idea of the shape of the original.

JEAN-CLAUDE RAGARU: Here, we have an extremely oversimplified drawing, which sums it up. It resembles the hot air balloon we're going to make. In effect, "If you make this balloon here, you won't have any problems."

NARRATOR: The balloon that Etienne and Joseph Montgolfier set out to make was comprised of three simple volumes. The top of the balloon resembled a cone, the middle of the balloon a cylinder, and its base a truncated cone.

MARIE-HÉLÈNE REYNAUD (Museum of Annonay): Here you have the calculations where they evaluated the force necessary to make a balloon rise.

NARRATOR: One of Joseph's letters gives the team the last piece of information they need. He had determined, by experimentation, that a volume of 35 cubic feet of air, heated to 212 degrees Fahrenheit, with surrounding air at 60 degrees, could lift 10.5 ounces.

Based on his assumptions about the weight of the balloon and its passengers, Joseph calculated that it would have to be almost 75 feet high, and 50 feet in diameter.

The team sets out to recreate this huge machine, which has nearly the volume of an Olympic swimming pool.

But how to build it?

Written accounts say that the Montgolfier balloons were constructed in two layers, cotton fabric and paper, the material most readily available at the family paper factory. But nothing is known of the weight or quality of the paper they used.

To find out more, the team visits one of two French paper factories still operating in the 18th century fashion.

SYLVAIN PERAUDEAU (Paper Mill Director): What are your specific needs for the construction of the balloon?

MERCEDES TARAVILLO: To start with, it mustn't be too heavy. In addition, it must be extremely sturdy, as little porous as possible, and very light.

NARRATOR: The strength and weight of paper varies tremendously, depending on the manufacturing method. At the time of Etienne and Joseph, people would bring cast off cotton, linen and hemp to the paper mill.

SYLVAIN PERAUDEAU: Rag pickers picked old rags, sheets, ropes. Papermaking was one of the first recycling industries.

NARRATOR: These pieces of fabric are cut into small strips and placed in a vat to ferment and break down. Then the stamping hammers go to work. Gradually, the rags disintegrate, creating a watery slurry, full of tiny fibers.

The longer the pounding and refining time, the shorter and more delicate the paper fibers.

The consistency of the slurry determines the weight of the paper. Scooping the mixture onto a framed filter sets the shape and thickness. The sheets are piled, one-by-one, separated by pieces of fabric to prevent them from sticking.

Once the stack reaches a pre-determined height, based on the type of paper, it goes through a mechanical press, which squeezes out excess water. Afterwards, the sheaves are separated and brought to the drying room. Finally, a process called sizing determines the finish of the paper.

SYLVAIN PERAUDEAU: The 180 grams we have here give the paper flexibility. And we also have 120 grams, which is a bit thinner.

GUILLAUME DE MONTGOLFIER: There's not much difference between the two, and this thicker one would give us a bit of a safety margin.

NARRATOR: Following the advice of the workers at the mill, the team decides to use a paper that weighs 180 grams per square meter.

With her research complete and the paper selected, Mercedes begins construction.

Though she has made more than a hundred hot air balloons, the 18th century paper and fabric construction technique is completely unknown territory. So she builds a one-tenth scale model to help her understand how best to shape the 24 identical pieces, called "gores," that must all fit together.

MERCEDES TARAVILLO: A nice-sized balloon, with a capacity of 77,500 cubic feet, that's a big baby! And it's got an enormous amount of weight. The final balloon will be 800 kilograms!

NARRATOR: Tom Crouch, a curator with the National Air and Space Museum, has flown from Washington, D.C. to lend a hand with the construction.

To duplicate the balloon designed by Joseph Montgolfier, they begin with long strips of lightweight cotton as a foundation. Then they use an 18th-century glue recipe, made with crushed fish scales. It's expensive, smelly, and makes it a messy job to stick 2,500 paper strips to the cotton sheets.

TOM CROUCH: This is an honor.

MERCEDES TARAVILLO: Let's turn it.

NARRATOR: So little is known about the construction of the original balloon, they have no idea if the material they are creating will be either too heavy or too flimsy.

The work proceeds quickly. Volunteers take turns gluing more than a hundred pieces of paper to each piece of fabric.

TOM CROUCH: The main difficulties, clearly, are getting the paper fixed to the fabric. It will be very interesting to see what it's like when it's dry.

NARRATOR: But the next morning, the whole project has come unglued, literally.

MERCEDES TARAVILLO: Oh, boy.

GUILLAUME DE MONTGOLFIER: Okay. Well then, that didn't work.

MERCEDES TARAVILLO: It didn't stick.

NARRATOR: It's a major setback. The paper does not stick to the fabric at all.

GUILLAUME DE MONTGOLFIER: Yeah. This throws into question our ideas about making these strips. Back to the drawing board!

NARRATOR: The team decides to start all over, this time using a modern wallpaper glue.

BENJAMIN CLEYET-MARREL (Balloon Builder): Overall, it adheres, so that's a good sign. From a purely mechanical point of view, we realize that paper is going to be extremely heavy, but it'll do the job. It's airtight, and so if we put air inside, it'll stay there, and if we heat the air, it'll rise.

TOM CROUCH: It's finished! One panel, one gore, one section of the balloon is finished. Twenty-three more to go, vingt-trois to go!

It's a good beginning.

NARRATOR: But in September, 1783, the Montgolfiers are dealing with their own setback. King Louis decides that allowing a person to fly is just too risky.

MI GYUNG KIM: As much as Louis XVI wanted to see the balloon go up, he wanted to be seen as a kind, gentle kind of king, so he didn't want anybody to die.

NARRATOR: But Etienne hits upon an ingenious compromise: he will fly animals instead of humans.

On the morning of September 19th, in the gardens of the Château de Versailles, he provides a wicker cage, carrying a sheep, a rooster and a duck, which is then tied to the huge balloon.

JEAN-CLAUDE RAGARU: The experiment was comparable to the one led by the Americans, with a monkey, and the Russians, with a dog, when they explored unknown universes. In fact, these animals were the first air travelers.

NARRATOR: Even those early air passengers had to fight for legroom. But there was a very real fear that an animal might not survive the ascent. This would be a voyage to a truly unknown realm, possibly higher than birds fly. No one knew for sure if it would be possible even to breathe.

TOM CROUCH: They knew that if you climbed to the top of the mountain, there was still air to breathe, but they weren't sure that the atmosphere perhaps didn't hug the contours of the earth. So, if you get 100 feet above the surface of the earth there would still be air to breathe, up there.

NARRATOR: Roland de Montgolfier, a descendant, owns a replica of the Versailles balloon.

ROLAND DE MONTGOLFIER (Descendent of the Montgolfier brothers): It's incredible. It was unhoped for, finding ourselves in a setting like this, flying a balloon like this. It's extraordinary.

MERCEDES TARAVILLO: I try to imagine myself in the context, in the shoes of the people back then. And in fact they must've thought, "It's magic, because you can't see how it works. It must be magic! How can it rise into the air?"

NARRATOR: Before the balloon takes off, the king asks Etienne to explain what's behind the force that drives the balloon. Still convinced that burning materials creates Montgolfier Gas, and that the thicker the smoke, the higher the concentration of this mystery gas, Etienne adds all sorts of strange things to his fire, including wool, meat and even old shoes.

In just a few minutes, the balloon inflates and, on the cue of a cannon burst, leaves the ground.

The balloon that flies before the king has been financed by the court and, accordingly, decorated in ways to flatter its patron.

The king, delighted, congratulates Etienne Montgolfier: "I am pleased to be seeing an experiment that will find echo in the glory of my reign."

After rising to about 1,500 feet and remaining aloft for eight minutes, the Montgolfiers' balloon slowly descends over a nearby wooded area. The gondola strikes a pile of wood and frees the animals, which are soon found by several who'd been chasing the balloon.

One of those on the scene is 26-year-old amateur scientist Pilâtre de Rozier, who will soon figure in the Montgolfiers' next attempt.

The Versailles flight sets off a new craze, "Balloon Mania!" Little toy balloons fill the skies of Paris. Hawkers sell them on every street corner. Everyone dreams of inventing new sky vessels. Surely, it's only a matter of time before a human will climb into a balloon and take to the sky.

The Montgolfiers are determined that that first flight will be their triumph. De Rozier, who had chased the earlier flight, begs to take the place of the barnyard animals, in hopes of earning the glory of being the first person to fly.

But for such a potentially momentous flight, the Montgolfiers know that they will need a truly spectacular balloon, lavishly decorated in honor of their patron, King Louis.

Etienne Montgolfier collaborates with Jean-Baptiste Réveillon, the owner of the royal wallpaper factory.

For Mercedes' team, the task of decoration raises its own questions: how were those complex designs originally made? How will they recreate the colors used by Réveillon, the royal azure blue and the ochre and gold shades?

To find out, they visit a paper manufacturer in the north of France, where the 18th century techniques are still practiced.

JEAN-BAPTISTE MARTIN (Decorator): To be able to find the true colors, well, we have this whole series of engravings that was done at the time of the flight. But each engraving has a different shade of blue. So we're going to have to base our decision on our knowledge of pigments used at the time.

NARRATOR: According to restorer and decorator Jean-Baptiste Martin, the shade of blue used by Etienne must have been a combination of cobalt and indigo, mixed with animal glue and a bit of water to bind the pigments.

GUILLAUME DE MONTGOLFIER: What about the gold shades? Are they really gold-based?

NARRATOR: These actual Réveillon wallpaper samples from the time reveal some of the techniques used to create the color gold.

JEAN-BAPTISTE MARTIN: Here, you can see it very well. Everything that was supposed to be gold, the color gold, was actually done with shades of ochre that look like gold.

We're going to use the exact same technique for the balloon. That is, we'll work with yellow shades of ochre and perhaps just do the highlights with real gold to give it a sparkle.

NARRATOR: By the fall of 1783, the Montgolfiers' balloon has now been outfitted with twin baskets for the pilots. They stand opposite one another and shovel hay into a firebox suspended beneath the neck of the balloon.

With the balloon securely tethered to the ground in the Réveillon gardens, Etienne practices controlling it by feeding the fire.

Throughout October, 1783, the pilot, Pilâtre de Rozier, carries out tethered liftoff and landing tests without incident. At last they feel ready to untie the ropes and fly.

But King Louis, who now accepts that it should be possible to survive the ascent, remains reluctant to put a human life at risk.

TOM CROUCH: Of course that first flight with human beings going into the air, on November 21, 1783, was going to be chancy. No one had ever built a balloon as large as that one. It was 70 feet tall, just a huge thing.

NARRATOR: Then a courtier, the Marquis d'Arlandes, asks the King to let him join De Rozier and attempt a manned flight, but at some distance from Versailles, so that the King and Queen will be protected from criticism if something goes amiss.

Finally reassured, Louis relents. In Annonay, the reconstruction is moving forward. The first two panels are finished, and the design work has begun.

The team, overseen by the decorator Jean-Baptiste, is attempting to reproduce the style of 18th-century wallpaper printers. And in another part of the workshop, Mercedes and several volunteers have started sewing the first two panels by hand, 18th-century style.

Inch by inch, they stitch the tough canvas-and-paper panels together, in a way that will prevent leaks.

MERCEDES TARAVILLO: It's just like cardboard.

ARMELLE: I feel like I'm sewing a piece of leather, that's how thick and hard it is.

NARRATOR: The work is exceedingly difficult. After four hours, the team has only completed 12 feet of the first two 100-foot panels. At this rate, it will take over six weeks of fulltime work to finish.

MERCEDES TARAVILLO: It's a painstaking job. It's titanic. It's…another needle just broke! How do you expect us to make progress?

NARRATOR: But then, a new development upends all their hard work. Historian Jean-Claude Ragaru has just found, through a private collector, a previously unknown letter. In it, the author writes that just five days before the manned flight, the paper and cotton balloon was severely damaged by a terrible storm.

Rather than postpone the event, the Réveillon workers hastily rebuild the balloon but without the paper layer.

JEAN-CLAUDE RAGARU: The author of the letter talks about his experience at Versailles: "To carry this out, I used cotton canvas, which I had painted on both sides, etc., etc."

NARRATOR: According to the letter, Etienne gave up on paper as a component in the balloon.

GUILLAUME DE MONTGOLFIER: Perhaps we should do the same and switch to some other material? We need to find a concrete solution that's somewhat sturdier and easier to make.

NARRATOR: In a way, it's a bit of good luck. Mercedes had worried about the combined weight of the paper and fabric. So, like Etienne more than 200 years before, the team decides to abandon the idea of making panels from paper and canvas.

They start over, this time using a modern material for added safety.

Now, they begin decorating the balloon in the style of Réveillon. Engravings help Jean-Baptiste to figure out the position of the motifs on the balloon. King Louis' double L, the signs of the zodiac, the fleurs-de-lis and the royal eagles will be copied onto the new panels.

The new balloon takes more than two long winter months to paint. Mercedes Taravillo and the team finish the decoration. And this time, Mercedes has decided to use her sewing machine to assemble the new panels.

MERCEDES TARAVILLO: It was very difficult and very long. The Montgolfier brothers had the Réveillon personnel at their disposal. I didn't have that kind of luck. I don't have 100 people who will come help me out for a project like this. Considering this, it would take years to finish it.

NARRATOR: In the end, it has taken five months to make the balloon.

It's April. The balloon is finally finished. After two and a half months of waiting for safe weather conditions, the day has finally come to restage the first human flight.

The balloon and all of its equipment are now at the historic Château de Brogieux, where the first tentative experiments with small paper balloons took place. After unpacking their huge creation, the team uses a crane to lift the 70-foot envelope to prepare it for inflation.

TOM CROUCH: You're seeing something that hasn't happened in a very long time, like this, anyway.

NARRATOR: In 1783, the brothers used two large mooring posts to position the balloon upright. Then, as now, the Montgolfiers lit the fire to cause the huge envelope to inflate. But in today's test, the team forgoes the exotic and smelly combustibles that the Montgolfiers thought were a key ingredient in the lifting gas.

JEAN-CLAUDE RAGARU: It happened more or less just like this, the combustible was hay, and then they added pieces of rotten meat and a little bit of sheep's wool. But, after a few days, they just preferred using dry straw, because, well, it smelled better, and it was just as efficient.

NARRATOR: After less than half an hour the balloon is filling and straining at its tethers. Now the team makes a calculated decision. Flying with an open fire was perilous at the time and unacceptable today. So they replace the straw-burning brazier with a modern gas burner.

MERCEDES TARAVILLO: We opted for the burner because the straw would not have been enough, especially if you want to mount it. It's a safety issue.

NARRATOR: The final step is to release the balloon from the crane so that only the tethers prevent it from taking off.

On the morning of November 21st, 1783, at the Château de la Muette, outside of Paris, a massive crowd has assembled.

Benjamin Franklin is also on hand. He watches anxiously as Pilâtre de Rozier and his co-pilot, the Marquis d'Arlandes climb onboard.

In Annonay, the balloon is finally inflated and free to lift off.

JEAN-CLAUDE RAGARU: The ropes! The ropes!

MERCEDES TARAVILLO: Let's go!

NARRATOR: Mercedes and her pilot climb into the gondola to test the balloon while still safely tethered to the ground.

De Rozier and d'Arlandes stoke their fire. Slowly, the balloon climbs, and the enthralled spectators, including Franklin, watch with astonishment and worry.

BENJAMIN FRANKLIN (From His Writings): When it went over our Heads, we could see the Fire which was very considerable. I was then in great Pain for the Men, thinking them in danger of being thrown out, or burnt."

NARRATOR: He has reason to be concerned. After a few minutes in the air, small flames lick at the lower border of the balloon, threatening to set it completely on fire.

TOM CROUCH: They had sponges on long sticks, so that they, looking through little square openings in front of them, they could, kind of, dab burning spots inside the balloon out.

NARRATOR: The two men are 3,000 feet in the air, with only a fragile balloon and an open, straw-fed fire to keep them aloft. Soon, they begin to fear for their lives. They have plenty of fuel left, but after about 25 minutes and five miles, they decide they've had enough, and land.

The short duration of the flight doesn't matter to the crowd, for whom it all seems miraculous.

For today's team, the time has come, at last, to take to the sky. Just like Pilâtre de Rozier and the Marquis d'Arlandes, Mercedes and André, her pilot, are finally ready to release their balloon.

GUILLAUME DE MONTGOLFIER: Well, we're starting to kind of want to fly. All the stress going away, all the stress dissipating. It's just great, just great.

TOM CROUCH: It's emotional, just to see it, here, in this field, something that looks like the first balloon to carry human beings aloft, you know? It's a real thrill for heaven's sakes!

NARRATOR: But at the last minute, French aviation authorities refuse to give permission for the balloon to fly untethered. It's a disappointment, but, as the balloon strains against its bonds, there's no doubt that it can fly.

On the evening of November 21st, Benjamin Franklin signs his eyewitness report of the first human flight, helping to assure the Montgolfier brothers' place in history.

But Jacques Charles, whose first hydrogen balloon had flown so well, remains intent on pursuing his own path into the sky.

The Montgolfiers' balloon is far from ideal. It is too large and difficult to control, since so much depends on maintaining the fire. With little knowledge of the Montgolfiers' craft, Charles builds a more compact balloon that can fly both higher and farther.

BENJAMIN FRANKLIN (From His Writings): It is a Globe of 26 feet diameter. The Gores that compose it are red and white Silk, so that it makes a beautiful appearance.

NARRATOR: Xavier Waymel is a gas-balloon enthusiast. Inspired by Charles' 18th-century craft, he has built his own version.

XAVIER WAYMEL (Balloonist): In terms of size, the two balloons are rather similar. This one has a 35-foot diameter and Charles' was around 30 feet. So we're looking at about the same dimensions.

NARRATOR: In 1783, Charles builds a very impressive machine. He chooses the latest material, a very lightweight fabric coated with rubber, which has been only recently been imported from the Americas.

XAVIER WAYMEL: It was one of the first times that rubber was used. They needed something that was airtight and waterproof and flexible.

NARRATOR: Charles also designs a spring-operated valve to release gas, in order to descend.

XAVIER WAYMEL: It opens like this; same thing on the other side. Opening the valve allows a bit of gas to escape and, therefore, makes the balloon a little heavier, and that's how the balloon descends.

NARRATOR: Lastly, Charles encloses the balloon in a net, which distributes the weight of the gondola around the entire globe, another feature of modern balloons.

On a Monday, December 1, 1783, in the Tuileries Gardens, a massive throng gathers, pushing and shoving and scaling walls to witness the liftoff.

TOM CROUCH: The crowd at the first manned Montgolfier flight was significant, but the crowd for Jacques Charles' first flight was huge. No one expected it. Some of the figures suggest as many as half of the people in Paris had gathered to witness this flight.

NARRATOR: Franklin, too, is there. But rather than join the throng, he prefers to stay in the comfort of his carriage. From this viewpoint, he sees Charles and his co-pilot take off.

BENJAMIN FRANKLIN (From His Writings): All Eyes were gratified with seeing it rise majestically from among the Trees, and ascend gradually above the Buildings, a most beautiful Spectacle! When it was about 200 feet high, the brave Adventurers held out and wav'd a little white Pennant, on both Sides their Carr, to salute the Spectators, who return'd loud Claps of Applause."

MI GYUNG KIM: One thing that keeps coming through in the newspaper accounts, and in personal accounts, in diaries, and so on, is a single adjective that says "majestic."

It's fabulous.

NARRATOR: In 1783, when Charles wants to go higher, he dumps ballast, just like Xavier Waymel does today.

XAVIER WAYMEL: "Dump ballast?" That means that I take the shovel and throw a small quantity of sand overboard, sprinkling it like this, or dumping it all in one go. And that is enough to rise a few feet.

NARRATOR: To descend, Charles and Xavier release gas from the balloon's envelope.

XAVIER WAYMEL: To descend, I pull on this rope, which activates the valve, the little wood valve up at the top that looks like a small window. It's a system that hasn't changed since the end of the 18th century. It's still the same system.

NARRATOR: Charles's first flight leaps past the Montgolfiers' achievement. He flies a distance of about 25 miles over two hours, five times farther and longer than the flight of Pilâtre de Rozier and Marquis d'Arlandes. The balloon lands in the countryside, north of Paris.

Charles' passenger gets off just after the sun sets.

Now, alone, as dusk falls, Charles immediately takes off again, rising so high that he sees over the horizon, bringing the sun back into view.

JEAN-CLAUDE RAGARU: When he left the ground, it was dusk and the sun was sinking on the horizon. Of course, at 10,000 feet of altitude, he saw the sun once again, and since he stayed in the air for half an hour, he saw it set again.

NARRATOR: He is the first person in history to see the sun set twice in the same day.

In just 19 months, between June 1783 and January 1785, the world sees six historic flights. Humanity has, at last, conquered the sky.

After the manned flights of de Rozier and Charles, a ballooning craze seizes all of Europe. All sorts of inventors join in the adventure. Many of their designs are breathtakingly innovative and impractical.

Soon the Montgolfier brothers run out of money, and Etienne is forced to return home to take up the family business.

Two other intrepid adventurers, however, are eager to pursue the brothers' dream. In Dover, England, a Frenchman, Jean-Pierre Blanchard, constructs a hydrogen balloon, complete with oars and a rudder. His co-pilot is John Jeffries, a Boston-born doctor and surgeon. Their plan is to fly across the English Channel.

The Channel is at least 22 miles wide, and weather conditions are rarely optimal. Even today, making such a crossing in a balloon requires skill and luck, something that Tom Crouch and balloonist Xavier Waymel are about to discover firsthand, as they attempt to cross the channel themselves.

XAVIER WAYMEL: It's a complicated flight to accomplish. For example, we've waited over one month for a good weather window, which, during this season is not so surprising. Back at the time, they themselves had to wait for weeks. They almost lost faith before having good weather conditions and succeeding in taking off.

TOM CROUCH: Flying that distance over open water, it's a daunting thing to do. It's something I really look forward to, having written about this flight over so many years of my own life. To actually be able to recreate that flight, just sends chills up and down your spine.

NARRATOR: On the morning of January 7, 1785, the sky is clear and calm. Just over a year after the first human flight, Blanchard and Jeffries lift off. Their balloon moves slowly towards the sea.

TOM CROUCH: Oh, it's wonderful! We're right where Blanchard and Jeffries were. When you look back, you can see Dover, all the little towns behind it.

NARRATOR: Their flight is not exactly restful. They try to navigate with the rudder, which doesn't work, and at times they dip perilously close to the water. After a two-hour flight, they reach the French coastline, at the whim of the winds. But a thick forest that appears below prevents them from landing.

TOM CROUCH: They didn't want to come down into the trees. And Jeffries said, "We were very close to the treetops. Fearing that the basket would be hit violently, I felt the need to throw something out in order to change our course. Recalling since Dover we had not satisfied any call of nature, I suggested to Mr. Blanchard to take this opportunity to urinate. He heartily approved the idea; I believe in good faith that we were able to produce 5-6 pounds of urine. We made a perfect landing beyond the trees."

NARRATOR: But for Xavier and Tom, their flight soon becomes even more fraught than that of their predecessors. The wind suddenly changes direction and blows them away from Calais and the French coast. After six long hours, three times longer than it took Blanchard and Jeffries, Xavier and Tom finally also reach dry land, but in Belgium.

XAVIER WAYMEL: It went fine, but it was a tough ride. At one point in time, I asked myself how long we were going to spend over the sea. We were scared.

NARRATOR: More than 200 years after the first flight across the Channel, balloons still remain at the mercy of the elements.

TOM CROUCH: To Jean Pierre Blanchard and John Jeffries and us.

XAVIER WAYMEL: They were great balloonists.

TOM CROUCH: They were indeed, as are you.

NARRATOR: After the flight of Blanchard and Jeffries, all of the essential features of modern ballooning technology have been developed. It is during this astonishing two-year burst of innovation and creativity, more than two centuries ago, that the first aeronauts dare to climb aboard these flimsy craft, to make history in the sky.