The hammer rang once. A spark jumped off the anvil and did not go out. It waited. They followed.

Tara followed it across the Green in the rain, past the print shop, through the door of the small museum, and down to the end of the long room, where it stopped above a glass case that nobody ever looked at.

Inside the case was a card, about the size of a hand. It was blank. At least, it looked blank. Then the light moved and Tara saw that it was covered in tiny bumps, pushed up from the back, arranged in little groups. Some groups had one bump. Some had four or five. None had more than six.

The label said: A page written by a fifteen-year-old.

This is a true story. Where nobody knows something, the story says so.

Louis Braille was born on 4 January 1809, in Coupvray, a village about forty kilometres east of Paris. His father, Simon-René, made harnesses and saddles for the farmers' horses. The workshop was full of leather, thread and sharp tools.

When Louis was three, he was playing in the workshop and hurt one of his eyes with one of those tools. Most accounts say it was an awl, the pointed spike his father used to punch holes in leather. The wound became infected. There were no antibiotics in 1812. The infection spread to his other eye, and by the time he was five Louis was completely blind.

That could have been the end of his education. In most villages it would have been. A blind child in 1814 was usually expected to stay at home, or to beg, or to learn some simple work with his hands. But his parents did not hide him. His father made him a cane. The village priest taught him about plants and animals by touch and by talking. The schoolteacher let him sit in the classroom with the other children, and Louis, who could not read the board, listened and remembered.

He was clever, everybody agreed. But he could not read. And a person who cannot read can only ever know what someone else chooses to tell him.

In February 1819, when Louis was ten, he went to Paris to the Royal Institute for Blind Youth. It was one of the first schools for blind children in the world. Its founder, Valentin Haüy, had invented a way of making books for blind readers: big letters, the ordinary Latin alphabet, pressed so hard into wet paper that they stood up on the other side.

It worked, in a way. You could feel the letters. But each one was large, so a page held very little. A single story needed several heavy volumes. The library had only a few books, because each one took so much work to make. And reading them was slow. A finger had to trace the outline of each letter, a curve, a line, another curve, and work out what it was before moving on.

Worst of all, the pupils could read these books but could not write them. You could not press a raised letter from the back of the page with a pen and get it the right way round. So a blind pupil could take in a few slow sentences, but could not put down a thought of his own.

The building itself was old and damp. The boys were often ill. Louis was a good pupil anyway. He learned to play the cello and the organ. He was quiet and careful, and the other boys liked him.

In 1821, when Louis was twelve, a visitor came to the school. His name was Charles Barbier. He had been a captain in the French army, and he had invented a way of writing with raised dots that he called night writing, or sonography.

Barbier's idea was that dots were easier for a fingertip than letters. A dot is a dot. You do not have to trace its outline. You just feel whether it is there or not. His system used a grid of up to twelve dots, in two columns of six, and each pattern stood for a sound, not a letter.

The pupils tried it. It was a real step forward. You could write it, too, with a frame and a pointed stylus, pushing the dots from the back of the paper.

But it had problems. A twelve-dot pattern was taller than a fingertip, so you could not feel a whole symbol at once. You had to move your finger up and down to find the dots. And because it wrote sounds, it had no spelling. It had no capital letters, no numbers, no punctuation, no way of writing music. Barbier had made a code for short messages. A school needs a way to write everything.

Louis was twelve. He began to work on it.

What happened next took about three years, and much of it happened at night, in the holidays at home in Coupvray, and in odd hours between lessons. Louis worked with a frame, a stylus and paper, the same tools Barbier used. He kept the dots. He changed nearly everything else.

The first change was size. He cut the cell down from twelve dots to six: two columns of three. A cell of six dots fits under one fingertip. You do not have to move your finger to find the whole symbol. You feel it in a single touch, the way a sighted reader sees a letter in a single glance.

Six dots, each either raised or flat, give exactly sixty-three patterns, not counting the blank. That was enough for the whole alphabet, with room left over for punctuation and numbers.

The second change was what the dots stood for. Louis made them stand for letters, not sounds. A blind reader could now spell, exactly as sighted readers spelled. A French word in his system was the same word, letter for letter, as in any book. That mattered more than it might seem. It meant blind and sighted people were reading the same language.

The third change was order. Louis did not just assign patterns at random. He built the alphabet in rows. The first ten letters used only the top four dots. The next ten were the first ten with one more dot added at the bottom left. The next row added another. It was a system you could learn, because it had a shape.

By 1824, when Louis was fifteen, it was done. Nobody knows the day. We know the year.

The pupils loved it at once. They could read it quickly. Better, they could write it. They took notes in class. They wrote letters to each other. For the first time, a blind pupil at the school could put down a thought and come back to it the next day.

Louis kept improving it. In 1829, when he was twenty, he published a short book explaining the whole system. Its title, in English, was Method of Writing Words, Music, and Plain Songs by Means of Dots, for Use by the Blind and Arranged for Them. In it he gave credit to Barbier, whose idea he had started from. The book already included a way of writing music, which Louis used himself as a church organist.

He became a teacher at the school where he had been a pupil. His students said he was patient and kind.

And still, the school did not officially adopt his system. Many of the sighted teachers and officials preferred the raised ordinary letters, which they could read themselves. The dots looked like a secret code. For years the pupils used Louis's system among themselves while their official books were still made the old, heavy way.

Louis Braille had tuberculosis for most of his adult life. He died on 6 January 1852, two days after his forty-third birthday.

In 1854, two years after he died, the institute in Paris officially adopted his system. It spread from there to the rest of the world. It has been adapted for hundreds of languages since, including languages that do not use the Latin alphabet at all.

In 1952, a hundred years after his death, the French government moved his body from the village churchyard in Coupvray to the Panthéon in Paris, where France buries the people it wants to honour most. The people of Coupvray asked to keep something. His hands are still buried in the village.

Tara stood by the case for a long time. The rain had stopped. The spark had settled on the edge of the glass, very small, and waited for her.

She thought about the twelve-year-old who had been handed someone else's idea, and found it nearly good, and had not been satisfied with nearly. She thought about the three years, which is a long time at that age, longer than it ever is again. She thought about the adults who had been given a better system by a teenager and had said no, for thirty years, because they could not read it themselves.

And she thought about the part that nobody tells in the short version: that he gave Barbier the credit. He could have called it his own and nobody would have argued.

She looked at the card. Six dots, raised or flat. Sixty-three patterns. A whole language under one fingertip.

If someone had handed you Barbier's twelve dots when you were twelve, would you have used them as they were, or would you have started cutting?

The spark dimmed to a warm dot and settled back on the anvil. The Green was just the Green again.

Back on the Green

At the Whetstone that evening Tara opened the notebook where she kept lines worth keeping. She did not write genius or never give up. She wrote one sentence, and then the date.

He kept the dots and changed nearly everything else.

Danya, at the next table, asked what she was writing. She showed him. He read it twice and said, "Who checked that?" She told him the label in the museum, and two books, and a website run by a society for the blind. He nodded, satisfied, and went back to his comic.

Which line from this story would you keep?