1You remember the chemist Davy, who caged the flame for the miners. In the same years a blacksmith's son named Michael Faraday was working in London as a bookbinder's boy. He had almost no schooling. But he read the books he was given to bind, and the ones about nature he read twice. He went to hear Davy lecture, and wrote out every word, and sent the bound pages to Davy, asking for any work at all. Davy took him on to wash bottles. It was Faraday's hands that helped to test the miners' lamp.
2He became the greatest finder of new things in his century, and he never learned mathematics. He thought in pictures. When he scattered iron dust on a paper above a magnet, the dust drew itself into curving lines from one end of the magnet to the other. Others saw a pretty trick. Faraday saw that the space around the magnet was not empty. It was full of something, stretched and straining, and the lines of dust were showing its shape. He called them lines of force. He found that when a magnet is moved near a wire, a current runs in the wire, as if the lines had plucked it.
3The men of numbers smiled at his lines. Forces, they knew, act straight across empty space, with nothing between.
4Now hear of the one who did not smile.
5He was born in Scotland, and grew up on his father's lonely farm among the hills of Galloway. His name was James Clerk Maxwell. From the time he could speak he had one question for everything in the house. "What's the go o' that?" he would say. And if the answer was too easy, he asked what the particular go of it was.
6His mother taught him herself. When he was eight she died, of a slow sickness in the belly, and she was not yet fifty. Remember that.
7He was sent to school in the city in clothes his father had designed, with square-toed shoes and a frilled collar. The other boys tore them and called him Dafty. He bore it without bitterness. At fourteen he found a new way to draw certain ovals with pins and thread, and a professor read it out before the learned men of Edinburgh, because a boy could not address them.
8When he was a young man, he read all that Faraday had written. He did not smile at the lines of force. He thought the old bookbinder had seen something true that the men of numbers had missed, and that it only wanted translating. So he translated it. He put Faraday's pictures into mathematics, line for line, and sent the paper to the old man with a respectful letter.
9Faraday was then past sixty-five, and his memory was beginning to fail him. He wrote back with great gentleness. He said he had been almost frightened at first to see so much mathematical power brought to bear on his subject, and then had wondered to see how well the subject stood it. No one of that kind had ever taken him at his word before.
10A few years later, Maxwell was a professor in London, and married to a woman named Katherine. In the autumn they went up to the farm, and he rode to a horse fair to buy her a pony. He came back with the pony and with the smallpox.
11It nearly killed him. Katherine nursed him alone, day and night, for weeks. He said afterward, plainly, that he owed her his life.
12The next summer he was at the farm again, well, and thinking about Faraday's stretched and straining space. He had made himself a picture of it. It was a strange picture, all little spinning wheels with smaller wheels between them. It was a scaffold to think on. But the scaffold showed him something. If you gave that straining stuff a shake at one place, the shake would not stay there. It would pass to the next place, and the next. A change in the electric strain would make a magnetic one beside it, and that would make an electric one beyond. It would travel. It would be a wave.
13How fast?
14That he could reckon. The speed must come out of two numbers: one that tells how strongly electric charges pull, and one that tells how strongly magnets do. Two Germans had measured those very numbers a few years before, with glass jars and coils and a hanging magnet, in a room. Nothing in their work had anything to do with speed, or with light.
15He did the sum on a table at the farm. The answer was a speed, and a very great one: about a hundred and ninety-three thousand miles in one second.
16He knew he had seen a number like that before. But where? He had none of his books with him. They were hundreds of miles away in London, and he was not due back till autumn.
17So he waited. All that summer he walked his fields with a number in his head and no way to check it.
18In the autumn he went south, and climbed the stairs to his room, and took down the book he wanted. Some years before, a Frenchman named Fizeau had measured the speed of light. He shone a beam between the teeth of a spinning wheel toward a mirror on a hill five miles off, and spun the wheel faster until the returning light struck a tooth and went dark. From that he had the speed.
19Maxwell found the page. Light travels about a hundred and ninety-five thousand miles in one second.
20The two numbers differed by little more than one part in a hundred. One had come out of jars and magnets in a German room. The other had come from a lamp and a mirror on a French hill. And they were the same.
21He wrote it down carefully, and for once he put the words in sloping letters, so no reader could miss them. We can scarcely avoid the conclusion, he said, that light is a waving in the very same medium that carries electric and magnetic force.
22Think what that sentence did. Since the first fire, people had asked what light was. Now here was the answer. Light is not a thing apart. It is electricity and magnetism handing a tremor to each other across space, each making the other, too fast to see the making. The lamp in the miner's hand, the lightning that struck the elm tree, the pull of the lodestone, and the light of the furthest star were one thing.
23And there was more in the sum than light. Nothing in it said the waves must be the size that eyes can see. There could be waves a thousand times longer, or a thousand times shorter. The space around us might be full of trembling that no one had ever felt. He could only say that the mathematics left the door open for them.
24Few believed him. Even his friend Thomson never wholly accepted it. Maxwell did not fight. He gave up his post in London and went home to the farm, and spent years writing it all out again, more cleanly, in a great book.
25Now you must hear of his other work, for it leads straight to the end of this book.
26He was one of those who believed that everything is made of grains too small to see, always moving. In a gas, such as the air in a room, the grains fly about freely and strike one another like a swarm of bees in a box. What we call the heat of the air is nothing but that flying. Hot air is fast grains. Cold air is slow ones.
27But not all at one speed. That was what he found. In any roomful of air, at any moment, a few grains are going very slowly, and a few very fast, and most are in the middle; and he worked out the exact share of each. He could not follow any one grain. No one could. There are more of them in a thimbleful of air than there are grains of sand on every shore of the world. But he did not need to follow them. He counted them as one counts a crowd: so many of this kind, so many of that.
28Then he made up a story, to test Clausius's law. He wrote it in a letter to a friend, half as a joke.
29Think of a box of air, he said, all at one warmth, with a wall across the middle. In the wall is a tiny door. And at the door stands a doorkeeper so small and so quick that he can see each single grain coming. He has one rule. When a fast grain comes from the left, he opens the door and lets it through to the right. When a slow one comes from the right, he lets it through to the left. All others he shuts out.
30What happens? After a while the right side is full of fast grains and the left of slow ones. The right side is hot and the left is cold. Heat has gone from cold to hot, uphill, and no work was done to push it. The doorkeeper only opened and shut a door that weighs nothing. The cold cup of tea has begun to steam.
31He did not think any such creature lived. That was not his point. His point was this. The law that heat falls and never climbs is not a law of the same kind as the law of the falling stone. A single grain knows nothing of it. Each grain flies as freely one way as the other. The law belongs to the crowd. It is true because we are too big and too blind to sort the grains one by one, and must take them as they come, all mixed.
32He said it another way. Throw a cupful of water into the sea. Now try to dip the same cupful out again. Nothing forbids it. Every drop of it is still there. You will never do it.
33And he left one thing unasked, which you may keep in your pocket for a later book. The doorkeeper must know which grains are fast. What does the knowing cost him? Maxwell did not say. No one would say for sixty years.
34When he was forty-seven he began to have pain after eating. He told no one for a long time, and went on with his lectures. When at last he saw a doctor, it was the sickness his mother had died of, in the same place. He was told he had a month.
35He went about setting things in order. His doctor wrote afterward that in all his years he had never seen a man meet death more calmly. Maxwell's chief trouble, to the end, was who would care for Katherine, who was ailing. He died in the autumn, at Cambridge. He was forty-eight years old, very nearly the age his mother had been.
36He died not knowing whether he was right. His great book was understood by a handful of people in the world. A sum on a farm table said that the dark was full of unseen light, and that was all.
37Eight years went by.
38In a German town called Karlsruhe there was a young professor named Heinrich Hertz, who had set himself to find out if the Scotsman's waves were real. He built a thing to make them: two brass balls with a small gap between, joined to a coil, so that a fat spark could be made to crack across the gap again and again. If Maxwell was right, each spark would send a tremor out through the room.
39To catch the tremor he had nothing but a ring of copper wire with a tiny gap in it, no wider than a hair. If a wave came, it should stir the ring. And if it stirred the ring enough, there might be a spark in that little gap too.
40It would be a spark so small that it could not be seen by day. So he darkened the room. He set the machine cracking at one end of the room and carried his ring to the other.
41Now picture him there, a man standing in the dark with his face close to a loop of wire, looking at nothing. There was no wire between the ring and the machine. There was only the air, and twelve paces of empty room.
42And in the gap of the ring, a point of light appeared. It was smaller than the head of a pin, and bluish, and it trembled. It lived as long as the machine cracked. When he had the machine stopped, it died. When the machine began again, it was born again.
43Something had crossed the room.
44He spent the next months proving what it was. He bounced it off a sheet of zinc as light bounces off a mirror. He bent it through a great block of pitch as light bends through glass. He measured its speed, and it was the speed of light. Everything the dead man had said was so.
45Hertz was thirty years old. He would live only six years more. Before the century was out, others were sending messages across the sea on those waves without any wire. The night air today is full of voices, and every one of them rides on the sum that waited a summer on a Scottish farm.
46A bookbinder's boy drew lines in iron dust. A farmer's son turned the lines to numbers, and the numbers told him of a thing no one had seen. A third man stood in a dark room, and a spark the size of a pin's head said yes. Not one of them could have done it alone. Two of the three were dead before it was finished.
47But the other door that Maxwell opened, the one with the doorkeeper standing at it, was still unanswered. If the law of heat is a law of crowds, then what is it that the crowd is doing? Why does a crowd of grains always go from sorted to mixed, and never back? The answer was a count. It was being worked out, in those same years, at a kitchen table in the Austrian town of Graz.