An Ocean of Air (29 page)

In some ways, Cambridge suited Appleton perfectly. When he arrived as an undergraduate at St. John's College Cambridge in 1911, his conservatism was already engrained. He wore stiff collars made by a Bradford tailor; he would continue to buy the same collars, from the same shop, for the rest of his life. He was also dazzled by the splendors of St. John's, one of the oldest and richest colleges in Cambridge. Almost immediately, he dispatched a postcard to a Bradford friend, saying, "I have fine rooms of my own, and can feel my importance, I can assure you." The picture on the front of the card showed a dining hall from one of the other Cambridge colleges, and Appleton added as a P.S.: "We at St. John's have a dining Hall even bigger and finer than this." More impressed postcards followed. "I went to have breakfast with a man I know—a tutor of Clare College," said another. "He had some of the College silver plate on his breakfast table. Being a tutor, the College lends it to him now and then. Jove it was a gorgeous sight."

Appleton excelled at Cambridge both athletically and academically, and he graduated in June 1914 with a dazzling double first in physics. Two months later Britain declared war on Germany, and Appleton immediately joined up. But when the war was over, he returned to St. John's as a Fellow. He was still entranced by the Cambridge traditions: the gowns and formal portraits, the silver and gold plate and flickering candles and Latin graces in the dining hall. But while part of him was glorying in the unex
pected free pass he had received into this august world, Appleton remained enough of a Bradford outsider to begin to notice some of its downsides.

For instance, when Appleton asked that the cockroaches in the college kitchen be disposed of, he was astonished by both the steward's refusal and the reason he gave. The St. John's cockroaches, it turned out, had been brought over from the continent sometime during the reign of Elizabeth I, and were not to be disturbed. And although Appleton relished the approval of his clever, confident peers, he didn't much like their snooty attitude toward the world outside the university walls. Later, he often mentioned a Cambridge don who boasted that he had never been inside a cinema: "He made the remark in a way which showed he expected admiration all round, and the sad thing is that he got it—nearly all round."

In that way, at least, Appleton would never fit in at the Cambridge of the time. For formal as he was, and as carefully as he had shaken off the appearances and accent of his working-class youth, he liked putting people at their ease. Years later, when he was chancellor of Edinburgh University, he would reach up and dust the parts of his filing cabinet that his diminutive cleaning lady couldn't reach. He would chat to servants about soccer, or anything else he could think of that they might like. And when he was meeting with his similarly illustrious colleagues and timid secretaries entered the room with tea, he would tease them with the declaration, "Here comes Hebe—cup bearer to the gods!"

He also talked about his scientific work to anybody who was curious enough to listen. That meant not just academics but ordinary people, the sort that many other dons disdained. He gave public lectures that were clear and entertaining, carefully practiced beforehand and then modulated by his fine tenor voice. His main motivation sprang from the exuberance he felt in finding out something unexpected and magical about the world. For Appleton, science was all about imagination.

Years later, in a presidential address to the British Association, he would say:

Perhaps the most striking fact about modern science is that, like poetry, like philosophy, it reveals depths and mysteries beyond—and, this is important,
quite different from—the ordinary matter-of-fact world we are used to. Science has given back to the universe ... that quality of inexhaustible richness and unexpectedness and wonder which at one time it seemed to have taken away.

And as Appleton performed his research in Cambridge in the early 1920s, he realized he was on to something that was very far from the ordinary, matter-of-fact world. Working in the Signal Service during the war, he had become intrigued by the new radio technology, especially devices called thermionic valves. These were so crucial for signaling that they were classified as a military secret. However, using them was an inefficient process of trial and error, since nobody seemed to understand how they worked. When Appleton returned to Cambridge after the war, he had with him several of these mysterious valves ("not I may add lifted from the British Army. Some were gifts from the lamp firms who had been making valves, and one German type was picked up by me from a captured pill box"). Using them, he began to pick apart how exactly this wireless technology of sending and receiving radio waves really worked.

And the more he studied Marconi's radio waves, the more Appleton became intrigued by how they managed to curve their way around the world. He had met Marconi and reported being most impressed by the way he never let a discouraging theory stand in the way of an experiment. Even now, more than twenty years after Marconi had bent his waves over the Atlantic, there was still much confusion about exactly what was causing them to bounce.

Appleton thought the likeliest explanation was Oliver Heaviside's idea: Somewhere high overhead, the air crackles with electrical energy, which acts like a mirror bouncing the radio waves back down to Earth. But he wanted to go further. What exactly was this mirror like? What formed it? And how did it work?

He believed that a clue lay in something the Marconi wireless boys had known for years: Certain times of day were better than others for sending wireless signals. As one commentator put it: "Every operator has experiences of his own to tell when all the elements seemed to unite in his favor and the mysterious spark has traveled for almost inconceivable distances." And the best time of all seemed to be at night. Nobody knew exactly why this should be, though some speculated that perhaps there was less interference between messages at night, when fewer stations were active. Appleton, though, had a better explanation. He thought the night/day difference meant that the sun had something to do with making Heaviside's electrical layer.

Perhaps something that arrived with the sun's rays somehow split the constituents of the upper atmosphere into their electrical pieces, ripping electrons off the floating atoms and molecules, and splattering positively and negatively charged shrapnel around the sky. That would certainly fill the sky with electricity. It would also happen in the outermost atmosphere, our first aerial rampart against invaders from space.

But if this was right, why should the layer reflect radio more efficiently at night, when the sun had vanished? Appleton thought he understood. He reasoned that at least remnants of the electrical layer would be there all the time, even when the sun had vanished. Because positive and negative charges attract each other, the electrical shrapnel will gradually recombine. But the uppermost air is thin, pieces don't encounter each other very often, and one night would not be long enough to lose everything.

However, the nighttime layer would be different from the daytime one in this crucial respect: It would be higher in the sky. During the day, the sun's rays, or particles, or whatever was responsible, would be able to penetrate deep into the atmosphere. Heaviside's reflecting layer would reach down into the part of the sky where the air is relatively dense. Any radio waves arriving at this low, dense electrical mirror would not only bounce off it; they would also collide and be partially absorbed, and would lose some of their energy in the process. At night, this low-lying layer would thin out and rise as the electrical shrapnel recombined. All that would be left were the remnants of electricity in the high, thin air where collisions were rare, and recombination slow. There, radio waves would be able to bounce off more efficiently, without losing so much energy. Hence radio would travel farther at night.

In April 1924, Appleton took on an assistant, Miles Barnett, from New Zealand, to test his ideas. Barnett immediately set to work measuring the
radio signal arriving in Cambridge from London. For wireless had come a long way from Marconi's initial dot-dot-dot across the ocean. Now its waves floated out accompanied by voices, and even music. Two years earlier, the newly formed British Broadcasting Company had started a station called 2LO in London, and their regular broadcasts could be picked up in Cambridge. Appleton asked Barnett to measure how strong this signal was at different times of day and night.

Barnett had no trouble picking up the 2LO signal, and he quickly confirmed that it was stronger at night than during the day. But he also spotted something curious. Every day, around dusk, the 2LO signal definitely wobbled. It faded into and out of existence, as if some cosmic sprite were fiddling with the volume. Both Appleton and Barnett realized immediately what this meant. The signal had to be tracking Heaviside's electrical layer as it made its nightly move upward.

The signal Barnett was measuring had two components: a wave that came to him directly, and another that bounced off the mirror in the sky. When these two waves arrived at his Cambridge transmitter, they had the potential to interfere with one another. If the difference between the two paths amounted to a whole number of wavelengths, the two waves would combine to make a superwave and the "volume" would lurch upward. If, on the other hand, one wave had traveled exactly half a wavelength farther than the other, it would hit its peak while the other still languished in its trough. Then the two waves would cancel each other out, and the signal would flatline.

It would be a tremendous coincidence if either of these things happened normally. The wavelength of the wireless waves was set by the BBC, and the distance they traveled by a combination of the location of Appleton and Barnett's lab and the height of Heaviside's layer. There was no earthly reason why these different random figures should conspire to make the waves neatly add up or subtract from one another. And normally, in full day or full night, they didn't.

However, at dusk something changed. The Heaviside layer began its nightly foray upward into the sky. As it did so, it passed through the exact heights that would make the reflected radio wave interfere with the one on
the ground. Imagine the layer as it gradually rises. First, it reaches a point where the reflected wave will exactly match the ground wave, peak for peak, and up goes the signal volume. The layer keeps on rising. Now it passes through the perfect height for the reflected radio wave to cancel out its ground-based twin. Suddenly, the signal drops to zero. The layer rises farther and hits another mutual peak, followed by another cancel point. Loud, soft, loud, soft—as the Heaviside layer rises, the signal in Barnett's measuring apparatus wobbles in volumetric sympathy. It was the first direct evidence that Heaviside had been right.

This gave Appleton an idea. Obviously he couldn't change the height of the Heaviside layer for his experiment, but he could, if he asked nicely, get the BBC to change their wavelength. If they could be prevailed upon to broadcast a gradually changing signal, that should have the same effect as the rising electrical layer—the waves would gradually move through points where they added together and subtracted from another, and the ultimate signal should have the same wobbles of interference. That would confirm the Heaviside layer was really there. But more than that, it would reveal exactly how high this mysterious mirror lay.

That's because Appleton could count the highs as he moved through them. Each one would show him the point where the new wavelengths added up. Knowing this, the broadcast wavelength, and the distance from the broadcasting station to his lab, he could work out how high the reflected wave had to go before it bounced back and arrived again at his apparatus.

It was a brilliant idea, and the BBC quickly agreed. Station 2LO couldn't easily broadcast a gradually changing wavelength, but they could do it instead from Bournemouth, on the south coast. That meant recalculating the appropriate distance from station to lab, and to Appleton's chagrin he realized he would have to move his experiment from his beloved Cambridge to a borrowed lab in—of all places—its sworn rival, Oxford University.

On December 11, 1924, Appleton and Barnett set up their equipment. They waited impatiently for Bournemouth to finish the regular broadcast. To Barnett, the last number, by the Savoy Orpheans, seemed to go on forever. "And I always thought I liked dance music," he groaned. Finally, just before midnight, the program ended. On the telephone Captain West, head of the Bournemouth station, told the two researchers to be ready. And then, a few minutes after midnight, the changing signal began. A few minutes later came the wobbles that Appleton had been looking for. Heaviside's crackling layer of earthly electricity was floating some sixty miles above his head.

Appleton had discovered what Heaviside had only imagined. Now the real work was to begin. From his new position as head of the physics department at the University of London, Appleton set up a network of researchers to study the new layer. The task of broadcasting ever-changing signals was switched to the National Physical Laboratory at Teddington, and Appleton set up various new receiving stations including two wooden huts, which were erected just outside Peterborough.

To run the Peterborough site, Appleton hired a new assistant, one Mr. W. C. Brown, who had been a shipboard radio operator in the war and had traveled very widely. Among other things, this had made him highly resourceful: "He could produce a cup of hot tea, in the middle of the night, when there was neither tea, nor milk, nor cups," Appleton said. "And when Mrs. Brown joined him as she did from time to time, the most delicious sausage rolls also used to appear, again from nowhere. All the early work on the ionosphere was done on tea and sausage rolls."

The first use of the Peterborough side was to test what happened at dawn. Using the National Physical Laboratory, Appleton had much more flexibility about when his test signal could be broadcast. Since he already knew that the Heaviside layer rose with the dusk, he wanted to check that it fell again with the dawn. As he expected, as the sun's rays returned to electrify the atmosphere, the reflection of the radio waves grew steadily fainter and the layer dropped—in some cases, to only thirty miles or so.