* * *
IN SOBRAL, MAY 29 was cloudy. The previous few days had been unusually rainy, dampening everyone’s spirits. The local community had been preparing to make the eclipse a public event, and festivities were ready to go. A small observatory near the edge of the eclipse path sold tickets to look through a telescope.
The clouds were still thick at the beginning of the eclipse. When the leading edge of the moon touched the solar disk (a moment called “first contact”), Crommelin estimated that 90 percent of the sky was clouds. But they rapidly diminished and the sun sat in a large clear patch as totality began. The landscape was plunged into surreal darkness and the astronomers began their work. Their focus was all on the instruments. One of the Brazilians watched a clock and called out the passage of seconds for timing the photographs. Nineteen photos were exposed with the large astrographic telescope and eight with the small four-inch lens. The clear sky held for the entire eclipse; everything had gone smoothly. They cabled home immediately: “Eclipse splendid.”
On the other side of the Atlantic, the Principe dignitaries came to visit Roça Sundy the morning of the eclipse. They were immediately greeted by a tremendous rainstorm, the heaviest the British visitors had seen, and quite unusual for that time of year. It ended around noon, with a couple hours to go before the eclipse. Eddington watched as there “were a few gleams of sunshine after the rain, but it soon clouded over again.” The clouds, he said, “almost took away all hope.”
At first contact the sun was invisible behind the clouds. It was not until 1:55 p.m. that the astronomers began to get glimpses of the sun, shaped into a crescent by the moon’s inexorable creep. It slipped in and out of cloud from moment to moment. Even in good conditions the last few seconds before totality have been described as “almost painful.” We can only imagine what this kind of knife-edge waiting would have felt like. Totality was calculated to begin five seconds after 2:13 p.m. At that moment the astronomers became machines, carrying out the planned procedures regardless of what they could see with the naked eye. Machines, though, driven by hope and anticipation. As Eddington described it: “We had to carry out our programme of photographs in faith.”
The telescope took all of their attention. Cottingham kept the coelostat mechanism running and handed Eddington fresh plates; Eddington removed the exposed plates and slid in the new ones. He had to pause for a delicate second after each swap, lest the motion cause some tiny tremor that would ruin the image.
Other than a quick look to make sure the eclipse had begun, Eddington did not get to see the celestial event on which he had gambled so much. There was no time to watch the sublime theatre going on:
There is a marvelous spectacle above, and, as the photographs afterwards revealed, a wonderful prominence-flame is poised a hundred thousand miles above the surface of the sun. . . . We are conscious only of the weird half-light of the landscape and the hush of nature, broken by the calls of the observers, and the beat of the metronome ticking out the 302 seconds of totality.
When totality ended, the world returned to normal, with no lasting marker of the disruption of the natural order that had just taken place. Within a few minutes the sky was perfectly clear, perhaps due to the temperature change of the eclipse itself.
At Roça Sundy, sixteen glass plates sat covered, holding the secrets of the stars until they could be scrutinized. Great efforts would be required until they gave up their message. But the event itself was over. Eddington could take a moment to breathe. His telegram to Dyson was succinct: “Through cloud. Hopeful.”
* * *
THE DECISION HAD been made to develop the photographs on-site in Brazil and Principe, and for reasons “not entirely from impatience.” The glass plates were delicate and could easily be damaged on the long journey home. Developing them in place and making preliminary measurements would at least guarantee some results, even if they were gathered in imperfect conditions.
Davidson and Crommelin in Sobral developed four of the astrographic photographs the next night. They were shocked to see that the star images were ever so slightly distorted, as though the focus on the telescope had been changed.
May 30, 3 am . . . It was found that there had been a serious change of focus, so that, while the stars were shown, the definition was spoilt. This change of focus can only be attributed to the unequal expansion of the mirror through the sun’s heat. The readings of the focusing scale were checked next day, but were found unaltered at 11.0 mm. It seems doubtful whether much can be got from these plates.
The coelostat mirror that reflected the sun’s image into the astrographic telescope was a thin sheet of metal. The portions of the mirror where the sun’s light was brightest would be slightly heated, and when metal is heated it expands. This expansion would be different from the unheated parts of the mirror and cause the surface to warp and bend. For normal eclipse observations this effect would be negligible. But the Einstein deflection was such a small effect that it could easily be swamped by such a phenomenon.
The images from the four-inch telescope, brought along as an afterthought, looked much better. So not all hope was lost. In any case, the pair of astronomers had a long wait ahead of them. They needed to stay in Brazil until July to take check photographs of the Hyades once the sun had moved out of the way.
Eddington was not in a mood to wait. While there were good technical reasons to examine the photographs right away, it seems his incentive may have been more personal. For the six nights after the eclipse he and Cottingham developed two plates each night. They were not quite what he wanted:
We took 16 photographs (of which 4 are not yet developed). They are all good pictures of the sun, showing a very remarkable prominence; but the cloud has interfered very much with the star-images. The first 10 photographs show practically no stars. The last 6 show a few images which I hope will give us what we need; but it is very disappointing. Everything shows that our arrangements were quite satisfactory, and with a little clearer weather we should have had splendid results.
Eddington then spent each day hunched over the photos with his micrometer making fine measurements. The effect he was looking for was “large as astronomical measures go” but still tiny by any ordinary consideration.
One of Eddington’s photographs from the eclipse at Principe
ROYAL ASTRONOMICAL SOCIETY
Even the measurements themselves were not enough to make a decision about the result of the Einstein test. The numbers had to be “reduced”—interference accounted for, optical effects eliminated, and so forth—before they became real data. Even with Eddington’s legendary mathematical speed it still took him three days of feverish work. It was more complicated than he expected because the cloudy images forced him to use different methods from those planned. Explaining this to his mother, he wrote:
. . . consequently I have not been able to make any preliminary announcement of the result. But the one good plate that I measured gave a result agreeing with Einstein and I think I have got a little confirmation from a second plate.
So at some point in the first week of June 1919, Eddington put down the pen he had been using for his calculations. Perhaps he rested his head in his hands. Three years after he’d received de Sitter’s first letter, a year after he’d walked freely out of the Cambridge Tribunal, Eddington had his answer: “I knew that Einstein’s theory had stood the test and the new outlook of scientific thought must prevail.” He called this the greatest moment of his life.
Despite that solemnity, Eddington could not let the opportunity slip—he turned to Cottingham, recalling Dyson’s warning, and quipped, “Cottingham, you won’t have to go home alone.” This moment was just a matter of Eddington persuading himself, though. A personal confirmation of faith. His preliminary calculations were not nearly enough to convince everyone back home. That would take months’ more measurement and calculation (and he didn’t eve
n know what the plates from Brazil might look like). Not to mention making sure the results had the political and social impact he was hoping for. A great deal of work remained.
Eddington had hoped to stay on Principe to complete some of that work but his plan was disrupted by labor issues with the local steamship line. If he did not depart immediately he might be stranded for an unknown length of time. The governor of Principe commandeered space for him and Cottingham on the last ship leaving that summer (the SS Zaire). The boat was extremely crowded. Aggravating the situation was the fever that Eddington had been struck with. It got bad enough that he passed out at least once, though the sea air on the ship set him to rights. He wrote one last letter to his mother from the ship on June 21. He would likely arrive home before the letter did, hopefully in time to have the English strawberries that were, he said, better than anything he could get in the tropics.
* * *
EINSTEIN PROBABLY DID not have any strawberries that June, though they would have been appropriately celebratory: he and Elsa got married. On the second day of the month, they went to the Berlin registration office and made it official (despite the Swiss court’s order that he wait). She had successfully pulled Einstein into a respectable middle-class life, much to the amazement of his friends.
Not much changed in their lives, since he had already been living in her apartment. The family took over the two attics above Elsa’s flat and renovated them as workspace for Albert. That study, known as the “turret room,” was distinguished by shelves of books and portraits of Newton and Faraday on the walls. No one was allowed to clean the study, save for light dusting. He sometimes received visitors there, but it was generally a place for solitary labor. He would often work for hours, come downstairs, strike a few chords on the piano, and then return to his study. In the weeks following the marriage he did not get much original work done (his illness was coming and going) but he was waiting anxiously for news from the eclipse. He had heard via the Dutch that Eddington had returned to Britain, and he hoped to hear results within six weeks or so.
Virtually no one else in Berlin was waiting for them, mostly because all of Germany was outraged by the recent news of the peace negotiations. They had been hoping that the final treaty would take Wilson’s Fourteen Points seriously. Instead, the country would lose 13 percent of its land, 10 percent of its population, all its overseas colonies, and Alsace-Lorraine. The Rhineland would be occupied. Their army would be shrunk to the point where it was unclear if they could maintain order inside the country.
Most insulting of all was the clause that established Germany’s sole guilt for the war. This became the justification for brutal monetary reparations. Prime Minister Lloyd George had won an election on the promise to squeeze the Germans: “We will search their pockets for it.” John Maynard Keynes was part of the diplomatic team that arranged the terms, and he was immensely frustrated by the “empty and arid intrigue” going on. Disgusted, he resigned from the negotiations and went home to write his prescient The Economic Consequences of the Peace that warned of the long-term damage of a vengeful treaty. Total reparations were eventually set at 132 billion marks (about $330 billion in modern money).
Two weeks after the Einstein wedding, Germany was informed they had three days to approve the treaty, or else (they were eventually given another week). The unstable German coalition government was deeply divided over whether to sign the treaty, and there was a great deal of popular resistance. Berlin had an official week of mourning in response to the terms. In the end, though, they had little choice and the treaty was signed at Versailles on June 28. Only then, more than half a year after the end of the fighting, was the British blockade finally lifted.
Einstein was irate over the Allies’ greed. “Just as well that we do not have to sell our brains or make an emergency sacrifice of them to the state.” He didn’t think all the provisions would be enforced, though. He was more worried about how the cruel terms had given a huge boost to right-wing politics in Berlin. The revolution’s initial promise of an inclusive socialist democracy looked more and more empty. “Here the political wave has subsided. There is no energy left for grand emotions; rather, one is more or less passive. The populace perceives the end of the war as a liberation, the reappearance of vegetables as a relief.” He continued to try to organize a commission to investigate wartime atrocities, with little support. Einstein had hoped that defeat would drive the Germans away from militarism. Now he worried that it would do just the opposite.
* * *
THE VICTORS, THOUGH, were generally pleased with how things were going. Along with the finalization of the peace treaty and the formation of the League of Nations came a rush of efforts to build a new international order: economic, military, and scientific. Part of the last was a group of American astronomers on its way to Brussels to help establish the new International Research Council (IRC). Led by W. W. Campbell of the Lick Observatory, they stopped in London en route to visit the Royal Astronomical Society. The RAS welcomed their visitors, arranging their first July meeting in sixty years. H. H. Turner, in the chair, explicitly greeted them as wartime allies: “We do not forget what we owe to our American friends for their help towards ending the war so successfully.” He commented that he had last seen many of these astronomers at a scientific meeting in Germany just before the war. “We look back at that meeting with somewhat mixed feelings.”
Campbell chose an interesting topic for his lecture—his observatory’s attempts to measure the gravitational deflection of light at the eclipse of the previous year, June 8, 1918. Eddington was still on his way home from Principe, so Britain was eager for news on the Einstein problem. The Lick expedition had been led by Campbell’s deputy, Heber Curtis. Their specialized eclipse telescopes were actually still in Russia, where they had hoped to observe the 1914 eclipse, when they were chased away by the start of the war. Without that equipment they had to borrow some lenses, and then Curtis was called to do war work. For some time. They did finally manage to observe the 1918 eclipse, though. Curtis measured the plates . . . and found no deflection.
Campbell was apologetic. He admitted that the telescopes used for the measurement were not the right type for this kind of work, and the star images were just too faint for much confidence in Curtis’s result. Nonetheless, he did not think the plates could be reconciled with the full Einstein deflection; perhaps with the half-deflection.
With relativity’s chief defender absent, Dyson was called to speak for the British expeditions. He had been reporting what little news there had been from Brazil and Africa. With no firm results yet, there was not much he could say beyond a mild statement that relativity was “an extremely difficult question to settle.” He had received a letter from Eddington two days before in which he said he had “some evidence” for deflection, but nothing had been fully determined.
Campbell’s closing message for the meeting was the American vision for the new international scientific community that the IRC embodied. He said the exclusion of the Germans and Austrians was a way of protesting the “over-development of militarism.” If that meant breaking some scientific bonds, so be it: “It chances that certain astronomers may be criticized and cut off somewhat from others. We feel, however, that it is clearly our duty to be men first and astronomers later.”
The Americans went directly from London to Brussels to inaugurate the new organization and its subsidiaries such as the International Astronomical Union. They saw themselves as inaugurating a new era for science of morality and responsibility, just as the founders of the League of Nations felt they were doing for politics. Of course, there was no chance that the recently enemy countries would be included in the new international scientific groups. The question was whether neutral countries would be allowed. Was the price of admission active engagement in the war, or just not being on the wrong side? In the end, thirteen countries that had been neutral during the war were allowed to join. A special rule w
as put in place to prevent them from using their numbers to vote the Germans in. Exactly one month after the signing of the Treaty of Versailles, the IRC statues were set in stone for twelve years. Some prominent scientists, including Eddington’s Dutch friend Jacobus Kapteyn, protested the German exclusion. Kapteyn circulated a public letter reminding the IRC, “Our grand governess, nature, mocks our petty hostilities.”
* * *
EDDINGTON CAME HOME to this new world of science. “International” science was now officially defined as “everyone except Germany and Austria.” But he had a trunk full of photographs intimately tied to a theory substantially developed in Berlin and had no intention of suspending his work on relativity. The next step was to turn those photographs into rigorous data. Scientific observations do not speak for themselves; they do not give up their secrets easily. Bringing the world around to his conclusion that Einstein was right would take months of tedious measurement and calculation.
Dyson and Eddington apparently decided to keep the expeditions separate even during the process of analyzing the data. Perhaps it was thought that independent measurements would be seen as more reliable. The Principe photographs would be analyzed in Cambridge, the Sobral ones in Greenwich. Eddington probably did the measurements and calculations for the former himself. Davidson worked with Royal Observatory staff on theirs.
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