Kaiser Wilhelm enlarged at the dedication on the dangers of firedamp, the explosive mixture of methane and other gases that accumulates in mines. He urged his chemists to find some early means of detection. That was a task, he said, “worthy of the sweat of noble brows.” Haber, noble brow — he shaved his bullet head, wore round horn-rimmed glasses and a toothbrush mustache, dressed well, wined and dined in elegance but suffered bitter marital discord — set out to invent a firedamp whistle that would sound a different pitch when dangerous gases were present. With a fine modern laboratory uncontaminated by old radioactivity Hahn and Meitner went to work at radiochemistry and the new field of nuclear physics. The Kaiser returned from Dahlem to his palace in Berlin, happy to have lent his name to yet another organ of burgeoning German power.
In the summer of 1913 Niels Bohr sailed with his young wife to England. He followed the second and third parts of his epochal paper, which he had sent ahead by mail to Rutherford; he wanted to discuss them before releasing them for publication. In Manchester he met his friend George de He-vesy again and some of the other research men. One he met, probably for the first time, was Henry Gwyn Jeffreys Moseley, called Harry, an Eton boy and an Oxford man who had worked for Rutherford as a demonstrator, teaching undergraduates, since 1910. Harry Moseley at twenty-six was poised for great accomplishment. He needed only the catalyst of Bohr's visit to set him off.
Moseley was a loner, “so reserved,” says A. S. Russell, “that I could neither like him nor not like him,” but with the unfortunate habit of allowing no loose statement of fact to pass unchallenged. When he stopped work long enough to take tea at the laboratory he even managed to inhibit Ernest Rutherford. Rutherford's other “boys” called him “Papa.” Moseley respected the boisterous laureate but certainly never honored him with any such intimacy; he rather thought Rutherford played the stage colonial.
Harry came from a distinguished line of scientists. His great-grandfather had operated a lunatic asylum with healing enthusiasm but without benefit of medical license, but his grandfather was chaplain and professor of natural philosophy and astronomy at King's College and his father had sailed as a biologist on the three-year voyage of H.M.S.
If he was reserved to the point of stuffiness he was also indefatigable at experiment. He would go all out for fifteen hours, well into the night, until he was exhausted, eat a spartan meal of cheese sometime before dawn, find a few hours for sleep and breakfast at noon on fruit salad. He was trim, carefully dressed and conservative, fond of his sisters and his widowed mother, to whom he regularly wrote chatty and warmly devoted letters. Hay fever threw off his final honors examinations at Oxford; he despised teaching the Manchester undergraduates — many were foreigners, “Hindoos, Burmese, Jap, Egyptian and other vile forms of Indian,” and he recoiled from their “scented dirtiness.” But finally, in the autumn of 1912, Harry found his great subject.
“Some Germans have recently got wonderful results by passing X rays through crystals and then photographing them,” he wrote his mother on October 10. The Germans, at Munich, were directed by Max von Laue. Von Laue had found that the orderly, repetitive atomic structure of a crystal produces monochromatic interference patterns from X rays just as the mirroring, slightly separated inner and outer surfaces of a soap bubble produce interference patterns of color from white light. X-ray crystallography was the discovery that would win von Laue the Nobel Prize. Moseley and C. G. Darwin set out with a will to explore the new field. They acquired the necessary equipment and worked through the winter. By May 1913 they had advanced to using crystals as spectroscopes and were finishing up a first solid piece of work. X rays are energetic light of extremely short wavelength. The atomic lattices of crystals spread out their spectra much as a prism does visible light. “We find,” Moseley wrote his mother on May 18, “that an X ray bulb with a platinum target gives out a sharp line spectrum of five wavelengths… Tomorrow we search for the spectra of other elements. There is here a whole new branch of spectroscopy, which is sure to tell one much about the nature of the atom.”
Then Bohr arrived and the question they discussed was Bohr's old insight that the order of the elements in the periodic table ought to follow the atomic number rather than, as chemists thought, the atomic weight. (The atomic number of uranium, for example, is 92; the atomic weight of the commonest isotope of uranium is 238; a rarer isotope of uranium has an atomic weight of 235 and the same atomic number.) Harry could look for regular shifts in the wavelengths of X-ray line spectra and prove Bohr's contention. Atomic number would make a place in the periodic table for all the variant physical forms that had been discovered and that would soon be named isotopes; atomic number, emphasizing the charge on the nucleus as the determiner of the number of electrons and hence of the chemistry, would strongly confirm Rutherford's nuclear model of the atom; the X-ray spectral lines would further document Bohr's quantized electron orbits. The work would be Moseley's alone; Darwin by then had withdrawn to pursue other interests.
Bohr and the patient Margrethe went on to Cambridge to vacation and polish Bohr's paper. Rutherford left near the end of July with Mary on an expedition to the idyllic mountains of the Tyrol. Moseley stayed in “unbearably hot and stuffy” Manchester, blowing glass. “Even now near midnight,” he wrote his mother two days after Rutherford's departure, “I discard coat and waistcoat and work with windows and door open to try to get some air. I will come to you as soon as I can get my apparatus to work before ever I start measurements.” On August 13 he was still at it. He wrote his married sister Margery to explain what he was after:
I want in this way to find the wave-lengths of the X ray spectra of as many elements as possible, as I believe they will prove much more important and fundamental than the ordinary light spectra. The method of finding the wavelengths is to reflect the X rays which come from a target of the element investigated [when such a target is bombarded with cathode rays]… I have then merely to find at which angles the rays are reflected, and that gives the wavelengths. I aim at an accuracy of at least one in a thousand.
The Bohrs returned to Copenhagen, the Rutherfords from the Tyrol, and now it was September and time for the annual meeting of the British Association, this year in Birmingham. Bohr had not planned to attend, especially after lingering overlong in Cambridge, but Rutherford thought he should: his quantized atom with its stunning spectral predictions would be the talk of the conference. Bohr relented and rushed over. Birmingham's hotels were booked tight. He slept the first night on a billiard table. Then the resourceful de Hevesy found him a berth in a girls' college. “And that was very, very practical and wonderful,” Bohr remembered afterward, adding quickly that “the girls were away.”
Sir Oliver Lodge, president of the British Association, mentioned Bohr's work in his opening address. Rutherford touted it in meetings. James Jeans, the Cambridge mathematical physicist, allowed wittily that “the only justification at present put forward for these assumptions is the very weighty one of success.” A Cavendish physicist, Francis W. Aston, announced that he had succeeded in separating two different weights of neon by tediously diffusing a large sample over and over again several thousand times through pipe clay — “a definite proof,” de Hevesy noted, “that elements of different atomic weight can have the same chemical properties.” Marie Curie came across from France, “shy,” says A. S. Eve, “retiring, self-possessed and noble.” She fended off the bulldog British press by praising Rutherford: “great developments,” she predicted, were “likely to transpire” from his work. He was “the one man living who promises to confer some inestimable boon on mankind.”
Harald Bohr reported to his brother that autumn that the younger men at Gottingen “do not dare to believe that [your paper] can be objectively right; they find the assumptions too ‘bold’ and ‘fantastic’” Against the continuing skepticism of many European physicists Bohr heard from de Hevesy that Einstein himself, encountered at a conference in Vienna, had been deeply impressed. De Hevesy passed along a similar tale to Rutherford:
Speaking with Einstein on different topics we came to speak on Bohr's theory, he told me that he had once similar ideas but he did not dare to publish them. “Should Bohr's theory be right, it is of the greatest importance.” When I told him about the [recent discovery of spectral lines where Bohr's theory had predicted they should appear] the big eyes of Einstein looked still bigger and he told me “Then it is one of the greatest discoveries.”
I felt very happy hearing Einstein saying so.
So did Bohr.
Moseley labored on. He had trouble at first making sharp photographs of his X-ray spectra, but once he got the hang of it the results were outstanding. The important spectral lines shifted with absolute regularity as he went
