Richard Rhodes - The Making of the Atomic Bomb

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.” 307On 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. 308

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. 309Then 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.” 310

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.” 311A 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.” 312Marie Curie came across from France, “shy,” says A. S. Eve, “retiring, self-possessed and noble.” 313She 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.” 314

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.’” 315Against 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.” 316

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 up the periodic table, one step at a time. He devised a little staircase of strips of film by matching up the lines. He wrote to Bohr on November 16: “During the last fortnight or so I have been getting results which will interest you…. So far I have dealt with the K [spectral line] series from Calcium to Zinc…. The results are exceedingly simple and largely what you would expect…. K = N − 1, very exactly, N being the atomic number.” He had calcium at 20, scandium at 21, titanium at 22, vanadium at 23, chromium at 24 and so on up to zinc at 30. He concludes that his results “lend great weight to the general principles which you use, and I am delighted that this is so, as your theory is having a splendid effect on Physics.” 317Harry Moseley’s crisp work gave experimental confirmation of the Bohr-Rutherford atom that was far more solidly acceptable than Marsden’s and Geiger’s alpha-scattering experiments. “Because you see,” Bohr said in his last interview, “actually the Rutherford work was not taken seriously. We cannot understand today, but it was not taken seriously at all…. The great change came from Moseley.” 318

Otto Hahn was called upon once more to demonstrate his radioactive preparations. In the early spring of 1914 the Bayer Dye Works at Leverkusen, near Cologne in the Rhineland, gave a reception to celebrate the opening of a large lecture hall. 319Germany’s chemical industry led the world and Bayer was the largest chemical company in Germany, with more than ten thousand employees. It manufactured some two thousand different dyestuffs, large tonnages of inorganic chemicals, a range of pharmaceuticals. The firm’s managing director, Carl Duisberg, a chemist who preferred industrial management along American lines, had invited the Oberpräsident of the Rhineland to attend the reception; he then invited Hahn to add a glow to the proceedings.

Hahn lectured to the dignitaries on radioactivity. Near the beginning of the lecture he wrote Duisberg’s name on a sealed photographic plate with a small glass tube filled with strong mesothorium. Technicians developed the plate while he spoke; at the end Hahn projected the radiographic signature onto a screen to appreciative applause.

The high point of the celebration at the vast 900-acre chemical complex came in the evening. “In the evening there was a banquet,” Hahn remembered with nostalgia; “everything was exquisite. On each of the little tables there was a beautiful orchid, brought from Holland by air.” Orchids delivered by swift biplane might be adequate symbols of German prosperity and power in 1914, but the managing director wanted to demonstrate German technological superiority as well, and found exotic statement: “At many of the tables,” says Hahn, evoking an unrecognizably futuristic past, “the wine was cooled by means of liquid air in thermos vessels.” 320

When war broke out Niels and Harald Bohr were hiking in the Austrian Alps, covering as much as twenty-two miles a day. “It is impossible to describe how amazing and wonderful it is,” Niels had written to Margrethe along the way, “when the fog on the mountains suddenly comes driving down from all the peaks, initially as quite small clouds, finally to fill the whole valley.” 321The brothers had planned to return home August 6; the war suddenly came driving down like the mountain fog and they rushed across Germany before the frontiers closed. In October Bohr would sail with his wife from neutral Denmark to teach for two years at Manchester. Rutherford, his boys off to war work, needed help.

Harry Moseley was in Australia with his mother at the beginning of August, attending the 1914 British Association meeting, in his spare time searching out the duck-billed platypus and picturesque silver mines. The patriotism of the Australians, who immediately began mobilizing, triggered his own Etonian spirit of loyalty to King and country. He sailed for England as soon as he could book passage. By late October he had gingered up a reluctant recruiting officer to arrange his commission as a lieutenant in the Royal Engineers ahead of the waiting list.