Alumnus Timothy Baker, son of the late Michael Baker of the Clarendon, rediscovered the typescript of an unpublished history of the Clarendon Laboratory written by AJ Croft, cryogenics expert and administrator of the Clarendon from the 1940s to the 1980s. Here, Timothy looks at Clarendon milestone, the first liquefaction of helium in Britain in 1933.
This year, 2023, marks the 90th anniversary of the historic experiment in which Kurt Mendelssohn achieved the first liquefaction of helium in Britain. As recounted by Nicholas Kurti in Nature, 302, 17 March 1983, for the 50th anniversary, the Department of Physics, now in the Lindemann, Townsend, and Simon Buildings, erected a plaque in its old home to commemorate this milestone of Oxford physics, see image above. The plaque has recently been rediscovered, having been saved several years ago by Building Manager Steven Hill, during refurbishment of the Robert Hooke Building, which stands on the site of the Old Clarendon.
Frederick Lindemann saw the achievement as significant, not least because it was the first occasion on which Oxford’s Clarendon Laboratory had beaten Cambridge’s Cavendish Laboratory to a major research milestone. The plaque also bears witness to what was truly a turning point in the history not only of physics at Oxford, but also of the world. It was the swansong of the great 19th-20th century school of German physics, which within months had been decimated by the Nazis' anti-semitic laws. Lindemann took a leading role in the rescue of the German refugees, who with their pupils built on Lindemann’s early-20th century revival of the Clarendon’s research programme, taking it to the fulness of its golden age.
Vigorous programme of research
In the late 19th and early 20th centuries, Oxford’s Clarendon badly lagged behind other leading universities' physics departments, and most especially Cambridge's Cavendish Laboratory under Lord Rayleigh and JJ Thomson. Frederick Lindemann became Professor in 1919 – almost at the same time as Ernest Rutherford at Cambridge – and Lindemann was determined to revitalise the Clarendon, and build it to an equivalent status with Cambridge’s Cavendish. He quickly recruited leading British physicists, and built a vigorous programme of research, which had more or less ground to a halt for most of the decades since the Clarendon Laboratory’s foundation in 1872.
Lindemann was however hampered by the difficulty of extracting funding for research from the Oxford University authorities. He relied heavily on self-funded wealthy physicists such as Thomas Merton, Derek Jackson, and Gordon Dobson. Meanwhile Rutherford's Cambridge laboratory continued to accumulate Nobel Prizes. 1932 was the Cavendish’s ‘annus mirabilis’, during which James Chadwick discovered the neutron, John Cockcroft and Ernest Walton artificial nuclear disintegration of light elements, and Patrick Blackett the positron.
Specialists in low-temperature physics
Lindemann wanted the Clarendon to lead in his own speciality – low-temperature physics – to match Cambridge's leadership in particle physics. Though Lindemann’s revitalised lab made important research discoveries in atmospheric physics, spectroscopy, and thermodynamics, it remained rather low-key until 1933.
In Cambridge in 1932, Rutherford opened the new lavishly equipped Mond Laboratory for low-temperature research, headed by the Russian Pyotr Kapitza. Cryogenic equipment at the time was very delicate and temperamental, and only the most skilled people – mostly in Germany – were able to make it work. There was an informal race between Oxford and Cambridge to become the first British laboratory to make liquid helium, which at about 4K was an essential for meaningful low-temperature research.
Historic experiment
So, in late 1932, Lindemann, himself an alumnus of Berlin University, bought an expansion liquefier from fellow Berlin alumnus Franz Simon of Breslau University, where he had established a laboratory that led the world in low-temperature apparatus and research. Simon’s colleague Kurt Mendelssohn came over to Oxford to get the equipment working and, as recorded on the plaque, Mendelssohn did so on 13 January 1933. The apparatus could produce 20cc of liquid helium per shot, which would then last for about 90 minutes. Lindemann’s and Thomas Keeley’s report of it in Nature on 11 February 1933, ‘Helium Liquefaction Plant at the Clarendon Laboratory, Oxford’, emphasised the equipment’s low cost (£350 for the hydrogen liquefaction plant, and £30 for the helium liquefier), and its equal efficiency with Kapitza’s design in Cambridge.
Two weeks after Mendelssohn’s historic experiment, Adolf Hitler was appointed Chancellor of Germany. A month after that he seized absolute power after the Reichstag Fire, and a month after that, from early April, Jewish scientists began to be dismissed en masse from their university positions.
Eminent scientists
Sensing an opportunity to build a staff of equivalent stature to Lord Rutherford’s at Cambridge, Lindemann used his contacts with his old Berlin University supervisor Walther Nernst to recruit refugees who suddenly found themselves without a career in Germany. Lindemann cultivated Sir Robert Mond (son of the benefactor of Rutherford’s laboratory, whose family chemicals business was one of the major constituents of the new conglomerate Imperial Chemical Industries) and ICI chairman Sir Harry McGowan, to obtain sponsorship in order to fund new positions at the Clarendon for the refugees. The first to arrive was Kurt Mendelssohn himself.
Lindemann toured Germany in his chauffeur-driven Rolls Royce in 1933, seeking additional refugee recruits for the ICI-funded scheme. The most eminent of the refugee scientists whom Lindemann recruited was Nernst’s pupil, and Kurt Mendelssohn’s cousin and supervisor, Francis Simon, who brought with him from Breslau his Hungarian pupil and colleague Nicholas Kurti. They recreated their low-temperature laboratory at Oxford, establishing its formidable reputation in this field, though they also experimented in Paris. Simon also brought with him the brothers Fritz and Heinz London, the latter also one of his pupils, who became pioneers of the theory of superconductivity. Other recruits were Erwin Schrödinger, not Jewish but an exile in protest against the Nazi policy; Leo Szilard, another Hungarian; and Heini Kuhn. Lindemann also tried to recruit Albert Einstein, Lise Meitner, and Hans Bethe.
Supercharged Clarendon
In 1934, Kapitza invented a new type of liquefier that enabled large-scale production of liquid helium, considerably easing low-temperature research, but his indefinite detention back in Russia from the same year meant that Oxford’s Clarendon was able to consolidate its lead in the field. Though the ICI grants were short term, Lindemann managed to continue to find funding from various sources to retain the majority of the most important of the refugees at Oxford until new government financing for military research became available on the outbreak of war. The new recruits supercharged Oxford’s Clarendon, which never looked back and, by the 1940s, led the world in many fields of low-temperature and solid-state physics.
Mr Hill now plans, with the Department of Physics’s Simon Probert, to reinstate the plaque near its original site, to renew its witness to a pivotal moment, not just in the history of physics at Oxford , but of the world as well.