John Frank Allen, the most senior of low-temperature physicists, died on 22 April 2001 near St. Andrews, Scotland, from age-related complications. Jack, as he was commonly called, was a physicist of many accomplishments, but none more remarkable than his discovery of superfluidity and the fountain effect in helium-II, the phase of liquid helium-4 below 2.17 K. The importance of this discovery has received much recent attention in connection with the discovery of superfluidity and Bose–Einstein condensation (BEC) in the condensates of dilute atomic alkali gases.
Even as late as 1938, theoretical physicist Fritz London was quoted as saying, “In the course of time the degeneracy of the Bose–Einstein gas has got the reputation of having only an imaginary existence.” The articles by Jack and Don Misener of the University of Cambridge and Peter Kapitza of the Institute for Physical Problems (now the Kapitza Institute for Physical Problems) announcing superfluidity appeared on adjoining pages of Nature in 1938. The discovery of superfluidity (see Physics Today, Physics Today 0031-9228 48 7 1995 30 https://doi.org/10.1063/1.881467 July 1995, page 30 ) induced a great step forward in London’s thinking. The first major post–World War II conference was organized in July 1946 by Jack and Lawrence Bragg of Cambridge. London gave the opening address, making a firm connection between superfluidity and BEC.
Jack was born on 6 May 1908 in Winnipeg, Canada, where his father, Frank, was the first professor of physics in the University of Manitoba. Jack took his BA in physics in 1928 at the University of Manitoba and moved to the University of Toronto to do a doctorate in superconductivity under John McLennan. He earned his PhD in 1933.
After a scientifically unrewarding two-year postdoc at Caltech, Jack wrote to Ernest Rutherford in Cambridge to see if he could work with Peter Kapitza, a Russian-born pioneer in low-temperature physics in the Royal Society Mond Laboratory. By the time Jack arrived in Cambridge in 1935, Kapitza had been permanently detained in Moscow by Josef Stalin, and Jack was on his own. His time in the Mond Laboratory was astonishingly productive: Not only did he discover superfluidity, but also the celebrated fountain effect. Jack told me that when he first demonstrated the fountain to the Royal Society, the novelist H. G. Wells crawled under the table to see if a hidden pump was producing the fountain. A great deal of early progress in superfluidity was due to the influence of major theoretical physicists. While Kapitza had Lev Landau to talk to about theory, Jack had Rudolph Peierls, Harry Jones, and Neville Mott—hardly lesser theoretical help!
One little known accomplishment of Jack’s is his invention of a vacuum seal in 1947. Pump connections in those days consisted of a piece of bicycle tube tightened with twisted 16- or 18-gauge copper wire, or flat glass flanges sealed with liberal quantities of plasticine and oil. Leaks were frequent and disastrous. It occurred to Jack that two ideally smooth parallel plates separated by an ideally smooth circular ring of precisely circular cross section should constitute a perfect vacuum seal. A telephone call to a company in Newcastle in the UK that made neoprene seals of all shapes and sizes for the oil and chemical industry yielded rings that worked perfectly the first time. Thus O-rings were born.
Jack always kicked himself for failing to appreciate Laszlo Tisza’s suggestion to him to look for “ondes de température” (temperature waves), now called second sound. Jack’s graduate student Ernest Ganz set out to measure the time a heat pulse took to traverse a capillary tube full of helium-II. The velocity turned out to be of order 100 meters per second, the same order of magnitude as second sound. Because pulses were also detected when only a film was present in the capillary, it is possible Jack was on track to find third sound as well. The war began a few months later and put a stop to basic research at Cambridge.
During the war Jack did work on antiaircraft shells. The Board of Ordnance, which is believed to be the oldest committee in the world, oversaw this work. The board was formed in 1346 to improve English artillery after what was perhaps its first use in the field at the Battle of Crécy. Jack assured me the original members were still sitting.
In 1947, Jack moved to the University of St. Andrews, taking with him a group of fine low-temperature physicists to build up the department there. Among his major accomplishments at St. Andrews was overseeing the design and construction of a new physics building with special amenities for conferences. He served in several administrative posts at the university. His own contributions to research declined there as he approached retirement and his attention turned to matters such as the history of Scottish physicists. Perhaps that change of emphasis has something to do with the startling omission of Jack’s name in the awarding of the Nobel Prize in Physics to Kapitza in 1978 for his “basic inventions and discoveries in the area of low-temperature physics.” Surely Jack made equally important and basic discoveries in this field.
Jack’s life was so varied and colorful, it certainly deserves a full-scale biography. I hope that will happen: Jack kept good records on practically everything.
