SIMON, FRANZ EUGEN (FRANCIS)

(b. Berlin, Germany, 2 July 1893; d. Oxford, England, 31 October 1956)

physics.

The son of a wealthy estate dealer, Simon, and his two sisters, grew up in comparative affluence. Although he received a classical education, he developed a strong interest in science; and in 1912 he went to Munich to read physics. A year later he was called up for military service; and from 1914 to 1918 he served as lieutenant in the field artillery. He resumed his studies at the University of Berlin in 1919, and the following year he started work for his Ph.D. under the supervision of Nernst. His dissertation concerned the measurement of specific heats at low temperatures, a line of research that was closely connected with Nernst’s heat theorem, now generally known as the third law of thermodynamics. The subject remained the basis of Simon’s scientific interest throughout his life. After obtaining his doctorate in 1921, Simon remained at Berlin, where in 1924 he became Privatdozent and, three years later, associate professor. It was during this period that his school of low-temperature physics was founded and that he did his outstanding work combining low-temperature and high-pressure techniques.

In 1931 Simon was appointed to the chair of physical chemistry at the Technical University of Breslau, succeeding Eucken. With some of the former members of his Berlin school he began to assemble and to set up low-temperature equipment, but the economic depression and political uncertainty severely hampered these efforts. Simon spent part of 1932 as visiting professor at Berkeley. When, a few months after his return from America, Hitler assumed power, Simon realized that despite his war service, his days in Germany were numbered. He tendered his resignation in June 1933 and accepted the invitation of F. A. Lindemann (later Lord Cherwell) to work at the Clarendon Laboratory, Oxford, where a small helium liquefaction plant had been set up by one of Simon’s former co-workers. K. Mendelssohn. Another member of his Berlin School, Nicholas Kurti, accompanied Simon to Oxford and worked with him until Simon’s death.

At first Simon occupied no regular position in Oxford but received a grant from Imperial Chemical Industries, which, through Lindemann’s efforts, was helping many scientific refugees to establish themselves. In 1935 Simon was appointed to the readership in thermodynamics, and in 1945 he became professor of thermodynamics. He held this post until 1956, when Lindemann retired as Lee professor of experimental philosophy and Simon became his successor. Simon died while making plans for the further development of the Clarendon Laboratory. only a few weeks after taking up his new appointment.

Except for the interruption by the war years, Simon devoted all his time at Oxford to building up a new research school in low-temperature physics. At his suggestion Kurti, while still at Berlin, had begun work on the low-temperature properties of paramagnetic salts; and after settling at Oxford, much of Simon’s work was taken up with developing the method of cooling by adiabatic demagnetization and with investigating the properties of matter at temperatures below ° During the last years of his life his interest shifted from the ordering of electron spins to that of nuclear spins, and in 1951 the first nuclear alignment was achieved by members of his research group. Although Simon was greatly interested in this combination of low temperatures and nuclear physics, it took second place to the aim that he and Kurti had pursued for many years, the cooling by adiabatic demagnetization of nuclear spins. After long preparations and often disappointing pilot experiments, the final goal was reached a few months before Simon’s death. The nuclear spin system of copper had been cooled to a temperature of less than 20 microdegrees absolute.

In addition to his magnetic work, Simon continued his interest in the general properties of matter at liquid helium temperatures, such as specific heats and thermal conductivities. He also resumed the research at high pressures, but perhaps not quite with the vigor it deserved. During the war Simon took part in the work on the atomic bomb and was particularly concerned with isotope separation by gaseous diffusion. In his later years he was much concerned with the problems of utilizing scientific advances technologically; and in his writings on these subjects politicians, as well as industry, came in for a good deal of criticism.

In 1941 Simon was elected a fellow of the Royal Society, and in 1948 he received its Rumford Medal. Two years later he was the first recipient of the Kamerlingh Onnes Medal of the Dutch Institute of Refrigeration, and in 1952 he was awarded the Linde Medal; in the same year he was elected an honorary foreign member of the American Academy of Arts and Sciences. For his war work on atomic energy he was given the C.B.E. in 1946, and in 1955 he was knighted.

When assessing Simon’s scientific achievement, it is tempting to rate the spectacular success of nuclear cooling highest, but this would not do justice to the large body of outstanding work directed toward the proof and elucidation of the third law of thermodynamics. When Simon came to Nernst in 1920, the latter had just written the famous monograph in which he had proved to his own satisfaction that the heat theorem was correct and that it should be regarded as a basic law of physics. There were many who did not share this conviction, however, and it was left to Simon to prove the validity of the law in which Nernst was now beginning to lose interest. The law requires that, as absolute zero is approached, any system must tend to a state of zero entropy (that is, to maximum statistical orderliness). It was pointed out that many systems, such as glasses, retained an obvious degree of disorder, even when cooled to the lowest possible temperatures. Simon noticed that these systems were not in thermodynamic equilibrium and that, if by magic or by waiting for immensely long times they could be guided into equilibrium, the process would be accompanied by the liberation of heat. In other words, none of these systems could be used to reach absolute zero and thereby infringe upon the third law.

Simon and his school also investigated systems, such as ortho-hydrogen, the chemical constant of which seemed to suggest the existence of a zeropoint entropy. Their experiments proved that some ordering always occurs. sometimes at less than °,which brings the system into agreement with the third law. Simon also provided the explanation for the very strange fact that under its own vapor pressure helium remains a liquid, even at absolute zero. He showed that this is due to the vibration of the atoms under the again is a consequence of Nernst’s theorem.

Simon’s work on high pressure was an investigation of the melting curves of solidified gases, especially that of helium. It was known that up to the highest pressures, the equilibrium between the solid and the fluid phase of any pure substance follows a smooth curve with no indication of a critical point or of a change in the temperature function. He had the brilliant idea of extending investigation to the substance with the lowest critical data: helium. Thus, using it as a model system, Simon eventually was able to explore the melting curve up to ten times the liquid-gas critical temperature. Even under these extreme conditions, however, no solid-fluid critical point was found. In fact, parallel experiments on the thermodynamic properties showed that with rising pressure and temperature, the two phases become increasingly dissimilar.

Curiously, Simon was at first less known through his scientific results than through the methods of obtaining them. When he began his work, only three laboratories in the world commanded the expensive means of liquefying helium. It was Simon’s great achievement to develop small-scale apparatus of novel and ingenious design that eventually permitted not only his but many other laboratories to experiment in this otherwise closed domain.

BIBLIOGRAPHY

Simon and his co-workers published more than 150 papers, only a few of which can be cited here: “Zur Frage der Nullpunktsenergie,” in Zeitschrift für Physik, 16 (1923), 183–199, written with K. Bennewitz; “Die Bestimmung der freien Energie,” in H. Geiger and K. Scheel, eds., Handbuch der Physik, X, pt. 7 (Berlin, 1926), 350; “Füufundzwanzig Jahre Nernstscher Wärmesatz,” in Ergebnisse der exakten Naturwissen-chaften, 9 (1930), 222–274; “The Approach to the Absolute Zero of Temperature,” in Proceedings of the Royal Institution, 28 (1935), 515–541; “On the Range of Stability of the Fluid State,” in Transactions of the Faraday Society, 33 (1936), 65–73; “The Determination of Temperature Below 1° K..” in Science Progress34 (July 1939), 31–46; The Neglect of Science (Oxford, 1951), “Low Temperature Problems. A General Survey,” in F. E. Simon et al., Low Temperature Physics (London, 1952), 1–29; and “The Third Law of Thermo-dynamics—a Historical Survey (40th Guthrie Lecture),” in Yearbook of the Physical Society (1956), 1.

For Simon’s life see N. Kurti’s obituary in Biographical Memoirs of Fellows of the Royal Society; and Nancy Arms. A Prophet in Two Countries: The Life of F. E. Simon (London, 1966).

Kurt Mendelssohn