## Fowler, Ralph Howard

## Fowler, Ralph Howard

# Fowler, Ralph Howard

(*b*. Roydon, Essex, England, 17 January 1889; *d*. Cambridge England, 28 July 1944)

*Physics*.

Fowler was the oldest son of Howard Fowler, a London businessman, and Ena, daughter of George Dewhurst, a Manchester businessman. He was educated at Winchester and at Trinity College, Cambridge (B. A., 1911); as a student he showed considerable ability in golf and cricket as well as winning prizes in mathematics. After taking his degree he published some work on the theory of solutions of differential equations and as a result was elected to a fellowship at Trinity in October 1914.

By this time Fowler had obtained a commission in the Royal Marine Artillery. He was wounded in the Gallipoli campaign, and while convalescing in 1916 was persuaded to join a group of scientists, led by A. V. Hill, who were doing research on such military problems as tracking the flight of airplanes and computing trajectories of cannon shells. This early introduction to applied mathematics seems to have influenced Fowler’s subsequent interest in physical problems, although he did not entirely abandon his earlier commitment to pure mathematics.

In 1921, two years after returning to Cambridge as a fellow, he married Eileen, the only daughter of Sir Ernest Rutherford. They had four children.

In 1922 Fowler and C. G. Darwin published a series of papers on statistical mechanics in which they developed methods for calculating the “partition functions” associated with the distribution of energy in quantum systems. (By using the theory of functions of a complex variable they were able to avoid some of the usual approximations.)

Fowler then extended these methods in statistical mechanics to deal with the equilibrium states of ionized gases at high temperatures. His results could be immediately applied to the interpretation of stellar spectra and provided a new method for estimating the temperatures and pressures of stellar interiors. Fowler also provided one of the earliest applications of the new “quantum statistics” of E. Fermi and P. A. M. Dirac when in 1926 he proposed that white dwarf stars consist of a “degenerate” gas of extremely high density. Thus Fowler was one of the founders of modern theoretical astrophysics. (His work on the solutions of Emden’s equation was another contribution to this field.)

By the early 1920’s Fowler was among the very few workers at Cambridge who maintained a continuing interest in the progress of the quantum theory; he kept in touch with recent developments through correspondence and visits to Copenhagen. Those students—such as Dirac—who turned their attention to the quantum theory had usually been introduced to it by Fowler, and it was he who gave Dirac the galley proofs of Heisenberg’s “matrix article” of 1925, which led to Dirac’s discovery of Poisson-Bracket relations (according to private communication from T. S. Kuhn, based on information in the Archive for History of Quantum Physics). Because of his connection with Rutherford, Fowler was particularly well placed to introduce problems from the quantum theory into the discussions of the more experimentally inclined physicists who gathered at the Cavendish Laboratory and in the Kapitza Club. Much of the early work at Cambridge on this aspect of physics was therefore stimulated by him.

Fowler was awarded the Adams Prize at Cambridge University in 1924 for an essay on statistical mechanics. In 1929 he published a revised version of this essay, including the application of quantum statistics and ionization theory to states of matter at high pressures and high temperatures. *Statistical Mechanics* became the standard reference work on the subject in English-speaking countries for the next decade; it was followed by a second edition (1936) and by *Statistical Thermodynamics* (1939), a book emphasizing applications to physical chemistry, written with E. A. Guggenheim.

Fowler was elected to the Plummer chair of theoretical physics at Cambridge in 1932 and continued to pioneer the applications of statistical mechanics and to explore other areas of theoretical physics. Together with such students and colleagues as E.A. Guggenheim and R. F. Peierls he developed the “Ising model” as a theory of phase transitions and cooperative phenomena in magnets, alloys, and solutions.

In 1938 he was appointed director of the National Physical Laboratory, to succeed Sir Lawrence Bragg, but had to decline the appointment almost immediately because of illness. In World War II he served as a consultant to the Ordnance Board and the Admiralty. In 1942 he was knighted for his services to the government, in particular for establishing scientific liaison between research efforts on military problems in England and in Canada, and for his accomplishments during an important mission to Canada and the United States.

## BIBLIOGRAPHY

The best source of information about Fowler is the comprehensive memoir by his friend and colleague E. A. Milne, in the *Obituary Notices of Fellows of the Royal Society of London*, **5** (1945–1948), 61–78, which contains a portrait, bibliography, and many personal recollections.

Stephen G. Brush