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Jeans, James Hopwood

Jeans, James Hopwood

(b. Ormskirk, Lancashire, England, 11 September 1877;d. Dorking, Surrey, England, 16 September 1946)

physics, astronomy.

Jeans was the son of William Tullock Jeans, a parliamentary journalist who wrote two books of lives of scientists. The family moved to London when Jeans was three. His childhood was not very happy and played an important role in forming his rather shy, apparently aloof personality. Jeans was a precocious child. His early passion was clocks, which he would dismantle, boil, and reassemble; he wrote a little booklet on clocks at the age of nine. He attended the Merchant Taylor’s School from 1890 to 1896 and entered Trinity College, Cambridge, in 1896; he was second wrangler on the mathematical tripos in 1898. While recovering from a tubercular infection of the joints, Jeans took a first class on part two of the tripos in 1900 and was awarded a Smith’s Prize. In the following year he was elected a fellow of Trinity College, and he obtained his M.A. in 1903. His first treatise, Dynamical Theory of Gases, was published in 1904. It became a standard textbook, both because of its clarity and elegance and because Jeans incorporated into it the results of his own research.”It is all a joyous adventure, “wrote E. A. Milne, the astrophysicist and Jeans’s biographer.

From 1905 to 1909 Jeans was professor of applied mathematics at Princeton University, where he wrote two textbooks, Theoretical Mechanics (1906) and Mathematical Theory of Electricity and Magnetism (1908). The latter work, written in Jeans’s fluent style, was widely used and went through many editions. In 1907 he was elected a fellow of the Royal Society and married an American from a wealthy family, Charlotte Tiffany Mitchell. They had one daughter.

Jeans was Stokes lecturer in applied mathematics at Cambridge from 1910 to 1912, when he retired from university duties, devoting himself to research and writing. His Report on Radiation and the Quantum Theory appeared in 1914 and helped to spread acceptance of the early quantum theory. From this time his interest turned more exclusively to astronomy, culminating in his Adams Prize essay, Problems of Cosmogony and Stellar Dynamics (1919), and his book Astronomy and Cosmogony (1928).He was elected a secretary of the Royal Society for 1919–1929, during which time he was instrumental in improving the quality of the physical section of the Proceedings. He was vice-president of the Royal Society for 19381940, president of the Royal Astronomical Society for 1925-1927, and president of the British Association for the Advancement of Science meeting at Aberdeen in 1934. In 1923 he was made a research associate of the Mt. Wilson Observatory;from its establishment in 1935 until the year of his death he held the chair of astronomy of the Royal Institution. He was knighted in 1928. Other honors included the Royal Medal of the Royal Society (1919), the Hopkins Prize of the Cambridge Philosophical Society (for 1921-1924), the gold medal of the Royal Astronomical Society (1922), and the Franklin Medal of the Franklin Institute (1931).

In 1928 Jeans ended his career in scientific research and devoted himself to the popular exposition of science for which he became so famous. His first wife died in 1934, and in 1935 he married Suzanne Hock, a concert organist. An accomplished organist himself, Jeans had a deep interest in music, as shown by his book on musical acoustics, Science and Music (1938), published in the year in which he became a director of the Royal Academy of Music. The couple had three children. Jeans died of coronary thrombosis in 1946.

Jean’s biographer E. A. Milne divides his scientific life into four parts. During the first of these, from the taking of his degree to 1914, Jeans devoted his major attention to problems of molecular physics. After an initial student work, with the assistance of J. J. Thomson, on electrical discharges in gases, he turned to the foundations of kinetic molecular theory. In his attempt to provide a new derivation of the theorems of kinetic theory avoiding the assumption of” molecular disorder “he was challenged by S. H. Burbury, with whom he carried on a controversy. His first book, The Dynamical Theory of Gases, includes his treatment of the persistence of molecular velocities after collisions. When a molecule undergoes a collision in gas there is, statistically, a tendency for it to maintain some motion in the direction that it took before collision. If account is taken of this favoring of forward motion over rebounding, correction factors must be included in the derivation of the coefficients of viscosity, heat conduction, and diffusion of gases. His major efforts, though, were devoted to the problems posed by the classical theorem of equipartition of energy in its application to specific heats and particularly to blackbody radiation.

In 1905, in connection with this work, Jeans corrected a numerical error in Rayleigh’s derivation of the classical distribution of blackbody radiation, so that the law has become known as the Rayleigh-Jeans law. This law states that if a hot body is placed inside a reflecting cavity, nearly all the heat energy will be associated with high-frequency radiation in the cavity when equilibrium is reached, the body cooling off and approaching absolute zero in temperature. But the Facts, which were well presented by Planck’s law, showed a reasonable distribution of energy between matter and radiation, with the highest concentrations of radiant energy associated with a finite frequency and relatively little of such energy concentrated in the high frequencies. Jeans hoped to preserve classical physical ideas, according to which the Rayleigh-Jeans law represented the true ultimate equilibrium distribution, by arguing that such a distribution would not be reached for an extremely long time under most conditions, because the usual processes generating radiation (such as collisions involving charged bodies) would produce very little high-frequency radiation at low or moderate temperatures. Jeans held that a steady-state distribution of radiant energy would quickly set in, which would not be the true equilibrium distribution because energy would be dissipated into the high frequencies at a very slow rate. He believed that Planck’s law represented such a steady-state distribution.

In 1914, when Jeans presented his Report on Radiation and the Quantum Theory to the Physical Society, he had abandoned these ideas. This report was strongly influenced by Poincaré’s important memoir of 1912, “Sur la théorie des quanta,” which demonstrated the near-impossibility of circumventing the quantum hypothesis by classical arguments. Jeans constructed arguments convincing himself that Planck’s law could not result as a steady-state distribution in classical physics; and in this report he stressed as sharply as possible the break which the early quantum theory represented with classical principles, and the inadequate state of the quantum theory of that time. Yet he did not contribute to the development of this theory, turning at this time almost exclusively to astrophysics.

As early as 1902-1903 Jeans had occupied himself with the forms and stability of rotating liquid masses, inspired in this by the work of George Darwin. Poincaré had traced the evolution of a rotating incompressible fluid mass slowly contracting gravitationally through ellipsoidal figures to a pear-shaped figure but was unable to decide the stability of the latter. By an incomplete argument Darwin concluded that the pear-shaped figure was stable, but in 1905 Lyapunov demonstrated the opposite. Jeans’s earliest work in this field had been to compute the equilibrium figures of rotating liquid cylinders; this simplified problem allowed him to refine the calculations to a much higher degree of accuracy while still showing characteristics of the more complex three-dimensional case. He returned to the general problem in papers published in 1914-1916, demonstrating that Darwin had not gone to a sufficiently high approximation in his calculations to be able to decide the stability of the pear-shaped figure and that, if this were done, the figure was indeed shown to be unstable.

Jeans went beyond his predecessors by treating compressible as well as incompressible fluids. His results, summarized in his Adams Prize essay, Problems of Cosmogony and Stellar Dynamics (1919), led him to distinguish two cases, represented in their extremes, respectively, by an incompressible mass of fluid and by a gas of negligible mass surrounding a mass concentrated at its center (Roche’s model). Upon contraction or, equivalently, upon attaining an increasing angular momentum, the incompressible mass underwent the evolution described above; but when the unstable pear-shaped configuration was reached, the furrow deepened and the mass split in two. In such a fashion double stars could be formed. On Roche’ model, on the other hand, the gas evolved through similar ellipsoidal figures to a lenticular shape, which ejected matter from its sharp, equatorial edge, a process which Jeans associated with the formation of spiral nebulae.

Fluid masses with properties intermediate between the incompressible fluid and Roche’s model behaved in either of these two ways, with the conditions for fissional or equatorial breakup well specified. As a result, Jeans concluded that rotation of a contracting mass evidently could not give rise to the formation of a planetary system. For this reason he rejected the theory of origin of the solar system of Kant and Laplace and favored a tidal theory somewhat like that of T.C.Chamberlin and F. R. Moulton, in which planetary systems were created during the close passage of two stars. Jeans had developed a formula giving the approximate distance between gravitational condensations in a gaseous medium, which he had applied to the matter in the arms of spiral nebulae. The same formula indicated that in the tidal case several small masses could be formed from the material drawn out in the cataclysm. Since such near collisions were extremely unlikely, this would mean that planetary systems were very rare. Jeans also treated a third situation (besides the rotation of a single mass and the near collision of two passing masses), the evolution of a double-star system, here drawing mainly on the classical work of Roche and George Darwin.

His masterful work on the equilibrium of rotating masses, culminating in the Adams Prize essay, constitutes the second phase of Jeans’s career. After this he continued to work on astrophysical problems for another decade, until 1928. In connection with his work on rotating stars, he introduced in 1926 the concept of radiative viscosity (viscosity mediated by the action of radiation on matter) and computed its coefficient. From 1913 he applied kinetic theory arguments to the stars making up a star cluster or a galaxy. An association of stars should approach a Maxwellian distribution of velocities over a very long period of time, as a result of their mutual gravitational interactions when they pass each other at moderate distances. Jeans developed this idea mathematically and used it to attempt estimates of the ages of stellar systems. Beginning in 1917, A. S. Eddington developed a theory of the internal constitution of stars. Jeans contributed the observation that because the internal matter of the stars should be highly ionized, the mean molecular weight, which enters into Eddington’s equations, should be much smaller than it would be if the atoms were not ionized. Eddington’s theory, treating the radiative equilibrium of a gaseous star, gave as a result a unique relation between mass and luminosity. Jeans believed that such a unique relation was spurious because it ignored the source of stellar energy, which he concluded to be a type of radioactive process involving massive atoms and independent of the temperature of the star’s interior. According to Jeans, the interior matter of these stars would progressively become more ionized and denser, causing the star to evolve from a red giant through a main sequence stage (in which most stars, including the sun, are found) to a white dwarf. With the aid of stability arguments he concluded that the material in stars could not obey the ideal gas law in their interiors, and he investigated the structure and stability of “liquid” stars, the substance of which does not behave like a gas. Much of this work on stellar interiors, based on assumptions which could not then be tested, has not held up with the passage of time. Jeans’s astrophysical investigations were gathered together in Astronomy and Cosmogony (1928), which was practically his last research work.

From 1928, Jeans occupied himself with the popularization of science. In that year he gave a series of radio lectures which served as a source for The Universe Around Us (1929). By impressive analogies Jeans conveyed to his readers some idea of the immense differences in scale from the atomic nucleus to the galaxies, then proceeded to sketch his ideas concerning the evolution of stars and the universe. The Rede lecture in 1930 led to The Mysterious Universe, in which, after a discussion of modern physics and astronomy, he propounded his rather uncritical idealistic speculations, picturing the universe as “the thought of . . .” a mathematical thinker.” The book was immensely popular and appeared in at least fourteen languages. Further works followed: The Stars in Their Courses and Through Space and Time, popularizing astronomy, and The New Back-ground of Science, treating modern physics, all written in Jeans’s fluent and exciting style. His final books, Physics and Philosophy (1942) and The Growth of Physical Science (1947), were written in a more historical and restrained manner.

BIBLIOGRAPHY

I. Original Works. A list of Jeans’s books and papers is included in Milne’s biography and in his obituary notice (see below). Among the most important technical books are The Dynamical Theory of Gases (Cambridge, 1904); The Mathematical Theory of Electricity and Magnetism (Cambridge, 1908); Problems of Cosmogony and Stellar Dynamics (Cambridge, 1919); and Astronomy and Cosmogony (Cambridge, 1928). The popular books include The Universe Around Us (Cambridge, 1929); The Mysterious Universe (Cambridge, 1930); and The Growth of Physical Science (Cambridge, 1947).

II. Secondary Literature.. See E. A. Milne, Sir James Jeans, a Biography (Cambridge, 1952); an obituary notice in Obituary Notices of Fellows of the Royal Society of London,5 (1945-1948), 573-589; and Sydney Chapman, in Dictionary of National Biography (1941-1950), pp. 430-432.

A. E. Woodruff

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Sir James Hopwood Jeans

Sir James Hopwood Jeans

The English mathematician, physicist, and astronomer Sir James Hopwood Jeans (1877-1946) made important contributions to the development of quantum theory and to theoretical astrophysics, especially to the theory of stellar structure.

On Sept. 11, 1877, James Jeans was born in Ormskirk, Lancashire, the son of a parliamentary journalist. He was brought up in a strict, very religious Victorian home atmosphere. A precocious child, he was reading by age 4 and had a remarkable ability to memorize numbers. At an early age he also became interested in physics, as well as in mechanical devices, especially clocks—the subject of a short book he wrote at age 9.

In 1897 Jeans entered Trinity College, Cambridge, and in 1903 received his master's degree. In 1904 he was appointed university lecturer in mathematics at Cambridge; and in 1906, at the very early age of 28, he was elected a fellow of the Royal Society—all this in spite of the fact that during 1902-1903 tuberculosis of the joints forced him to go to several sanatoriums. During his illness, from which he completely recovered, he wrote his first book, The Dynamical Theory of Gases.

Jeans taught applied mathematics at Princeton University, N.J., from 1905 to 1909. He returned to Cambridge as Stokes lecturer in 1910 but 2 years later relinquished the position and thereafter devoted full time to research and writing.

In 1907 Jeans married Charlotte Tiffany Mitchell; she died in 1934, leaving one daughter. The following year he married Suzanne Hock, a concert organist, with whom Jeans wrote his very popular and informative book Science and Music (1938). They had two sons and a daughter.

In the first period of his scientific life (1901-1914), Jeans's interests were centered mainly on the kinetic theory of gases and the theory of radiation, especially applied to the new quantum theory of Max Planck and others. Through a vigorous interchange of ideas, Lord Rayleigh and Jeans, in 1905, separately derived what later came to be called the Rayleigh-Jeans law. Despite the fact that this law implied a failure of classical theory when applied to blackbody radiation, Jeans, during the ensuing years, repeatedly attempted to sustain classical theory instead of accepting quantum theory. Only after Henri Poincaré's 1912 paper on the quantum theory did Jeans become convinced. Two years later Jeans wrote a brief but comprehensive Report on Radiation and the Quantum Theory, which, after World War I, was extremely influential in convincing physicists of the importance of the new quantum ideas.

During the war years Jeans experienced his finest hour as a scientist—now a theoretical astrophysicist. His researches on stellar structure were most significant, especially his proof that a rotating incompressible mass will, with increasing rotational velocity, first become pearshaped and then cataclysmically fission into two parts (one model for a single star evolving into a double-star system). This and other important results, including a tidal encounter nebular hypothesis that replaced the classical Kant-Laplace nebular hypothesis, were published in his 1919 Adams Prize essay, Problems of Cosmogony and Stellar Dynamics.

The next decade of Jeans's life (1918-1928) was marked by a rather sharp decrease in his reputation as a theoretical astrophysicist. Already, in 1917, he had a famous debate with Arthur S. Eddington on stellar structure and, though not really apparent at the time, Jeans by and large emerged the loser. In 1929 Jeans turned to popular science writing, especially in astronomy, and soon became very successful. His Universe around Us ushered in a series of eight books between 1929 and 1942. All are stimulating expositions, though they suffer in one degree or another from presenting the results of scientific research a bit too dogmatically, thereby giving a distorted picture of such research in progress.

Jeans was awarded numerous honorary degrees and professional offices. He was knighted in 1928 and won the coveted Order of Merit in 1939. He was a modest and unassuming man and a devoted father. Jeans died on Sept. 16, 1946, at his home in Dorking, Surrey.

Further Reading

A study of Jeans is E. A. Milne, Sir James Jeans (1952). Milne also wrote a short obituary notice of Jeans in Biographical Memoirs of the Fellows of the Royal Society, 1945-1948, vol. 5 (1947). There is a bibliography of Jeans's writings in both of these works. □

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