# James Hopwood Jeans

James Hopwood Jeans
Born 11 September 1877
Ormskirk, Lancashire, England
Died 16 September 1946 (aged 69)
Dorking, Surrey, England
Nationality British
Fields astronomy, mathematics, physics
Institutions Trinity College, Cambridge; Princeton University
Alma mater Merchant Taylors' School; Cambridge University
Notable students Ronald Fisher
Known for Rayleigh–Jeans law
Jeans mass
Jeans length
Royal Medal (1919)

Sir James Hopwood Jeans OM FRS[1] MA DSc ScD LLD[2] (11 September 1877 – 16 September 1946[3]) was an English physicist, astronomer and mathematician.

## Background

Born in Ormskirk, Lancashire, Jeans was educated at Merchant Taylors' School, Northwood, Wilson's Grammar School,[4] Camberwell and Trinity College, Cambridge.[5] His coach for Cambridge Mathematical Tripos was Robert Alfred Herman, and in 1898 he came out Second Wrangler. Jeans was elected Fellow of Trinity College in October 1901,[6] and taught at Cambridge, but went to Princeton University in 1904 as a professor of applied mathematics. He returned to Cambridge in 1910.

He made important contributions in many areas of physics, including quantum theory, the theory of radiation and stellar evolution. His analysis of rotating bodies led him to conclude that Laplace's theory that the solar system formed from a single cloud of gas was incorrect, proposing instead that the planets condensed from material drawn out of the sun by a hypothetical catastrophic near-collision with a passing star. This theory is not accepted today.

Jeans, along with Arthur Eddington, is a founder of British cosmology. In 1928 Jeans was the first to conjecture a steady state cosmology based on a hypothesized continuous creation of matter in the universe.[7] This theory was ruled out when the 1965 discovery of the cosmic microwave background was widely interpreted as the tell-tale signature of the Big Bang.

His scientific reputation is grounded in the monographs The Dynamical Theory of Gases (1904), Theoretical Mechanics (1906), and Mathematical Theory of Electricity and Magnetism (1908). After retiring in 1929, he wrote a number of books for the lay public, including The Stars in Their Courses (1931), The Universe Around Us, Through Space and Time (1934), The New Background of Science (1933), and The Mysterious Universe. These books made Jeans fairly well known as an expositor of the revolutionary scientific discoveries of his day, especially in relativity and physical cosmology.

In 1939, the Journal of the British Astronomical Association reported that Jeans was going to stand as a candidate for parliament for the Cambridge University constituency. The election, expected to take place in 1939 or 1940 did not take place until 1945, and without his involvement.

He also wrote the book "Physics and Philosophy" (1943) where he explores the different views on reality from two different perspectives: science and philosophy.

On his religious views, Jeans was an agnostic Mason.[8] [9]

Jeans married twice, first to the American poet Charlotte Tiffany Mitchell in 1907,[10] then the Austrian organist and harpsichordist Suzanne Hock (better known as Susi Jeans) in 1935. He died in Dorking, Surrey.

At Merchant Taylors' School there is a James Jeans Academic Scholarship for the candidate in the entrance exams who displays outstanding results across the spectrum of subjects but notably in Mathematics and Sciences.

## Major accomplishments

One of Jeans' major discoveries, named Jeans length, is a critical radius of an interstellar cloud in space. It depends on the temperature, and density of the cloud, and the mass of the particles composing the cloud. A cloud that is smaller than its Jeans length will not have sufficient gravity to overcome the repulsive gas pressure forces and condense to form a star, whereas a cloud that is larger than its Jeans length will collapse.

$\lambda_J=\sqrt{\frac{15k_{B}T}{4\pi Gm\rho}}$

Jeans came up with another version of this equation, called Jeans mass or Jeans instability, that solves for the critical mass a cloud must attain before being able to collapse.

Jeans also helped to discover the Rayleigh–Jeans law, which relates the energy density of blackbody radiation to the temperature of the emission source.

$f(\lambda) = 8\pi c \frac{k_{B}T}{\lambda^4}$

## Bibliography

Available online from the Internet Archive

Other:

## References

1. ^ Milne, E. A. (1947). "James Hopwood Jeans. 1877-1946". Obituary Notices of Fellows of the Royal Society 5 (15): 573–570. doi:10.1098/rsbm.1947.0019. edit
2. ^ Sir James Jeans 1938 (reprint of 1931's edition of 1930 book): The Mysterious Universe.
3. ^ GRO Register of Deaths: SEP 1946 5g 607 SURREY SE – James H. Jeans, aged 69
4. ^ Allport, D.H. & Friskney, N.J. "A Short History of Wilson's School", Wilson's School Charitable Trust, 1987, pg 234
5. ^ "Jeans, James Hopwood (JNS896JH)". A Cambridge Alumni Database. University of Cambridge.
6. ^ "University intelligence - Cambridge" The Times (London). Friday, 11 October 1901. (36583), p. 4.
7. ^ Astronomy and Cosmogony, Cambridge U Press, p 360
8. ^ Pierre Teilhard De Chardin (2004). The Future of Man. Random House LLC. p. 212. ISBN 9780385510721. "We can hardly wonder, in the circumstances, that agnostics such as Sir James Jeans and Marcel Boll, and even convinced believers like Guardini, have uttered expressions ol amazement (tinged with heroic pessimism or triumphant detachment) at the apparent insignificance of the phenomenon of Life in terms of the cosmos— a little mold on a grain of dust..."
9. ^ E.T. Bell (1986). Men of Mathematics. Simon and Schuster. p. xvii. ISBN 0-671-62818-6. "The Great Architect of The Universe Now begins to apper as a pure mathemetician."
10. ^ J J O'Connor and E F Robertson (October 2003). "Sir James Hopwood Jeans". School of Mathematics and Statistics, University of St Andrews, Scotland. Retrieved 28 November 2011.