Dyson, Frank Watson

(b. Measham, near Ashby-de-la-Zouch, Leicestershire, England, 8 January 1868; d. on board ship near Cape Town, South Africa, 25 May 1939)

astronomy.

On graduating in the mathematical tripos at Cambridge, England, as second wrangler in 1889, Dyson began research on gravitational problems. He was appointed chief assistant at the Royal Observatory at Greenwich in 1894; astronomer royal for Scotland in 1905; and in 1910 he returned to Greenwich to become the eleventh astronomer royal. It was by cooperation in, and direction of, the preparation of fundamental astronomical measurements that he contributed significantly to the progress of astronomy.

From 1894 Dyson improved the methods used at Greenwich for reduction of the measurement of star positions from photographs, and during the opposition of Eros in 1900–1901 he organized the observations and reduction of the data compiled from them to provide new standards of accuracy. With W. G. Thackeray he reobserved the 4,239 stars that had been cataloged by Stephen Groombridge from 1806 to 1816 and compared positions so that proper motions of the stars could be determined over an eighty-year interval. Following this, Dyson extended J. C. Kapteyn’s hypothesis of two star streams to fainter stars and rephotographed the stars in the internationally delimited Greenwich astrographic zone to allow more proper motions to be determined.

In observing the total solar eclipses of 1900, 1901, and 1905, Dyson measured the wavelengths of 1,200 lines in the spectrum of the chromosphere and compared the strengths with those for which laboratory evidence was available. His intensity measurements confirmed the work of J. N. Lockyer and A. Fowler, which was then subject to much criticism. It was due to Dyson that two Greenwich expeditions, one to Principe Island off Spanish Guinea and one to Sobral in Brazil, were sent to observe the 1919 solar eclipse. They verified the deflection of starlight by the sun’s gravitational field to the degree predicted by relativity theory.

Dyson developed geophysical work at Greenwich by bringing up to date the observatory’s equipment and techniques for measurements of terrestrial magnetism and by moving the department to the country when local railroad electrification made this necessary. He also reorganized accurate latitude measurement, developing the methods for using the floating zenith telescope with great success. Dyson took much interest in time determination: he installed the Shortt synchronome free-pendulum clocks in 1924 and arranged for public radio time signals that were soon extended to give worldwide coverage.

Dyson had a genius for collaboration, and the majority of his published work was as joint author. A strong supporter of the International Astronomical Union, he attended every meeting from 1922 to 1935; his charming hospitality at Greenwich was a byword among astronomers from every country. In 1931 W. J. Yapp, a wealthy manufacturer, donated a thirty-six-inch reflector to commemorate Dyson’s tenure as astronomer royal; it was first used in April 1934. Dyson retired on 28 February 1933 but continued to offer advice, particularly on the removal of the Radcliffe Observatory from Oxford to Pretoria, South Africa.

Dyson received many honors, including four gold medals from learned societies. He was elected a fellow of the Royal Society in 1901, was president of the Royal Astronomical Society from 1911 to 1913, was created a knight bachelor in 1915, and received the K.C.B. in 1926.

BIBLIOGRAPHY

Dyson’s important writings (alone or in collaboration) include “On the Determination of Positions of Stars for the Astrographic Catalogue at the Royal Observatory,” Monthly Notices of the Royal Astronomical Society, 51 (1896), 114–134; “Determination of the Constant of Precession and the Direction of the Solar Motion From a Comparison of Groombridge’s Catalogue (1810) With Modern Greenwich Observations,” ibid., 65 (1905), 428– 457; “Determinations of Wavelengths From Spectra Obtained at the Total Solar Eclipses of 1900, 1901 and 1905,” in Philosophical Transactions of the Royal Society, 206A (1906), 403–452; “A Statistical Discussion of the Proper Motions of the Stars in the Greenwich Catalogue for 1910,” in Monthly Notices of the Royal Astronomical Society, 77 (1917), 212–219; “A Determination of the Deflection of Light by the Sun’s Gravitational Field, From Observations Made at the Total Eclipse of 1919 May 29,” in Philosophical Transactions of the Royal Society, 220A (1920), 291–333; “Variability of the Earth’s Rotations.” in Monthly Notices of the Royal Astronomical Society, 89 (1929), 549–557; and Eclipses of the Sun and Moon (Oxford, 1937). Manuscript material is in the archives of the Royal Greenwich Observatory, Herstmonceux, Sussex, England.

Obituaries of Dyson are A. S. Eddington, in Obituary Notices of Fellows of the Royal Society of London, 3 (1940), 159–172; and J. Jackson, in Monthly Notices of the Royal Astronomical Society, 100 (1940), 236–246. A biography is M. Wilson, Ninth Astronomer Royal (Cambridge, 1951).

Colin A. Ronan