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William Campbell. Portrait of William Wallace Campbell (1862-1938), American astronomer. He joined the Lick Observatory, California, in 1891 and was its director during 1901-30. From 1896 Campbell did pioneering studies on the speed and direction of travel of the Sun and other stars. The data on nearly 3000 such radial velocities were published in 1928, and were subsequently used to study galactic rotation. In 1922 he helped to verify Einstein's theory of relativity by measuring during a solar eclipse how starlight bends as it skims the surface of the Sun.
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