From Scientific American:
On May 29, 1919, two British expeditions, positioned on opposite sides of the planet, aimed telescopes at the sun during a total eclipse. Their mission: to test a radical theory of gravity dreamed up by a former patent clerk, who predicted that passing starlight should bend toward the sun. Their results, announced that November, vaulted Albert Einstein into the public consciousness and confirmed one of the most spectacular experimental successes in the history of science. In recent decades, however, some science historians have argued that astronomer Sir Arthur Eddington, the junior member of the 1919 expedition, believed so strongly in Einstein’s theory of general relativity that he discounted data that clashed with it. In 1919 general relativity was on the cusp of eclipsing Sir Isaac Newton’s law of universal gravitation, put forth in 1687. Newton’s law cast gravity as a type of bond between objects, all floating within the gridlike arena of space and time. Einstein’s insight was that gravity is the grid, which is wrapped by massive objects such as the sun. As a consequence, light passing the sun should literally fall toward it like a moon rover clipping the edge of a giant crater and falling in.
Eddington, then director of the University of Cambridge Observatory, convinced his senior colleague and England’s Astronomer Royal, Sir Frank Dyson, to mount the expedition. The group split into two teams: Dyson’s crew from what was then the Royal Observatory in Greenwich headed to the town of Sobral, Brazil, as Eddington and cohorts set up on the western African island of Príncipe. Their task was to independently record the positions of the stars near the moon-blotted sun and compare them with the positions of the same stars at night.
If general relativity was right, the apparent positions of the nearest stars would drift 1.75 arc seconds (a measure of angularity) closer to its rim during the eclipse (a pencil width seen at half a mile). Eddington was hampered by overcast skies on the long-awaited day and photographed only five stars. It was too few for a solid result, but he gave some weight to his final value of 1.61 arc seconds. Dyson’s team had mixed results. One of the group’s two telescopes functioned correctly and gave them a value of 1.98 arc seconds. The second instrument yielded a value of 0.93 arc second, which was rather close to the Newtonian prediction of 0.87. The instrument, however, had lost focus during the eclipse, which cast doubt on the accuracy of the photo comparison, so they excluded the measurement from their final result. Based on the remaining evidence, they declared general relativity triumphant.
More here. (Note: This article is for Abbas whose birthday present to me one year was to fly to Chicago and explain The Theory of Special Relativity to me!)