Telescope used to observe a total solar eclipse, Sobral, Brazil, 1919.
© Science Museum / Science & Society Picture Library
Photograph (bromide print) showing the instruments used by the British expedition sent to observe total solar eclipse on 29 May 1919 from Sobral in Brazil. Sir Arthur Eddington at Cambridge University organised the eclipse trip to try and test Einstein's Theory of Relativity. During the event, two heliostats with moveable mirrors were used to direct images of the eclipsed Sun into a pair of horizontal telescopes. Measurement of photographs taken through these instruments was checked for any deflection of star positions adjacent to the Sun. Einstein suggested that the large mas of a star like our Sun would bend the path of any starlight if it pased close-by.