Photograph of the instruments used by the British expedition when observing the 1919 total solar eclipse in Brazil.

Mounted photograph (passe partout) showing the instruments used at Sobral, Brazil, during the total solar eclipse of 1919 May 29. The expedition organised by Sir Arthur Eddington of the Royal Greenwich Observatory used photographs taken during the eclipse to measure the deflection of star light adjacent to the Sun as predicted by Einstein in his Theory of Relativity.

Photograph (bromide print) showing the instruments used by the British expedition sent to observe the 29th May 1919 total solar eclipse 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 mass of a star like our Sun would bend the path of any starlight if it passed close-by.