The modern era of cosmology really began with the publication of Einstein's
general theory of relativity in 1915 because it was this theoretical
breakthrough that allowed cosmologists such as de Sitter, Friedman and Lemaitre
to construct the first self-consistent mathematical models of cosmic evolution.
The first experimental test of general relativity was Eddington's famous
expedition(s) to measure the bending of light at a total solar eclipse in 1919.
So famous is this experiment, and so dramatic was the impact on Einstein
himself, and so essential was it for the development of relativistic cosmology
that history tends not to recognize the controversy that surrounded the results
at the time. In this talk I discuss the experiment in its historical context
as well as showing the results of a re-analysis of the data using more modern
statistical methods. This experiment, and the controversy surrounding it, still
provides valuable lessons for modern astronomy and cosmology.