One thing we've discussed: Eddington claimed to confirm one of Einstein's theories, I can never remember which is which (general) by his observations of a total eclipse. It has been established in recent times that he was actually unable to measure what he claimed to have measured.
Here's the CRU quote:
In other words, Eddington believed in Einstein’s theory and wanted to prove that it was true, and therefore he subconsciously minimised his errors in order to get the right result. Regardless of whether or not this was the case, Eddington’s result was hailed as a wondrous piece of science, experimental validation of the greatest intellectual achievement of the of the youthful twentieth century, a sign of optimism in a world that had been torn apart by war. J.P. McEvoy, author of the “Eclipse”, encapsulated the significance of the announcement: “A new theory of the universe, the brain-child of a German Jew working in Berlin, had been confirmed by an English Quaker on a small African island.”
See also here.
Of course, Eddington turned out to be right--or the theory by a much smarter person he was defending was right--but he still seems to show how enthusiasm can get the better of a scientist.