The first entry is always the pin's source. Overall confidence is a weighted average of how firmly each reference supports the start and end times used above; a reference counts half as much for every 180 days older than the newest.
Wikipedia's[2][3] Eddington experiment article dates the session: "The presentation of the results at the joint 6 November 1919 session of Royal Society and Royal Astronomical Society led to intensive press coverage first in Great Britain and a few days later in the US press". The eclipse itself was on 29 May 1919; this pin is the announcement, which is what made Einstein famous.
The theory the expeditions tested, for what a deflection of starlight near the Sun means and why the measurement settled the question.[1]
The astronomer who led the Principe expedition and presented the results at Burlington House, for who he was and what he did with the plates; the RAS homepage, cited here before, states nothing about 1919 and was dropped.[1]
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