So, are we looking for something which is:
Simple,
True,
Not obvious,
Was claimed as true by someone or other,
But mostly ignored?
Perhaps Aristarchus and his heliocentrism would fit the bill (while not strictly true, it was truer than the alternative).
So, are we looking for something which is:
Simple,
True,
Not obvious,
Was claimed as true by someone or other,
But mostly ignored?
Perhaps Aristarchus and his heliocentrism would fit the bill (while not strictly true, it was truer than the alternative).