“It wasn’t too long after Newton published his laws of motion that people noticed something was off about them. To be specific, they were off by the orbit of an entire planet. And they remained off until Einstein, and general relativity, explained why Mercury moves the way it does.”
http://io9.com/the-200-year-old-mystery-of-mercurys-orbit-solved-1458642219
Another article on the same topic
http://www.techinsider.io/einstein-planet-vulcan-myth-relativity-2015-11
TOK Topics 