The muon was discovered while studying cosmic ray bombardment and identified as a particle more massive than an electron but less than a proton. It was theorized to sit between the proton and neutron to help resolve the mysterious strong force. When it was later found that this "meson" had no interaction with atomic nuclei, it was renamed muon to avoid confusion.
A visual chronology of Asimov's ~1500 scientific inventions and discoveries.
