By this time, cloud chamber observations had clarified the nature of the hard component. In 1936, Anderson and his student, Seth Neddermeyer, discovered cosmic ray particles with mass intermediate between those of the electron and the proton, which Anderson called "mesotrons". The mesotron subsequently became the known as the "μ meson", which was shortened to " muon ". Just before the Copenhagen conference, Blackett suggested that observed variations of cosmic ray intensity with atmospheric temperature could be an indication that mesotrons are unstable, and he held intense discussions with Rossi on this subject. As a result, Rossi left Manchester determined to confirm their decay and to measure the lifetime.