At Cornell, Rossi met his first American graduate student, Kenneth Greisen, with whom he wrote an article, "Cosmic-Ray Theory", which was published in the Reviews of Modern Physics and became known among cosmic-ray researchers as "The Bible". During the summer of 1941, Greisen and physicists from Denver and Boulder accompanied Rossi to Mount Evans, where they refined the knowledge of proportionality between mesotron momentum and lifetime before decay. Greisen and Rossi also carried out experiments, which showed, in terms of processes documented in the "Bible", that not all particles of the soft component, could be produced by mesotrons of the hard component. They interpreted this as evidence for primary electrons or photons, but it became evident later that the soft excess arises from the decay of neutral pions.