The maximum energy of a particle recorded by Agassiz experiment, 10 electron volt, is close to energies beyond which charged particles can not be confined to the galactic disc by typical interstellar magnetic fields of 10 gauss. A detector array of very large dimensions is needed to detect showers of these energies. John Linsley agreed to take on responsibility for building such an array. He came to MIT in 1954 from the University of Minnesota, where he completed a PhD under Edward P. Ney. Soon, he was joined by Livio Scarsi, whom Rossi had recruited from Occhialini's group at the University of Milan.