A complete treatise on the subject of the neutrino includes interpretation of experimental results in terms of existing theories on this nuclear particle. It incorporates material on post-parity experiments which appeared following the Lee and Yang discoveries in 1956 concerning parity non-conservation in weak interactions. Originally published in 1958. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.