1. H. Yukawa, Proc. Phys. Math. Soc. Japan.17, 48 (1935).
2. The termmeson was introduced at a later date, but it is convenient to use it when referring to the early work. Ameson may be defined as any particle with a rest mass intermediate between that of an electron and that of a proton.
3. For an elementary account of the nature of the cosmic radiation reference should be made to the article byH. L. Bradt,Why are we studying Cosmic Rays?, Exper.4, 41 (1948).
4. C. D. Anderson andS. H. Neddermeyer, Phys. Rev.51, 884 (1937);54, 88 (1938).
5. E. J. Williams andG. E. Roberts, Nature145, 202 (1940),