1. See Bhabha, NATURE (in the Press).
2. Kemmer, Proc. Roy. Soc., A, 166, 127 (1938); Proc. Camb. Phil. Soc., 34, 354 (1938).
3. Independently of our work, essentially the same method has been proposed by Stückelberg (Phys. Rev., 54, 889; 1938), to whom we are very thankful for the kind communication of his manuscript.
4. Yukawa, Sakata, Kobayasi, Taketani, Proc. Phys. Math. Soc. Japan, 20, 720 (1938).