1. Neddermeyer and Anderson, Phys. Rev., 51, 884 (1937).
2. Yukawa, Proc. Phys. Math. Soc. Japan, 19, 1084 (1935); Yukawa and Taketani, M., ibid., 20 (1938).
3. Bhabha, NATURE, 141, 117 (1938).
4. Heisenberg and Euler, in the Press. (I am greatly indebted to Prof. Heisenberg and Dr. Euler for communicating these new results to me.)
5. Follett and Crawshaw, Proc. Roy. Soc., A, 155, 546 (1936).