1. J. Nishimura:Soryushiron Kenkyu (in Japanese),12, 24 (1956);Z. Koba:Proc. of the VI-th Rochester Conference (1956), p. iv-43.
2. O. Minakawa, Y. Nishimura, M. Tsuzuki, H. Yamanouchi, H. Aizu, H. Hasegawa, Y. Ishii, S. Tokunaga, Y. Fujimoto, S. Hasegawa, J. Nishimura, K. Niu, K. Nishikawa, K. Imaeda andM. Kazuno:Suppl. Nuovo Cimento,11, 112 (1959).
3. B. Edwards, J. Losty, D. H. Perkins, K. Pinkau andJ. Reynolds:Phil. Mag.,3, 237 (1958).
4. S. N. Nikol’skii et al.: Oxford Conference (1956). They investigated the hard component in the air shower and found some suggestions for the discontinuity of the collision feature at the energy exceeding about 1015 eV of the primary energy of the air shower, though the unresolved questions are left.
5. P. H. Fowler:Seventh Rochester Conf. on High Energy Nuclear Physics (1957).