1. P. Budini, G. Poiani andI. Reina:Int. Conf. Padua,IX, 17 (1957).
2. S. D. Deell:Ann. Phys.,4, 75 (1958).
3. G. Poiani andI. Reina:Nuovo Cimento: to be published.
4. W. K. H. Panofsky:Ann. Int. Conf. CERN Geneve, (1958), p. 3.
5. B. Richter:Phys. Rev. Lett.,3, 114 (1958).