1. We wish to take this opportunity of thanking the staff at Berkeley for their generous help for this exposure, and Dr.Slater of EFINS, Chicago, who personally made this exposure for the K− collaboration.
2. P. Fowler andH. Perkins:Phil. Mag.,46, 587 (1955).
3. A. Bonetti, C. Dilworth, M. Ladu andG. Occhialini:Rend. Acad. Naz. Lincei. 17 311 (1954);G. Alvial andS. Stantic:Nuovo Cimento,5, 1333 (1957);S. Colombo, G. Gabba, E. Gandolfi andE. Querigh:Comptes Rendus, 2me Colloque de Photographic Corpusculaire, Montréal (1958).
4. W. G. Holladay, quoted byR. G. Sachs:Phys. Rev.,99, 1573 (1955).
5. R. H. Dalitz:Nucl. Phys.,1, 372 (1956).