1. A. D. Krisch:Phys. Rev. Lett.,19, 1149 (1967)
2. F. Cerulus andA. Martin:Phys. Lett.,8, 80 (1964).
3. J. Orear:Phys. Rev. Lett.,12, 112 (1964);Phys. Lett.,13, 190 (1964).
4. H. Fleming, A. Giovannini andE. Predazzi: to be published.
5. It should be stressed that the values given in eq. (3) for the parameters are not obtained from a best fit of the experimental points but from a simple trial procedure, and by asking that the first few terms reproduce Krisch's formula.