1. Honda, M., and Arnold, J. R., Science, 143, 203 (1964).
2. Moreland, P. E., and Heymann, D., J. Inorg. Nuc. Chem. (in the press).
3. Sharp, R. A., and Diamond, R. M., Phys. Rev., 93, 358 (1954); 96, 1713 (1954).
4. Huizenga, J. R., and Wing, J., Phys. Rev., 106, 90 (1957).
5. Lipschutz, M. E., Signer, P., and Anders, E., J. Geophys. Res. (in the press).