1. Callear, A. B., App. Optics, Second Laser Suppl., 145 (1965).
2. Callear, A. B., and Tyerman, W. J. R., Trans. Faraday Soc., 61, 2395 (1965).
3. Donovan, R. J., and Husain, D., Nature, 206, 171 (1965).
4. Corliss, C. H., and Bozman, W. R., Transition Probabilities, Nat. Bur. Stand. Monograph 53 (1962).
5. Moore, C. E., Atomic Energy Levels, Nat. Bur. Stand. Circular 467, 2 (1952).