1. Mulliken, R. S., The Threshold of Space, edit. by Zelikoff (London, 1957).
2. Vago, E. E., and Barrow, R. F., Proc. Phys. Soc., 68, 538 (1946).
3. Barrow, R. F., Deutsch, J. L., Lagerqvist, A., and Westerlund, B. (in the press).
4. Lagerqvist, A., Nilheden, G., and Barrow, R. F., Proc. Phys. Soc., A, 65, 419 (1952).
5. Nilheden, G., Ark. Fys., 10, 19 (1955).