1. Shutt, F. T., Roy. Soc. Canad. Trans., Ser. 3, 1 (3), 35 (1907).
2. Fonselius, S., Tellus, 6, 90 (1954).
3. Munczak, T., Tellus, 12, 282 (1960).
4. Head, R. B., Abst. Intern. Conf. Cloud Phys., Canberra, Abst. Paper No. 7.5 (1961).
5. Zettlemoyer, A. C., Tcheurekdjian, N., and Chessick, J. J., Nature, 192, 653 (1961).