1. Aller, L. H.: 1961,The Abundance of the Elements Interscience, New York.
2. Alvial, G., Silva, E., Stantic, S., and Riquelme, J.: 1965,Proc. 9th Int. Conf. Cosmic Rays. London, Vol.1, p. 417.
3. Anand, K. C., Biswas, S., Lavakare, P. J., Ramadurai, S., Sreenivasan, N., Bhatia, V. S., Chohan, V. S., and Pabbi, S. D.: 1966,J. Geophys. Res. 71, 4687.
4. Augason, G. C. and Herbig, G. H.: 1967,Astrophys. J. 150, 728.
5. Beck, F. and Yiou, F.: 1968,Astrophys. Letters 1, 75.