1. Adgie, R., and F.G. Smith. 1956. Observatory 76:181.
2. Alfvèn, H.,and N. Herlofson. 1950. Phys. Rev. 78:616.
3. Allen, C.W., and C.S. Gum. 1950. Aust. J. Sei. Res. 3A:224.
4. Altenhoff, W. 1968.In Y. Terzian (ed.), Interstellar Ionized Hydrogen. New York: Benjamin, p. 519.
5. Altenhoff, W., D. Downes, T. Pauls, and J. Schraml. 1978. Astron. Astrophys. Suppl.35:23.