1. Burton, W. B., Gallagher, J. S., and McGrath, M. A.: 1977, Astr. and Astrophys. Suppl. 29, pp. 123–138.
2. Burton, W. B., and Liszt, H. S.: 1978, Astrophys. J., in press.
3. Cohen, R. J.: 1975, M.N.R.A.S. 171, pp. 659–696.
4. Heiles, C., and Wrixon, G. T.: 1976, in “Methods of Experimental Physics”, ed. M. L. Meeks, 12C, pp. 58–77.
5. Kerr, F. J.: 1967, in “Radio Astronomy and the Galactic System”, ed. H. van Woerden (London: Academic Press), pp. 239–251.