1. Boynton, P. E., Groth, E. J., III, Partridge, R. B., and Wilkinson, D. T.: 1969a, Astrophys. J. Letters 157, L197.
2. Boynton, P. E., Groth, E. J., III, Partridge, R. B., and Wilkinson, D. T.: 1969b, IAU Circ. No. 2179.
3. Buckingham, R. A.: 1957, Numerical Methods, Pitman, London, p. 92.
4. Counselman, C. C., III, and Shapiro, I. I.: 1968, Science 162, 352.
5. Hoffman, B.: 1968, Nature 218, 667.