1. Shapley Harlow, Through rugged ways to the stars (New York, 1969), 90.
2. The Galactocentric Revolution, A Reminiscent Narrative
3. See, for example, the discussion in Smith Robert W., The expanding universe (Cambridge, 1982), 55–96.
4. The story of the discovery of the first globular cluster variables is recounted by Bailey S. I., Annals of the Astronomical Observatory of Harvard College, xxxviii (1902), 1–5, and summarized in Smith H. A., RR Lyrae stars (Cambridge, 1995), 1–5.