Figures 22, 23, 29, 30: By permission of the Master and Fellows of St. John’s College, Cambridge.

Figures 32, 34, 35: Einstein, Albert; The Collected Papers of Albert Einstein. © 1987–Current Year. Hebrew University of Jerusalem and Princeton University Press. Reprinted by permission of Princeton University Press.

Figures 9, 20: Courtesy of Institute of Astronomy, University of Cambridge, through the assistance of Mark Hurn.

Figure 16: Courtesy of the author, processed by Amanda Smith, Graphics Office, Institute of Astronomy, University of Cambridge.

Figure 31: Courtesy of Amanda Smith, Graphics Office, Institute of Astronomy, University of Cambridge.