Einstein and W de Sitter Proceedings of the National Academy of Sciences 18 213 1932

14. Chandrasekhar's book on Eddington cited above tells this curious anecdote, which seems too neatly symmetric to be the whole story of Einstein, de Sitter, and A.

15. The critical density is given by 3H>2/8kC7, where <7is Newton's gravitational constant. P'or Hc, = 70 kilometers per second per megaparsec, this is 1 X 10"*' kilogram per cubic meter—a very low density, indeed! Then ii is the actual density divided by the critical density, so it is exactly one when the observed density is equal to the critical density.

16. A. R. Sandage, "The Ability of the 200-Inch Telescope to Discriminate Between Selected World Models," The AstrophysicalJournal 133, 355 (1961).

17. A universe described by just two numbers is too simple For a modern view that includes the fluctuations from the Big Bang and their effect on the growth of structure in the universe, see Just Six Numbers by Martin Rees (Basic Books, New York, 2000)

18 For a recent scientific portrait of Sandage, Dennis Overbye's Lonely Hearts of the Cosmos, is unique Be certain to get the 1999 paperback edition (Little, Brown, Boston) with the precisely observed Afterword on cosmic acceleration.

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