HubbleEdwin, “Angular rotation of spiral nebulae”, Astrophysical journal, lxxxi (1935), 334–5; van MaanenA., “Internal motions in spiral nebulae”, ibid., 336–7.
2.
These papers are now available in HetheringtonNorriss S. (ed.), The Edwin Hubble papers: Previously unpublished papers on the extragalactic nature of spiral nebulae (Tucson, 1990).
3.
HoskinMichael A., “Edwin Hubble and the existence of external galaxies”, Actes of the 12th International Congress on the History of Science (Paris, 1971), v, 49–53. See also his “Island universes: An overview”, in Stellar astronomy: Historical studies (Chalfont St Giles, 1982), 154–67.
4.
AdamsWalter S., “Mount Wilson Observatory Confidential Statement for President Merriam”, twelve-page, typed, double-spaced memorandum, Adams Papers, box 43, Mount Wilson Observatory Archives, Henry E. Huntington Library, San Marino, California. The document, dated 15 August 1935, is addressed to John C. Merriam, president of the Carnegie Institution of Washington. (The observatory was a research department of the institution.) Adams's memorandum was in response to a routine request for information on recent and current activities of the observatory, for use by Merriam in his annual report; see the letter from GilbertW.M. (administrative secretary to Merriam) to AdamsWalter S., 28 May 1935, Adams Papers, box 20.
