The letters in this article are quoted with the kind permission of the Harvard University Archives, and except where noted, are found in the A. Lawrence Lowell papers, UAI 5.160 (1919–22) # 14 Observatory.
2.
AgassizG. R. to Lowell, 7 March 1919.
3.
AgassizG. R. to Lowell, 3 May 1919.
4.
Lowell to AgassizG. R., 31 October 1919.
5.
Scientia, xxvi (1919), 269–76.
6.
Lane's Law had shown that a collapsing gaseous body would paradoxically become hotter as it gave off energy. Russell supposed this applied to the giant branch of his luminosity-temperature diagram (where Shapley located the cepheids), but that stars like the Sun were no longer gaseous throughout and therefore cooled as they evolved down the main sequence, creating the apparent contradiction noted by Lowell.
7.
AgassizG. R. to Lowell, 17 December 1919.
8.
LuceMatthew to Lowell, 30–31 December 1919.
9.
ShapleyHarlow, Through rugged ways to the stars (New York, 1969), 83–84.
10.
Lowell to AgassizG. R., 19 December 1919.
11.
CoolidgeJulian to Lowell, 5 January 1920.
12.
Lowell to Hale, 27 February 1920.
13.
Hale to Lowell, 12 March 1920.
14.
AgassizG. R. to Lowell, 19 March 1920.
15.
AgassizG. R. to Lowell, 20–21 March 1920.
16.
Lowell to Hale, 20 March 1920.
17.
Hale to Lowell, 29 March 1920.
18.
HoskinM. A., “The ‘great debate’: What really happened”, in Stellar astronomy: Historical studies (Chalfont St Giles, 1982), 175–88; BerendzenRichardHartRichard and SeeleyDaniel, Man discovers the galaxies (New York, 1976), 35–37; SmithRobert, The expanding universe: Astronomy's ‘great debate’ 1900–1931 (Cambridge, 1981); HoskinM. A., “Shapley's debate”, in GrindlayJ. E. and PhillipDavis A. G. (eds), The Harlow-Shapley symposium on globular cluster systems in galaxies (International Astronomical Union symposium 126) (Dordrecht, 1988), 3–9.
19.
AgassizG. R. to Lowell, 28 April 1920.
20.
RussellH. N. to HaleG. E., 13 June 1920 (Hale microfilm, California Institute of Technology).
21.
Russell to Lowell, 15 June 1920, acknowledging receipt of Lowell's telegram.
22.
Lowell to AgassizG. R., 25 June 1920.
23.
Russell to Shapley, 25 January 1921 (Shapley papers, Harvard Archives).
24.
CoolidgeJ. to Lowell, 1 October 1920.
25.
Bentinck-SmithWilliam, “Archibald Cary Coolidge and the Harvard Library”, Harvard Library bulletin, xxi (1973), 229, beginning a six-part series.
26.
CoolidgeJ. to Shapley, 28 October 1920.
27.
Lowell to Shapley, 10 November 1920.
28.
Shapley to CoolidgeJ., 17 November 1920.
29.
CoolidgeJ. to Lowell, 23 November 1920.
30.
CoolidgeJ. to Shapley, 24 November 1920.
31.
Shapley to Lowell, 10 December 1920.
32.
Hale to Lowell, handwritten, 11 December 1920.
33.
Hale to Lowell, 26 October 1921.
34.
Lowell to Hale, 31 October 1921.
35.
Shapley's scrapbook of press clippings for this period is preserved among his papers in the Harvard Archives.