From COMM 455 student Alexis Mott:

Robert Sobel’s biography of Calvin Coolidge contains an extensive account of an interaction between JW and Calvin Coolidge after JW left the Coolidge White House. The discussion involved the economic theories of Harvard economist William Z. Ripley (right) who was concerned about the American economy as early as the mid-twenties. Ripley also authored some unusual theories about the racial composition of Europe.

Citation: Robert Sobel, Coolidge: An American Enigma (Washington, DC: Regnery, 1998), particularly at pp. 360-375.