1. Hall A. to Pickering E. C., 30 Oct. 1877, 14 Feb. 1888, quoted in Jones B. Z. and Boyd L. G., The Harvard College Observatory: The first four directorships 1839–1919 (Cambridge, Mass., 1971), 304–5. Astronomical and meteorological observations 1877, U.S. Naval Observatory (1881), 209–16.