Hubble, Edwin, Edwin Hubble to V.M. Slipher, February 23, 1922, and his response to Slipher's Nebulae Questions, 1922-02-23
Hubble describes characteristics of nebulae to Slipher and attempts to answer Slipher's questions. This includes types of nebulae and associated stars…
Hubble, Edwin, Edwin Hubble to V. M. Slipher, February 9, 1924, on unclassified nebulae and institutional establishment, 1924-02-09
Hubble sent Slipher a memorandum with the letter to pass on to the Committee on Nebulae at the International Astronomy Union, regarding a proposal for…