- H. Shapley & M. B. Shapley, 1919 "Studies based on the colors and magnitudes in stellar clusters. XIV. Further remarks on the structure of the galactic system." (Astrophysical Journal, vol. 50, p. 107)
- C. Wirtz, 1924 "De Sitters Kosmologie und die Radialbewegungen der Spiralnebel" (Astronomische Nachrichten, volume 222, p.21)
- K. Lundmark, 1924 "The determination of the curvature of space-time in de Sitter's world" (Monthly Notices of the Royal Astronomical Society, Vol. 84, p.747-770)
- K. Lundmark, 1925 "Nebulae, The motions and the distances of spiral" (Monthly Notices of the Royal Astronomical Society, Vol. 85, p.865)
- G. Stromberg, 1925 "Analysis of radial velocities of globular clusters and non-galactic nebulae" (Astrophys. J., 61, 353-362)
- E. Hubble, 1926 "Extragalactic nebulae" (Astrophys. J., 64, 321-369)
- G. Lemaitre, 1927 "Un Univers homogene de masse constante et de rayon croissant rendant compte de la vitesse radiale des nebuleuses extra-galactiques" (Annales de la Societe Scientifique de Bruxelles, A47, p. 49-59)
- H. P. Robertson, 1928 "On Relativistic Cosmology" (Phil. Mag., 5, 835)
- E. Hubble, 1929 "A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae" (Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173)
- W. De Sitter, 1930 "On the magnitudes, diameters and distances of the extragalactic nebulae and their apparent radial velocities" (Bulletin of the Astronomical Institutes of the Netherlands, Vol. 5, p.157)
- E. Hubble, 1934 "The Distribution of Extra-Galactic Nebulae" (Astrophysical Journal, vol. 79, p.8)

- J. H. Reynolds, 1932 "Physical and Observational Evidence for the Expanding Universe" (Nature, 130, 458)
- J. H. Plaskett, 1932 "A Review of the Progress of Astronomy" (PASP, 44, 215)
- H. P. Robertson, 1933 "Relativistic Cosmology" (Rev. Mod. Phys., 5, 62)
- E. A. Milne, 1933 "World-Structure and the Expansion of the Universe. Mit 6 Abbildungen." (Zeitschrift fur Astrophysik, Vol. 6, p.1)

Shapley & Shapley (1919) noted a correlation in brightness and redshift: "The speed of spiral nebulae is dependant to some extent upon apparent brightness, indicating a relation of speed to distance or, possibly, to mass."

Wirtz (1924) assumed that galaxy diameters are "standard rulers" and found a loose correlation between velocity and diameter. He did not list his set of galaxies nor did he make any figures. He did not have any absolute distance calibration.

Stromberg (1925) assumed that galaxy absolute magnitudes are "standard candles". He did not find any significant correlation between velocity and apparent magnitude.

Lundmark (1924, 1925) combined both diameter and magnitude information to estimate galaxy distances, thus combining the "standard ruler" and "standard candle" assumptions. He used a variety of distance indicators (novae; Opiks' method) to set the distance scale. He found a quadratic polynomial relation between distance and velocity with a large constant offset. (Beware: Lundmark's distances from apparent magnitudes are a complete mess.)

Lemaitre (1927) assumed that galaxy absolute magnitudes are "standard candles". He used Hubble's 1926 calibration but ignore Hubble's caveats about the standard candle assumption. He assumed a linear relationship between velocity and distance and made the first estimate of the slope (625 km/s/Mpc).

Robertson (1928) largely repeated Lemaitre's analysis and made the second estimate of the slope (463 km/s/Mpc).

Hubble (1929) assumed that the brightest stars in late-type spirals are "standard candles". (Additionally, for the Virgo cluster, he assumed that the cluster galaxy luminosity function matches the luminosity function of nearby field galaxies.) He used his distances to 7 nearby galaxies to calibrate the brightest star intrinsic magnitude. He derived a linear relation between velocity and distance and made the third estimate of the slope (500 km/s/Mpc).

`"When the influence of the cluster in Virgo is eliminated the density
appears to be roughly uniform for all latitudes greater than about 25
degrees."`