What was the title of Hubble's 1929 paper on the velocity-distance relation?

Hubble's 1929 paper on the velocity-distance relation was titled “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae.” Published in the Proceedings of the National Academy of Sciences, the paper presented evidence that more distant galaxies generally have greater recession velocities.

Hubble based the work on distance estimates for extragalactic nebulae and radial-velocity measurements, many of which had been obtained through the earlier spectroscopic work of Vesto Slipher and observations by Milton Humason. The relationship later became known as Hubble's law and provided important observational evidence that the universe is expanding.

The title uses historical terminology: “nebulae” was still commonly used for objects now recognized as galaxies, and “extra-galactic” referred to objects beyond the Milky Way. The underlying expansion idea had also been derived and discussed by Georges Lemaître in 1927, two years before Hubble's paper.