The above-mentioned systematic eect" was modeled by Hubble simply as
Kr | a constant times the distance to the galaxy |, dierently of others in his
days who added quadratic terms and even logarithmic ones in r.
Quantitatively, we follow Hubble (1929). The velocity of a galaxy observed
from Earth, after the heliocentric correction, may be written, according to classical
relativity, as the composition of two velocities