On the Shapley-Curtis debate concerning the extent of the Milky Way and the existence of other galaxies. What are the two best ways to measure the distance to a distant, isolated spiral galaxy, and ho...On the Shapley-Curtis debate concerning the extent of the Milky Way and the existence of other galaxies. What are the two best ways to measure the distance to a distant, isolated spiral galaxy, and how would it be measured? What sorts of things would you have to do to convince yourself (and others) that the relationship you were seeing between the two quantities was a real feature of the behavior of the universe? (For example, would data from two galaxies be enough to demonstrate Hubble’s law?