Hubble and Shapley - Two Early Giants of Observational Cosmology
  Observational cosmology of the first decades of the Twentieth Century was
dominated by two giants: Edwin Hubble and Harlow Shapley. Hubble's major
contributions were to the study and classification of individual galaxies with
large telescopes, whereas Shapley is best remembered for his work on groups and
clusters of galaxies using telescopes of more modest aperture.
