C. Earliest impressions on galaxy clustering
In the 19th century William Herschel and Charles Messier noted that the amorphous objects they referred to as "nebulae" were more common in some parts of the sky than others and in particular in the constellation of Virgo.
However, clusters of galaxies were not described in detail until the work of Wolf (1924) who described the Virgo and Coma clusters of galaxies. It was not known at that time that the nebulae, as they were then called, were in fact extragalactic systems of stars comparable with our own Galaxy.
Hubble, using the largest telescopes, noted the remarkable overall homogeneity and isotropy of the distribution of galaxies. The first systematic surveys of the galaxy distribution were undertaken by Shapley and his collaborators (often uncited and under-acknowledged wealthy Bostonian women). This lead to the discovery of numerous galaxy clusters and even groups of galaxy clusters.