At the Carnegie Institution, Rubin began work related to her controversial thesis regarding galaxy clusters with Ford, making hundreds of observations using Ford's image-tube spectrograph. This image intensifier allowed resolving the spectra of astronomical objects that were previously too dim for spectral analysis. The Rubin–Ford effect, an apparent anisotropy in the expansion of the Universe on the scale of 100 million light years, was discovered through studies of spiral galaxies, particularly the Andromeda Galaxy, chosen for its brightness and proximity to Earth. The idea of peculiar motion on this scale in the universe was a highly controversial proposition, which was first published in journals in 1976. It was dismissed by leading astronomers but ultimately shown to be valid. The effect is now known as large scale streaming. The pair also briefly studied quasars, which had been discovered in 1963 and were a popular topic of research.