Magellanic Clouds
His work on the structure of the Milky Way and the Magellanic Clouds was held in high regard. He contributed significantly in studies of star clusters, stellar populations, carbon stars, planetary nebulae, Wolf-Rayet stars, stellar classification and supernova remnants. He was regarded as an expert on the Magellanic Clouds and wrote a book on them (The Magellanic Clouds, Cambridge University Press, 1997 ).