ɪn wˈʌn θˈaʊzənd ˈeɪthˈʌndɹɪd ˈeɪɾi wˈʌn hiː dʒˈɔɪnd ðɪ ˌæstɹəfˈɪzɪkəl əbzˈɜːvətˌoːɹi pˈɑːtsdəm ˌeɪˌoʊpˈiː æz ɐn ɐsˈɪstənt, ænd wʊd ɹᵻmˈeɪn ðɛɹ ʌntˈɪl hiː ɹᵻtˈaɪɚd.
In 1881 he joined the Astrophysical Observatory Potsdam (AOP) as an assistant, and would remain there until he retired.