Original: During Mengelberg 's time as chief conductor , several of these first conductors included Karl Muck ( 1921 â '' 1925 ) , Pierre Monteux ( 1924 â '' 1934 ) , Bruno Walter ( 1934 â '' 1939 ) , and Eugen Jochum ( 1941 â '' 1943 ) . Musicians who served as '' second conductor '' included the composer Cornelis Dopper , Evert Cornelis and Eduard van Beinum .
Simplified: During Mengelbergâ s time the â first conductorsâ included Karl Muck ( 1921-1925 ) , Pierre Monteux ( 1924-1934 ) , Bruno Walter ( 1934-1939 ) , and Eugen Jochum ( 1941-1943 ) , and the second conductors included the composer Cornelis Dopper , Evert Cornelis and Eduard van Beinum .