His famous book on Mozart, published in 1947, is available to read in German, but not to download at DNB
here. Similarly his book on Schutz (1928) is on BSB
here and his
History of Music (1918) is
hereHe had an ambiguous relationship with his PhD supervisor
Adolf Sandberger (1864—1943), who refused him a
Habilitation in 1903, but later helped him into a job in academic publishing. After a career as a newspaper music critic he was sacked by the NS regime in 1933, but finally taught at Smith College, MA, USA from 1939 to 1950. His reputation rests on his revised
Köchel catalog (1936) and his books on Mozart and Schubert.