By a transposing instrument we mean one in the case of which the performer either plays from a part that is written in a different key from that of the composition, or that sounds pitches an octave higher or lower than the notes indicate. Thus, e.g., in a composition written in the key of E-flat, and actually played in that key by the strings, piano, et cetera, the clarinet part would probably be written in the key of F, i.e., it would be transposed a whole step upward; but, of course, the actual tones would be in the key of E-flat. The player, in this case, would perform upon a B-flat clarinet—i.e., a clarinet sounding pitches a whole step lower than indicated by the notes. (It is called a B-flat clarinet because its fundamental gives us the pitch B-flat this pitch being a whole-step lower than C; and it is because the pitch sounded is a whole step lower that the music has to be transposed a whole step higher in order to bring it into the correct key when played.) In the case of the clarinet in A, the pitches produced by the instrument are actually a minor third lower than the notes indicate (A is a minor third lower than C, just as B-flat is a wholestep lower). In writing music for clarinet in A, therefore, the music will need to be transposed upward a minor third in order that when played it may be in the right key; just as in the case of the clarinet in B-flat, it has to be transposed upward a whole-step.
"Clarinet or cornet in B-flat" means, therefore, an instrument that sounds pitches a whole-step lower than written; "clarinet or cornet in A" means one that sounds pitches a minor third lower than written; "horn in F" means an instrument sounding pitches a perfect fifth lower than written (because F is a perfect fifth below C); while the "clarinet in E-flat" sounds pitches a minor third higher than written. Whether the pitches sounded are higher or lower than the notes indicate will have to be learned by experience or study.
If the passage marked Fig. 1 were to be orchestrated
