I feel like I have been improving myself a lot by practicing out of method books lately--I now have a pretty solid routine that consists of etudes from Arban, Clarke, and Schlossberg.
Now, about the Schlossberg book--there is a chapter called "Long Note Drills" at the beginning of the book, but they are quite different from the typical long tones that I know. I mean, most of them aren't holding notes that are whole notes or longer; they are rather mostly legato exercises and tonguing exercises that involve quarter notes or eighth notes. In fact, most of these are lip slurs rather than long tones. Is it that the idea behind this section is to play “through” the notes, and keep the air moving as if it was one long note?