In paragraph 23, chapter 4, page 58 of On playing the Flute Quantz writes on intonating:
Ã¢Â€ÂœThe flute has the innate defect that some of its notes when sharpened [playing sharps] are not quite true, some being a little too low, some a little to high. For in tuning the flute you must first see to it that the natural [diatonic] notes are tuned truly in accordance with their proportions. The faulty ones you must, as much as possible, seek to play in tune with the help of your embouchure and your ear.Ã¢Â€?
This is a little note to those who claim that you should play any instrument as is and that some instruments can never be played in tune. Many other instruments have the same problems (i.e. saxophone and recorder) and the players of all the instruments that have these problems should seek to play them as well intonated as possible.
In paragraph 16 he writes: Ã¢Â€ÂœThis defect can be easily remedied, however, if the player possesses a good embouchure, a good musical ear, a correct system of fingering, and an adequate knowledge of the proportions of the notes.Ã¢Â€?
Now, if youÃ¢Â€Â™ll excuse me I have to go practice playing in tune