The mouthpiece should be placed in the middle of the lips — two-thirds on the lower lip, and one-third on the upper lip. At any rate, this is the position which I myself have adopted, and which I believe to be the best.*
Horn players generally place the mouthpiece two-thirds on the upper lip, and one-third on the lower, which is precisely the reverse of what I have just recommended for the cornet. But it must not be forgotten that great difference exists in the formation of this instrument, as well as the method of holding it; and that which may admirably suit the horn, is attended with very bad results when applied to the cornet. What, after all is the great desideratum (prerequisite), as regards the position of the cornet? Why, that it should be perfectly horizontal. Well then, if the mouthpiece were placed as though the performer were playing the horn, the instrument would have a falling position, resembling that of a clarinet.
Some professors make a point of changing the position of the mouthpiece previously adopted by the pupils who apply to them. I have seldom known this method to succeed. To my own knowledge, several artists, already possessed of remarkable talents, have attempted what we call at the Conservatory, the “orthopedic system”; which consists in rectifying and correcting the wrong placing of the moutpiece. I consider it my duty to say that these artists, after having wasted several years in uselessly trying the system in question, were compelled to return to their primitive (previous) mode of placing the mouthpiece; not one of them having obtained any advantage, while some of them were no longer able to play at all.
From all this, I conclude that when an artist has commenced his studies wrongly, he must, of course, endeavor to improve himself, but must not change the position of his mouthpiece, especially if he has already attained a certain degree of proficiancy; it being a known fact that there is no lack of artists who play perfectly, and who even possess a most beautiful tone, and who, nevertheless, place their mouthpiece at the side, aye, and even at the corners of the mouth. All that can be done, is to beware of acquiring this faulty habit. In short, there is no absolute rule for the position of the mouthpiece; for everything depends upon the conformation of the mouth, and the regularity of the teeth.
The mouthpiece once placed, it must not be moved either to ascend or descend: it would be impossible to execute certain passages, if the performer were compelled to change the position of the mouthpiece whenever he wished to take, in rapid succession, a low note after a high one.
In order to emit the higher notes, it is necessary to press the instrument against the lips** so as to produce an amount of tension proportionate to the exigencies (demands) of the note to be produced: the lips being thus stretched, the vibrations are shorter, and the sounds are consequently of a higher nature.
In descending, it is, on the contrary, necessary to apply the mouthpiece more lightly, in order to allow a larger opening for the passage of air. The vibrations then become slower, owing to the relaxation of the muscles, and grave (lower) sounds are thus obtained in proportion to the extent to which the lips are opened.
The lips must never be protruded. On the contrary, the corners of the mouth must be drawn down: by this means a more open sound is produced. When the lips begin to tire, the performer should never force the tone. He should then play more piano; for by playing loudly the lips swell, and at last it becomes impossible to emit a note. The performer should cease to play the moment the lips begin to feel weak and fatigued. It is, indeed, utter folly to continue playing under such circumstances, as it might lead to an affection of the lip, which would prove of long continuance.
* Contemporary thought on mouthpiece placement has reached a concensus that the mouthpiece should placed where it is most comfortable for the indivual player, that still allows for a free vibration of the lip.
** It is better to think in terms of pressing the lips together more firmly, rather than pressing the mouthpiece against the lips. Pressing the lips together creates the correct compression to achieve higher notes, whareas pressing the mouthpiece into the lips creates the risk of damaging the soft lip tissue.