Sir Morell Mackenzie states the correct emission of the tone as one of the three cardinal principles of the vocal action. "The regulation of the force of the blast which strikes against the vocal cords, the placing of these in the most favourable position for the effect which it is desired to produce, and the direction of the vibrating column of air which issues from the larynx are the three elements of artistic production." (_The Hygiene of the Vocal Organs_, London, 1886.) His analysis of the mechanical and acoustic processes involved in emission may be cited as typical of the views of the great majority of vocal scientists. "It (the column of sound) must be projected against the roof of the cavity behind the upper front teeth, from which it rebounds sharply and clearly to the outside." Mme. Seiler expresses the idea somewhat differently, but the meaning is about the same. "A correct disposition of the tones of the voice consists in causing the air, brought into vibration by the vocal ligaments, to rebound from immediately above the front teeth, where it must be concentrated as much as possible, rebounding thence to form in the mouth continuous vibrations." (_The Voice in Singing_, Phila., 1886.) To the vocal theorists this is no doubt thoroughly convincing and satisfactory. But as a topic of practical instruction in singing this theory of tone emission is utterly valueless. How can the "column of vocalized breath" be voluntarily directed in its passage through the pharynx and mouth? No muscular process has ever been located, by which the singer can influence the course of the expired breath, and direct it to any specific point in the mouth. Even if the expired breath does, in perfect singing, take the course described, knowledge of this fact cannot enable the singer to bring this about. The accepted doctrine of tone emission is of no benefit whatever to the teacher of singing. He knows what the "forward tone" is, that is, what it sounds like, just as well no doubt as did the old Italian master. But if the latter knew how to enable his pupils to obtain the "forward" character of tone, the modern teacher is to that extent not so well off. In view of the prevailing ignorance of any means for securing the (supposedly) correct emission of tone, intelligible instruction on this topic is hardly to be expected. But the great majority of teachers lay great stress on the need of acquiring the correct emission. The best they can do is to explain the scientific doctrine to their pupils; the students are generally left to find for themselves some way of applying the explanation. In many cases the master tries to assist the student by describing the singer's sensations, experienced when producing a "forward" tone.