Sir Morell Mackenzie's analysis of the acoustic principle supposedly involved in "forward emission" has already been quoted. That this analysis involves a complete misunderstanding of the laws of acoustics need hardly be said. When stated in precise terms, the fallacy of the "forward emission" theory is evident: "On issuing from the vocal cords the tone is directed in a curved path, around the back of the tongue. There the tone is straightened out, and made to impinge on the roof of the mouth at a precisely defined point. From this point the tone is reflected, not directly back, as it should be, since the angles of incidence and reflection must be equal. Instead of this, the tone is reflected forward, out of the mouth, necessarily again taking a curved path, to avoid striking the front teeth." Naturally, no muscular action has ever been defined for causing the tone to perform this remarkable feat. The "forward emission" theory assumes the existence of a current of air, issuing from the vocal cords as a tone. In other words, the tone is supposed to consist of a stream of air, which can be voluntarily directed in the mouth, and aimed at some precise point on the roof of the mouth. This is an utter mistake. There is no "column of vibrating air," or "stream of vocalized breath," in the mouth during tone-production. In the acoustic sense, the air in the mouth-pharynx is still air, not air in a current. The only motion which takes place in the air in this cavity is the oscillatory swing of the air particles. To imagine the directing of air vibrations in the mouth, as we direct a stream of water out of a hose, is absurd. What then is the "forward tone"? There must be some reason for this well-known effect of a perfectly produced voice,--the impression made on the hearer that the tones are formed in the front of the mouth. There ought also to be some way for the singer to learn to produce tones of this character. A consideration of this feature of the vocal action is reserved for Chapter IV of part III. _Chest Resonance_ Who was originally responsible for the doctrine of chest resonance, it would be impossible now to determine. Were it not for the fact of this doctrine having received the support of eminent scientists (Holmes, Mackenzie, Curtis, and many others), it might be looked upon as a mere figure of speech. That the tones of the voice are reinforced by the resonance of the air in the chest cavity, is an utter absurdity. In the acoustic sense, the thorax is not a cavity at all. The thorax is filled with the spongy tissue of the lungs, not to mention the heart. It is no better adapted for air resonance than an ordinary spherical resonator would be, if filled with wet sponges. _Nasal Resonance_