There is also a great deal of instruction based frankly and directly on the singer's sensations. Instruction of this type usually takes the form of special exercises on certain vowels and consonants, which are believed to be peculiarly suited for imparting command of particular features of the correct vocal action. The topics generally covered are chest resonance, nasal resonance, open throat, and forward placing of the tone. This form of instruction is held to be referable in some way to scientific principles. The laws of vowel and consonant formation formulated by Helmholtz are often cited in proof of the efficacy of exercises of this type. There is also much discussion of the "location" of the tone. But there is little justification for the statement that instruction based on the singer's sensations is scientific in character. A misconception of acoustic principles is evidenced by most of the statements made concerning the use of special vowels and consonants in securing the correct vocal action. The exercises which aim to utilize the singer's sensations in producing particular vowels and consonants are now to be described. _Exercises on Special Vowels and Consonants_ Of the rules concerning the use of special vowels, probably the most important is that _a_ (as in _far_) is the most favorable vowel for the general purposes of voice training. Teachers generally have their pupils sing most of their exercises on this vowel. Much attention is paid to the exact pronunciation of the vowel, and fine distinctions are drawn between its various sounds in Italian, French, German, and English. The preference for the Italian pronunciation is very general. It is claimed for this sound that it helps materially in acquiring command of the "open throat." Indeed, a peculiar virtue in this regard is ascribed to the Italian vowels generally. No convincing reason has ever been given for this belief. But the usual custom is to "place the voice" on the Italian _a_, and then to take up, one at a time, the other Italian vowels.