A music-lover whose experience of hearing singing and instrumental music has been wide enough to develop the mental voice in a fair degree, possesses in this faculty a valuable means for judging singers. The mental voice carries on a running commentary on the manner of production of all the voices to which this music-lover listens. At every instant he is informed of the exact condition of the singer's throat. For him there is an almost infinite variety of throaty tones, each one indicating some degree and form of throat tension or stiffening. A perfect vocal tone, on the other hand, is _felt_ to be perfectly produced, as well as _heard_ to be musically perfect. Equipped with a highly trained sense of hearing, and the resulting faculty of mental voice, the lover of singing has an unfailing insight into the operations of the vocal mechanism. This understanding of the workings of the vocal organs is the empirical knowledge of the voice. This empirical knowledge of the voice can be possessed only by one who is equipped with a highly cultivated ear. The keener the ear the more precise and definite is this understanding of the voice. Season after season, as the music-lover continues to attend concerts, operas, and recitals, his feeling for the voice becomes gradually more keen and discerning. Further, empirical knowledge of the voice can be acquired in no other way than by actual experience in listening to voices. No matter how keen and definite are the impressions of throat action felt by the experienced hearer, these impressions cannot be described to the uninitiated. In fact, these impressions are to a great extent of a character not capable of being recorded in precise terms. The general nature of a throaty tone, for example, is thoroughly understood. But of the thousands of varieties of the throaty tone no adequate description can be given. Each observer must learn for himself to hear these fine shades of difference in tone quality. Every experienced music lover has his own mental standard of tonal perfection. The trained ear knows how a perfect musical tone should sound, independent of the precise quality of the tone. The tone quality is determined, of course, by the instrument on which it is sounded. But along with the individual characteristics of the sound, the tones drawn from every instrument, to be available in the artistic performance of music, must conform to the correct standard. Knowing the general musical character of the tones of all instruments, the cultured hearer can at once detect any variation from this character. Further, he knows how the tones of a badly-played instrument would sound if the instrument were correctly handled. An unskilled trumpeter in an orchestra, for example, may draw from his instrument tones that are too brassy, blatant, or harsh. An observant hearer knows exactly what these tones would be if the instrument were skilfully played.