_Timbre_ is the quality of sound which identifies it with the instrument of its production. Although many instruments can be convincingly gay or subdued, most authors are agreed that some instruments emit prejudicing tones. Chomet[18] considered the bassoon mournful, the flute tender, and the trombone harrowing. He found that the clarinet expresses grief, the oboe suggests reverie, but that the violin “seems suited to express all sentiments common to humanity.” Mursell[60] finds consistent tactile values in tone. Low tones are dull and high tones cutting. He speaks of the French horn as smooth, the piccolo sharp, the oboe as stringent, the cello velvety and the bassoon rough. Gundlach[38] believes that the timbre of an instrument is significant in mood response. He finds the brasses triumphant and grotesque, never melancholy or tranquil, delicate or sentimental; the woodwinds mournful, awkward, uneasy, never brilliant or glad. The human voice also has timbre, and distinctive values. There is the dramatic quality of Marian Anderson and the syrupy flow of Bing Crosby; the virility of the basso and the sparkle of the coloratura. _Duration._ The sounding of a single note will attract attention, but if the note continues for a sufficient period without changing its characteristics it will become monotonous, annoying and finally exasperating. If the sound is interrupted at equal intervals, this reaction will take longer to develop, but if the intervals between them are irregular, interest is sustained, especially if these variations occur periodically; that is, with a certain rhythm.[8] _Rhythm._ It is possible to have music without rhythm, but as Rameau[68] pointed out long ago, “Music without rhythm loses all its grace.” Since percussion instruments probably preceded all others, rhythm was the first stage in the evolution of music. The proponents of the motor theory of rhythm feel that muscular response to music with pronounced rhythm is a physiological reflex. They point out that it is difficult to walk deliberately out of time to a well accentuated march, and Dunlap[26] has shown that in reclining subjects “With the utmost possible relaxation of the entire body, good rhythmic grouping of an auditory series can be obtained.” With the aid of the electromyograph Jacobson[50] has shown that in complete relaxation mental activity results in fleeting but specific muscle contractions invisible to the eye and unknown to the subject. Rhythm perception is a mental stimulant. Reade[69] observed that African negroes when ordered to row a boat always began to sing as an aid to overcome their natural laziness. Bücher[14] believed that rhythm as exemplified in working songs facilitates the synchronous expenditure of energy by individuals engaged in a common task.