But Mozart knew how to compose. Nor does his ingenuity fail him when in the last section of the piece he wishes, while repeating the essence of his idea, to reach the tonic instead of the dominant key. Simply dropping out the second A-phrase, he writes: [Music: score] [Illustration: FIGURE XVII.] and the trick is done. It was by a steadily broader application of principles such as are here illustrated that he gradually became so marvelously skilful in composition. Concerning the extraordinary physical delicacy of the young Mozart’s ear there are many stories, some of which are probably true. He is said to have fainted on hearing a trumpet. According to Schachtner, an intimate friend of the Mozarts, he was able to perceive an interval of pitch so small as the eighth of a tone. The story is that Wolfgang was allowed to play one day on Schachtner’s violin, which he called, on account of its full, rich tone, “Butter-fiddle.” “Herr Schachtner,” he announced a few days later, “your violin is half a quarter of a tone lower than mine; that is, if it is tuned as it was when I played it last.” The violin was brought out, and proved, Schachtner says, to be pitched as the boy had stated. As Schachtner, trained in literature by Jesuits, had the literary man’s instinct for effective statement, it is necessary to discount such tales a little; but the extraordinary delicacy of Mozart’s ear is sufficiently proved. For that matter, it needs no proof; so keen a sense of design would have been impossible to him had he lacked the requisite physical basis of accurate perception and discrimination of tones.