The next day he performed before a crowded audience in the Church of the Holy Ghost, and on the same evening appeared again before the king at his palace, where, at Frederick's request, he improvised a six-part fugue. From Potsdam he went to Berlin and, among other objects of interest, visited the opera-house, built in 1743. After his return to Leipsic he employed the theme given him by the king as the basis of a series of artistic compositions of varying length, which he caused to be engraved and dedicated to Frederick, under the title: "_Musikalisches Opfer_." During the last years of his life, Bach was several times drawn into literary controversies. One of his adversaries was Johann Adolf Scheibe, who, born in Leipsic in 1708, resided there as music-teacher till 1735 and then went to Hamburg, where he published a periodical to which he gave the title of "Critische Musikus." In this he attacked Bach on account of his confused and turgid style, which he characterized as both painful and ineffective, because it was opposed to common sense. Scheibe cherished a personal resentment against Bach, believing that he had judged him unjustly on the occasion of his candidacy for the position of organist at St. Thomas's Church in 1727. The attack caused great excitement and called forth a polemical discussion between Scheibe and Bach's friend, the university teacher, Johann Abraham Birnbaum, in which the former was finally worsted. After the lapse of some years, he seems to have realized that he had gone too far, and endeavored in his later works to efface the unfavorable impression produced by his immature criticism of the great artist. In 1749 the school rector, Biedermann, of Freiburg in Saxony, published a Latin treatise containing a warning to youth against an excessive devotion to music, as "easily leading to a dissipated life." In illustration of his theory, he cites a number of profligate characters, belonging to antiquity, and also dwells upon the small esteem in which the musicians of those days were held. The effect of this tirade was to excite the animosity of the whole musical profession, and Bach, whose pupil, Johann Friedrich Doles, was cantor of the Freiburg school, felt himself called upon to retaliate. He induced the organist Schröter to write a reply, which, however, did not appear in print until it had undergone a number of unwarrantable alterations, falsely attributed by the author to Bach himself. As a result of this, the latter was subjected to all sorts of annoyances, and though he did not defend himself with his pen, he was driven to do so through the medium of music. A Latin cantata, "Phöbus und Pan," which evidently referred to Scheibe's hostility, was composed by him in 1731 and performed by a society of musical students. At the time of the Birnbaum controversy, he again brought it to light, inserted a few appropriate allusions in the text, and produced it anew. He was not the man to suffer