This triumph was followed by Bach's appointment as Kapellmeister to the duke of Cöthen, a post which he held from 1717 to 1723. The Cöthen period is that of Bach's central instrumental works, such as the first book of the Wohltemperirtes Klavier, the solo violin and violoncello sonatas, the Brandenburg concertos, and the French and English suites.

In 1723, finding his position at Cöthen uninspiring for choral music, he removed to Leipzig, where he became cantor of the Thomasschule, being still able to retain his post as visiting Kapellmeister at Cöthen, besides a similar position at Weissenfels. His wife had died in 1720, leaving seven children, of whom Friedermann and Philipp Emanuel had a great future before them. (For his sons see Bach, K. P. E., below.) In December 1721 Bach married again, and for the beautiful soprano voice of his second wife he wrote many of his most inspired arias. She was a great help to him with all his work, and her musical handwriting soon became so like his own that her copies are difficult to distinguish from his autographs. In 1729 Bach heard that Handel was for a second time visiting Halle on his way back to London from Italy. A former attempt of Bach's to meet Handel had failed, and now he was too ill to travel, so he sent his son to Halle to invite Handel to Leipzig; but the errand was not successful, and much to Bach's disappointment he never met his only compeer.

Bach so admired Handel that he made a manuscript copy of his Passion nach Brockes. This work, though almost unknown in England then as now, was, next to the oratorios of Keiser, incomparably the finest Passion then accessible, as Graun's beautiful masterpiece, Der Tod Jesu, was not composed until four years after Bach's death. The disgusting poem of Brockes (which was set by every German composer of the time) was transformed by Bach with real literary skill as the groundwork of the non-scriptural numbers in his Passion according to St John.

All Bach's most colossal achievements, such as the Passion according to St Matthew and the B Minor Mass (for discussion of which see Oratorio and Mass), date from his cantorship at Leipzig. But, important and congenial as was his position there, and smooth as the course of his life seems to have been until his death in 1750, he must have had quite as much experience as can have been good for him. He was often ruffled by the town councillors of Leipzig, who (like his earlier employers at Arnstadt) were shocked by the "unecclesiastical style" of his compositions and by his independent bearing. But he had more serious troubles. Of his seven children by his first wife only three survived him. By his second wife he had thirteen children, of whom he lost four of the six sons. For the head of so large a family his post was dignified rather than lucrative, and few documents tell a prouder tale of uncomplaining thrift than the inventory of his possessions made after his death. One can only be thankful that he did not live to see anything but the wonderful promise of his son Friedermann, who, in the words of the brilliantly successful K. Philipp Emanuel Bach, was more nearly capable of replacing his father than all the rest of the family together.

The prospect of complete loss of the tradition of his own polyphonic art he faced with equanimity, saying of the new style, which in the hands of his own son, Philipp Emanuel, was soon to eclipse it for the next hundred years, "The art has advanced to great heights: the old style of music no longer pleases our modern ears." But it would have broken his heart if he had forseen that Friedermann Bach was to attain a disreputable old age after a dissolute and unproductive life.

The brilliant successes of Philipp Emanuel led to his appointment as court-composer to the king of Prussia and hence, in 1747, to Sebastian's being summoned to visit Frederick the Great at Potsdam, an incident which Bach always regarded as the culmination of his career, much as Dr Johnson regarded his interview with George III. Bach had to play on the numerous newly invented pianofortes of Silbermann which the king had bought, and also to try the organs of the churches of Potsdam. Frederick, whose musical reputation rested on a genuine if narrow basis, gave him a splendid theme on which to extemporize; and on that theme Bach afterwards wrote Das musikalische Opfer. Two years after this event his sight began to fail, and before long he shared the fate of Handel in becoming perfectly blind.[2]

Bach died of apoplexy on the 28th of July 1750. His loss was deplored as that of one of the greatest organists and clavier players of his time. Of his compositions comparatively little was known. At his death his MS. works were divided amongst his sons, and many of them have been lost; only a small fraction of his greater works was recovered when, after the lapse of nearly a century, the verdict of his neglectful posterity was reversed by the modern upholders of polyphonic art. Even now some important works are still apparently irrecoverable.

The rediscovery of Bach is closely connected with the name Work and influence. of Mendelssohn, who was amongst the first to proclaim by word and deed the powers of a genius too gigantic to be grasped by three generations. By the enthusiastic endeavours of Mendelssohn, Schumann and others, and in England still earlier by the performances and publications of Wesley and Crotch, the circle of Bach's worshippers rapidly increased. In 1850, a century after his death, a society was started for the correct publication of all Bach's remaining works. Robert Franz, the great song-writer, did good service in arranging some of Bach's finest works for modern performance, until the experience of a purer scholarship could prove not only the possibility but the incomparably greater beauty of a strict adherence to Bach's own scoring. The Porson of Bach-scholarship, however, is Wilhelm Rust (grandson of the interesting composer of that name who wrote polyphonic suites and fantasias early in the 19th century). During the fourteen years of his editorship of the Bach-Gesellschaft he displayed a steadily increasing insight into Bach's style which has never since been rivalled.