<P> Haydn struggled at first, working at many different jobs: as a music teacher, as a street serenader, and eventually, in 1752, as valet--accompanist for the Italian composer Nicola Porpora, from whom he later said he learned "the true fundamentals of composition". He was also briefly in Count Friedrich Wilhelm von Haugwitz's employ, playing the organ in the Bohemian Chancellery chapel at the Judenplatz . </P> <P> While a chorister, Haydn had not received any systematic training in music theory and composition . As a remedy, he worked his way through the counterpoint exercises in the text Gradus ad Parnassum by Johann Joseph Fux and carefully studied the work of Carl Philipp Emanuel Bach, whom he later acknowledged as an important influence . </P> <P> As his skills increased, Haydn began to acquire a public reputation, first as the composer of an opera, Der krumme Teufel, "The Limping Devil", written for the comic actor Johann Joseph Felix Kurz, whose stage name was "Bernardon". The work was premiered successfully in 1753, but was soon closed down by the censors due to "offensive remarks". Haydn also noticed, apparently without annoyance, that works he had simply given away were being published and sold in local music shops . Between 1754 and 1756 Haydn also worked freelance for the court in Vienna . He was among several musicians who were paid for services as supplementary musicians at balls given for the imperial children during carnival season, and as supplementary singers in the imperial chapel (the Hofkapelle) in Lent and Holy Week . </P> <P> With the increase in his reputation, Haydn eventually obtained aristocratic patronage, crucial for the career of a composer in his day . Countess Thun, having seen one of Haydn's compositions, summoned him and engaged him as her singing and keyboard teacher . In 1756, Baron Carl Josef Fürnberg employed Haydn at his country estate, Weinzierl, where the composer wrote his first string quartets . Fürnberg later recommended Haydn to Count Morzin, who, in 1757, became his first full - time employer . </P>

What is franz joseph haydn's most famous piece of music