Public performers took the principal parts in these concerts, which fact was taken into consideration in forming the choir; care was taken to attract foreign artists, and in the larger towns many public performers depended on the daily concerts for their means of subsistence.[19] The performances were long, and included a great deal of orchestral music. Count Firmian's musical soirées lasted from five to eleven o'clock, and at one concert several symphonies by J. C. Bach and four symphonies by Martini were played.[20] Dittersdorf produced twelve new violin concertos by Benda on one evening;[21] at a concert given by the Elector of Bavaria Burney heard two symphonies by Schwindl, a song by Panzacchi, a scena by the Electress of Saxony, a trio for bass-viols by the Elector, a song by Rauzzini, a song by Guadagni, and a bass-viol solo by the Elector;, and at a private concert in Dresden both parts contained a symphony, a violin concerto, a flute concerto, and an oboe concerto.[22] The evening's amusement was generally further provided for by card-playing and conversation. Archbishop Hieronymus limited the duration of his concerts. L. Mozart wrote to his son (September 17, 1778) that they only lasted from seven to a quarter past eight, and included only four pieces--a symphony, a song, another symphony or concerto, another song, and then _addio_.[23] The court composer took the direction of the court music in turn with the kapellmeister every alternate week, and the director for the time being had the choice and {INSTRUMENTAL MUSIC.} (290) arrangement of the music[24] except so far as it was dictated by superior authority. The position of Mozart's father gave him constant opportunities of bringing his son's instrumental compositions before the public. The fame of the band was enhanced by the performance of works by one of the members, and at every festival something new was performed. Dittersdorf relates that for the fête-day of the Bishop of Grosswardein he composed not only a grand cantata with choruses and a solo cantata, but also two grand symphonies at the beginning and close, a middle symphony, with obbligato wind instruments, and a violin concerto.[25] In a similar position, under Prince Esterhazy, Josef Hadyn produced his incredibly numerous instrumental compositions. Mozart's fertility during the period of his independent activity at Salzburg, from 1770 to the autumn of 1777, was equally great, but the merit of industry and fertility was one which these great masters shared with many contemporary lesser ones. The skilful treatment of the orchestra rests mainly on the composer being so imbued with the spirit of the work as a whole as to be able to render the separate parts conducive to the general effect. This can only be accomplished by continuous practical study.