A year before writing the masterly Midsummer Night's Dream Overture, Mendelssohn had already taught his elf and fairy cohorts to fly: in the Scherzo of the Octet op.20, the centrepiece of a work composed in 1825, when its composer was only sixteen! Here, in evanescent, whispering semiquavers, a host of scintillating, fleeting sylphlike figures perform an extraordinary ghostly dance. But that is only one aspect of this dazzling youthful creation, which contains many other treasures. With just four violins, two violas and two cellos, the Octet opens wide the gates to a symphonic world full of promise…