A LITTLE knowledge is a dangerous thing. This might seem an absurd dart to hurl at Donald Clarke, who after all compiled the Penguin Encyclopedia of Popular Music, but in many ways The Rise and Fall of Popular Music is an absurd book. Clarke's big idea - to reclaim the idea of popular music from "the post-Beatles industry that separates adolescents from their pocket money" and give it back its historical context - is a fine one. His book might, and sometimes does, trace changes in the ways music is produced and consumed through the developing apparatus of commerce and technology. More often though, the author chooses to ride his team of hobby horses off the track and into the …