T he discovery of a new work by Ralph Vaughan Williams has set the world alight this week. Well, not quite, but it’s a great story. In a box in the archives of London’s Morley College Elaine Andrews came across a previously unknown Vaughan Williams song. Titled Before the Mirror, it sets a Swinburne poem that itself was inspired by a Whistler painting. Hearing it played on Radio 4’s PM on Monday [58 mins in] reveals music of surprising tonal adventure and expressive ambiguity, written shortly after Vaughan Williams married Adeline Fisher in 1897. And the manuscript’s workings, its crossings-out and corrections, are a fascinating insight into Vaughan Williams’s creative process. But a single song pales into comparison compared to the musical riches that may be lying dormant in libraries, archives and lofts all over the world.…