Martyrs (Earth, Air, Fire, Water)St Paul’s Cathedral, London It was the pre-Socratic philosopher Empedocles who first named earth, air, fire and water as the basic elements of existence, and ended his life, so legend has it, by leaping into the fires of Etna and becoming the first martyr to philosophy. His theory outlived him by 2,000 years and has never lost its appeal to the imagination, as proved by its recent re-emergence in St Paul’s Cathedral. “Martyrs (Earth, Air, Fire, Water)” is the new permanent commission by American video artist Bill Viola unveiled in the cathedral last week, nearly two decades after his earlier work The Messenger, installed in Durham Cathedral in 1996, offended some traditionalists with its nudity. Like the new work in St Paul’s