It was never given the choicest slot in the schedule, airing first thing on Sunday morning with a repeat at the end of the day. But in its 24 years Something Understood, guided and often presented by the esteemed foreign correspondent Mark Tully, has gathered an impressive audience. Its blend of poetry, prose and music from a huge variety of thinkers, theologians, scientists, poets and composers, carefully (but not artificially) edited around a theme, is for many listeners the best of Radio 4, challenging yet always accessible, highly selective but broad in content.