The opening orchestral strains of Wagner's opera Lohengrin with its high shimmering strings prompted the French poet Charles Baudelaire to observe that in Wagner's music he found "something rapt and enthralling, something aspiring to mount higher, something excessive and superlative". The ability of music to evoke a sense of the ethereal has a strange and powerful effect on listeners, something that composers have been aware of across the ages. Tom Service examines how this music creates its affect and to what ends. He draws on examples from Hldegard of Bingen, Gregorio Allegri, Wolfgang Mozart, James Horner, Einojuhani Rautavaara and George Crumb - among others - and of course Richard Wagner.