Fono Forum: outstanding. These two organ works from 1950–51 stand at the heart of Messiaen’s so-called experimental period, where rhythm becomes the generative force of musical thought. Drawing on Greek metre, Indian rhythmic cycles and his own “non-retrogradable” patterns, he seeks to free time from the constraints of regular pulse, shaping sound as a living, breathing mystery . The Messe de la Pentecôte, conceived for liturgical use at La Trinité in Paris, unfolds as a sequence of meditations on the descent of the Spirit: tongues of fire flicker in restless figures, invisible realities are evoked through layered rhythmic “personages,” and a violent rushing wind culminates in radiant birdsong. In Livre d’orgue, theological symbolism and structural refinement deepen further. Heterophonic textures, cyclic design and the celebrated movement of birdsong suggest a music that seeks to “touch all things without ceasing to touch God.” In this repertoire, the organ becomes both cosmic instrument and contemplative voice, uniting intellectual rigor with visionary colour and spiritual intensity.