In his search to master new organ-playing techniques he was both challenged and stimulated by his third and last change in organ posts. On 22 January 1858, he became organist and maître de chapelle at the newly consecrated Sainte-Clotilde (from 1896 the Basilique-Sainte-Clotilde), where he remained until his death. Eleven months later, the parish installed a new three-manual Cavaillé-Coll instrument, whereupon he was made titulaire, Théodore Dubois taking over as choirmaster and assistant organist. The impact of this organ on Franck's performance and composition cannot be overestimated; together with his early pianistic experience it shaped his music-making for the remainder of his life. Norbert Dufourcq described this instrument as "unquestionably the constructor's masterpiece up to this time". Franck himself told the curé of Sainte-Clotilde: "If you only knew how I love this instrument . . . it is so supple beneath my fingers and so obedient to all my thoughts!". To prepare himself for this organ's capabilities (including its thirty-note pedal), Franck purchased a practice pedalboard from Pleyel et Cie for home practice to improve his technique, as well as spending many hours at the organ keyboard. The beauty of its sound and the mechanical facilities provided by the instrument assisted his reputation as improviser and Composer, not only for organ music but in other genres as well. Pieces for organ, for choir, and for harmonium began to circulate, among the most notable of which was the Messe à 3 voix (1859). The quality of the movements in this work, composed over a number of years, is uneven, but from it comes one of Franck's most enduring compositions, the communion anthem "Panis Angelicus". More notable still is the set of Six Pièces for organ, written 1860–1862 (although not published until 1868). These compositions (dedicated to fellow organists and Pianists, to his old master Benoist, and to Cavaillé-Coll) remain part of modern organ repertory and were, according to Rollin Smith, the first major contribution to French organ literature in over a century, and "the most important organ music written since Mendelssohn's." The group includes two of his best-known organ works, the "Prélude, Fugue et Variation", op. 18 and the "Grande Pièce Symphonique", op. 17.