First World War (Drei Klavierstücke in 1909 and Pierrot lunaire in 1912). In 1921, after several years of research, he developed the twelve-tone technique of composition, which he first described privately to his associates in 1923. His first large-scale work entirely composed using this technique was the Wind Quintet, Op. 26, written in 1923–24. Later examples include the Variations for Orchestra, Op. 31 (1926–28), the Third and Fourth String Quartets (1927 and 1936, respectively), the Violin Concerto (1936) and Piano Concerto (1942). In later years, he intermittently returned to a more tonal style (Kammersymphonie no. 2, begun in 1906 but completed only in 1939; Variations on a Recitative for organ in 1941). He taught Anton Webern and Alban Berg and these three composers are often referred to as the principal members of the Second Viennese School (Haydn, Mozart and Beethoven—and sometimes Schubert—being regarded as the First Viennese School in this context). Webern wrote works using a rigorous twelve-tone method and influenced the development of total serialism. Berg, like Schoenberg, employed twelve-tone technique within a late-romantic or post-romantic style (Violin Concerto, which quotes a Bach Choral and uses Classical form). He wrote two major operas (Wozzeck and Lulu). Electronic music The development of recording technology made all sounds available for potential use as musical material. Electronic music generally refers to a repertory of art music developed in the 1950s in Europe, Japan, and the Americas. The increasing availability of magnetic tape in this decade provided composers with a medium which allowed recording sounds and then manipulating them in various ways. All electronic music depends on transmission via loudspeakers, but there are two broad types: acousmatic music, which exists only in recorded form meant for loudspeaker listening, and live electronic music, in which electronic apparatus are used to generate, transform, or trigger sounds during performance by musicians using voices, traditional instruments, electro-acoustic instruments, or other devices. Beginning in 1957, computers became increasingly important in this field. When the source material was acoustical sounds from the everyday world, the term musique concrète was used; when the sounds were produced by electronic generators, it was designated electronic music. After the 1950s, the term "electronic music" came to be used for both types. Sometimes such electronic music was combined with more conventional instruments, Edgard Varèse's Déserts (1954), Stockhausen's Hymnen (1969), Claude Vivier's Wo bist du Licht! (1981), and Mario Davidovsky's series of Synchronisms (1963–2006) are