Quarter tone has its roots in the music of the Middle East and more specifically in Persian traditional music. However, the first evidenced proposal of quarter tones, or the quarter-tone scale (24 equal temperament), was made by 19th-century music theorists Heinrich Richter in 1823 and Mikha'il Mishaqah about 1840. Composers who have written music using this scale include: Pierre Boulez, Julián Carrillo, Mildred Couper, George Enescu, Alberto Ginastera, Gérard Grisey, Alois Hába, Ljubica Marić, Charles Ives, Tristan Murail, Krzysztof Penderecki, Giacinto Scelsi, Ammar El Sherei, Karlheinz Stockhausen, Tui St. George Tucker, Ivan Alexandrovich Wyschnegradsky, and Iannis Xenakis. (See List of quarter tone pieces.)