Hornbostel-Sachs (or Sachs-Hornbostel) is a system of musical instrument classification devised by Erich Moritz von Hornbostel and Curt Sachs, and first published in the Zeitschrift für Ethnologie in 1914. An English translation was published in the Galpin Society Journal in 1961. It is the most widely used system for classifying musical instruments by ethnomusicologists and organologists (people who study musical instruments). The system is based on one devised in the late 19th century by Victor-Charles Mahillon, the curator of Brussels Conservatory's musical instrument collection. Mahillon divided instruments into four broad categories according to the nature of the sound-producing material (air column, string, membrane, the body of the instrument). He took these categories from the Natya Sastra, a roughly two-thousand-year-old Indian theoretical treatise on music and dramaturgy. Mahillon's system was limited, for the most part, to instruments used in European classical music.