On Air showcases a distinctive art form, the sound sculpture, retracing its evolution from the early 1950s, when artists begin dismantling the conventional boundaries of art, to the early 1970s. In no more than a quarter-century, the range of possible answers to the question "What is art?" grows vastly larger. Propelled by the idea of the work of art as a machine and instrument, sounds, noises, tones, vibrations, silence, words, breath become a "tangible" sculptural material. Artists enrich visual perception by adding the acoustic dimension, interweave seeing and hearing, explore time and space with fresh zeal. In emerging artistic genres such as performance, installation, or media art, sound is an integral component of the work. The book focuses on sound objects by Yaakov Agam, Joseph Beuys, Hermann Goepfert, Yves Klein, Jannis Kounellis, Bruce Nauman, Robert Rauschenberg, Jean Tinguely, David Tudor, Timm Ulrichs, and others. With five scholarly essays and numerous illustrations and notes on individual works, the comprehensive publication offers an attractive introduction to the subject.