The Art of Noises () is a Futurist manifesto written by Luigi Russolo in a 1913 letter to friend and Futurist composer Francesco Balilla Pratella. In it, Russolo argues that the human ear has become accustomed to the speed, energy, and noise of the urban industrial soundscape; furthermore, this new sonic palette requires a new approach to musical instrumentation and composition. He proposes a number of conclusions about how electronics and other technology will allow futurist musicians to "substitute for the limited variety of timbres that the orchestra possesses today the infinite variety of timbres in noises, reproduced with appropriate mechanisms". The Art of Noises is considered by some authors to be one of the most important and influential texts in 20th-century musical aesthetics. The evolution of sound Russolo's essay explores the origins of man made sounds. Ancient life was all silence Russolo states that "noise" first came into existence as the result of 19th century machines. Before this time the world was a quiet, if not silent, place. With the exception of storms, waterfalls, and tectonic activity, the noise that did punctuate this silence were not loud, prolonged, or varied. Early sounds He notes that the earliest "music" was very simplistic and was created with very simple instruments, and that many early civilizations considered the secrets of music sacred and reserved it for rites and rituals. The Greek musical theory was based on the tetrachord mathematics of Pythagoras, and featured very limited use of harmony. Developments and modifications to the Greek musical system were made during the Middle Ages, which led to music like Gregorian chant. Russolo notes that during this time sounds were still narrowly seen as "unfolding in time." The chord did not yet exist. The complete sound Russolo refers to the chord as the "complete sound," the conception of various parts that make and are subordinate to the whole. He notes that chords developed gradually, first moving from the "consonant triad to the consistent and complicated dissonances that characterize contemporary music." He notes that while early music tried to create sweet and pure sounds, it progressively grew more and more complex, with musicians seeking to create new and more dissonant chords. This, he says, comes ever closer to the "noise-sound" typical of noise music. Musical noise Russolo compares the evolution of music to the multiplication of machinery, pointing out that our once desolate sound environment has