The origin of the concept of 4'33", i.e., a silent frame filled with non-intentional environmental sounds, is debatable. But when Cage was a Fellow at Wesleyan's Center of Advanced Studies (1960-61), he was asked to compile a list of books having the greatest influence on his thought. One of these was Luigi Russolo's , the Italian Futurist, The Art of Noises (1916). Cage referred to The Art of Noises in his 1948 lecture at Vassar. In this book there is a chapter that presages 4'33", i.e.,"The Noises of Nature and Life". Russolo begins by poetically describing many of the sounds of nature. Then comes a remarkable statement:

And here it can be demonstrated that the much poeticized silences with which the country restores nerves shaken by city life are made up of an infinity of noises, and that these noises have their own timbres, their own rhythms, and a scale that is very delicately enharmonic in its pitches. It has been neither said nor proven that these noises are not a very important part (or in many cases the most important part) of the emotions that accompany the beauty of certain panoramas, the smile of certain countrysides!

But let us leave nature and the country (which would be a tomb without noises) and enter a noisy modern city. Here, with machines, life has created the most immense, the most varied sources of noise. But if the noises of the country are few, small, and pleasing, then those of the city ... Oh! To have to listen to noises from dawn to dusk, eternal noise!

http://solomonsmusic.net/4min33se.htm