Book excerpt: This book explains the nature of sound both as a physical phenomenon and as a sensation, how it travels through air and water, and how the hearing system evolved to convert these vibrations into sensations. Drawing on physics, biology, neuroscience, philosophy, literature, history, anecdote, and personal experience, "Now Hear This" is a wide-ranging exploration of the nature of sound and hearing that opens up a fascinating world of sounds from the mundane to the unusual and seeks above all to persuade the reader of the wisdom of John Cage’s advice that “Wherever we are what we hear is mostly noise. When we ignore it, it disturbs us. When we listen to it, we find it fascinating.”